{"id": "c81e728d9d4c-0", "text": "TABLE OF CONTENTS\nCOVER\nTITLE PAGE\nCOPYRIGHT\nDEDICATION\nABOUT THE AUTHORS\nPREFACE\nPURPOSE OF THIS BOOK\nWHAT\u2019S NEW IN THIS EDITION\nLAB EXERCISES\nONLINE SUPPLEMENTS FOR INSTRUCTORS\nE-BOOK\nACKNOWLEDGMENTS\nPART ONE: INTRODUCTION\nCHAPTER 1: INTRODUCTION TO DATA COMMUNICATIONS\n1.1 INTRODUCTION\n1.2 DATA COMMUNICATIONS NETWORKS\n1.3 NETWORK MODELS\n1.4 NETWORK STANDARDS\n1.5 FUTURE TRENDS\n1.6 IMPLICATIONS FOR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS\nEXERCISES\nMINICASES\nTECH UPDATES\nHANDS-ON ACTIVITY 1A\nHANDS-ON ACTIVITY 1B\nPART TWO: FUNDAMENTAL CONCEPTS\nCHAPTER 2: APPLICATION LAYER\n2.1 INTRODUCTION\n2.2 APPLICATION ARCHITECTURES\n2.3 WORLD WIDE WEB\n2.4 ELECTRONIC MAIL\n2.5 OTHER APPLICATIONS\n2.6 IMPLICATIONS FOR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS\nEXERCISES\nMINICASES\nTECH UPDATES", "source": "Page 2", "chapter_title": "Chapter 1"}
{"id": "37693cfc7480-0", "text": "HANDS-ON ACTIVITY 2A\nHANDS-ON ACTIVITY 2B\nCHAPTER 3: PHYSICAL LAYER\n3.1 INTRODUCTION\n3.2 CIRCUITS\n3.3 COMMUNICATION MEDIA\n3.4 DIGITAL TRANSMISSION OF DIGITAL DATA\n3.5 ANALOG TRANSMISSION OF DIGITAL DATA\n3.6 DIGITAL TRANSMISSION OF ANALOG DATA\n3.7 IMPLICATIONS FOR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS\nEXERCISES\nMINICASES\nTECH UPDATES\nHANDS-ON ACTIVITY 3A\nHANDS-ON ACTIVITY 3B\nHANDS-ON ACTIVITY 3C\nCHAPTER 4: DATA LINK LAYER\n4.1 INTRODUCTION\n4.2 MEDIA ACCESS CONTROL\n4.3 ERROR CONTROL\n4.4 DATA LINK PROTOCOLS\n4.5 TRANSMISSION EFFICIENCY\n4.6 IMPLICATIONS FOR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS\nEXERCISES\nMINICASES\nTECH UPDATES\nHANDS-ON ACTIVITY 4A\nCHAPTER 5: NETWORK AND TRANSPORT LAYERS\n5.1 INTRODUCTION\n5.2 TRANSPORT AND NETWORK LAYER PROTOCOLS\n5.3 TRANSPORT LAYER FUNCTIONS\n5.4 ADDRESSING\n5.5 ROUTING\n5.6 TCP/IP EXAMPLE\n5.7 IMPLICATIONS FOR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS", "source": "Page 3", "chapter_title": "Chapter 3"}
{"id": "289dff07669d-0", "text": "EXERCISES\nMINICASES\nTECH UPDATES\nHANDS-ON ACTIVITY 5A\nHANDS-ON ACTIVITY 5B\nHANDS-ON ACTIVITY 5C\nHANDS-ON ACTIVITY 5D\nHANDS-ON ACTIVITY 5E\nHANDS-ON ACTIVITY 5F\nPART THREE: NETWORK TECHNOLOGIES\nCHAPTER 6: NETWORK DESIGN\n6.1 INTRODUCTION\n6.2 NEEDS ANALYSIS\n6.3 TECHNOLOGY DESIGN\n6.4 COST ASSESSMENT\n6.5 IMPLICATIONS FOR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS\nEXERCISES\nMINICASES\nTECH UPDATES\nHANDS-ON ACTIVITY 6A\nCHAPTER 7: WIRED AND WIRELESS LOCAL AREA NETWORKS\n7.1 INTRODUCTION\n7.2 LAN COMPONENTS\n7.3 WIRED ETHERNET\n7.4 WIRELESS ETHERNET\n7.5 THE BEST PRACTICE LAN DESIGN\n7.6 IMPROVING LAN PERFORMANCE\n7.7 IMPLICATIONS FOR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS\nEXERCISES\nMINICASES\nTECH UPDATES\nHANDS-ON ACTIVITY 7A\nHANDS-ON ACTIVITY 7B\nHANDS-ON ACTIVITY 7C\nCHAPTER 8: BACKBONE NETWORKS\n8.1 INTRODUCTION\n8.2 SWITCHED BACKBONES\n8.3 ROUTED BACKBONES", "source": "Page 4", "chapter_title": "Chapter 6"}
{"id": "81b073de9370-0", "text": "8.4 VIRTUAL LANS\n8.5 THE BEST PRACTICE BACKBONE DESIGN\n8.6 IMPROVING BACKBONE PERFORMANCE\n8.7 IMPLICATIONS FOR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS\nEXERCISES\nMINICASES\nTECH UPDATES\nHANDS-ON ACTIVITY 8A\nHANDS-ON ACTIVITY 8B\nCHAPTER 9: WIDE AREA NETWORKS\n9.1 INTRODUCTION\n9.2 DEDICATED-CIRCUIT NETWORKS\n9.3 PACKET-SWITCHED NETWORKS\n9.4 VIRTUAL PRIVATE NETWORKS\n9.5 THE BEST PRACTICE WAN DESIGN\n9.6 IMPROVING WAN PERFORMANCE\n9.7 IMPLICATIONS FOR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS\nEXERCISES\nMINICASES\nTECH UPDATES\nHANDS-ON ACTIVITY 9A\nHANDS-ON ACTIVITY 9B\nHANDS-ON ACTIVITY 9C\nHANDS-ON ACTIVITY 9D\nCHAPTER 10: THE INTERNET\n10.1 INTRODUCTION\n10.2 HOW THE INTERNET WORKS\n10.3 INTERNET ACCESS TECHNOLOGIES\n10.4 THE FUTURE OF THE INTERNET\n10.5 IMPLICATIONS FOR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS\nEXERCISES\nMINICASES\nTECH UPDATES\nHANDS-ON ACTIVITY 10A\nHANDS-ON ACTIVITY 10B", "source": "Page 5", "chapter_title": "Chapter 9"}
{"id": "adcaec3805aa-0", "text": "HANDS-ON ACTIVITY 10C\nPART FOUR: NETWORK MANAGEMENT\nCHAPTER 11: NETWORK SECURITY\n11.1 INTRODUCTION\n11.2 RISK ASSESSMENT\n11.3 ENSURING BUSINESS CONTINUITY\n11.4 INTRUSION PREVENTION\n11.5 BEST PRACTICE RECOMMENDATIONS\n11.6 IMPLICATIONS FOR YOUR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS\nEXERCISES\nMINICASES\nTECH UPDATES\nHANDS-ON ACTIVITY 11A\nHANDS-ON ACTIVITY 11B\nHANDS-ON ACTIVITY 11C\nHANDS-ON ACTIVITY 11D\nCHAPTER 12: NETWORK MANAGEMENT\n12.1 INTRODUCTION\n12.2 DESIGNING FOR NETWORK PERFORMANCE\n12.3 CONFIGURATION MANAGEMENT\n12.4 PERFORMANCE AND FAULT MANAGEMENT\n12.5 END USER SUPPORT\n12.6 COST MANAGEMENT\n12.7 IMPLICATIONS FOR CYBER SECURITY\nSUMMARY\nKEY TERMS\nQUESTIONS\nEXERCISES\nMINICASES\nTECH UPDATES\nHANDS-ON ACTIVITY 12A\nHANDS-ON ACTIVITY 12B\nHANDS-ON ACTIVITY 12C\nINDEX\nEND USER LICENSE AGREEMENT\nList of Illustrations\nChapter 1\nFIGURE 1-1 What is MIS?\nFIGURE 1-2 Example of a local area network (LAN)", "source": "Page 6", "chapter_title": "Chapter 11"}
{"id": "508df4cb2f4d-0", "text": "FIGURE 1-3 Network architecture components\nFIGURE 1-4 Network models. OSI = Open Systems Interconnection Reference\nFIGURE 1-5 Message transmission using layers. IP = Internet Protocol; HTTP =...\nFIGURE 1-6 Some common data communications standards. HTML = Hypertext Marku...\nFIGURE 1-7 A security robot on the IOT\nFIGURE 1-8 One server farm with more than 1,000 servers\nFIGURE 1-9 Wireshark capture\nChapter 2\nFIGURE 2-1 Host-based architecture\nFIGURE 2-2 Client-based architecture\nFIGURE 2-3 Two-tier thick client client\u2013server architecture\nFIGURE 2-4 Three-tier thin client client\u2013server architecture\nFIGURE 2-5 The n-tier thin client client\u2013server architecture\nFIGURE 2-6 The typical two-tier thin-client architecture of the Web\nFIGURE 2-7 Cloud architecture models compared to thin client\u2013server architec...\nFIGURE 2-8 One row of a server farm at Indiana University\nFIGURE 2-9 Peer-to-peer architecture\nFIGURE 2-10 How the Web works\nFIGURE 2-11 An example of a request from a Web browser to a Web server using...\nFIGURE 2-12 An example of a response from a Web server to a Web browser usin...\nFIGURE 2-13 How SMTP (Simple Mail Transfer Protocol) email works. IMAP = Int...\nFIGURE 2-14 Inside the Web. HTTP = Hypertext Transfer Protocol; IMAP = I...\nFIGURE 2-15 An example of an email message using the SMTP (Simple Mail Trans...\nFIGURE 2-16 A Cisco telepresence system\nFIGURE 2-17 Desktop videoconferencing", "source": "Page 7", "chapter_title": "Chapter 11"}
{"id": "95525872e442-1", "text": "FIGURE 2-17 Desktop videoconferencing\nFIGURE 2-18 Viewing the SMTP packet header\nFIGURE 2-19 Viewing the source of the SMTP packet\nFIGURE 2-20 SMTP packets in Wireshark\nFIGURE 2-21 POP packets in Wireshark\nChapter 3\nFIGURE 3-1 Point-to-point circuit\nFIGURE 3-2 Multipoint circuit\nFIGURE 3-3 Simplex, half-duplex, and full-duplex transmissions\nFIGURE 3-4 Multiplexed circuit\nFIGURE 3-5 Category 5e twisted-pair wire\nFIGURE 3-6 Coaxial cables. Thinnet and Thicknet Ethernet cables (right)\u2014(1) ...\nFIGURE 3-7 Fiber-optic cable\nFIGURE 3-8 A microwave tower. The round antennas are microwave antennas and ...\nFIGURE 3-9 Satellites in operation", "source": "Page 7", "chapter_title": "Chapter 11"}
{"id": "bb0f169a5947-0", "text": "FIGURE 3-10 Binary numbers used to represent different characters using ASCI...\nFIGURE 3-11 Parallel transmission of an 8-bit code\nFIGURE 3-12 Serial transmission of an 8-bit code\nFIGURE 3-13 Unipolar, bipolar, and Manchester signals (digital)\nFIGURE 3-14 Sound wave\nFIGURE 3-15 Amplitude modulation\nFIGURE 3-16 Frequency modulation\nFIGURE 3-17 Phase modulation\nFIGURE 3-18 Two-bit amplitude modulation\nFIGURE 3-19 Pulse amplitude modulation (PAM)\nFIGURE 3-20 Pulse amplitude modulation (PAM)\nFIGURE 3-21 VoIP phone\nFIGURE 3-22 Cat 5 cable\nFIGURE 3-23 Inside a Cat 5 cable\nFIGURE 3-24 Pin connection for Cat 5 at the computer end\nFIGURE 3-25 Tools and materials for making a patch cable\nChapter 4\nFIGURE 4-1 Relative response times\nFIGURE 4-2 Sources of errors and ways to minimize them\nFIGURE 4-3 Using parity for error detection\nFIGURE 4-4 Hamming code for forward error correction\nFIGURE 4-5 Protocol summary\nFIGURE 4-6 Asynchronous transmission. ASCII = United States of America Stand...\nFIGURE 4-7 SDLC (synchronous data link control) frame layout\nFIGURE 4-8a Ethernet 802.3ac frame layout\nFIGURE 4-8b Ethernet II frame layout\nFIGURE 4-9 PPP frame layout\nFIGURE 4-10 Frame size effects on throughput\nFIGURE 4-11 Capturing packets with Wireshark\nFIGURE 4-12 Analyzing packets with Wireshark\nChapter 5", "source": "Page 8", "chapter_title": "Chapter 11"}
{"id": "6c4628b734cd-1", "text": "FIGURE 4-12 Analyzing packets with Wireshark\nChapter 5\nFIGURE 5-1 Message transmission using layers. SMTP = Simple Mail Transfer Pr...\nFIGURE 5-2 Transmission Control Protocol (TCP) segment. ACK = Acknowledgment...\nFIGURE 5-3 Internet Protocol (IP) packet (version 4). CRC = Cyclical Redunda...\nFIGURE 5-4 Internet Protocol (IP) packet (version 6)\nFIGURE 5-5 Linking to application layer services\nFIGURE 5-6 Stop-and-wait ARQ (Automatic Repeat reQuest). ACK = Acknowledgmen...\nFIGURE 5-7 Continuous ARQ (Automatic Repeat reQuest). ACK = Acknowledgment; ...\nFIGURE 5-8 Types of addresses", "source": "Page 8", "chapter_title": "Chapter 11"}
{"id": "c68f3a4055bc-0", "text": "FIGURE 5-9 IPv4 public address space\nFIGURE 5-10 IPv4 private address space\nFIGURE 5-11 Address subnets\nFIGURE 5-12 How the DNS system works?\nFIGURE 5-13 A small corporate network\nFIGURE 5-14 Sample routing tables\nFIGURE 5-15 Routing on the Internet with Border Gateway Protocol (BGP), Open...\nFIGURE 5-16 Anatomy of a router\nFIGURE 5-17 Example Transmission Control Protocol/Internet Protocol (TCP/IP)...\nFIGURE 5-18 TCP/IP configuration information\nFIGURE 5-19 Packet nesting. HTTP = Hypertext Transfer Protocol; IP = Interne...\nFIGURE 5-20 How messages move through the network layers.\nFIGURE 5-25 DNS cache\nFIGURE 5-27 DNS capture\nChapter 6\nFIGURE 6-1 Network architecture components\nFIGURE 6-2 Network design\nFIGURE 6-3 The cyclical nature of network design\nFIGURE 6-4 Sample needs assessment logical network design for a single build...\nFIGURE 6-5 Physical network design for a single building\nFIGURE 6-7 SmartDraw software\nChapter 7\nFIGURE 7-1 Local area network components\nFIGURE 7-2 LAN switches\nFIGURE 7-3 Wireless access points\nFIGURE 7-4 Ethernet topology using hubs\nFIGURE 7-5 Ethernet topology using switches\nFIGURE 7-6 Types of Ethernet\nFIGURE 7-7 A wireless Ethernet frame\nFIGURE 7-8 Design parameters for Wi-Fi access point range\nFIGURE 7-9 A Wi-Fi design (the numbers indicate the channel numbers)\nFIGURE 7-10 A Wi-Fi design in the three dimensions (the numbers indicate the...", "source": "Page 9", "chapter_title": "Chapter 11"}
{"id": "ac3b73049879-1", "text": "FIGURE 7-11 The data center at Indiana University\nFIGURE 7-12 Network with load balancer\nFIGURE 7-13 The storage area network (SAN) at the Kelley School of Business ...\nFIGURE 7-14 SOHO LAN designs\nFIGURE 7-15 Powerline adapter\nFIGURE 7-17 TracePlus\nFIGURE 7-18 WLANs in a neighborhood in Bloomington, Indiana", "source": "Page 9", "chapter_title": "Chapter 11"}
{"id": "59c299cb0aee-0", "text": "FIGURE 7-19 WLANs at Indiana University\nFIGURE 7-20 Plans for Floors 3\u20138 of Apollo Residence\nFIGURE 7-21 LAN equipment price list\nChapter 8\nFIGURE 8-1 Rack-mounted switched backbone network architecture\nFIGURE 8-2 An MDF with rack-mounted equipment. A layer 2 chassis switch with...\nFIGURE 8-3 MDF network diagram. MDF = main distribution facility\nFIGURE 8-4 Switched backbones at Indiana University\nFIGURE 8-5 Routed backbone architecture\nFIGURE 8-6 VLAN-based backbone network architecture\nFIGURE 8-7 Multiswitch VLAN-based backbone network design\nFIGURE 8-8 The best practice network design\nFIGURE 8-10 Facility map of the Western Trucking headquarters\nFIGURE 8-11 Computers and devices at Alan's house\nFIGURE 8-12 Network map for Alan's house\nFIGURE 8-13 System information for 192.168.1.188\nFIGURE 8-14 Apollo Residence first floor\nFIGURE 8-15 Apollo Residence second floor\nFIGURE 8-16 Equipment price list\nChapter 9\nFIGURE 9-1 Dedicated-circuit services. CSU = channel service unit; DSU = dat...\nFIGURE 9-2 Ring-based design\nFIGURE 9-3 Star-based design\nFIGURE 9-4 Mesh design\nFIGURE 9-5 T-carrier services\nFIGURE 9-6 SONET and SDH services. OC = optical carrier (level); SDH = synch...\nFIGURE 9-7 Packet-switched services. PAD = packet assembly/disassembly devic...\nFIGURE 9-8 Virtual private network (VPN) services\nFIGURE 9-9 A virtual private network (VPN)", "source": "Page 10", "chapter_title": "Chapter 11"}
{"id": "729c70f33509-1", "text": "FIGURE 9-9 A virtual private network (VPN)\nFIGURE 9-10 Using VPN software. Shaded area depicts encrypted packets\nFIGURE 9-11 WAN services\nFIGURE 9-14 100 Gbps network for a U.S. Internet service provider\nFIGURE 9-15 Starting Wireshark\nFIGURE 9-16 Viewing encrypted packets\nFIGURE 9-17 Packets that enter the VPN tunnel\nFIGURE 9-18 Tracert without a VPN\nFIGURE 9-19 Tracert with a VPN\nChapter 10\nFIGURE 10-1 The Internet is a lot like the universe\u2014many independent systems...", "source": "Page 10", "chapter_title": "Chapter 11"}
{"id": "c8c7bdfbbab7-0", "text": "FIGURE 10-2 Basic Internet architecture. ISP = Internet service provider; IX...\nFIGURE 10-3 A typical Internet backbone of a major ISP\nFIGURE 10-4 DSL architecture. DSL = digital subscriber line; ISP = Internet ...\nFIGURE 10-5 Some typical digital subscriber line data rates\nFIGURE 10-6 Cable modem architecture. ISP = Internet service provider; POP =...\nFIGURE 10-7 Internet2 network map\nFIGURE 10-9 Visual trace route\nFIGURE 10-10 Internet traffic reports\nFIGURE 10-11 A speed test on my computer in Indiana\nChapter 11\nFIGURE 11-4 Likelihood of a threat\nFIGURE 11-5 Threat scenario for theft of customer information\nFIGURE 11-6 Threat scenario for destruction of customer information by a tor...\nFIGURE 11-7 A distributed denial-of-service attack\nFIGURE 11-8 Traffic analysis reduces the impact of denial-of-service attacks...\nFIGURE 11-9 Security cables protecting computers\nFIGURE 11-12 Using a firewall to protect networks\nFIGURE 11-13 How packet-level firewalls work\nFIGURE 11-14 A typical network design using firewalls\nFIGURE 11-15 One menu on the control console for the Optix Pro Trojan\nFIGURE 11-16 Secure transmission with public key encryption\nFIGURE 11-17 Authenticated and secure transmission with public key encryptio...\nFIGURE 11-18 Two-factor authentication with the Duo app for mobile phones\nFIGURE 11-19 Intrusion prevention system (IPS). DMZ = demilitarized zone; DN...\nFIGURE 11-20 Commonly used security controls\nFIGURE 11-21 BitLocker\nFIGURE 11-22 Selecting the encryption mode\nFIGURE 11-23 Starting the encryption", "source": "Page 11", "chapter_title": "Chapter 11"}
{"id": "26d79f8d1b5b-1", "text": "FIGURE 11-23 Starting the encryption\nFIGURE 11-24 System Preferences for a Mac\nFIGURE 11-25 Searching system preferences\nFIGURE 11-26 Security & Privacy: FileVault\nFIGURE 11-27 PGP key generator\nFIGURE 11-28 PGP encryption\nFIGURE 11-29 PGP decryption\nFIGURE 11-30 Selecting a recipient of an encrypted message\nFIGURE 11-31 Security hardware, software, and services\nChapter 12\nFIGURE 12-1 Device management software used on Indiana University\u2019s core bac...\nFIGURE 12-2 Network management with Simple Network Management Protocol (SNMP...", "source": "Page 11", "chapter_title": "Chapter 11"}
{"id": "617332afd17b-0", "text": "FIGURE 12-3 Network with load balancer\nFIGURE 12-4 Capacity management software\nFIGURE 12-5 Network with content engine\nFIGURE 12-6 Network with content delivery\nFIGURE 12-7 Network configuration diagram\nFIGURE 12-8 Part of the Network Operations Center at Indiana University\nFIGURE 12-9 Network traffic versus network management budgets\nFIGURE 12-11 Network management personnel costs\nFIGURE 12-13 Total cost of ownership (per client computer per year) for a Mi...\nFIGURE 12-14 SolarWinds network management software, used with permission\nFIGURE 12-15 SolarWinds network management software, used with permission\nFIGURE 12-16 SolarWinds network management software, used with permission\nFIGURE 12-17 Equipment list", "source": "Page 12", "chapter_title": "Chapter 11"}
{"id": "d7c4e61be700-0", "text": "Business Data Communications and Networking\nFourteenth Edition\n \n \nJerry FitzGerald\nJerry FitzGerald & Associates\nAlan Dennis\nIndiana University\nAlexandra Durcikova\nUniversity of Oklahoma", "source": "Page 13", "chapter_title": "Chapter 11"}
{"id": "5ea438bb2205-0", "text": "VP AND EDITORIAL DIRECTOR\nMike McDonald\nPUBLISHER\nLise Johnson\nEDITOR\nJennifer Manias\nEDITORIAL ASSISTANT\nKali Ridley\nSENIOR MANAGING EDITOR\nJudy Howarth\nDIRECTOR OF CONTENT OPERATIONS\nMartin Tribe\nSENIOR MANAGER OF CONTENT OPERATIONS Mary Corder\nPRODUCTION EDITOR\nUmamaheswari Gnanamani\nASSISTANT MARKETING MANAGER\nRachel Karach\nCOVER PHOTO CREDIT\n\u00a9 Photographer is my life./Getty Images\nFounded in 1807, John Wiley & Sons, Inc. has been a valued source of knowledge and understanding for more than 200 years, helping people\naround the world meet their needs and fulfill their aspirations. Our company is built on a foundation of principles that include responsibility\nto the communities we serve and where we live and work. In 2008, we launched a Corporate Citizenship Initiative, a global effort to address\nthe environmental, social, economic, and ethical challenges we face in our business. Among the issues we are addressing are carbon impact,\npaper specifications and procurement, ethical conduct within our business and among our vendors, and community and charitable support.\nFor more information, please visit our website: www.wiley.com/go/citizenship.\nCopyright \u00a9 2021, 2017, 2015, 2012, 2009, 2007 John Wiley & Sons, Inc. All rights reserved. No part of this publication may be reproduced,\nstored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or\notherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission\nof the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood", "source": "Page 14", "chapter_title": "Chapter 11"}
{"id": "6bf63901053f-1", "text": "Drive, Danvers, MA 01923 (Web site: www.copyright.com). Requests to the Publisher for permission should be addressed to the Permissions\nDepartment, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, (201) 748-6011, fax (201) 748-6008, or online at:\nwww.wiley.com/go/permissions.\nEvaluation copies are provided to qualified academics and professionals for review purposes only, for use in their courses during the next\nacademic year. These copies are licensed and may not be sold or transferred to a third party. Upon completion of the review period, please\nreturn the evaluation copy to Wiley. Return instructions and a free of charge return shipping label are available at:\nwww.wiley.com/go/returnlabel. If you have chosen to adopt this textbook for use in your course, please accept this book as your\ncomplimentary desk copy. Outside of the United States, please contact your local sales representative.\nISBN: 978-1-119-70284-9 (PBK)\nISBN: 978-1-119-71365-4 (EVALC)\nLibrary of Congress Cataloging-in-Publication Data:\nNames: FitzGerald, Jerry, 1936- author. | Dennis, Alan, author. | Durcikova, Alexandra, author.\nTitle: Business data communications and networking / Jerry FitzGerald, Alan Dennis, Alexandra Durcikova.\nDescription: Fourteenth edition. | Hoboken, NJ : Wiley, [2021] | Includes index.\nIdentifiers: LCCN 2020028461 (print) | LCCN 2020028462 (ebook) | ISBN 9781119702849 (paperback) | ISBN 9781119713661 (adobe pdf) |", "source": "Page 14", "chapter_title": "Chapter 11"}
{"id": "ea28d914bcc6-2", "text": "ISBN 9781119702665 (epub)\nSubjects: LCSH: Data transmission systems. | Computer networks. | Office practice\u2013Automation.\nClassification: LCC TK5105 .F577 2021 (print) | LCC TK5105 (ebook) | DDC 004.6\u2013dc23\nLC record available at https://lccn.loc.gov/2020028461\nLC ebook record available at https://lccn.loc.gov/2020028462\nThe inside back cover will contain printing identification and country of origin if omitted from this page. In addition, if the ISBN on the back\ncover differs from the ISBN on this page, the one on the back cover is correct.", "source": "Page 14", "chapter_title": "Chapter 11"}
{"id": "2ede479f4a85-0", "text": "To my son Alec,\nAlan\n \nTo all curious minds who want to know how today\u2019s modern world works.\nAlexandra", "source": "Page 15", "chapter_title": "Chapter 11"}
{"id": "4bbed9fe1c0c-0", "text": "ABOUT THE AUTHORS\nAlan Dennis is a Fellow of the Association for Information Systems and a professor of information\nsystems in the Kelley School of Business at Indiana University. He holds the John T. Chambers Chair in\nInternet Systems, which was established to honor John Chambers, president and chief executive officer of\nCisco Systems, the worldwide leader of networking technologies for the Internet.\nPrior to joining Indiana University, Alan spent nine years as a professor at the University of Georgia,\nwhere he won the Richard B. Russell Award for Excellence in Undergraduate Teaching. He has a\nbachelor\u2019s degree in Computer Science from Acadia University in Nova Scotia, Canada, and an MBA from\nQueen\u2019s University in Ontario, Canada. His PhD in management of information systems is from the\nUniversity of Arizona. Prior to entering the Arizona doctoral program, he spent three years on the faculty\nof the Queen\u2019s School of Business.\nAlan has extensive experience in the development and application of groupware and Internet technologies\nand co-founded Courseload, an electronic textbook company whose goal is to improve learning and\nreduce the cost of textbooks. He has won many awards for theoretical and applied research and has\npublished more than 150 business and research articles, including those in Management Science, MIS\nQuarterly, Information Systems Research, Academy of Management Journal, Organization Behavior\nand Human Decision Making, Journal of Applied Psychology, Communications of the ACM, and IEEE\nTransactions of Systems, Man, and Cybernetics. His first book was Getting Started with\nMicrocomputers, published in 1986. Alan is also an author of two systems analysis and design books\npublished by Wiley. He is the cochair of the Internet Technologies Track of the Hawaii International\nConference on System Sciences. He has served as a consultant to BellSouth, Boeing, IBM, Hughes Missile\nSystems, the U.S. Department of Defense, and the Australian Army.", "source": "Page 16", "chapter_title": "Chapter 11"}
{"id": "d3c2826a5fd3-1", "text": "Systems, the U.S. Department of Defense, and the Australian Army.\nAlexandra Durcikova is an Associate Professor at the Price College of Business, University of Oklahoma.\nAlexandra has a PhD in management information systems from the University of Pittsburgh. She has\nearned an MSc degree in solid state physics from Comenius University, Bratislava, worked as an\nexperimental physics researcher in the area of superconductivity and as an instructor of executive MBA\nstudents prior to pursuing her PhD. Alexandra\u2019s research interests include knowledge management and\nknowledge management systems, the role of organizational climate in the use of knowledge management\nsystems, knowledge management system characteristics, governance mechanisms in the use of knowledge\nmanagement systems, and human compliance with security policy and characteristics of successful\nphishing attempts within the area of network security. Her research appears in Information Systems\nResearch, MIS Quarterly, Journal of Management Information Systems, Information Systems Journal,\nJournal of Organizational and End User Computing, International Journal of Human\u2013Computer\nStudies, International Journal of Human\u2013Computer Studies, and Communications of the ACM.\nAlexandra has been teaching business data communications to both undergraduate and graduate students\nfor several years. In addition, she has been teaching classes on information technology strategy and most\nrecently won the Dean\u2019s Award for Undergraduate Teaching Excellence while teaching at the University of\nArizona.\nDr. Jerry FitzGerald wrote the early editions of this book in the 1980s. At the time, he was the principal in\nJerry FitzGerald & Associates, a firm he started in 1977.", "source": "Page 16", "chapter_title": "Chapter 11"}
{"id": "75ca7225c221-0", "text": "PREFACE\nThe field of data communications has grown faster and become more important than computer\nprocessing itself. Though they go hand in hand, the ability to communicate and connect with other\ncomputers and mobile devices is what makes or breaks a business today. There are three trends that\nsupport this notion. First, the wireless LAN and Bring-Your-Own-Device (BYOD) allow us to stay\nconnected not only with the workplace but also with family and friends. Second, computers and networks\nare becoming an essential part of not only computers but also devices we use for other purpose, such as\nhome appliances. This Internet of Things allows you to set the thermostat in your home from your mobile\nphone, can help you cook a dinner, or eventually can allow you to drive to work without ever touching the\nsteering wheel. Lastly, we see that a lot of life is moving online. At first this started with games, but\neducation, politics, and activism followed swiftly. Therefore, understanding how networks work; how they\nshould be set up to support scalability, mobility, and security; and how to manage them is of utmost\nimportance to any business. This need will call not only for engineers who deeply understand the technical\naspects of networks but also for highly social individuals who embrace technology in creative ways to\nallow business to achieve a competitive edge through utilizing this technology. So the call is for you who\nare reading this book\u2014you are at the right place at the right time!\nPURPOSE OF THIS BOOK\nOur goal is to combine the fundamental concepts of data communications and networking with practical\napplications. Although technologies and applications change rapidly, the fundamental concepts evolve\nmuch more slowly; they provide the foundation from which new technologies and applications can be\nunderstood, evaluated, and compared.\nThis book has two intended audiences. First and foremost, it is a university textbook. Each chapter", "source": "Page 17", "chapter_title": "Chapter 11"}
{"id": "1a77dd76cf0c-1", "text": "This book has two intended audiences. First and foremost, it is a university textbook. Each chapter\nintroduces, describes, and then summarizes fundamental concepts and applications. Management Focus\nboxes highlight key issues and describe how networks are actually being used today. Technical Focus\nboxes highlight key technical issues and provide additional detail. Mini case studies at the end of each\nchapter provide the opportunity to apply these technical and management concepts. Hands-on exercises\nhelp to reinforce the concepts introduced in the chapter. Moreover, the text is accompanied by a detailed\nInstructor\u2019s Manual that provides additional background information, teaching tips, and sources of\nmaterial for student exercises, assignments, and exams. Finally, our Web page contains supplements to\nour book.\nSecond, this book is intended for the professional who works in data communications and networking.\nThe book has many detailed descriptions of the technical aspects of communications from a business\nperspective. Moreover, managerial, technical, and sales personnel can use this book to gain a better\nunderstanding of fundamental concepts and trade-offs not presented in technical books or product\nsummaries.\nWHAT\u2019S NEW IN THIS EDITION\nThis edition maintains the three main themes of the prior edition, namely, (1) how networks work\n(Chapters 1\u20135); (2) network technologies (Chapters 6\u201310); and (3) network security and management\n(Chapters 11 and 12). In the new edition, we removed older technologies and replaced them with new\nones. Accordingly, new hands-on activities and questions have been added at the end of each chapter that\nguide students in understanding how to select technologies to build a network that would support an\norganization\u2019s business needs. In addition to this overarching change, the thirteenth edition has three\nmajor changes from the twelfth edition:\nFirst, at the end of each chapter, in addition to providing key implications for cyber security that arise", "source": "Page 17", "chapter_title": "Chapter 11"}
{"id": "71dc7c223102-2", "text": "from the topics discussed in the chapter, we also introduce Tech Updates. We draw implications that focus\non improving the management of networks and information systems as well as implications for cyber\nsecurity of an individual and an organization. Tech Updates offer two cybersecurity topics per chapter that", "source": "Page 17", "chapter_title": "Chapter 11"}
{"id": "5049ab7b3718-0", "text": "help students to expand their knowledge of cybersecurity and see how it relates to the material covered in\nthe chapter.\nSecond, we have revised Chapter 2 to use a new framework for application architecture that includes\napplication services.\nThird, we have revised the WAN chapter (Chapter 9) to include the rapidly changing WAN environment\nand Software Defined Networking.\nLAB EXERCISES\nwww.wiley.com/go/fitzgerald/datacommunications14e\nThis edition includes an online lab manual with many hands-on exercises that can be used in a\nnetworking lab. These exercises include configuring servers and other additional practical topics.\nONLINE SUPPLEMENTS FOR INSTRUCTORS\nwww.wiley.com/go/fitzgerald/datacommunications14e\nInstructor\u2019s supplements comprise an Instructor\u2019s Manual that includes teaching tips, war stories, and\nanswers to end-of-chapter questions; a Test Bank that includes true-false, multiple choice, short answer,\nand essay test questions for each chapter; and Lecture Slides in PowerPoint for classroom presentations.\nAll are available on the instructor\u2019s book companion site.\nE-BOOK\nWiley E-Text: Powered by VitalSource offers students continuing access to materials for their\ncourse. Your students can access content on a mobile device, online from any Internet-connected\ncomputer, or by a computer via download. With dynamic features built into this e-text, students can\nsearch across content, highlight, and take notes that they can share with teachers and classmates. Readers\nwill also have access to interactive images and embedded podcasts. Visit\nwww.wiley.com/go/fitzgerald/datacommunications14e for more information.\nACKNOWLEDGMENTS\nOur thanks to the many people who helped in preparing this edition. Specifically, we want to thank the\nstaff at John Wiley & Sons for their support.\nAlan Dennis\nBloomington, Indiana\nwww.kelley.indiana.edu/ardennis", "source": "Page 18", "chapter_title": "Chapter 11"}
{"id": "0e76b4a4b586-1", "text": "Bloomington, Indiana\nwww.kelley.indiana.edu/ardennis\n \nAlexandra Durcikova\nNorman, Oklahoma\nhttp://www.ou.edu/price/mis/people/alexandra_durcikova.html", "source": "Page 18", "chapter_title": "Chapter 11"}
{"id": "6150ca05e1f0-0", "text": "PART ONE INTRODUCTION", "source": "Page 19", "chapter_title": "Chapter 11"}
{"id": "923d0b06c1d8-0", "text": "CHAPTER 1\nINTRODUCTION TO DATA COMMUNICATIONS\nThis chapter introduces the basic concepts of data communications. It describes why it is important to\nstudy data communications, how data communications fit within the discipline of Management\nInformation Systems (MIS), and introduces you to the three fundamental questions that this book\nanswers. Next, it discusses the basic types and components of a data communications network. Also, it\nexamines the importance of a network model based on layers. Finally, it describes the three key trends in\nthe future of networking.\nOBJECTIVES\nBe aware of the three fundamental questions this book answers\nBe aware of the applications of data communications networks\nBe aware of how data communications fit within the discipline of MIS\nBe familiar with the major components of and types of networks\nUnderstand the role of network layers\nBe familiar with the role of network standards\nBe aware of cyber security issues\nBe aware of three key trends in communications and networking\nOUTLINE\n1.1 Introduction\n1.2 Data Communications Networks\n1.2.1 Components of a Network\n1.2.2 Types of Networks\n1.3 Network Models\n1.3.1 Open Systems Interconnection Reference Model\n1.3.2 Internet Model\n1.3.3 Message Transmission Using Layers\n1.4 Network Standards\n1.4.1 The Importance of Standards\n1.4.2 The Standards-Making Process\n1.4.3 Common Standards\n1.5 Future Trends\n1.5.1 Wireless LAN and BYOD\n1.5.2 The Internet of Things\n1.5.3 Massively Online\n1.6 Implications for Cyber Security\nSummary", "source": "Page 20", "chapter_title": "Chapter 11"}
{"id": "04c54b563141-0", "text": "1.1 INTRODUCTION\nWhat Internet connection should you use? Cable modem or DSL (formally called Digital Subscriber Line)?\nCable modems are supposedly faster than DSL, providing data speeds of 50 Mbps to DSL\u2019s 1.5\u201325 Mbps\n(million bits per second). One cable company used a tortoise to represent DSL in advertisements. So\nwhich is faster? We\u2019ll give you a hint. Which won the race in the fable, the tortoise or the hare? By the time\nyou finish this book, you\u2019ll understand which is faster and why, as well as why choosing the right company\nas your Internet service provider (ISP) is probably more important than choosing the right\ntechnology.\nOver the past decade or so, it has become clear that the world has changed forever due to the third and\nfourth Industrial Revolutions. The first Industrial Revolution revolutionized the way people worked at the\nend of the 18th century by introducing machines, steam and water power. New companies and industries\nemerged, and old ones died off. The second Industrial Revolution in the late 19th century is known for\nstarting mass production, electricity, and the telephone. The third Industrial Revolution, in the second\nhalf of the 20th century, is revolutionizing the way people work through electronics and information\ntechnology (IT) to automate production.\nThe fourth Industrial Revolution is currently underway. It builds on the technological advances of the\nthird Industrial Revolution, but the way it merges the physical, digital, and biological worlds is\nunprecedented. It is deeply rooted in the Internet and digitization. Digitization enables us to build a world\nwhere interactions can happen in real time across different continents (think about email, instant\nmessaging, and exchange of data between different devices). These interactions are possible because of", "source": "Page 21", "chapter_title": "Chapter 11"}
{"id": "de6c8e705aa4-1", "text": "messaging, and exchange of data between different devices). These interactions are possible because of\ntechnologies such as cloud, big data, big data analytics, and the Internet of Things. But the technology that\nenables all these technologies to communicate is the high-speed data communication network, that is, the\nInternet.\nToday, the value of a high-speed data communications network is that it brings people together in a way\nnever before possible. In the 1800s, it took several weeks for a message to reach North America by ship\nfrom England. By the 1900s, it could be transmitted within an hour. Today, it can be transmitted in\nseconds. Collapsing the information lag to Internet speeds means that people can communicate and\naccess information anywhere in the world regardless of their physical location. In fact, today\u2019s problem is\nthat we cannot handle the quantities of information we receive.\nData communications and networking is a truly global area of study, both because the technology enables\nglobal communication and because new technologies and applications often emerge from a variety of\ncountries and spread rapidly around the world. The World Wide Web, for example, was born in a Swiss\nresearch lab, was nurtured through its first years primarily by European universities and exploded into\nmainstream popular culture because of a development at an American research lab.\nOne of the problems in studying a global phenomenon lies in explaining the different political and\nregulatory issues that have evolved and currently exist in different parts of the world. Rather than attempt\nto explain the different paths taken by different countries, we have chosen simplicity instead. Historically,\nthe majority of readers of previous editions of this book have come from North America. Therefore,\nalthough we retain a global focus on technology and its business implications, we focus mostly on North\nAmerica.\nThis book answers three fundamental questions.", "source": "Page 21", "chapter_title": "Chapter 11"}
{"id": "fdb6a1f8ed7d-2", "text": "America.\nThis book answers three fundamental questions.\nFirst, how does the Internet work? When you access a website using your computer, laptop, iPad, or\nsmartphone, what happens so that the page opens in your Web browser? This is the focus in Chapters 1\u20135.\nThe short answer is that the software on your computer (or any device) creates a message composed in\ndifferent software languages (HTTP, TCP/IP, and Ethernet are common) that requests the page you\nclicked. This message is then broken up into a series of smaller parts that we call packets. Each packet is\ntransmitted to the nearest router, which is a special-purpose computer whose primary job is to find the\nbest route for these packets to their final destination. The packets move from router to router over the\nInternet until they reach the Web server, which puts the packets back together into the same message that\nyour computer created. The Web server reads your request and then sends the page back to you in the\nsame way\u2014by composing a message using HTTP, TCP/IP, and Ethernet and then sending it as a series of\nsmaller packets back through the Internet that the software on your computer puts together into the page", "source": "Page 21", "chapter_title": "Chapter 11"}
{"id": "f534a39fb39a-0", "text": "you requested. You might have heard a news story that the U.S. or Chinese government can read your\nemail or see what websites you\u2019re visiting. A more shocking truth is that the person sitting next you at a\ncoffee shop might be doing exactly the same thing\u2014reading all the packets that come from or go to your\nlaptop. How is this possible, you ask? After finishing Chapter 5, you will know exactly how this is possible.\nSecond, how do I design a network? This is the focus of Chapters 6\u201310. We often think about networks in\nfour layers. The first layer is the Local Area Network, or the LAN (either wired or wireless), which enables\nusers like you and me to access the network. The second is the backbone network that connects the\ndifferent LANs within a building. The third is the core network that connects different buildings on a\ncompany\u2019s campus. The final layer is connections we have to the other campuses within the organization\nand to the Internet. Each of these layers has slightly different concerns, so the way we design networks for\nthem and the technologies we use are slightly different. Although this describes the standard for building\ncorporate networks, you will have a much better understanding of how your wireless router at home\nworks. Perhaps more importantly, you\u2019ll learn why buying the newest and fastest wireless router for your\nhouse or apartment is probably not a good way to spend your money.\nFinally, how do I manage my network to make sure it is secure, provides good performance, and doesn\u2019t\ncost too much? This is the focus of Chapters 11 and 12. Would it surprise you to learn that most companies\nspend between $1,500 and $3,500 per computer per year on network management and security? Yup, we\nspend way more on network management and security each year than we spend to buy the computer in", "source": "Page 22", "chapter_title": "Chapter 11"}
{"id": "3cc44403b6ef-1", "text": "spend way more on network management and security each year than we spend to buy the computer in\nthe first place. And that\u2019s for well-run networks; poorly run networks cost a lot more. Many people think\nnetwork security is a technical problem, and, to some extent, it is. However, the things people do and\ndon\u2019t do cause more security risks than not having the latest technology. According to Symantec, one of\nthe leading companies that sell antivirus software, about half of all security threats are not prevented by\ntheir software. These threats are called targeted attacks, such as phishing attacks (which are emails that\nlook real but instead take you to fake websites) or ransomware (software apps that appear to be useful but\nactually lock your computer and demand a payment to unlock it). Therefore, network management is as\nmuch a people management issue as it is a technology management issue.\nMost readers of this book will be taking classes towards their degree in management information systems\n(MIS) or a closely related field. How does this book relate to what MIS? Let us explain!\nMIS begins with an IT strategy\u2014a plan for buying and/or building IT to help the organization accomplish\nits goals. For most companies, this means increasing revenues and/or decreasing costs. Companies must\ndeploy the right IT to support their business operations. IT has four core capabilities within organizational\nsettings:\n1. Storing and Retrieving Data\u2014Just like humans live in houses, data created by businesses and\nsocieties must live somewhere. The \u201chouse\u201d for data is a database. There are many different kinds of\ndatabases, just like many different kinds of houses. The most frequently used database in\norganizations is an SQL database.\n2. Analyzing and Visualizing Data\u2014Managers need to able to make decisions regarding their business,\nsuch as: What is our bestselling product? Which regions bring in the most revenue? Which regions", "source": "Page 22", "chapter_title": "Chapter 11"}
{"id": "5ab3bb1fc6be-2", "text": "such as: What is our bestselling product? Which regions bring in the most revenue? Which regions\nare losing money? These decisions are made using the data stored in databases. Data is retrieved\nfrom a database and imported to a software like Excel, Tableau, or PowerBI so that these business\nquestions can be answered using a variety of techniques (e.g., aggregation, conditional aggregation,\nand charting).\n3. Automating Data Operations\u2014Many business operations are repeated over and over again, such as\ncalculating the total amount of a items bought at a local store or an e-commerce web site, applying\nany discounts, and determining appropriate taxes. To automate these kinds of every day transactions\non data, we have a wide variety of IT we can buy or build using a variety of programming languages.\n4. Protecting Data\u2014The first three core capabilities are designed to make it easy to store and access\ndata. However, this means that an intruder or malicious employee could also access the data.\nTherefore, organizations must spend resources to protect their data and ensuring the confidentiality,\nintegrity, and availability of the data. We will discuss security capability in Chapter 11.", "source": "Page 22", "chapter_title": "Chapter 11"}
{"id": "50751c6b5812-0", "text": "FIGURE 1-1 What is MIS?\nIn order for the IT strategy to implement the core capabilities, data communications and networking\ninfrastructure must be available. You are using this infrastructure anytime you use the Internet on your\nlaptop and even your cell phone. MIS core capabilities and the IT strategy rest on a solid infrastructure\n(see Figure 1-1). Therefore, understanding how data communications and networking works will enable\nyou to understand what it takes for a modern organization to stay in business and for you to be able to\nwork and connect with your family and friends.\nMANAGEMENT FOCUS 1-1\nCareer Opportunities\nIt\u2019s a great time to be in information technology (IT)! The technology-fueled new economy has\ndramatically increased the demand for skilled IT professionals. According to the U.S. Bureau of\nLabor Statistics and Career Profiles (http://www.careerprofiles.info), 2 out of 10 fastest growing\noccupations are computer network administrator and computer systems analyst, which is expected\nto grow by 22% over the next 10 years with an annual median salary of $72,500\u2014not counting\nbonuses. There are two reasons for this growth. First, companies have to continuously upgrade their\nnetworks and thus need skilled employees to support their expanding IT infrastructure. Second,\npeople are spending more time on their mobile devices, and because employers are allowing them to\nuse these personal devices at work (i.e., BYOD, or bring your own device), the network infrastructure\nhas to support the data that flow from these devices as well as to make sure that they don\u2019t pose a\nsecurity risk.", "source": "Page 23", "chapter_title": "Chapter 11"}
{"id": "8b0d9893a51e-0", "text": "With a few years of experience, there is the possibility to work as an information systems manager,\nfor which the median annual pay is as high as $117,780. An information systems manager plans,\ncoordinates, and directs IT-related activities in such a way that they can fully support the goals of\nany business. Thus, this job requires a good understanding not only of the business but also of the\ntechnology so that appropriate and reliable technology can be implemented at a reasonable cost to\nkeep everything operating smoothly and to guard against cybercriminals.\nBecause of the expanding job market for IT and networking-related jobs, certifications become\nimportant. Most large vendors of network technologies, such as the Microsoft Corporation and Cisco\nSystems Inc., provide certification processes (usually a series of courses and formal exams) so that\nindividuals can document their knowledge. Certified network professionals often earn $10,000 to\n$15,000 more than similarly skilled uncertified professionals\u2014provided that they continue to learn\nand maintain their certification as new technologies emerge.\nSources: http://jobs.aol.com, \u201cIn Demand Careers That Pay $100,00 a Year or More\u201d; www.careerpath.com, \u201cToday\u2019s 20 Fastest-\nGrowing Occupations\u201d; www.cnn.com, \u201c30 Jobs Needing Most Workers in Next Decade,\u201d http://www.careerprofiles.info/top-\ncareers.html.\nBy the time you finish this book, you\u2019ll understand how networks work, how to design networks, and how\nto manage networks. You won\u2019t be an expert, but you\u2019ll be ready to enter an organization and have an\neducated conversation about the role of data communications and networks or move on to more advanced\ncourses and workshops.\n1.2 DATA COMMUNICATIONS NETWORKS\nData communications is the movement of computer information from one point to another by means of\nelectrical or optical transmission systems. Such systems are often called data communications networks.", "source": "Page 24", "chapter_title": "Chapter 11"}
{"id": "f389bb799a30-1", "text": "electrical or optical transmission systems. Such systems are often called data communications networks.\nThis is in contrast to the broader term telecommunications, which includes the transmission of voice and\nvideo (images and graphics) as well as data and usually implies longer distances. In general, data\ncommunications networks collect data from personal computers and other devices and transmit those\ndata to a central server that is a more powerful personal computer, minicomputer, or mainframe, or they\nperform the reverse process, or some combination of the two. Data communications networks facilitate\nmore efficient use of computers and improve the day-to-day control of a business by providing faster\ninformation flow. They also provide message transfer services to allow computer users to talk to one\nanother via email, chat, and video streaming.\nTECHNICAL FOCUS 1-1\nInternet Domain Names\nInternet address names are strictly controlled; otherwise, someone could add a computer to the\nInternet that had the same address as another computer. Each address name has two parts, the\ncomputer name and its domain. The general format of an Internet address is therefore\ncomputer.domain. Some computer names have several parts separated by periods, so some\naddresses have the format computer.computer.computer.domain. For example, the main university\nWeb server at Indiana University (IU) is called www.indiana.edu, whereas the Web server for the\nKelley School of Business at IU is www.kelley.indiana.edu.\nSince the Internet began in the United States, the American address board was the first to assign\ndomain names to indicate types of organizations. Some common U.S. domain names are as follows:\nEDU for an educational institution, usually a university\nCOM for a commercial business\nGOV for a government department or agency\nMIL for a military unit\nORG for a nonprofit organization", "source": "Page 24", "chapter_title": "Chapter 11"}
{"id": "b469db1ca758-0", "text": "As networks in other countries were connected to the Internet, they were assigned their own domain\nnames. Some international domain names are as follows:\nCA for Canada\nAU for Australia\nUK for the United Kingdom\nDE for Germany\nNew top-level domains that focus on specific types of businesses continue to be introduced, such as\nthe following:\nAERO\nfor aerospace companies\nMUSEUM for museums\nNAME\nfor individuals\nPRO\nfor professionals, such as accountants and lawyers\nBIZ\nfor businesses\nMany international domains structure their addresses in much the same way as the United States\ndoes. For example, Australia uses EDU to indicate academic institutions, so an address such as\nxyz.edu.au would indicate an Australian university.\nFor a full list of domain names, see www.iana.org/domains/root/db.\n1.2.1 Components of a Network\nThere are three basic hardware components for a data communications network: a server (e.g., personal\ncomputer, mainframe), a client (e.g., personal computer, terminal), and a circuit (e.g., cable, modem) over\nwhich messages flow. Both the server and client also need special-purpose network software that enables\nthem to communicate.\nThe server stores data or software that can be accessed by the clients. In client\u2013server computing, several\nservers may work together over the network with a client computer to support the business application.\nThe client is the input\u2013output hardware device at the user\u2019s end of a communication circuit. It typically\nprovides users with access to the network and the data and software on the server.\nThe circuit is the pathway through which the messages travel. It is typically a copper wire, although\nfiber-optic cable and wireless transmission are becoming common. There are many devices in the circuit\nthat perform special functions such as switches and routers.", "source": "Page 25", "chapter_title": "Chapter 11"}
{"id": "bd68910041d3-1", "text": "that perform special functions such as switches and routers.\nStrictly speaking, a network does not need a server. Some networks are designed to connect a set of\nsimilar computers that share their data and software with each other. Such networks are called peer-to-\npeer networks because the computers function as equals, rather than relying on a central server to store\nthe needed data and software.\nFigure 1-2 shows a small network that has several personal computers (clients) connected through a\nswitch and cables (circuit) and wirelessly through a wireless access point (AP). In this network,\nmessages move through the switch to and from the computers. The router is a special device that\nconnects two or more networks. The router enables computers on this network to communicate with\ncomputers on the same network or on other networks (e.g., the Internet).\nThe network in Figure 1-3 has three servers. Although one server can perform many functions, networks\nare often designed so that a separate computer is used to provide different services. The file server\nstores data and software that can be used by computers on the network. The Web server stores\ndocuments and graphics that can be accessed from any Web browser, such as Internet Explorer. The Web\nserver can respond to requests from computers on this network or any computer on the Internet. The\nmail server handles and delivers email over the network. Servers are usually personal computers (often\nmore powerful than the other personal computers on the network) but may be mainframes too.", "source": "Page 25", "chapter_title": "Chapter 11"}
{"id": "4049247d344e-0", "text": "FIGURE 1-2 Example of a local area network (LAN)\nFIGURE 1-3 Network architecture components\nThere are three computers that make networks what they are. These are the client, the server, and the\nrouter. The client initiates a communication with the server by sending a request to the server. Once the\nserver receives the request, it processes it, and responds with a response. The router makes this", "source": "Page 26", "chapter_title": "Chapter 11"}
{"id": "1a2b13dc5b74-0", "text": "connection possible.\nAll three devices are computers, and their hardware is pretty much the same\u2014they have a motherboard\nwith CPU (central processing unit), memory, and some storage space. However, only the client had a\nscreen, keyboard, and mouse. Why? Are the server and router less deserving? No. Their purpose is not to\nreceive an input from the user (keyboard or mouse) or display output (screen) but rather to respond to\nrequests, so they have no need for. Pretty clever, isn\u2019t it!\nYou probably know that a client can have a variety of client operating systems (e.g., Windows, Mac OS, or\nLinux) and application software (e.g., a web browser, outlook). Likewise, a server can have different\noperating systems (e.g., Windows, Linux, or z/OS) and application software (e.g., web server software,\nExchange). What do you think is the operating system on a router? It turns out that about 90% of routers\nrun Cisco IOS (Inter-operating system) that was specifically created for routers. In fact, Cisco IOS is the\nsecond most popular operating system in the world, ahead of Mac and Linux. Interesting, right?\n1.2.2 Types of Networks\nThere are many different ways to categorize networks. One of the most common ways is to look at the\ngeographic scope of the network. Figure 1-3 illustrates three types of networks: local area networks\n(LANs), backbone networks (BNs), and wide area networks (WANs). The distinctions among these are\nbecoming blurry because some network technologies now used in LANs were originally developed for\nWANs, and vice versa. Any rigid classification of technologies is certain to have exceptions.\nA local area network (LAN) is a group of computers located in the same general area. A LAN covers a", "source": "Page 27", "chapter_title": "Chapter 11"}
{"id": "2069ae518ff2-1", "text": "clearly defined small area, such as one floor or work area, a single building, or a group of buildings. The\nupper-left diagram in Figure 1-3 shows a small LAN located in the records building at the former\nMcClellan Air Force Base in Sacramento. LANs support high-speed data transmission compared with\nstandard telephone circuits, commonly operating 100 million bits per second (100 Mbps). LANs and\nwireless LANs are discussed in detail in Chapter 6.\nMost LANs are connected to a backbone network (BN), a larger, central network connecting several\nLANs, other BNs, MANs, and WANs. BNs typically span from hundreds of feet to several miles and\nprovide very high-speed data transmission, commonly 100\u20131,000 Mbps. The second diagram in Figure 1-\n3 shows a BN that connects the LANs located in several buildings at McClellan Air Force Base. BNs are\ndiscussed in detail in Chapter 7.\nWide area networks (WANs) connect BNs and MANs (see Figure 1-1). Most organizations do not\nbuild their own WANs by laying cable, building microwave towers, or sending up satellites (unless they\nhave unusually heavy data transmission needs or highly specialized requirements, such as those of the\nDepartment of Defense). Instead, most organizations lease circuits from IXCs (e.g., AT&T, Sprint) and use\nthose to transmit their data. WAN circuits provided by IXCs come in all types and sizes but typically span\nhundreds or thousands of miles and provide data transmission rates from 64 Kbps to 10 Gbps. WANs are\ndiscussed in detail in Chapter 8.\nTwo other common terms are intranets and extranets. An intranet is a LAN that uses the same", "source": "Page 27", "chapter_title": "Chapter 11"}
{"id": "e11d2f5775f6-2", "text": "technologies as the Internet (e.g., Web servers, Java, HTML [Hypertext Markup Language]) but is open to\nonly those inside the organization. For example, although some pages on a Web server may be open to the\npublic and accessible by anyone on the Internet, some pages may be on an intranet and therefore hidden\nfrom those who connect to the Web server from the Internet at large. Sometimes, an intranet is provided\nby a completely separate Web server hidden from the Internet. The intranet for the Information Systems\nDepartment at Indiana University, for example, provides information on faculty expense budgets, class\nscheduling for future semesters (e.g., room, instructor), and discussion forums.\nAn extranet is similar to an intranet in that it, too, uses the same technologies as the Internet but instead\nis provided to invited users outside the organization who access it over the Internet. It can provide access\nto information services, inventories, and other internal organizational databases that are provided only to\ncustomers, suppliers, or those who have paid for access. Typically, users are given passwords to gain\naccess, but more sophisticated technologies such as smart cards or special software may also be required.\nMany universities provide extranets for Web-based courses so that only those students enrolled in the\ncourse can access course materials and discussions.", "source": "Page 27", "chapter_title": "Chapter 11"}
{"id": "62afdd3e5d40-0", "text": "1.3 NETWORK MODELS\nThere are many ways to describe and analyze data communications networks. All networks provide the\nsame basic functions to transfer a message from sender to receiver, but each network can use different\nnetwork hardware and software to provide these functions. All of these hardware and software products\nhave to work together to successfully transfer a message.\nOne way to accomplish this is to break the entire set of communications functions into a series of layers,\neach of which can be defined separately. In this way, vendors can develop software and hardware to\nprovide the functions of each layer separately. The software or hardware can work in any manner and can\nbe easily updated and improved, as long as the interface between that layer and the ones around it\nremains unchanged. Each piece of hardware and software can then work together in the overall network.\nThere are many different ways in which the network layers can be designed. The two most important\nnetwork models are the Open Systems Interconnection Reference (OSI) model and the Internet model. Of\nthe two, the Internet model is the most commonly used; few people use the OSI model, although\nunderstand it is commonly required for network certification exams.\n1.3.1 Open Systems Interconnection Reference Model\nThe Open Systems Interconnection Reference model (usually called the OSI model for short)\nhelped change the face of network computing. Before the OSI model, most commercial networks used by\nbusinesses were built using nonstandardized technologies developed by one vendor (remember that the\nInternet was in use at the time but was not widespread and certainly was not commercial). During the late\n1970s, the International Organization for Standardization (ISO) created the Open System Interconnection\nSubcommittee, whose task was to develop a framework of standards for computer-to-computer\ncommunications. In 1984, this effort produced the OSI model.", "source": "Page 28", "chapter_title": "Chapter 11"}
{"id": "630066a855b1-1", "text": "communications. In 1984, this effort produced the OSI model.\nThe OSI model is the most talked about and most referred to network model. If you choose a career in\nnetworking, questions about the OSI model will be on the network certification exams offered by\nMicrosoft, Cisco, and other vendors of network hardware and software. However, you will probably never\nuse a network based on the OSI model. Simply put, the OSI model never caught on commercially in North\nAmerica, although some European networks use it, and some network components developed for use in\nthe United States arguably use parts of it. Most networks today use the Internet model, which is discussed\nin the next section. However, because there are many similarities between the OSI model and the Internet\nmodel, and because most people in networking are expected to know the OSI model, we discuss it here.\nThe OSI model has seven layers (see Figure 1-4).\nLayer 1: Physical Layer\nThe physical layer is concerned primarily with transmitting data bits (zeros or ones) over a\ncommunication circuit. This layer defines the rules by which ones and zeros are transmitted, such as\nvoltages of electricity, number of bits sent per second, and the physical format of the cables and\nconnectors used.\nLayer 2: Data Link Layer\nThe data link layer manages the physical transmission circuit in layer 1 and transforms it into a circuit\nthat is free of transmission errors as far as layers above are concerned. Because layer 1 accepts and\ntransmits only a raw stream of bits without understanding their meaning or structure, the data link layer\nmust create and recognize message boundaries; that is, it must mark where a message starts and where it\nends. Another major task of layer 2 is to solve the problems caused by damaged, lost, or duplicate\nmessages so the succeeding layers are shielded from transmission errors. Thus, layer 2 performs error", "source": "Page 28", "chapter_title": "Chapter 11"}
{"id": "7a734b999759-2", "text": "messages so the succeeding layers are shielded from transmission errors. Thus, layer 2 performs error\ndetection and correction. It also decides when a device can transmit so that two computers do not try to\ntransmit at the same time. We say, that data link layer has a local responsibility.", "source": "Page 28", "chapter_title": "Chapter 11"}
{"id": "1c0fb952ef95-0", "text": "FIGURE 1-4 Network models. OSI = Open Systems Interconnection Reference\nLayer 3: Network Layer\nThe network layer performs routing. It determines the next computer to which the message should be\nsent, so it can follow the best route through the network and finds the full address for that computer if\nneeded.\nLayer 4: Transport Layer\nThe transport layer deals with end-to-end issues, such as procedures for entering and departing from the\nnetwork. It establishes, maintains, and terminates logical connections for the transfer of data between the\noriginal sender and the final destination of the message. It is responsible for breaking a large data\ntransmission into smaller packets (if needed), ensuring that all the packets have been received,\neliminating duplicate packets, and performing flow control to ensure that no computer is overwhelmed by\nthe number of messages it receives. Although error control is performed by the data link layer, the\ntransport layer can also perform error checking. Therefore, transport layer has a global responsibility.\nLayer 5: Session Layer\nThe session layer is responsible for managing and structuring all sessions. Session initiation must arrange\nfor all the desired and required services between session participants, such as logging on to circuit\nequipment, transferring files, and performing security checks. Session termination provides an orderly\nway to end the session, as well as a means to abort a session prematurely. It may have some redundancy\nbuilt in to recover from a broken transport (layer 4) connection in case of failure. The session layer also\nhandles session accounting so the correct party receives the bill.\nLayer 6: Presentation Layer\nThe presentation layer formats the data for presentation to the user. Its job is to accommodate different\ninterfaces on different computers so the application program need not worry about them. It is concerned\nwith displaying, formatting, and editing user inputs and outputs. For example, layer 6 might perform data", "source": "Page 29", "chapter_title": "Chapter 11"}
{"id": "2b0ee964b6c8-1", "text": "compression, translation between different data formats, and screen formatting. Any function (except\nthose in layers 1 through 5) that is requested sufficiently often to warrant finding a general solution is\nplaced in the presentation layer, although some of these functions can be performed by separate hardware\nand software (e.g., encryption).\nLayer 7: Application Layer\nThe application layer is the end user\u2019s access to the network. The primary purpose is to provide a set of", "source": "Page 29", "chapter_title": "Chapter 11"}
{"id": "39b301c0b527-0", "text": "utilities for application programs. Each user program determines the set of messages and any action it\nmight take on receipt of a message. Other network-specific applications at this layer include network\nmonitoring and network management.\n1.3.2 Internet Model\nThe network model that dominates current hardware and software is a more simple five-layer Internet\nmodel. Unlike the OSI model that was developed by formal committees, the Internet model evolved from\nthe work of thousands of people who developed pieces of the Internet. The OSI model is a formal standard\nthat is documented in one standard, but the Internet model has never been formally defined; it has to be\ninterpreted from a number of standards. The two models have very much in common (see Figure 1-4);\nsimply put, the Internet model collapses the top three OSI layers into one layer. Because it is clear that the\nInternet has won the \u201cwar,\u201d we use the five-layer Internet model for the rest of this book.\nLayer 1: The Physical Layer\nThe physical layer in the Internet model, as in the OSI model, is the physical connection between the\nsender and receiver. Its role is to transfer a series of electrical, radio, or light signals through the circuit.\nThe physical layer includes all the hardware devices (e.g., computers, modems, and switches) and\nphysical media (e.g., cables and satellites). The physical layer specifies the type of connection and the\nelectrical signals, radio waves, or light pulses that pass through it. Chapter 3 discusses the physical layer\nin detail.\nLayer 2: The Data Link Layer\nThe data link layer is responsible for moving a message from one computer to the next computer in the\nnetwork path from the sender to the receiver. The data link layer in the Internet model performs the same\nthree functions as the data link layer in the OSI model. First, it controls the physical layer by deciding", "source": "Page 30", "chapter_title": "Chapter 11"}
{"id": "8a1d1b2a718f-1", "text": "when to transmit messages over the media. Second, it formats the messages by indicating where they start\nand end. Third, it detects and may correct any errors that have occurred during transmission. Chapter 4\ndiscusses the data link layer in detail.\nLayer 3: The Network Layer\nThe network layer in the Internet model performs the same functions as the network layer in the OSI\nmodel. First, it performs routing, in that it selects the next computer to which the message should be sent.\nSecond, it can find the address of that computer if it doesn\u2019t already know it. Chapter 5 discusses the\nnetwork layer in detail.\nLayer 4: The Transport Layer\nThe transport layer in the Internet model is very similar to the transport layer in the OSI model. It\nperforms two functions. First, it is responsible for linking the application layer software to the network\nand establishing end-to-end connections between the sender and receiver when such connections are\nneeded. Second, it is responsible for breaking long messages into several smaller messages to make them\neasier to transmit and then recombining the smaller messages back into the original larger message at the\nreceiving end. The transport layer can also detect lost messages and request that they be resent. Chapter 5\ndiscusses the transport layer in detail.\nLayer 5: Application Layer\nThe application layer is the application software used by the network user and includes much of what\nthe OSI model contains in the application, presentation, and session layers. It is the user\u2019s access to the\nnetwork. By using the application software, the user defines what messages are sent over the network.\nBecause it is the layer that most people understand best and because starting at the top sometimes helps\npeople understand better, Chapter 2 begins with the application layer. It discusses the architecture of\nnetwork applications and several types of network application software and the types of messages they\ngenerate.\nGroups of Layers", "source": "Page 30", "chapter_title": "Chapter 11"}
{"id": "1f354ca1c507-0", "text": "The layers in the Internet are often so closely coupled that decisions in one layer impose certain\nrequirements on other layers. The data link layer and the physical layer are closely tied together because\nthe data link layer controls the physical layer in terms of when the physical layer can transmit. Because\nthese two layers are so closely tied together, decisions about the data link layer often drive the decisions\nabout the physical layer. For this reason, some people group the physical and data link layers together and\ncall them the hardware layers. Likewise, the transport and network layers are so closely coupled that\nsometimes these layers are called the internetwork layers (see Figure 1-4). When you design a\nnetwork, you often think about the network design in terms of three groups of layers: the hardware layers\n(physical and data link), the internetwork layers (network and transport), and the application layer.\n1.3.3 Message Transmission Using Layers\nEach computer in the network has software that operates at each of the layers and performs the functions\nrequired by those layers (the physical layer is hardware, not software). Each layer in the network uses a\nformal language, or protocol, that is simply a set of rules that define what the layer will do and that\nprovides a clearly defined set of messages that software at the layer needs to understand. For example, the\nprotocol used for Web applications is HTTP (Hypertext Transfer Protocol, which is described in more\ndetail in Chapter 2). In general, all messages sent in a network pass through all layers. All layers except\nthe physical layer create a new Protocol Data Unit (PDU) as the message passes through them. The\nPDU contains information that is needed to transmit the message through the network. Some experts use\nthe word packet to mean a PDU. Figure 1-5 shows how a message requesting a Web page would be sent on\nthe Internet.", "source": "Page 31", "chapter_title": "Chapter 11"}
{"id": "1ad761bd9b41-1", "text": "the Internet.\nFIGURE 1-5 Message transmission using layers. IP = Internet Protocol; HTTP = Hypertext Transfer\nProtocol; TCP = Transmission Control Protocol", "source": "Page 31", "chapter_title": "Chapter 11"}
{"id": "bf550c38aed9-0", "text": "Application Layer\nFirst, the user creates a message at the application layer using a Web browser by clicking on a link (e.g.,\nget the home page at www.somebody.com). The browser translates the user\u2019s message (the click on the\nWeb link) into HTTP. The rules of HTTP define a specific PDU\u2014called an HTTP packet\u2014that all Web\nbrowsers must use when they request a Web page. For now, you can think of the HTTP packet as an\nenvelope into which the user\u2019s message (get the Web page) is placed. In the same way that an envelope\nplaced in the mail needs certain information written in certain places (e.g., return address, destination\naddress), so too does the HTTP packet. The Web browser fills in the necessary information in the HTTP\npacket, drops the user\u2019s request inside the packet, then passes the HTTP packet (containing the Web page\nrequest) to the transport layer.\nTransport Layer\nThe transport layer on the Internet uses a protocol called TCP (transmission control protocol), and it, too,\nhas its own rules and its own PDUs. TCP is responsible for breaking large files into smaller packets and for\nopening a connection to the server for the transfer of a large set of packets. The transport layer places the\nHTTP packet inside a TCP PDU (which is called a TCP segment), fills in the information needed by the\nTCP segment, and passes the TCP segment (which contains the HTTP packet, which, in turn, contains the\nmessage) to the network layer.\nNetwork Layer\nThe network layer on the Internet uses a protocol called IP (Internet Protocol), which has its rules and\nPDUs. IP selects the next stop on the message\u2019s route through the network. It places the TCP segment\ninside an IP PDU, which is called an IP packet, and passes the IP packet, which contains the TCP segment,", "source": "Page 32", "chapter_title": "Chapter 11"}
{"id": "ff6dbeb754fa-1", "text": "which, in turn, contains the HTTP packet, which, in turn, contains the message, to the data link layer.\nData Link Layer\nIf you are connecting to the Internet using a LAN, your data link layer may use a protocol called Ethernet,\nwhich also has its own rules and PDUs. The data link layer formats the message with start and stop\nmarkers, adds error checks information, places the IP packet inside an Ethernet PDU, which is called an\nEthernet frame, and instructs the physical hardware to transmit the Ethernet frame, which contains the IP\npacket, which contains the TCP segment, which contains the HTTP packet, which contains the message.\nPhysical Layer\nThe physical layer in this case is network cable connecting your computer to the rest of the network. The\ncomputer will take the Ethernet frame (complete with the IP packet, the TCP segment, the HTTP packet,\nand the message) and send it as a series of electrical pulses through your cable to the server.\nWhen the server gets the message, this process is performed in reverse. The physical hardware translates\nthe electrical pulses into computer data and passes the message to the data link layer. The data link layer\nuses the start and stop markers in the Ethernet frame to identify the message. The data link layer checks\nfor errors and, if it discovers one, requests that the message be resent. If a message is received without\nerror, the data link layer will strip off the Ethernet frame and pass the IP packet (which contains the TCP\nsegment, the HTTP packet, and the message) to the network layer. The network layer checks the IP\naddress and, if it is destined for this computer, strips off the IP packet and passes the TCP segment, which\ncontains the HTTP packet and the message, to the transport layer. The transport layer processes the\nmessage, strips off the TCP segment, and passes the HTTP packet to the application layer for processing.", "source": "Page 32", "chapter_title": "Chapter 11"}
{"id": "e72693efdc9b-2", "text": "The application layer (i.e., the Web server) reads the HTTP packet and the message it contains (the\nrequest for the Web page) and processes it by generating an HTTP packet containing the Web page you\nrequested. Then the process starts again as the page is sent back to you.\nThe Pros and Cons of Using Layers\nThere are three important points in this example. First, there are many different software packages and\nmany different PDUs that operate at different layers to successfully transfer a message. Networking is in\nsome ways similar to the Russian matryoshka, nested dolls that fit neatly inside each other. This is called", "source": "Page 32", "chapter_title": "Chapter 11"}
{"id": "e35107a1af15-0", "text": "encapsulation, because the PDU at a higher level is placed inside the PDU at a lower level so that the\nlower-level PDU encapsulates the higher-level one. The major advantage of using different software and\nprotocols is that it is easy to develop new software, because all one has to do is write software for one level\nat a time. The developers of Web applications, for example, do not need to write software to perform error\nchecking or routing, because those are performed by the data link and network layers. Developers can\nsimply assume those functions are performed and just focus on the application layer. Similarly, it is\nsimple to change the software at any level (or add new application protocols), as long as the interface\nbetween that layer and the ones around it remains unchanged.\nSecond, it is important to note that for communication to be successful, each layer in one computer must\nbe able to communicate with its matching layer in the other computer. For example, the physical layer\nconnecting the client and server must use the same type of electrical signals to enable each to understand\nthe other (or there must be a device to translate between them). Ensuring that the software used at the\ndifferent layers is the same as accomplished by using standards. A standard defines a set of rules, called\nprotocols, that explain exactly how hardware and software that conform to the standard are required to\noperate. Any hardware and software that conform to a standard can communicate with any other\nhardware and software that conform to the same standard. Without standards, it would be virtually\nimpossible for computers to communicate.\nThird, the major disadvantage of using a layered network model is that it is somewhat inefficient. Because\nthere are several layers, each with its own software and PDUs, sending a message involves many software\nprograms (one for each protocol) and many PDUs. The PDUs add to the total amount of data that must be", "source": "Page 33", "chapter_title": "Chapter 11"}
{"id": "70f7b9080072-1", "text": "sent (thus increasing the time it takes to transmit), and the different software packages increase the\nprocessing power needed in computers. Because the protocols are used at different layers and are stacked\non top of one another (take another look at Figure 1-5), the set of software used to understand the\ndifferent protocols is often called a protocol stack.\n1.4 NETWORK STANDARDS\n1.4.1 The Importance of Standards\nStandards are necessary in almost every business and public service entity. For example, before 1904,\nfire hose couplings in the United States were not standard, which meant a fire department in one\ncommunity could not help in another community. The transmission of electric current was not\nstandardized until the end of the nineteenth century, so customers had to choose between Thomas\nEdison\u2019s direct current (DC) and George Westinghouse\u2019s alternating current (AC).\nThe primary reason for standards is to ensure that hardware and software produced by different vendors\ncan work together. Without networking standards, it would be difficult\u2014if not impossible\u2014to develop\nnetworks that easily share information. Standards also mean that customers are not locked into one\nvendor. They can buy hardware and software from any vendor whose equipment meets the standard. In\nthis way, standards help to promote more competition and hold down prices.\nThe use of standards makes it much easier to develop software and hardware that link different networks\nbecause software and hardware can be developed one layer at a time.\n1.4.2 The Standards-Making Process\nThere are two types of standards: de jure and de facto. A de jure standard is developed by an official\nindustry or a government body and is often called a formal standard. For example, there are de jure\nstandards for applications such as Web browsers (e.g., HTTP, HTML), for network layer software (e.g.,", "source": "Page 33", "chapter_title": "Chapter 11"}
{"id": "2a235f6608c8-2", "text": "IP), for data link layer software (e.g., Ethernet IEEE 802.3), and for physical hardware (e.g., V.90\nmodems). De jure standards typically take several years to develop, during which time technology\nchanges, making them less useful.\nDe facto standards are those that emerge in the marketplace and are supported by several vendors but\nhave no official standing. For example, Microsoft Windows is a product of one company and has not been\nformally recognized by any standards organization, yet it is a de facto standard. In the communications\nindustry, de facto standards often become de jure standards once they have been widely accepted.", "source": "Page 33", "chapter_title": "Chapter 11"}
{"id": "74fc8a44cb98-0", "text": "The de jure standardization process has three stages: specification, identification of choices, and\nacceptance. The specification stage consists of developing a nomenclature and identifying the problems to\nbe addressed. In the identification of choices stage, those working on the standard identify the various\nsolutions and choose the optimum solution from among the alternatives. Acceptance, which is the most\ndifficult stage, consists of defining the solution and getting recognized industry leaders to agree on a\nsingle, uniform solution. As with many other organizational processes that have the potential to influence\nthe sales of hardware and software, standards-making processes are not immune to corporate politics and\nthe influence of national governments.\nInternational Organization for Standardization\nOne of the most important standards-making bodies is the International Organization for Standardization\n(ISO), which makes technical recommendations about data communication interfaces (see www.iso.org).\nISO is based in Geneva, Switzerland. The membership is composed of the national standards\norganizations of each ISO member country.\nInternational Telecommunications Union-Telecommunications Group\nThe International Telecommunications Union-Telecommunications Group (ITU-T) is the\ntechnical standards-setting organization of the United Nations International Telecommunications Union,\nwhich is also based in Geneva (see www.itu.int). ITU is composed of representatives from about 200\nmember countries. Membership was originally focused on just the public telephone companies in each\ncountry, but a major reorganization in 1993 changed this, and ITU now seeks members among public- and\nprivate-sector organizations who operate computer or communications networks (e.g., RBOCs) or build\nsoftware and equipment for them (e.g., AT&T).\nAmerican National Standards Institute\nThe American National Standards Institute (ANSI) is the coordinating organization for the U.S.\nnational system of standards for both technology and nontechnology (see www.ansi.org). ANSI has about", "source": "Page 34", "chapter_title": "Chapter 11"}
{"id": "ce4fdeaeb561-1", "text": "1,000 members from both public and private organizations in the United States. ANSI is a standardization\norganization, not a standards-making body, in that it accepts standards developed by other organizations\nand publishes them as American standards. Its role is to coordinate the development of voluntary national\nstandards and to interact with the ISO to develop national standards that comply with the ISO\u2019s\ninternational recommendations. ANSI is a voting participant in the ISO.\nMANAGEMENT FOCUS 1-2\nHow Network Protocols Become Standards\nThere are many standards organizations around the world, but perhaps the best known is the\nInternet Engineering Task Force (IETF). IETF sets the standards that govern how much of the\nInternet operates.\nThe IETF, like all standards organizations, tries to seek consensus among those involved before\nissuing a standard. Usually, a standard begins as a protocol (i.e., a language or set of rules for\noperating) developed by a vendor (e.g., HTML). When a protocol is proposed for standardization, the\nIETF forms a working group of technical experts to study it. The working group examines the\nprotocol to identify potential problems and possible extensions and improvements, and then issues a\nreport to the IETF.\nIf the report is favorable, the IETF issues a Request for Comment (RFC) that describes the\nproposed standard and solicits comments from the entire world. Most large software companies\nlikely to be affected by the proposed standard prepare detailed responses. Many \u201cregular\u201d Internet\nusers also send their comments to the IETF.\nThe IETF reviews the comments and possibly issues a new and improved RFC, which again is posted\nfor more comments. Once no additional changes have been identified, it becomes a proposed\nstandard.", "source": "Page 34", "chapter_title": "Chapter 11"}
{"id": "b19e9d9531d8-0", "text": "Usually, several vendors adopt the proposed standard and develop products based on it. Once at\nleast two vendors have developed hardware or software based on it and it has proven successful in\noperation, the proposed standard is changed to a draft standard. This is usually the final\nspecification, although some protocols have been elevated to Internet standards, which usually\nsignifies mature standards not likely to change.\nThe process does not focus solely on technical issues; almost 90% of the IETF\u2019s participants work for\nmanufacturers and vendors, so market forces and politics often complicate matters. One former\nIETF chairperson who worked for a hardware manufacturer has been accused of trying to delay the\nstandards process until his company had a product ready, although he and other IETF members\ndeny this. Likewise, former IETF directors have complained that members try to standardize every\nproduct their firms produce, leading to a proliferation of standards, only a few of which are truly\nuseful.\nSources: \u201cHow Networking Protocols Become Standards,\u201d PC Week, March 17, 1997; \u201cGrowing Pains,\u201d Network World, April 14,\n1997.\nMANAGEMENT FOCUS 1-3\nKeeping Up with Technology\nThe data communications and networking arena changes rapidly. Significant new technologies are\nintroduced and new concepts are developed almost every year. It is therefore important for network\nmanagers to keep up with these changes.\nThere are at least three useful ways to keep up with change. First and foremost for users of this book\nis the website for this book, which contains updates to the book, additional sections, teaching\nmaterials, and links to useful websites.\nSecond, there are literally hundreds of thousands of websites with data communications and\nnetworking information. Search engines can help you find them. A good initial starting point is the", "source": "Page 35", "chapter_title": "Chapter 11"}
{"id": "5c0efe87405c-1", "text": "networking information. Search engines can help you find them. A good initial starting point is the\ntelecom glossary at http://www.atis.org. Three other useful sites are http://www.zdnet.com,\nhttp://www.networkcomputing.com, and http://www.zdnet.com.\nThird, there are many useful magazines that discuss computer technology in general and networking\ntechnology in particular, including Network Computing, Info World, Info Week, and CIO Magazine.", "source": "Page 35", "chapter_title": "Chapter 11"}
{"id": "d70ea1d79d1c-0", "text": "FIGURE 1-6 Some common data communications standards. HTML = Hypertext Markup Language;\nHTTP = Hypertext Transfer Protocol; IMAP = Internet Message Access Protocol; IP = Internet Protocol;\nLAN = Local Area Network; MPEG = Motion Picture Experts Group; POP = Post Office Protocol; TCP =\nTransmission Control Protocol\nInstitute of Electrical and Electronics Engineers\nThe Institute of Electrical and Electronics Engineers (IEEE) is a professional society in the\nUnited States whose Standards Association (IEEE-SA) develops standards (see www.standards.ieee.org).\nThe IEEE-SA is probably most known for its standards for LANs. Other countries have similar groups; for\nexample, the British counterpart of IEEE is the Institution of Electrical Engineers (IEE).\nInternet Engineering Task Force\nThe Internet Engineering Task Force (IETF) sets the standards that govern how much of the\nInternet will operate (see www.ietf.org). The IETF is unique in that it doesn\u2019t really have official\nmemberships. Quite literally anyone is welcome to join its mailing lists, attend its meetings, and comment\non developing standards. The role of the IETF and other Internet organizations is discussed in more detail\nin Chapter 8; also, see the box entitled \u201cHow Network Protocols Become Standards.\u201d\n1.4.3 Common Standards\nThere are many different standards used in networking today. Each standard usually covers one layer in a\nnetwork. Some of the most commonly used standards are shown in Figure 1-6. At this point, these models\nare probably just a maze of strange names and acronyms to you, but by the end of the book, you will have", "source": "Page 36", "chapter_title": "Chapter 11"}
{"id": "6be45f861a0b-0", "text": "a good understanding of each of these. Figure 1-6 provides a brief road map for some of the important\ncommunication technologies we discuss in this book.\nFor now, there is one important message you should understand from Figure 1-6: For a network to\noperate, many different standards must be used simultaneously. The sender of a message must use one\nstandard at the application layer, another one at the transport layer, another one at the network layer,\nanother one at the data link layer, and another one at the physical layer. Each layer and each standard is\ndifferent, but all must work together to send and receive messages.\nEither the sender and receiver of a message must use the same standards or, more likely, there are devices\nbetween the two that translate from one standard into another. Because different networks often use\nsoftware and hardware designed for different standards, there is often a lot of translation between\ndifferent standards.\n1.5 FUTURE TRENDS\nThe field of data communications has grown faster and become more important than computer\nprocessing itself. Both go hand in hand, but we have moved from the computer era to the communication\nera. Three major trends are driving the future of communications and networking.\n1.5.1 Wireless LAN and BYOD\nThe rapid development of mobile devices, such as smartphones and tablets, has encouraged employers to\nallow their employees to bring these devices to work and use them to access data, such as their work\nemail. This movement, called bring your own device, or Bring Your On Device (BYOD), is a great way\nto get work quickly, saves money, and makes employees happy. But BYOD also brings its own problems.\nEmployers need to add or expand their Wireless Local Area Networks (WLANs) to support all these new\ndevices.\nAnother important problem is security. Employees bring these devices to work so that they can access not", "source": "Page 37", "chapter_title": "Chapter 11"}
{"id": "e7a87890302a-1", "text": "Another important problem is security. Employees bring these devices to work so that they can access not\nonly their email but also other critical company assets, such as information about their clients, suppliers,\nor sales. Employers face myriad decisions about how to manage access to company applications for\nBYOD. Companies can adopt two main approaches: (1) native apps or (2) browser-based technologies.\nNative apps require an app to be developed for each application that an employee might be using for\nevery potential device that the employee might use (e.g., iPhone, Android, Windows). The browser-\nbased approach (often referred to as responsive design using HTML5) doesn\u2019t create an app but rather\nrequires employees to access the application through a Web browser. Both these approaches have their\npros and cons, and only the future will show which one is the winner.\nWhat if an employee loses his or her mobile phone or tablet so that the application that accesses critical\ncompany data now can be used by anybody who finds the device? Will the company\u2019s data be\ncompromised? Device and data loss practices now have to be added to the general security practices of the\ncompany. Employees need to have apps to allow their employer to wipe their phones clean in case of loss\nso that no company data are compromised (e.g., SOTI\u2019s MobiControl). In some cases, companies require\nthe employee to allow monitoring of the device at all times, to ensure that security risks are minimized.\nHowever, some argue that this is not a good practice because the device belongs to the employee, and\nmonitoring it 24/7 invades the employee\u2019s privacy.\n1.5.2 The Internet of Things\nTelephones and computers used to be separate. Today voice and data have converged into unified\ncommunications, with phones plugged into computers or directly into the LAN using Voice over Internet", "source": "Page 37", "chapter_title": "Chapter 11"}
{"id": "f33910b95e52-2", "text": "communications, with phones plugged into computers or directly into the LAN using Voice over Internet\nProtocol (VoIP). Vonage and Skype have taken this one step further and offer telephone service over the\nInternet at dramatically lower prices than traditional separate landline phones, whether from traditional\nphones or via computer microphones and speakers.\nComputers and networks can also be built into everyday things, such as kitchen appliances, doors, and\nshoes. In the future, the Internet will move from being a Web of computers to also being an Internet of\nThings (IoT), as smart devices become common, that creates the Network of Things (NoT) where all", "source": "Page 37", "chapter_title": "Chapter 11"}
{"id": "5d885c517b3e-0", "text": "this interaction between IoT devices will happen seamlessly, without human intervention. And you might\nalready be asking Alexa or Siri for advice on where to eat, lock, and unlock your apartment, turn on/off\nyour lights, or change the thermostat setting. For this to happen, Alexa/Siri must be able to communicate\nwith your lock or thermostat without any intervention from you.\nGoogle is a leading innovator in the IoT world. It entered the IoT playground with the Nest thermostat.\nGoogle has also been developing a self-driving car that not only passes a standard driving test but also has\nfewer collisions than cars driven by humans. Other car developers are also developing autonomous\nvehicles.", "source": "Page 38", "chapter_title": "Chapter 11"}
{"id": "f9384d5af2ed-0", "text": "FIGURE 1-7 A security robot on the IOT\nIoT technologies are not restricted to consumer use. To the contrary, they are used in many places such as\nmanufacturing, process automation, decision analytics, and smart electrical grids. However, the\nunderlying principle of all the applications is that IoT devices are connected to the Internet either through\nwired or wireless Ethernet. Figure 1-7 shows an IOT device that we encountered in a mall in Boston. It is\nsemi-autonomous security robot, meaning it can be controlled by a human or set to roam its environment.", "source": "Page 39", "chapter_title": "Chapter 11"}
{"id": "750b039d2ba8-0", "text": "Ten years ago, network managers would never have thought about the need to manage robots over their\nnetworks.\n1.5.3 Massively Online\nYou have probably heard of massively multiplayer online games, such as World of Warcraft, where you\ncan play with thousands of players in real time. Well, today not only games are massively online.\nEducation is massively online. Edx, Khan Academy, Lynda.com, or Code Academy have websites that offer\nthousands of education modules for children and adults in myriad fields to help them learn. Your class\nvery likely also has an online component. You may even use this textbook online and decide whether your\ncomments are for you only, for your instructor, or for the entire class to read. In addition, you may have\nheard about massive open online courses, or MOOC. MOOC enable students who otherwise wouldn\u2019t have\naccess to elite universities to get access to top knowledge without having to pay the tuition. These classes\nare offered by universities, such as Stanford, UC Berkeley, MIT, UCLA, Carnegie Mellon, and of course,\nIndiana University, free of charge and for no credit (although at some universities, you can pay and get\ncredit toward your degree).\nPolitics has also moved massively online. President Obama reached out to the crowds and ordinary voters\nnot only through his Facebook page but also through Reddit and Google Hangouts. President Trump\u2019s use\nof Twitter is unprecedented. He can directly reach millions of followers\u2014a strategy that paid off in the\n2016 elections. Finally, massively online allows activists to reach masses of people in a very short period of\ntime to initiate change. Examples of use of YouTube videos or Facebook for activism include the Arab\nSpring, Kony 2012, or the use of sarin gas in Syria.\nSo what started as a game with thousands of people being online at the same time is being reinvented for", "source": "Page 40", "chapter_title": "Chapter 11"}
{"id": "48d7fbe44cac-1", "text": "good use in education, politics, and activism. Only the future will show what humanity can do with what\nmassively online has to offer.\nWhat these three trends have in common is that there will be an increasing demand for professionals who\nunderstand development of data communications and networking infrastructure to support this growth.\nThere will be more and more need to build faster and more secure networks that will allow individuals\nand organizations to connect to resources, probably stored on cloud infrastructure (either private or\npublic). This need will call not only for engineers who deeply understand the technical aspects of networks\nbut also for highly social individuals who embrace technology in creative ways to allow business to achieve\na competitive edge through utilizing this technology. So the call is for you who are reading this book\u2014you\nare in the right place at the right time!\n1.6 IMPLICATIONS FOR CYBER SECURITY\nAt the end of each chapter, we provide key implications for cyber security that arise from the topics\ndiscussed in the chapter. We draw implications that focus on improving the management of networks and\ninformation systems as well as implications for cyber security of an individual and an organization.\nThere are three key implications for management from this chapter. First, networks and the Internet\nchange almost everything. Computer networks and the Internet are designed to quickly and easily move\ninformation from distant locations and to enable individuals inside and outside the firm to access\ninformation and products from around the world. However, this ease of doing work on the Internet makes\nit also easy for cyber criminals to steal files from your computer or to put files on your computer (such as\nviruses or malware). Understanding how computer networks and the Internet work and how computers\ncommunicate via networks is the first step toward defending your own computer and the computers on a\ncompany\u2019s network.\nSecond, today\u2019s networking environment requires that a wide variety of devices could connect. Employees\u2019", "source": "Page 40", "chapter_title": "Chapter 11"}
{"id": "5e1f3b505f6b-2", "text": "Second, today\u2019s networking environment requires that a wide variety of devices could connect. Employees\u2019\nuse of their own devices under BYOD policies increases security risks, as does the move to the IoT. Several\nsecurity experts say that IoT doesn\u2019t stand for Internet of Things; it stands for Internet of Targets.\nIndividuals and companies have to balance BYOD and IoT risks and rewards to create a useful and secure\ncomputing infrastructure.\nThird, as the demand for network services and network capacity increases, so too will the need for secure\nstorage and server space and secure transfer of data. Finding efficient ways to securely store all the", "source": "Page 40", "chapter_title": "Chapter 11"}
{"id": "efd4bae3d1a6-0", "text": "information we generate will open new market opportunities. Today, Google has almost a million Web\nservers (see Figure 1-8). If we assume that each server costs an average of $1,000, the money large\ncompanies spend on storage is close to $1 billion. Capital expenditure of this scale is then increased by\nmoney spent on power and staffing. One way companies can reduce this amount of money is to store their\ndata using cloud computing. The good news is that more and more cloud providers meet or exceed\ngovernment required security measures for data storage and transfer.\nFIGURE 1-8 One server farm with more than 1,000 servers\nSUMMARY\nIntroduction The information society, where information and intelligence are the key drivers of\npersonal, business, and national success, has arrived. Data communications is the principal enabler\nof the rapid information exchange and will become more important than the use of computers\nthemselves in the future. Successful users of data communications, such as Wal-Mart, can gain\nsignificant competitive advantage in the marketplace.\nNetwork Definitions A LAN is a group of computers located in the same general area. A BN is a\nlarge central network that connects almost everything on a single company site. A metropolitan area\nnetwork (MAN) encompasses a city or county area. A wide area network (WAN) spans city, state, or\nnational boundaries.\nNetwork Model Communication networks are often broken into a series of layers, each of which\ncan be defined separately, to enable vendors to develop software and hardware that can work\ntogether in the overall network. In this book, we use a five-layer model. The application layer is the\napplication software used by the network user. The transport layer takes the message generated by\nthe application layer and, if necessary, breaks it into several smaller messages. The network layer\naddresses the message and determines its route through the network. The data link layer formats the", "source": "Page 41", "chapter_title": "Chapter 11"}
{"id": "3e082cbb1a3c-1", "text": "addresses the message and determines its route through the network. The data link layer formats the\nmessage to indicate where it starts and ends, decides when to transmit it over the physical media, and\ndetects and corrects any errors that occur in transmission. The physical layer is the physical\nconnection between the sender and receiver, including the hardware devices (e.g., computers,\nterminals, and modems) and physical media (e.g., cables and satellites). Each layer, except the", "source": "Page 41", "chapter_title": "Chapter 11"}
{"id": "dfa25c05f8bb-0", "text": "physical layer, adds a Protocol Data Unit (PDU) to the message.\nStandards Standards ensure that hardware and software produced by different vendors can work\ntogether. A de jure standard is developed by an official industry or a government body. De facto\nstandards are those that emerge in the marketplace and are supported by several vendors but have no\nofficial standing. Many different standards and standards-making organizations exist.\nFuture Trends At the same time as the use of BYOD offers efficiency at the workplace, it opens up\nthe doors for security problems that companies need to consider. Our interactions with colleagues\nand family will very likely change in the next 5\u201310 years because of the Internet of Things (IoT),\nwhere devices will interact with each other without human intervention. Finally, massively online not\nonly changed the way we play computer games but also showed that humanity can change its history.\nKEY TERMS\nAmerican National Standards Institute (ANSI)\napplication layer\nattacks\nbackbone network (BN)\nBring Your On Device (BYOD)\nbrowser-based\ncable\ncircuit\nclient\ncyber security\ndata link layer\nextranet\nfile server\nhardware layers\nInstitute of Electrical and Electronics Engineers (IEEE)\nInternational Telecommunications Union-Telecommunications Group (ITU-T)\nInternet Engineering Task Force (IETF)\nInternet model\nInternet of Things (IoT)\nInternet service provider (ISP)\ninternetwork layers\nintranets\nlayers\nlocal area network (LAN)\nmail server\nNative apps\nnetwork layer\nNetwork of Things (NoT)\nOpen Systems Interconnection Reference model (OSI model)", "source": "Page 42", "chapter_title": "Chapter 11"}
{"id": "c28fb3d815ce-0", "text": "OSI model\npeer-to-peer networks\nphysical layer\nProtocol Data Unit (PDU)\nprotocol stack\nprotocol\nRequest for Comment (RFC)\nrouter\nserver\nStandards\nswitch\ntransport layer\nWeb server\nwide area networks (WANs)\nwireless access point\nQUESTIONS\n1. How can data communications networks affect businesses?\n2. How do data communications networks support the four core capabilities of MIS?\n3. Discuss three important applications of data communications networks in business and personal use.\n4. How do LANs differ from WANs and BNs?\n5. What is a circuit?\n6. What is a client?\n7. What is a server?\n8. What is a router?\n9. There are three computers that make the Internet work. Name them and describe their similarities\nand differences.\n10. Why are network layers important?\n11. Describe the seven layers in the OSI network model and what they do.\n12. Describe the five layers in the Internet network model and what they do.\n13. Explain how a message is transmitted from one computer to another using layers.\n14. Describe the three stages of standardization.\n15. How are Internet standards developed?\n16. Describe two important data communications standards-making bodies. How do they differ?\n17. What is the purpose of a data communications standard?\n18. Discuss three trends in communications and networking.\n19. Why has the Internet model replaced the OSI model?\n20. In the 1980s, when we wrote the first edition of this book, there were many, many more protocols in\ncommon use at the data link, network, and transport layers than there are today. Why do you think\nthe number of commonly used protocols at these layers has declined? Do you think this trend will", "source": "Page 43", "chapter_title": "Chapter 11"}
{"id": "276ca8d04908-0", "text": "continue? What are the implications for those who design and operate networks?\n21. The number of standardized protocols in use at the application layer has significantly increased since\nthe 1980s. Why? Do you think this trend will continue? What are the implications for those who\ndesign and operate networks?\n22. How many bits (not bytes) are there in a 10-page text document? Hint: There are approximately 350\nwords on a double-spaced page. We need 8 bits to encode each character.\n23. What are three current cyber security issues we face on the Internet?\n24. What is the Internet of Things (IoT)? What are the benefits and risks of IoT?\nEXERCISES\nA. Investigate the latest cyber security threats. What services and/or data were affected by these threats?\nWhat was done to recover from this situation?\nB. It turns out that not all industries are equally sensitive to cyber-attacks. There are multiple industries\nthat belong to the \u201ccritical infrastructure.\u201d Investigate which industries belong to the critical\ninfrastructure, why are they part of it, and what laws govern this group of industries regarding cyber\nsecurity.\nC. Discuss the issue of communications monopolies and open competition with an economics instructor\nand relate his or her comments to your data communication class.\nD. Find a college or university offering a specialized degree in telecommunications or data\ncommunications and describe the program.\nE. Investigate the IoT. What IoT devices are you most interested in? Why?\nF. Investigate the networks in your school or organization. Describe the important LANs and BNs in use\n(but do not describe the specific clients, servers, or devices on them).\nG. Visit the Internet Engineering Task (IETF) website (www.ietf.org). Describe one standard that is in\nthe RFC stage.", "source": "Page 44", "chapter_title": "Chapter 11"}
{"id": "fbb74639092f-1", "text": "the RFC stage.\nH. Discuss how the revolution/evolution of communications and networking is likely to affect how you\nwill work and live in the future.\nI. Investigate the pros and cons of developing native apps versus taking a browser-based approach.\nMINICASES\nI. Global Consultants John Adams is the chief information officer (CIO) of Global Consultants (GC),\na very large consulting firm with offices in more than 100 countries around the world. GC is about to\npurchase a set of several Internet-based financial software packages that will be installed in all of\ntheir offices. There are no standards at the application layer for financial software but several\nsoftware companies that sell financial software (call them group A) use one de facto standard to\nenable their software to work with one another\u2019s software. However, another group of financial\nsoftware companies (call them group B) use a different de facto standard. Although both groups have\nsoftware packages that GC could use, GC would really prefer to buy one package from group A for one\ntype of financial analysis and one package from group B for a different type of financial analysis. The\nproblem, of course, is that then the two packages cannot communicate and GC\u2019s staff would end up\nhaving to type the same data into both packages. The alternative is to buy two packages from the\nsame group\u2014so that data could be easily shared\u2014but that would mean having to settle for second\nbest for one of the packages. Although there have been some reports in the press about the two\ngroups of companies working together to develop one common standard that will enable software to\nwork together, there is no firm agreement yet. What advice would you give Adams?\nII. Atlas Advertising Atlas Advertising is a regional advertising agency with offices in Boston, New\nYork, Providence, Washington, D.C., and Philadelphia. (1) Describe the types of networks you think", "source": "Page 44", "chapter_title": "Chapter 11"}
{"id": "2301b83dea36-0", "text": "they would have (e.g., LANs, BNs, WANs) and where they are likely to be located. (2) What types of\nstandard protocols and technologies do you think they are using at each layer (e.g., see Figures 1-3\nand 1-5)?\nIII. Consolidated Supplies Consolidated Supplies is a medium-sized distributor of restaurant supplies\nthat operates in Canada and several northern U.S. states. They have 12 large warehouses spread\nacross both countries to service their many customers. Products arrive from the manufacturers and\nare stored in the warehouses until they are picked and put on a truck for delivery to their customers.\nThe networking equipment in their warehouses is old and is starting to give them problems; these\nproblems are expected to increase as the equipment gets older. The vice president of operations, Pat\nMcDonald, would like to replace the existing LANs and add some new wireless LAN technology into\nall the warehouses, but he is concerned that now may not be the right time to replace the equipment.\nHe has read several technology forecasts that suggest there will be dramatic improvements in\nnetworking speeds over the next few years, especially in wireless technologies. He has asked you for\nadvice about upgrading the equipment. Should Consolidated Supplies replace all the networking\nequipment in all the warehouses now, should it wait until newer networking technologies are\navailable, or should it upgrade some of the warehouses this year, some next year, and some the year\nafter, so that some warehouses will benefit from the expected future improvements in networking\ntechnologies?\nIV. Asia Importers Caisy Wong is the owner of a small catalog company that imports a variety of\nclothes and houseware from several Asian countries and sells them to its customers over the Web and\nby telephone through a traditional catalog. She has read about the convergence of voice and data and", "source": "Page 45", "chapter_title": "Chapter 11"}
{"id": "d5a98a96f82d-1", "text": "by telephone through a traditional catalog. She has read about the convergence of voice and data and\nis wondering about changing her current traditional, separate, and rather expensive telephone and\ndata services into one service offered by a new company that will supply both telephone and data over\nher Internet connection. What are the potential benefits and challenges that Asia Importers should\nconsider in making the decision about whether to move to one integrated service?\nTECH UPDATES\nIn every chapter, we will offer couple ideas to investigate.\nTopic A: From ARPANET To NoT: What Happened to the Internet?\nWhat started as a secret military project in the 1960s, grew to the largest network of interconnected\ncomputers known as the Internet, which is changing into the largest network of interconnected devices\nthat (at the time they were discovered) were not meant to talk to each other. Discuss the history of the\nInternet (ARPANET) and the future of it (NoT).\nTopic B: A Brief History of Cyber Attacks\nWe all heard about modern ransomware that encrypts every file on your computer and you must pay a\nransom (in bitcoin, of course!) to get these files unencrypted, or phishing attacks (emails that pretend to\nbe real) that ask you to download a file or click on link and can cause lot of harm to you and your data.\nBut, when did this start? What was the evolution of attacks on the Internet? How did individuals,\nbusiness, and governments respond to these attacks? What is the current citation with cyber-attacks?\nDeliverables\nYour job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title Slide\n2. Short description of topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.", "source": "Page 45", "chapter_title": "Chapter 11"}
{"id": "e9ebe5e71d2f-2", "text": "3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along", "source": "Page 45", "chapter_title": "Chapter 11"}
{"id": "0781c1dc936c-0", "text": "5. How does it relate to material covered in class so far (and in the future)\n6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 1A\nInternet as We Know It Today\nWe think about access to the Internet as a daily normal. We check our email, news, chat with friends and\nfamily, and do shopping on the Internet. The objective of this activity is for you to experience this\nconvergence.\n1. Investigate the history of the Internet at http://www.vox.com/a/internet-maps that shows you a\nhistory of the Internet through maps.\n2. See how many people are using the Internet in your state/country at\nhttps://www.akamai.com/us/en/resources/visualizing-akamai/real-time-web-monitor.jsp?\ntab=traffic&theme=dark.\n3. See the cyber security attacks in progress on information systems connected to the Internet by\nclicking on the Attacks tab at https://www.akamai.com/us/en/resources/visualizing-akamai/real-\ntime-web-monitor.jsp?tab=attacks&theme=dark.\nDeliverable\nDeliverable Write a one-page summary of the history and current state of the Internet. What was the most\nsurprising thing you learned during your investigation?\nHANDS-ON ACTIVITY 1B\nSeeing the PDUs in Your Messages\nWe talked about how messages are transferred using layers and the different PDUs used at each layer. The\nobjective of this activity is for you to see the different PDUs in the messages that you send. To do this, we\u2019ll\nuse Wireshark, which is one of the world\u2019s foremost network protocol analyzers and is the de facto", "source": "Page 46", "chapter_title": "Chapter 11"}
{"id": "76fc8cf02723-1", "text": "standard that most professional and education institutions use today. It is used for network\ntroubleshooting, network analysis, software and communications protocol development, and general\neducation about how networks work.\nWireshark enables you to see all messages sent by your computer, as well as some or all of the messages\nsent by other computers on your LAN, depending on how your LAN is designed. Most modern LANs are\ndesigned to prevent you from eavesdropping on other computer\u2019s messages, but some older ones still\npermit this. Normally, your computer will ignore the messages that are not addressed for your computer,\nbut Wireshark enables you to eavesdrop and read messages sent to and from other computers.\nWireshark is free. Before you start this activity, download and install it from https://www.wireshark.org.\n1. Start Wireshark.\n2. Click on Capture and then Interfaces. Click the Start button next to the active interface (the one that\nis receiving and sending packets). Your network data will be captured from this moment on.\n3. Open your browser and go to a Web page that you have not visited recently (a good one is\nwww.iana.org).\n4. Once the Web page has loaded, go back to Wireshark and stop the packet capture by clicking on\nCapture and then Stop (the hot key for this is Ctrl + E).", "source": "Page 46", "chapter_title": "Chapter 11"}
{"id": "7256ff20eac9-0", "text": "5. You will see results similar to those in Figure 1-9. There are three windows below the tool bar:\na. The top window is the Packet List. Each line represents a single message or packet that was\ncaptured by Wireshark. Different types of packets will have different colors. For example, HTTP\npackets are colored green. Depending on how busy your network is, you may see a small number\nof packets in this window or a very large number of packets.\nb. The middle window is the Packet Detail. This will show the details for any packet you click on in\nthe top window.\nc. The bottom window shows the actual contents of the packet in hexadecimal format, so it is\nusually hard to read. This window is typically used by network programmers to debug errors.\n6. Let\u2019s take a look at the packets that were used to request the Web page and send it to your computer.\nThe application layer protocol used on the Web is HTTP, so we\u2019ll want to find the HTTP packets. In\nthe Filter toolbar, type http and hit enter.\nFIGURE 1-9 Wireshark capture\n7. This will highlight all the packets that contain HTTP packets and will display the first one in Packet\nDetail window. Look at the Packet Detail window in Figure 1-8 to see the PDUs in the message we\u2019ve\nhighlighted. You\u2019ll see that it contains an Ethernet II Frame, an IP packet, a TCP segment, and an\nHTTP packet. You can see inside any or all of these PDUs by clicking on the +box in front of them. In\nFigure 1-8, you\u2019ll see that we\u2019ve clicked the +box in front of the HTTP packet to show you what\u2019s\ninside it.\nDeliverables", "source": "Page 47", "chapter_title": "Chapter 11"}
{"id": "e1cce0645035-1", "text": "inside it.\nDeliverables\n1. List the PDU at layers 2, 3, and 4 that were used to transmit your HTTP GET packet.\na. Locate your HTTP GET packet in the Packet List and click on it.\nb. Look in the Packet Detail window to get the PDU information.\n2. How many different HTTP GET packets were sent by your browser? Not all the HTTP packets are\nGET packets, so you\u2019ll have to look through them to answer this question.", "source": "Page 47", "chapter_title": "Chapter 11"}
{"id": "cd928447495f-0", "text": "3. List at least five other protocols that Wireshark displayed in the Packet List window. You will need to\nclear the filter by clicking on the \u201cClear\u201d icon that is on the right of the Filter toolbar.", "source": "Page 48", "chapter_title": "Chapter 11"}
{"id": "cd17c1d7da51-0", "text": "PART TWO FUNDAMENTAL CONCEPTS", "source": "Page 49", "chapter_title": "Chapter 11"}
{"id": "09c04aba2d66-0", "text": "CHAPTER 2\nAPPLICATION LAYER\nThe application layer (also called layer 5) is the software that enables the user to perform useful work. The\nsoftware at the application layer is the reason for having the network because it is this software that\nprovides the business value. This chapter focuses on the four fundamental types of application\narchitectures used at the application layer (host-based, client-based, client\u2013server, cloud-based), plus a\nfifth legacy architecture (peer-to-peer). It then looks at the Internet and the primary software application\npackages it enables: the Web, email, and Telnet.\nOBJECTIVES\nUnderstand host-based, client-based, client\u2013server, and cloud-based application architectures\nUnderstand how the Web works\nUnderstand how email works\nBe aware of how Telnet and instant messaging work\nOUTLINE\n2.1 Introduction\n2.2 Application Architectures\n2.2.1 Host-Based Architectures\n2.2.2 Client-Based Architectures\n2.2.3 Client\u2013Server Architectures\n2.2.4 Cloud Computing Architectures\n2.2.5 Peer-to-Peer Architectures\n2.2.6 Choosing Architectures\n2.3 World Wide Web\n2.3.1 How the Web Works\n2.3.2 Inside an HTTP Request\n2.3.3 Inside an HTTP Response\n2.4 Electronic Mail\n2.4.1 How Email Works\n2.4.2 Inside an SMTP Packet\n2.4.3 Attachments in Multipurpose Internet Mail Extension\n2.5 Other Applications\n2.5.1 Telnet\n2.5.2 Videoconferencing\n2.6 Implications for Cyber Security\nSummary", "source": "Page 50", "chapter_title": "Chapter 11"}
{"id": "4b3b20b723c2-0", "text": "2.1 INTRODUCTION\nNetwork applications are the software packages that run in the application layer. You should be quite\nfamiliar with many types of network software, because it is these application packages that you use when\nyou use the network. In many respects, the only reason for having a network is to enable these\napplications.\nIn this chapter, we first discuss five basic architectures for network applications and how each of those\narchitectures affects the design of networks. Because you probably have a good understanding of\napplications such as the Web and word processing, we will use those as examples of different application\narchitectures. We then examine several common applications used on the Internet (e.g., Web, email) and\nuse those to explain how application software interacts with the networks. By the end of this chapter, you\nshould have a much better understanding of the application layer in the network model and what exactly\nwe meant when we used the term protocol data unit in Chapter 1.\n2.2 APPLICATION ARCHITECTURES\nIn Chapter 1, we discussed how the three basic components of a network (client computer, server\ncomputer, and circuit) worked together. In this section, we will get a bit more specific about how the client\ncomputer and the server computer can work together to provide application software to the users. An\napplication architecture is the way in which the functions of the application layer software are spread\namong the clients and servers in the network.\nThe work done by any application program can be divided into five general functions. The first is data\nstorage. Most application programs require data to be stored and retrieved, whether it is a small file such\nas a memo produced by a word processor or a large database such as an organization\u2019s accounting\nrecords. The second function is data access logic, the processing required to access data, which often\nmeans database queries in SQL (structured query language). The third function is the application logic", "source": "Page 51", "chapter_title": "Chapter 11"}
{"id": "4b6a393a2034-1", "text": "means database queries in SQL (structured query language). The third function is the application logic\n(sometimes called business logic), which also can be simple or complex, depending on the application.\nThe fourth function is the presentation logic (sometimes called the user interface), the presentation of\ninformation to the user and the acceptance of the user\u2019s commands. The fifth function is services logic,\nwhich is the provision of services to other applications (e.g., application program interfaces (API)). This is\nlike the user interface, but enables other application software packages to make requests, rather than\nusers. Not every application has services logic. These five functions\u2014data storage, data access logic,\napplication logic, presentation logic, and services logic\u2014are the basic building blocks of any application.\nTECHNICAL FOCUS 2-1\nCloud Computing Deployment Models\nWhen an organization decides to use cloud-based architecture, it needs to decide on which\ndeployment model will it use. There are three deployment models from which to choose:\nPrivate cloud As the name suggests, private clouds are created for the exclusive use of a single\nprivate organization. The cloud (hardware and software) would be hosted by the organization in\na private data center. This deployment model provides the highest levels of control, privacy, and\nsecurity. This model is often used by organizations needing to satisfy regulations posed by\nregulators, such as in the financial and health-care industries.\nPublic cloud This deployment model is used by multiple organizations that share the same\ncloud resources. The level of control is lower than in private clouds, and many companies are\nconcerned with the security of their data. However, this deployment model doesn\u2019t require any\nupfront capital investment, and the selected service can be up and running in a few days. Public\nclouds are a good choice when a lot of people in the organization are using the same application.", "source": "Page 51", "chapter_title": "Chapter 11"}
{"id": "29d92f559e2e-2", "text": "Because of this, the most frequently used software as a service (SaaS) is email. For example,\nmany universities have moved to this model for their students.", "source": "Page 51", "chapter_title": "Chapter 11"}
{"id": "8f1eaa221720-0", "text": "Community cloud This deployment model is used by organizations that have a common\npurpose. Rather than each organization creating its own private cloud, organizations decide to\ncollaborate and pool their resources. Although this cloud is not private, only a limited number of\ncompanies have access to it. Community clouds are considered to be a subset of public clouds.\nTherefore, community clouds realize the benefits from cloud infrastructure (such as speed of\ndeployment) with the added level of privacy and security that private clouds offer. This\ndeployment model is often used in the government, health care, and finance industries,\nmembers of which have similar application needs and require a very high level of security.\nSometimes an organization will choose to use only one of these deployment models for all its\ncloud-based applications. This strategy is called a pure strategy, such as a pure private cloud\nstrategy or a pure public cloud strategy. In other cases, the organization is best supported by a\nmix of public, private, and community clouds for different applications. This strategy is called a\nhybrid cloud strategy. A hybrid cloud strategy allows the organization to take advantage of\nthe benefits that these different cloud deployment models offer. For example, a hospital can use\nGmail for its email application (public cloud) but a private cloud for patient data, which require\nhigh security. The downside of a hybrid cloud strategy is that an organization has to deal with\ndifferent platforms and cloud providers. However, the truth is that this strategy offers the\ngreatest flexibility, so most organizations eventually end up with this strategy.\nThere are many ways in which these five functions can be allocated between the client computers and the\nservers in a network. There are four fundamental application architectures in use today. In host-based\narchitectures, the server (or host computer) performs virtually all of the work. In client-based\narchitectures, the client computers perform most of the work. In client\u2013server architectures, the", "source": "Page 52", "chapter_title": "Chapter 11"}
{"id": "1e59e3a77dff-1", "text": "work is shared between the servers and clients. In cloud-based architectures, the cloud provides services\n(software, platform, and/or infrastructure) to the client. Although the client\u2013server architecture is the\ndominant application architecture, cloud-based architecture is becoming the runner-up because it\noffers rapid scalability and deployability of computer resources.\n2.2.1 Host-Based Architectures\nThe very first data communications networks developed in the 1960s were host-based, with the server\n(usually a large mainframe computer) performing all functions. The clients (usually terminals) enabled\nusers to send and receive messages to and from the host computer. The clients merely captured\nkeystrokes, sent them to the server for processing, and accepted instructions from the server on what to\ndisplay (see Figure 2-1).\nThis very simple architecture often works very well. Application software is developed and stored on the\none server along with all data. If you\u2019ve ever used a terminal or Citrix Receiver, you\u2019ve used a host-based\napplication. There is one point of control, because all messages flow through the one central server. In\ntheory, there are economies of scale, because all computer resources are centralized (but more on cost\nlater).\nThere are two fundamental problems with host-based networks. First, the server must process all\nmessages. As the demands for more and more network applications grow, many servers become\noverloaded and unable to quickly process all the users\u2019 demands. Prioritizing users\u2019 access becomes\ndifficult. Response time becomes slower, and network managers are required to spend increasingly more\nmoney to upgrade the server. Unfortunately, upgrades to the mainframes that are usually the servers in\nthis architecture are \u201clumpy.\u201d That is, upgrades come in large increments and are expensive (e.g.,\n$500,000); it is difficult to upgrade \u201ca little.\u201d", "source": "Page 52", "chapter_title": "Chapter 11"}
{"id": "b863f3e76138-0", "text": "FIGURE 2-1 Host-based architecture\n2.2.2 Client-Based Architectures\nIn the late 1980s, there was an explosion in the use of personal computers. Today, more than 90% of most\norganizations\u2019 total computer processing power now resides on personal computers, not in centralized\nmainframe computers. Part of this expansion was fueled by a number of low-cost, highly popular\napplications such as word processors, spreadsheets, and presentation graphics programs. It was also\nfueled in part by managers\u2019 frustrations with application software on host mainframe computers. Most\nmainframe software is not as easy to use as personal computer software, is far more expensive, and can\ntake years to develop. In the late 1980s, many large organizations had application development backlogs\nof 2\u20133 years; that is, getting any new mainframe application program written would take years. New York\nCity, for example, had a 6-year backlog. In contrast, managers could buy personal computer packages or\ndevelop personal computer-based applications in a few months.\nWith client-based architectures, the clients are personal computers on a LAN, and the server is usually\nanother personal computer on the same network. The application software on the client computers is\nresponsible for the presentation logic, the application logic, and the data access logic; the server simply\nstores the data (Figure 2-2). There is no services logic.\nThis simple architecture often works very well. If you\u2019ve ever used a word processor and stored your\ndocument file on a server (or written a program in Visual Basic or C that runs on your computer but stores\ndata on a server), you\u2019ve used a client-based architecture.\nThe fundamental problem in client-based networks is that all data on the server must travel to the client\nfor processing. For example, suppose the user wishes to display a list of all employees with company life", "source": "Page 53", "chapter_title": "Chapter 11"}
{"id": "00c20cc8eb52-1", "text": "insurance. All the data in the database (or all the indices) must travel from the server where the database\nis stored over the network circuit to the client, which then examines each record to see if it matches the\ndata requested by the user. This can overload the network circuits because far more data are transmitted\nfrom the server to the client than the client actually needs.\n2.2.3 Client\u2013Server Architectures\nMost applications written today use client\u2013server architectures. Client\u2013server architectures attempt to\nbalance the processing between the client and the server by having both do some of the logic. In these\nnetworks, the client is responsible for the presentation logic, whereas the server is responsible for the data\naccess logic and data storage. The application logic may either reside on the client, reside on the server, or", "source": "Page 53", "chapter_title": "Chapter 11"}
{"id": "b24435aeb2ed-0", "text": "be split between both.\nFigure 2-3 shows one example, with the presentation logic and application logic on the client, and services\nlogic, application logic, data access logic and data storage on the server. In this case, the client software\naccepts user requests and performs the application logic that produces database requests that are\ntransmitted to the server. The server software accepts the database requests, performs the data access\nlogic, and transmits the results to the client. The client software accepts the results and presents them to\nthe user.\nWhen you used a Web browser to get pages from a Web server, you used a client\u2013server architecture.\nLikewise, if you\u2019ve ever written a program that uses SQL to talk to a database on a server, you\u2019ve used a\nclient\u2013server architecture.\nFIGURE 2-2 Client-based architecture\nFIGURE 2-3 Two-tier thick client client\u2013server architecture\nFor example, if the user requests a list of all employees with company life insurance, the client would\naccept the request, format it so that it could be understood by the server and transmit it to the server. On\nreceiving the request, the server searches the database for all requested records and then transmits only\nthe matching records to the client, which would then present them to the user. The same would be true for\ndatabase updates; the client accepts the request and sends it to the server. The server processes the update\nand responds (either accepting the update or explaining why not) to the client, which displays it to the\nuser.\nOne of the strengths of client\u2013server networks is that they enable software and hardware from different", "source": "Page 54", "chapter_title": "Chapter 11"}
{"id": "c4a206255238-0", "text": "vendors to be used together. But this is also one of their disadvantages, because it can be difficult to get\nsoftware from different vendors to work together. One solution to this problem is middleware, software\nthat sits between the application software on the client and the application software on the server.\nMiddleware does two things. First, it provides a standard way of communicating that can translate\nbetween software from different vendors. Many middleware tools began as translation utilities that\nenabled messages sent from a specific client tool to be translated into a form understood by a specific\nserver tool.\nThe second function of middleware is to manage the message transfer from clients to servers (and vice\nversa) so that clients need not know the specific server that contains the application\u2019s data. The\napplication software on the client sends all messages to the middleware, which forwards them to the\ncorrect server. The application software on the client is therefore protected from any changes in the\nphysical network. If the network layout changes (e.g., a new server is added), only the middleware must be\nupdated.\nThere are literally dozens of standards for middleware, each of which is supported by different vendors\nand provides different functions. Two of the most important standards are Distributed Computing\nEnvironment (DCE) and Common Object Request Broker Architecture (CORBA). Both of these standards\ncover virtually all aspects of the client\u2013server architecture but are quite different. Any client or server\nsoftware that conforms to one of these standards can communicate with any other software that conforms\nto the same standard. Another important standard is Open Database Connectivity (ODBC), which\nprovides a standard for data access logic.\nTwo-Tier, Three-Tier, and n-Tier Architectures\nThere are many ways in which the application logic can be partitioned between the client and the server.\nThe example in Figure 2-3 is one of the most common. In this case, the server is responsible for the data", "source": "Page 55", "chapter_title": "Chapter 11"}
{"id": "7c5fc8ce47c7-1", "text": "and the client, the application and presentation. This is called a two-tier architecture, because it uses\nonly two sets of computers, one set of clients and one set of servers.\nA three-tier architecture uses three sets of computers, as shown in Figure 2-4. In this case, the\nsoftware on the client computer is responsible for presentation logic, an application server is responsible\nfor the services logic and application logic, and a separate database server is responsible for the data\naccess logic and data storage.\nn-tier architecture uses more than three sets of computers. In this case, the client is responsible for\npresentation logic, a database server is responsible for the data access logic and data storage, and the\nservices logic and application logic are spread across two or more different sets of servers. Figure 2-5\nshows an example of an n-tier architecture. The client uses the Web browser (presentation logic). The\nWeb server that responds to the user\u2019s requests, either by providing Hypertext Markup Language (HTML)\npages and graphics (application logic) or by sending the request to the application server that perform\nvarious tasks (services logic and application logic). The database server stores all the data (data access\nlogic and data storage). Each of these four components is separate, making it easy to spread the different\ncomponents on different servers and to partition the application logic on two different servers.", "source": "Page 55", "chapter_title": "Chapter 11"}
{"id": "a5603135c084-0", "text": "FIGURE 2-4 Three-tier thin client client\u2013server architecture\nFIGURE 2-5 The n-tier thin client client\u2013server architecture\nThe primary advantage of an n-tier client\u2013server architecture compared with a two-tier architecture (or a\nthree-tier compared with a two-tier) is that it separates the processing that occurs to better balance the\nload on the different servers; it is more scalable. In Figure 2-5, we have three separate servers, which", "source": "Page 56", "chapter_title": "Chapter 11"}
{"id": "d8a2b79bdab7-0", "text": "provides more power than if we had used a two-tier architecture with only one server. If we discover that\nthe application server is too heavily loaded, we can simply replace it with a more powerful server, or even\nput in two application servers. Conversely, if we discover the database server is underused, we could put\ndata from another application on it.\nThere are two primary disadvantages to an n-tier architecture compared with a two-tier architecture (or a\nthree-tier with a two-tier). First, it puts a greater load on the network. If you compare Figures 2-3, 2-4,\nand 2-5, you will see that the n-tier model requires more communication among the servers; it generates\nmore network traffic so you need a higher capacity network. Second, it is much more difficult to program\nand test software in n-tier architectures than in two-tier architectures because more devices have to\ncommunicate to complete a user\u2019s transaction.\nFIGURE 2-6 The typical two-tier thin-client architecture of the Web\nThin Clients versus Thick Clients\nAnother way of classifying client\u2013server architectures is by examining how much of the application logic\nis placed on the client computer. A thin-client architecture places little or no application logic on the\nclient (e.g., Figure 2-5), whereas a thick-client architecture places all or almost all of the application\nlogic on the client (e.g., Figure 2-3). There is no direct relationship between thin and thick clients and two-\n, three-, and n-tier architectures. For example, Figure 2-6 shows a typical Web architecture: a two-tier\narchitecture with a thin client. One of the biggest forces favoring thin clients is the Web.\nThin clients are much easier to manage. If an application changes, only the server with the application", "source": "Page 57", "chapter_title": "Chapter 11"}
{"id": "86ca628dd96c-1", "text": "Thin clients are much easier to manage. If an application changes, only the server with the application\nlogic needs to be updated. With a thick client, the software on all of the clients would need to be updated.\nConceptually, this is a simple task; one simply copies the new files to the hundreds of affected client\ncomputers. In practice, it can be a very difficult task. The thin-client architecture also enables cloud-based\narchitecture, which is discussed next.\n2.2.4 Cloud Computing Architectures\nThe traditional client\u2013server architecture can be complicated and expensive to deploy. Every application\nhas to be hosted on a server so that it can fulfill requests from potentially thousands of clients. An\norganization has hundreds of applications, so running a successful client\u2013server architecture requires a\nvariety of software and hardware and the skilled personnel who can build and maintain this architecture.\nCloud computing architectures are different because they outsource part or all of the infrastructure to\nother firms that specialize in managing that infrastructure. Thus, cloud computing utilizes a network of\nremote servers hosted by an organization to store, manage, and process data. There are three common\ncloud-based architecture models that an organization can pick from. Figure 2-7 summarizes these three", "source": "Page 57", "chapter_title": "Chapter 11"}
{"id": "cb7a9babcd9a-0", "text": "models and compares them to the client\u2013server architecture.\nThe first column of this figure shows the thin client\u2013server architecture, in which the organization\nmanages the entire application software and hardware. In addition to the software components we\u2019ve\ndiscussed previously (the application logic, data access logic, and the data themselves), the servers need\nan operating system (e.g., Windows, Linux). Most companies also use virtualization software to install\nmany virtual or logical servers on the same physical computer. This software (VMware is one of the\nleaders) creates a separate partition on the physical server for each of the logical servers. Each partition\nhas its own operations system and its own server software and works independently from the other\npartitions.\nThis software must run on some hardware, which includes a server, a storage device, and the network\nitself. The server may be a large computer or a server farm. A server farm is a cluster of computers\nlinked together so that they act as one computer. Requests arrive at the server farm (e.g., Web requests)\nand are distributed among the computers so that no one computer is overloaded. Each computer is\nseparate so that if one fails, the server farm simply bypasses it. Server farms are more complex than single\nservers because work must be quickly coordinated and shared among the individual computers. Server\nfarms are very scalable because one can always add another computer. Figure 2-8 shows one row of a\nserver farm at Indiana University. There are seven more rows like this one in this room, and another room\ncontains about the same number.\nFIGURE 2-7 Cloud architecture models compared to thin client\u2013server architecture\nSource: Adapted from www.cbc.radio-canada.ca/en/reporting-to-canadians/sync/sync-issue-1-2012/cloud-services", "source": "Page 58", "chapter_title": "Chapter 11"}
{"id": "26dbc57af571-0", "text": "FIGURE 2-8 One row of a server farm at Indiana University\nMany companies use separate storage devices instead of the hard disks in the servers themselves. These\nstorage devices are special-purpose hard disks designed to be very large and very fast. The six devices on\nthe left of Figure 2-8 comprise a special storage device called a storage area network (SAN).\nSoftware as a Service (SaaS)\nSaaS is one of the three cloud computing models. With SaaS, an organization outsources the entire\napplication to the cloud provider (see the last column of Figure 2-7) and uses it as any other application\nthat is available via a browser (thin client). SaaS is based on multitenancy. This means that rather than\nhaving many copies of the same application, there is only one application that everybody shares, yet\neverybody can customize it for his or her specific needs. Imagine a giant office building in which all people\nshare the infrastructure (water, A/C, electricity) but can customize the offices they are renting. The\ncustomers can customize the app and don\u2019t have to worry about upgrades, security, or underlying\ninfrastructure because the cloud provider does it all. The most frequently used SaaS application is email.\nAt Indiana University, all student email is outsourced to Google\u2019s Gmail. Customer relationship\nmanagement (CRM) from Salesforce.com is another very commonly used SaaS.\nPlatform as a Service (PaaS)\nPaaS is another of the three cloud computing models. What if there is an application you need but no\ncloud provider offers one you like? You can build your own application and manage your own data on the\ncloud infrastructure provided by your cloud supplier. This model is called Platform as a Service\n(PaaS). The developers in your organization decide what programming language to use to develop the\napplication of choice. The needed hardware and software infrastructure, called the platform, is rented", "source": "Page 59", "chapter_title": "Chapter 11"}
{"id": "904cc12f77fb-1", "text": "application of choice. The needed hardware and software infrastructure, called the platform, is rented\nfrom the cloud provider (see Figure 2-7). In this case, the organization manages the application and its\nown data but uses the database software (data access logic) and operating system provided by the cloud\nprovider. PaaS offers a much faster development and deployment of custom applications at a fraction of", "source": "Page 59", "chapter_title": "Chapter 11"}
{"id": "98d5b63c588d-0", "text": "the cost required for the traditional client\u2013server architecture. PaaS providers include Amazon Elastic\nCloud Compute (EC2), Microsoft Windows Azure, and Google App Engine.\nInfrastructure as a Service (IaaS)\nAs you can see in Figure 2-7, with Infrastructure as a Service (IaaS), the cloud provider manages the\nhardware, including servers, storage, and networking components. The organization is responsible for all\nthe software, including operating system (and virtualization software), database software, and its\napplications and data. IaaS is sometimes referred to also as HaaS, or Hardware as a Service, because\nin this cloud model, only the hardware is provided; everything else is up to the organization. This model\nallows a decrease in capital expenditures for hardware and maintaining the proper environment (e.g.,\ncooling) and redundancy, and backups for data and applications. Providers of IaaS are Amazon Web\nServices, Microsoft Windows Azure, and Akamai.\nIn conclusion, cloud computing is a technology that fundamentally changed the way we think about\napplications in that they are rented and paid for as a service. The idea is the same as for utilities\u2014water,\ngas, cable, and phone. The provider of the utility builds and is running the infrastructure; you plug in and\nsign up for a type of service. Sometimes you pay as you go (water, gas), or you sign up for a level of service\n(phone, cable).\n2.2.5 Peer-to-Peer Architectures\nPeer-to-peer (P2P) architectures are very old, but their modern design became popular in the early 2000s\nwith the rise of P2P file-sharing applications (e.g., Napster). With a P2P architecture, all computers act as\nboth a client and a server. Therefore, all computers perform all four functions: presentation logic,", "source": "Page 60", "chapter_title": "Chapter 11"}
{"id": "2c78222bfbf8-1", "text": "both a client and a server. Therefore, all computers perform all four functions: presentation logic,\napplication logic, data access logic, and data storage (see Figure 2-9). With a P2P file-sharing application,\na user uses the presentation, application, and data access logic installed on his or her computer to access\nthe data stored on another computer in the network. With a P2P application-sharing network (e.g., grid\ncomputing such as seti.org), other users in the network can use others\u2019 computers to access application\nlogic as well.\nFIGURE 2-9 Peer-to-peer architecture\nThe advantage of P2P networks is that the data can be installed anywhere on the network. They spread the\nstorage throughout the network, even globally, so they can be very resilient to the failure of any one\ncomputer. The challenge is finding the data. There must be some central server that enables you to find\nthe data you need, so P2P architectures often are combined with a client\u2013server architecture. Security is a\nmajor concern in most P2P networks, so P2P architectures are not commonly used in organizations,\nexcept for specialized computing needs (e.g., grid computing).", "source": "Page 60", "chapter_title": "Chapter 11"}
{"id": "b044483a74e1-0", "text": "2.2.6 Choosing Architectures\nEach of the preceding architectures has certain costs and benefits, so how do you choose the \u201cright\u201d\narchitecture? In many cases, the architecture is simply a given; the organization has a certain architecture,\nand one simply has to use it. In other cases, the organization is acquiring new equipment and writing new\nsoftware and has the opportunity to develop a new architecture, at least in some part of the organization.\nAlmost all new applications today are client\u2013server applications. Client\u2013server architectures provide the\nbest scalability, the ability to increase (or decrease) the capacity of the servers to meet changing needs.\nFor example, we can easily add or remove application servers or database servers depending on whether\nwe need more or less capacity for application software or database software and storage.\nClient\u2013server architectures are also the most reliable. We can use multiple servers to perform the same\ntasks, so that if one server fails, the remaining servers continue to operate and users don\u2019t notice\nproblems.\nFinally, client\u2013server architectures are usually the cheapest because many tools exist to develop them.\nAnd lots of client\u2013server software exists for specific parts of applications so we can more quickly buy parts\nof the application we need. For example, no one writes Shopping Carts anymore; it\u2019s cheaper to buy a\nShopping Carts software application and put it on an application server than it is to write your own.\nMANAGEMENT FOCUS 2-1\nCloud Computing with Salesforce.com\nSalesforce.com, the world\u2019s number one cloud platform, is the poster child for cloud computing.\nCompanies used to buy and install software for CRM, the process of identifying potential customers,\nmarketing to them, converting them into customers, and managing the relationship to retain them.\nThe software and needed servers were expensive and took a long time to acquire and install.\nTypically, only large firms could afford it.", "source": "Page 61", "chapter_title": "Chapter 11"}
{"id": "d9526f2ef6fe-1", "text": "Typically, only large firms could afford it.\nSalesforce.com changed this by offering a cloud computing solution. The CRM software offered by\nsalesforce.com resides on the salesforce.com servers. There is no need to buy and install new\nhardware or software. Companies just pay a monthly fee to access the software over the Internet.\nCompanies can be up and running in weeks, not months, and it is easy to scale from a small\nimplementation to a very large one. Because salesforce.com can spread its costs over so many users,\nthey can offer deals to small companies that normally wouldn\u2019t be able to afford to buy and install\ntheir own software. Salesforce is a very competitive organization that is keeping up with the mobile\nworld too. In fall 2013, it announced the \u201cSalesforce $1 Million Hackathon,\u201d where hundreds of\nteams competed to build the next killer mobile app on the Salesforce platform. Yup, the winning\nteam will walk away with $1 million! Although we don\u2019t know the winner of this largest single\nhackathon, the reader can discover this easily by googling it.\nClient\u2013server architectures also enable cloud computing. As we mentioned in Section 2.2.4, companies\nmay choose to run a SaaS because of low price and high scalability compared to traditional client\u2013server\narchitecture hosted at home. One major issue that companies face when choosing SaaS is the security of\nthe data. Each company has to evaluate the risk of its data being compromised and select its cloud\nprovider carefully. However, SaaS is gaining popularity and companies are becoming more and more\naccustomed to this solution.\n2.3 WORLD WIDE WEB\nThe Web was first conceived in 1989 by Sir Tim Berners-Lee at the European Particle Physics Laboratory\n(CERN) in Geneva. His original idea was to develop a database of information on physics research, but he", "source": "Page 61", "chapter_title": "Chapter 11"}
{"id": "5609e37b79b0-2", "text": "found it difficult to fit the information into a traditional database. Instead, he decided to use a hypertext\nnetwork of information. With hypertext, any document can contain a link to any other document.", "source": "Page 61", "chapter_title": "Chapter 11"}
{"id": "f14bb2b6b82f-0", "text": "CERN\u2019s first Web browser was created in 1990, but it was 1991 before it was available on the Internet for\nother organizations to use. By the end of 1992, several browsers had been created for UNIX computers by\nCERN and several other European and American universities, and there were about 30 Web servers in the\nentire world. In 1993, Marc Andreessen, a student at the University of Illinois, led a team of students that\nwrote Mosaic, the first graphical Web browser, as part of a project for the university\u2019s National Center for\nSupercomputing Applications (NCSA). By the end of 1993, the Mosaic browser was available for UNIX,\nWindows, and Macintosh computers, and there were about 200 Web servers in the world. Today, no one\nknows for sure how many Web servers there are. There are more than 250 million separate websites, but\nmany of these are hosted on the same servers by large hosting companies such as godaddy.com or Google\nsites.\n2.3.1 How the Web Works\nThe Web is a good example of a two-tier client\u2013server architecture (Figure 2-10). Each client computer\nneeds an application layer software package called a Web browser. There are many different browsers,\nsuch as Microsoft\u2019s Internet Explorer. Each server on the network that will act as a Web server needs an\napplication layer software package called a Web server. There are many different Web servers, such as\nthose produced by Microsoft and Apache.\nTo get a page from the Web, the user must type the Internet uniform resource locator (URL) for the\npage he or she wants (e.g., www.yahoo.com) or click on a link that provides the URL. The URL specifies\nthe Internet address of the Web server and the directory and name of the specific page wanted. If no", "source": "Page 62", "chapter_title": "Chapter 11"}
{"id": "635c05f28e36-1", "text": "directory and page are specified, the Web server will provide whatever page has been defined as the site\u2019s\nhome page.\nFIGURE 2-10 How the Web works\nFor the requests from the Web browser to be understood by the Web server, they must use the same\nstandard protocol or language. If there were no standard and each Web browser used a different\nprotocol to request pages, then it would be impossible for a Microsoft Web browser to communicate with\nan Apache Web server, for example.\nThe standard protocol for communication between a Web browser and a Web server is Hypertext\nTransfer Protocol (HTTP). To get a page from a Web server, the Web browser issues a special packet\ncalled an HTTP request that contains the URL and other information about the Web page requested\n(see Figure 2-10). Once the server receives the HTTP request, it processes it and sends back an HTTP\nresponse, which will be the requested page or an error message (see Figure 2-10).\nThis request\u2013response dialogue occurs for every file transferred between the client and the server. For\nexample, suppose the client requests a Web page that has two graphic images. Graphics are stored in\nseparate files from the Web page itself using a different file format than the HTML used for the Web page\n(e.g., in JPEG [Joint Photographic Experts Group] format). In this case, there would be three request\u2013", "source": "Page 62", "chapter_title": "Chapter 11"}
{"id": "a28e688de630-0", "text": "response pairs. First, the browser would issue a request for the Web page, and the server would send the\nresponse. Then, the browser would begin displaying the Web page and notice the two graphic files. The\nbrowser would then send a request for the first graphic and a request for the second graphic, and the\nserver would reply with two separate HTTP responses, one for each request.\n2.3.2 Inside an HTTP Request\nThe HTTP request and HTTP response are examples of the packets we introduced in Chapter 1 that are\nproduced by the application layer and sent down to the transport, network, data link, and physical layers\nfor transmission through the network. The HTTP response and HTTP request are simple text files that\ntake the information provided by the application (e.g., the URL to get) and format it in a structured way so\nthat the receiver of the message can clearly understand it.\nAn HTTP request from a Web browser to a Web server has three parts. The first two parts are required;\nthe last is optional. The parts are as follows:\nThe request line, which starts with a command (e.g., get), provides the Web page, and ends with the\nHTTP version number that the browser understands; the version number ensures that the Web\nserver does not attempt to use a more advanced or newer version of the HTTP standard that the\nbrowser does not understand.\nThe request header, which contains a variety of optional information such as the Web browser\nbeing used (e.g., Internet Explorer) and the date.\nThe request body, which contains information sent to the server, such as information that the user\nhas typed into a form.\nFigure 2-11 shows an example of an HTTP request for a page on our Web server, formatted using version\n1.1 of the HTTP standard. This request has only the request line and the request header, because no", "source": "Page 63", "chapter_title": "Chapter 11"}
{"id": "766bfc556a1f-1", "text": "request body is needed for this request. This request includes the date and time of the request (expressed\nin Greenwich Mean Time [GMT], the time zone that runs through London) and name of the browser used\n(Mozilla is the code name for the browser). The \u201cReferrer\u201d field means that the user obtained the URL for\nthis Web page by clicking on a link on another page, which in this case is a list of faculty at Indiana\nUniversity (i.e., www.indiana.edu/\u223cisdept/faculty.htm). If the referrer field is blank, then it means the\nuser typed the URL himself or herself. You can see inside HTTP headers yourself at\nwww.rexswain.com/httpview.html.\nFIGURE 2-11 An example of a request from a Web browser to a Web server using the HTTP (Hypertext\nTransfer Protocol) standard", "source": "Page 63", "chapter_title": "Chapter 11"}
{"id": "16ffb5127ce7-0", "text": "MANAGEMENT FOCUS 2-2\nTop Players in Cloud Email\nAmong the wide variety of applications that organizations are using, email is most frequently\ndeployed as SaaS. Four major industry players provide email as SaaS: Google, Microsoft, USA.NET,\nand Intermedia. Although cloud-based email seems to appeal more to smaller companies, it provides\na cost\u2013effective solution for organizations with up to 15,000 users (as a rule of thumb). Google was\nthe first company to enter this market and offered Google Apps, Calendar, and 30 Gb of storage in\naddition to email. Microsoft entered this market in 2008 and offered Microsoft Office 365. Microsoft\noffers not only email but the whole MS Office Suite. And, of course, all the office applications are\naccessible from multiple devices. USA.NET is a SaaS company that offers Microsoft Exchange and\nrobust security features that meet the federal and industry regulations, such as FINRA and HIPAA.\nIt services approximately 6,000 organizations worldwide that provide financial, health care, energy,\nand critical infrastructure services. In addition, USA.NET offers Security-as-a-Service platform from\nthe cloud. Finally, Intermedia, which was founded in 1995, is the largest Microsoft-hosted Exchange\nprovider. This was the first company to offer Hosted Microsoft Exchange, and today, it has 90,000\ncustomers and more than 700,000 users. Just like Microsoft, Intermedia delivers the Office Suite in\nthe cloud.\nThe prices for the services these companies offer differ quite a bit. The cheapest of these four\ncompanies is Google, starting at $4.17 per user per month. However, these are basic prices that\nincrease with the number of features and services added.\nThe response body in this example shows a Web page in Hypertext Markup Language (HTML).", "source": "Page 64", "chapter_title": "Chapter 11"}
{"id": "85787ec31542-1", "text": "The response body in this example shows a Web page in Hypertext Markup Language (HTML).\nThe response body can be in any format, such as text, Microsoft Word, Adobe PDF, or a host of other\nformats, but the most commonly used format is HTML. HTML was developed by CERN at the same\ntime as the first Web browser and has evolved rapidly ever since. HTML is covered by standards\nproduced by the IETF, but Microsoft keeps making new additions to HTML with every release of its\nbrowser, so the HTML standard keeps changing.\n2.3.3 Inside an HTTP Response\nThe format of an HTTP response from the server to the browser is very similar to that of the HTTP\nrequest. It, too, has three parts, with the first required and the last two optional:\nThe response status, which contains the HTTP version number the server has used, a status code\n(e.g., 200 means \u201cOK\u201d; 404 means \u201cnot found\u201d), and a reason phrase (a text description of the status\ncode).\nThe response header, which contains a variety of optional information, such as the Web server\nbeing used (e.g., Apache), the date, and the exact URL of the page in the response.\nThe response body, which is the Web page itself.\nFigure 2-12 shows an example of a response from our Web server to the request in Figure 2-11. This\nexample has all three parts. The response status reports \u201cOK,\u201d which means the requested URL was found\nand is included in the response body. The response header provides the date, the type of Web server\nsoftware used, the actual URL included in the response body, and the type of file. In most cases, the actual\nURL and the requested URL are the same, but not always. For example, if you request an URL but do not", "source": "Page 64", "chapter_title": "Chapter 11"}
{"id": "7969938b78a6-2", "text": "specify a file name (e.g., www.indiana.edu), you will receive whatever file is defined as the home page for\nthat server, so the actual URL will be different from the requested URL.", "source": "Page 64", "chapter_title": "Chapter 11"}
{"id": "32dce3eee3b3-0", "text": "FIGURE 2-12 An example of a response from a Web server to a Web browser using the HTTP standard\n2.4 ELECTRONIC MAIL\nElectronic mail (or email) was one of the earliest applications on the Internet and is still among the most\nheavily used today. With email, users create and send messages to one user, several users, or all users on a\ndistribution list. Most email software enables users to send text messages and attach files from word\nprocessors, spreadsheets, graphics programs, and so on. Many email packages also permit you to filter or\norganize messages by priority.", "source": "Page 65", "chapter_title": "Chapter 11"}
{"id": "d6d439b468b4-0", "text": "Several standards have been developed to ensure compatibility between different email software\npackages. Any software package that conforms to a certain standard can send messages that are formatted\nusing its rules. Any other package that understands that particular standard can then relay the message to\nits correct destination; however, if an email package receives a mail message in a different format, it may\nbe unable to process it correctly. Many email packages send using one standard but can understand\nmessages sent in several different standards. The most commonly used standard is SMTP (Simple Mail\nTransfer Protocol). Other common standards are X.400 and CMC (Common Messaging Calls). In this\nbook, we will discuss only SMTP, but CMC and X.400 both work essentially the same way. SMTP, X.400,\nand CMC are different from one another (in the same way that English differs from French or Spanish),\nbut several software packages are available that translate between them, so that companies that use one\nstandard (e.g., CMC) can translate messages they receive that use a different standard (e.g., SMTP) into\ntheir usual standard as they first enter the company and then treat them as \u201cnormal\u201d email messages after\nthat.\n2.4.1 How Email Works\nThe Simple Mail Transfer Protocol (SMTP) is the most commonly used email standard simply\nbecause it is the email standard used on the Internet. Email works similarly to how the Web works, but it\nis a bit more complex. SMTP email is usually implemented as a two-tier thick client\u2013server application,\nbut not always. We first explain how the normal two-tier thick client architecture works and then quickly\ncontrast that with two alternate architectures.\nTwo-Tier Email Architecture\nWith a two-tier thick client\u2013server architecture, each client computer runs an application layer software\npackage called a mail user agent, which is usually more commonly called an email client (Figure 2-12).", "source": "Page 66", "chapter_title": "Chapter 11"}
{"id": "aa2f3db60478-1", "text": "There are many common email client software packages such as Eudora and Outlook. The user creates the\nemail message using one of these email clients, which formats the message into an SMTP packet that\nincludes information such as the sender\u2019s address and the destination address.\nThe user agent then sends the SMTP packet to a mail server that runs a special application layer software\npackage called a mail transfer agent, which is more commonly called mail server software (see Figure\n2-13).\nThis email server reads the SMTP packet to find the destination address and then sends the packet on its\nway through the network\u2014often over the Internet\u2014from mail server to mail server, until it reaches the\nmail server specified in the destination address (see Figure 2-13). The mail transfer agent on the\ndestination server then stores the message in the receiver\u2019s mailbox on that server. The message sits in the\nmailbox assigned to the user who is to receive the message until he or she checks for new mail.\nThe SMTP standard covers message transmission between mail servers (i.e., mail server to mail server)\nand between the originating email client and its mail server. A different standard is used to communicate\nbetween the receiver\u2019s email client and his or her mail server. Two commonly used standards for\ncommunication between email client and mail server are Post Office Protocol (POP) and Internet\nMessage Access Protocol (IMAP). Although there are several important technical differences\nbetween POP and IMAP, the most noticeable difference is that before a user can read a mail message with\na POP (version 3) email client, the email message must be copied to the client computer\u2019s hard disk and\ndeleted from the mail server. With IMAP, email messages can remain stored on the mail server after they\nare read. IMAP therefore offers considerable benefits to users who read their email from many different", "source": "Page 66", "chapter_title": "Chapter 11"}
{"id": "6e876cdbb9db-2", "text": "are read. IMAP therefore offers considerable benefits to users who read their email from many different\ncomputers (e.g., home, office, computer labs) because they no longer need to worry about having old\nemail messages scattered across several client computers; all email is stored on the server until it is\ndeleted.", "source": "Page 66", "chapter_title": "Chapter 11"}
{"id": "60ea68e8ab2d-0", "text": "FIGURE 2-13 How SMTP (Simple Mail Transfer Protocol) email works. IMAP = Internet Message Access\nProtocol; LAN = Local Area Network; POP = Post Office Protocol\nIn our example in Figure 2-13, when the receiver next accesses his or her email, the email client on his or\nher computer contacts the mail server by sending an IMAP or a POP packet that asks for the contents of\nthe user\u2019s mailbox. In Figure 2-13, we show this as an IMAP packet, but it could just as easily be a POP\npacket. When the mail server receives the IMAP or POP request, it converts the original SMTP packet\ncreated by the message sender into a POP or an IMAP packet that is sent to the client computer, which the\nuser reads with the email client. Therefore, any email client using POP or IMAP must also understand\nSMTP to create messages. POP and IMAP provide a host of functions that enable the user to manage his\nor her email, such as creating mail folders, deleting mail, creating address books, and so on. If the user", "source": "Page 67", "chapter_title": "Chapter 11"}
{"id": "133ffef4d575-0", "text": "sends a POP or an IMAP request for one of these functions, the mail server will perform the function and\nsend back a POP or an IMAP response packet that is much like an HTTP response packet.\nThree-Tier Thin Client\u2013Server Architecture\nThe three-tier thin client\u2013server email architecture uses a Web server and Web browser to provide access\nto your email. With this architecture, you do not need an email client on your client computer. Instead,\nyou use your Web browser. This type of email is sometimes called Web-based email and is provided by a\nvariety of companies such as Hotmail and Yahoo!.\nYou use your browser to connect to a page on a Web server that lets you write the email message by filling\nin a form. When you click the send button, your Web browser sends the form information to the Web\nserver inside an HTTP request (Figure 2-14). The Web server runs a program (e.g., written in C or Perl)\nthat takes the information from the HTTP request and builds an SMTP packet that contains the email\nmessage. Although not important to our example, it also sends an HTTP response back to the client. The\nWeb server then sends the SMTP packet to the mail server, which processes the SMTP packet as though it\ncame from a client computer. The SMTP packet flows through the network in the same manner as before.\nWhen it arrives at the destination mail server, it is placed in the receiver\u2019s mailbox.", "source": "Page 68", "chapter_title": "Chapter 11"}
{"id": "d701be9c31c6-0", "text": "FIGURE 2-14 Inside the Web. HTTP = Hypertext Transfer Protocol; IMAP = Internet Message Access\nProtocol; LAN = Local Area Network; POP = Post Office Protocol; SMTP = Simple Mail Transfer Protocol\nWhen the receiver wants to check his or her mail, he or she uses a Web browser to send an HTTP request\nto a Web server (see Figure 2-14). A program on the Web server (e.g., in C or Perl) processes the request\nand sends the appropriate POP request to the mail server. The mail server responds with a POP packet,\nwhich is a program on the Web server converts into an HTTP response and sends to the client. The client\nthen displays the email message in the Web browser Web-based email.\nTECHNICAL FOCUS 2-2\nSMTP Transmission", "source": "Page 69", "chapter_title": "Chapter 11"}
{"id": "b16b06a81b3b-0", "text": "SMTP (Simple Mail Transfer Protocol) is an older protocol, and transmission using it is rather\ncomplicated. If we were going to design it again, we would likely find a simpler transmission method.\nConceptually, we think of an SMTP packet as one packet. However, SMTP mail transfer agents\ntransmit each element within the SMTP packet as a separate packet and wait for the receiver to\nrespond with an \u201cOK\u201d before sending the next element. For example, in Figure 2-15, the sending\nmail transfer agent would send the from address and wait for an OK from the receiver. Then it would\nsend the to address and wait for an OK. Then it would send the date, and so on, with the last item\nbeing the entire message sent as one element.\nFIGURE 2-15 An example of an email message using the SMTP (Simple Mail Transfer Protocol) standard\nA simple comparison of Figures 2-13 and 2-14 will quickly show that the three-tier approach using a Web\nbrowser is much more complicated than the normal two-tier approach. So why do it? Well, it is simpler to\nhave just a Web browser on the client computer rather than to require the user to install a special email\nclient on his or her computer and then set up the special email client to connect to the correct mail server\nusing either POP or IMAP. It is simpler for the user to just type the URL of the Web server providing the\nmail services into his or her browser and begin using mail. This also means that users can check their\nemail from a public computer anywhere on the Internet.\nIt is also important to note that the sender and receiver do not have to use the same architecture for their\nemail. The sender could use a two-tier client\u2013server architecture, and the receiver, a host-based or three-\ntier client\u2013server architecture. Because all communication is standardized using SMTP between the", "source": "Page 70", "chapter_title": "Chapter 11"}
{"id": "320f7375c159-1", "text": "tier client\u2013server architecture. Because all communication is standardized using SMTP between the\ndifferent mail servers, how the users interact with their mail servers is unimportant. Each organization\ncan use a different approach.\nIn fact, there is nothing to prevent one organization from using all three architectures simultaneously. At\nIndiana University, email is usually accessed through an email client (e.g., Microsoft Outlook) but is also\naccessed over the Web because many users travel internationally and find it easier to borrow a Web\nbrowser with Internet access than to borrow an email client and set it up to use the Indiana University\nmail server.\n2.4.2 Inside an SMTP Packet\nSMTP defines how message transfer agents operate and how they format messages sent to other message\ntransfer agents. An SMTP packet has two parts:\nThe header, which lists source and destination email addresses (possibly in text form [e.g., \u201cPat\nSmith\u201d]) as well as the address itself (e.g., psmith@somewhere.com), date, subject, and so on.\nThe body, which is the word DATA, followed by the message itself.", "source": "Page 70", "chapter_title": "Chapter 11"}
{"id": "da48fc9dd56b-0", "text": "Figure 2-15 shows a simple email message formatted using SMTP. The header of an SMTP message has a\nseries of fields that provide specific information, such as the sender\u2019s email address, the receiver\u2019s\naddress, date, and so on. The information in quotes on the from and to lines is ignored by SMTP; only the\ninformation in the angle brackets is used in email addresses. The message ID field is used to provide a\nunique identification code so that the message can be tracked. The message body contains the actual text\nof the message itself.\n2.4.3 Attachments in Multipurpose Internet Mail Extension\nAs the name suggests, SMTP is a simple standard that permits only the transfer of text messages. It was\ndeveloped in the early days of computing, when no one had even thought about using email to transfer\nnontext files such as graphics or word processing documents. Several standards for nontext files have\nbeen developed that can operate together with SMTP, such as Multipurpose Internet Mail\nExtension (MIME), uuencode, and binhex.\nEach of the standards is different, but all work in the same general way. The MIME software, which exists\nas part of the email client, takes the nontext file, such as a PowerPoint graphic file, and translates each\nbyte in the file into a special code that looks like regular text. This encoded section of \u201ctext\u201d is then labeled\nwith a series of special fields understood by SMTP as identifying a MIME-encoded attachment and\nspecifying information about the attachment (e.g., name of file, type of file). When the receiver\u2019s email\nclient receives the SMTP message with the MIME attachment, it recognizes the MIME \u201ctext\u201d and uses its\nMIME software (i.e., part of the email client) to translate the file from MIME \u201ctext\u201d back into its original\nformat.\n2.5 OTHER APPLICATIONS", "source": "Page 71", "chapter_title": "Chapter 11"}
{"id": "5a8def1463a6-1", "text": "format.\n2.5 OTHER APPLICATIONS\nThere are literally thousands of applications that run on the Internet and on other networks. Most\napplication software that we develop today, whether for sale or for private internal use, runs on a network.\nWe could spend years talking about different network applications and still cover only a small number.\nA Day in the Life: Network Manager\nIt was a typical day for a network manager. It began with the setup and troubleshooting for a\nvideoconference. Videoconferencing is fairly routine activity but this one was a little different; we\nwere trying to videoconference with a different company who used different standards than we did.\nWe attempted to use our usual Web-based videoconferencing but could not connect. We fell back to\nvideoconferencing over telephone lines, which required bringing in our videoconferencing services\ngroup. It took 2 hours, but we finally had the technology working.\nThe next activity was building a Windows database server. This involved installing software, adding\na server into our ADS (Active Directory Services) domain, and setting up the user accounts. Once the\nserver was on the network, it was critical to install all the security patches for both the operating\nsystem and database server. We receive so many security attacks that it is our policy to install all\nsecurity patches on the same day that new software or servers are placed on the network or the\npatches are released.\nAfter lunch, the next 2 hours was spent in a boring policy meeting. These meetings are a necessary\nevil to ensure that the network is well-managed. It is critical that users understand what the network\ncan and can\u2019t be used for, and our ability to respond to users\u2019 demands. Managing users\u2019\nexpectations about support and use rules helps ensure high user satisfaction.\nThe rest of the day was spent refining the tool we use to track network utilization. We have a simple", "source": "Page 71", "chapter_title": "Chapter 11"}
{"id": "d73914492312-2", "text": "intrusion detection system to detect hackers, but we wanted to provide more detailed information on\nnetwork errors and network utilization to better assist us in network planning.\nSource: With thanks to Jared Beard", "source": "Page 71", "chapter_title": "Chapter 11"}
{"id": "e13e8893ee25-0", "text": "Fortunately, most network application software works in much the same way as the Web or email. In this\nsection, we will briefly discuss only three commonly used applications: Telnet, instant messaging, and\nvideoconferencing.\n2.5.1 Telnet\nTelnet enables users to log in to servers (or other clients). It requires an application layer program on the\nclient computer and an application layer program on the server or host computer. Once Telnet makes the\nconnection from the client to the server, you must use the account name and password of an authorized\nuser to log in.\nAlthough Telnet was developed in the very early days of the Internet (actually, the very first application\nthat tested the connectivity on ARPANET was Telnet), it is still widely used today. Because it was\ndeveloped so long ago, Telnet assumes a host-based architecture. Any key strokes that you type using\nTelnet are sent to the server for processing, and then the server instructs the client what to display on the\nscreen.\nOne of the most frequently used Telnet software packages is PuTTY. PuTTY is open source and can be\ndownloaded for free (and in case you\u2019re wondering, the name does not stand for anything, although TTY is\na commonly used abbreviation for \u201cterminal\u201d in UNIX-based systems).\nThe very first Telnet applications posed a great security threat because every key stroke was sent over the\nnetwork as plain text. PuTTY uses secure shell (SSH) encryption when communicating with the server so\nthat no one can read what is typed. An additional advantage of PuTTY is that it can run on multiple\nplatforms, such as Windows, Mac, or Linux. Today, PuTTY is routinely used by network administrators to\nlog in to servers and routers to make configuration changes.\nMANAGEMENT FOCUS 2-3\nTagging People", "source": "Page 72", "chapter_title": "Chapter 11"}
{"id": "bd5ae0018e79-1", "text": "MANAGEMENT FOCUS 2-3\nTagging People\nJoseph Krull has a chip on his shoulder\u2014well, in his shoulder to be specific. Krull is one of a small\nbut growing number of people who have a Radio Frequency Identification (RFID) chip implanted in\ntheir bodies.\nRFID technology has been used to identify pets, so that lost pets can be easily reunited with their\nowners. Now, the technology is being used for humans.\nKrull has a blown left pupil from a skiing accident. If he were injured in an accident and unable to\ncommunicate, an emergency room doctor might misinterpret his blown pupil as a sign of a major\nhead injury and begin drilling holes to relieve pressure. Now doctors can use the RFID chip to\nidentify Krull and quickly locate his complete medical records on the Internet.\nCritics say such RFID chips pose huge privacy risks because they enable any firms using RFID to\ntrack users such as Krull. Retailers, for example, can track when he enters and leaves their stores.\nKrull doesn\u2019t care. He believes the advantages of having his complete medical records available to\nany doctor greatly outweigh the privacy concerns.\nTagging people is no longer the novelty it once was; in fact, today it is a U.S. Food and Drug\nAdministration approved procedure. More than 10% of all RFID research projects worldwide involve\ntagging people. There are even do-it-yourself RFID tagging kits available\u2014not that we would\nrecommend them (www.youtube.com/watch?v= vsk6dJr4wps).\nBesides the application to health records, RFID is also being used for security applications, even\nsomething as simple as door locks. Imagine having an RFID-based door lock that opens\nautomatically when you walk up to it because it recognizes the RFID tag in your body.\nSources: Adapted from NetworkWorld, ZDNet, and GizMag.com.", "source": "Page 72", "chapter_title": "Chapter 11"}
{"id": "d39c8297b330-2", "text": "Sources: Adapted from NetworkWorld, ZDNet, and GizMag.com.", "source": "Page 72", "chapter_title": "Chapter 11"}
{"id": "b58b7061956d-0", "text": "2.5.2 Videoconferencing\nVideoconferencing provides real-time transmission of video and audio signals to enable people in two\nor more locations to have a meeting. In some cases, videoconferences are held in special-purpose meeting\nrooms with one or more cameras and several video display monitors to capture and display the video\nsignals (Figure 2-16). Special audio microphones and speakers are used to capture and play audio signals.\nThe audio and video signals are combined into one signal that is transmitted through a WAN or the\nInternet to people at the other location. Most of this type of videoconferencing involves two teams in two\nseparate meeting rooms, but some systems can support conferences of up to eight separate meeting\nrooms. Some advanced systems provide telepresence, which is of such high quality that you feel you are\nface-to-face with the other participants.\nThe fastest growing form of videoconferencing is desktop videoconferencing. Small cameras installed\non top of each computer permit meetings to take place from individual offices (Figure 2-17). Special\napplication software (e.g., WebEx, Zoom, and Skype) is installed on the client computer and transmits the\nimages across a network to application software on a videoconferencing server. The server then sends the\nsignals to the other client computers that want to participate in the videoconference. In some cases, the\nclients can communicate with one another without using the server. The cost of desktop\nvideoconferencing ranges from less than $20 per computer for inexpensive systems to more than $1,000\nfor high-quality systems. Some systems have integrated conferencing software with desktop\nvideoconferencing, enabling participants to communicate verbally and, by using applications such as\nwhite boards, to attend the same meeting while they are sitting at the computers in their offices. Among", "source": "Page 73", "chapter_title": "Chapter 11"}
{"id": "54021da1238e-1", "text": "today\u2019s contenders of desktop videoconferencing are RingCentral Meetings, Skype for Business, Zoom,\nJoin.me, and GoToMeeting. These providers enable up to 500 participants to join a meeting, screen\nsharing, and conference recording, and run on a wide variety of clients.\nThe transmission of video requires a lot of network capacity. Most videoconferencing uses data\ncompression to reduce the amount of data transmitted. Surprisingly, the most common complaint is not\nthe quality of the video image but the quality of the voice transmissions. Special care needs to be taken in\nthe design and placement of microphones and speakers to ensure quality sound and minimal feedback.\nFIGURE 2-16 A Cisco telepresence system", "source": "Page 73", "chapter_title": "Chapter 11"}
{"id": "af0b22a3758c-0", "text": "FIGURE 2-17 Desktop videoconferencing\nMost videoconferencing systems were originally developed by vendors using different formats, so many\nproducts were incompatible. The best solution was to ensure that all hardware and software used within\nan organization was supplied by the same vendor and to hope that any other organizations with whom you\nwanted to communicate used the same equipment. Today, three standards are in common use: H.320,\nH.323, and MPEG-2 (also called ISO 13818-2). Each of these standards was developed by different\norganizations and is supported by different products. They are not compatible, although some application\nsoftware packages understand more than one standard. H.320 is designed for room-to-room\nvideoconferencing over high-speed telephone lines. H.323 is a family of standards designed for desktop\nvideoconferencing and just simple audio conferencing over the Internet. MPEG-2 is designed for faster\nconnections, such as a LAN or specially designed, privately operated WAN.\nWebcasting is a special type of one-directional non-interactive videoconferencing in which content is\nsent from the server to the user. The developer creates content that is downloaded as needed by the users\nand played by a plug-in to a Web browser. At present, there are no standards for Webcast technologies,\nbut the products by RealNetworks.com are the de facto standards. There are many different products one\ncan choose from to do a webcast, for example, GoToWebinar, ClickMeeting, or Yondo.\n2.6 IMPLICATIONS FOR CYBER SECURITY\nThe first implication for security from this chapter is that the primary purpose of a network is to provide a\nworry-free and secure environment in which applications can run. However, a secure network is not\nenough. All applications that are allowed on the network must be secure too. Application security must", "source": "Page 74", "chapter_title": "Chapter 11"}
{"id": "c75411c053e5-1", "text": "enough. All applications that are allowed on the network must be secure too. Application security must\nbe implemented at the time when the application is coded and if any security holes are discovered,\nupdates (also called patches) must be issued by the vendor of the application. Users then must install the\nupdate as soon as the patch is available; otherwise, they are not only compromising their application and\ncomputer but also the whole network to which this computer is connected.\nOne of the most commonly used business application is an SQL database server, a common part of a", "source": "Page 74", "chapter_title": "Chapter 11"}
{"id": "9fbaebcacd89-0", "text": "three- or four-tier client\u2013server architecture. You might have heard of SQL injection\u2014one of the top\nthree security risks on the Internet that is enabled by unsecured websites that allow you to enter text\ninformation into a form, such as registering for an event. SQL injections area vulnerability where the\nwebsite allows an attacker to enter SQL commands through the textbox rather than just plain text.\nBecause the attacker can enter a command, he or she can then hijack the whole database and take all the\ndata that is stored in it. Here is a good video that explains it in more detail:\nhttps://www.youtube.com/watch?v=FwIUkAwKzG8. Therefore, when designing any applications, one\nmust pay lot of attention to potential security holes and exploits.\nFinally, another very frequently used hacking technique is email spoofing. Email spoofing is the creation\nof email messages that have forged the sender address. It turns out that it is very easy to spoof an email\naddress, check it out for yourself: https://www.youtube.com/watch?v=rCnz6cfqnWc. So, before you reply\nto any email that sounds suspicious, check the IP address where the email came from. We will learn about\nIP addresses in Chapters 5 and 7.\nMANAGEMENT FOCUS 2-4\nCloud-Hosted Virtual Desktops\nWhile cloud computing started on the server side, it is quickly moving to the client side\u2014the\ndesktop. Imagine that you work for a multinational organization and fly several times a year to\ndifferent parts of the world to do your job. Your organization doesn\u2019t want you to travel with a laptop\nbecause they fear that you can lose the laptop with the data on it but they want you to be able to log\nin to any desktop in any office around the world and have your desktop appear on the screen. Well,", "source": "Page 75", "chapter_title": "Chapter 11"}
{"id": "fdc0245618b3-1", "text": "with the cloud technology, this is possible, and many companies are taking advantage of this new\nservice. Could you guess its name? Yes, Desktop-as-a-Service (DaaS). Several companies offer DaaS\nwithout the infrastructure cost and with reduced complexity of deploying desktops. This service\nworks as a monthly subscription service and includes data center hardware and facilities and also\nsecurity. Dell DaaS on Demand and Amazon WorkSpaces are among the service providers of DaaS.\nSUMMARY\nApplication Architectures There are four fundamental application architectures, plus a fifth\nlegacy architecture. In host-based networks, the server performs virtually all of the work. In client-\nbased networks, the client computer does most of the work; the server is used only for data storage.\nIn client\u2013server networks, the work is shared between the servers and clients. The client performs all\npresentation logic, the server handles all data storage and data access logic, and one or both perform\nthe application logic. With P2P networks, client computers also play the role of a server. Client\u2013\nserver networks can be cheaper to install and often better balance the network loads but are more\ncomplex to develop and manage. Cloud computing is a form of client\u2013server architecture.\nWorld Wide Web One of the fastest growing Internet applications is the Web, which was first\ndeveloped in 1990. The Web enables the display of rich graphical images, pictures, full-motion video,\nand sound. The Web is the most common way for businesses to establish a presence on the Internet.\nThe Web has two application software packages: a Web browser on the client and a Web server on the\nserver. Web browsers and servers communicate with one another using a standard called HTTP. Most\nWeb pages are written in HTML, but many also use other formats. The Web contains information on\njust about every topic under the sun, but finding it and making sure the information is reliable are", "source": "Page 75", "chapter_title": "Chapter 11"}
{"id": "8174e9e11664-2", "text": "just about every topic under the sun, but finding it and making sure the information is reliable are\nmajor problems.\nElectronic Mail With email, users create and send messages using an application layer software\npackage on client computers called user agents. The user agent sends the mail to a server running an\napplication layer software package called a mail transfer agent, which then forward the message\nthrough a series of mail transfer agents to the mail transfer agent on the receiver\u2019s server. Email is\nfaster and cheaper than regular mail and can substitute for telephone conversations in some cases.", "source": "Page 75", "chapter_title": "Chapter 11"}
{"id": "1c86ccd1fca6-0", "text": "Several standards have been developed to ensure compatibility between different user agents and\nmail transfer agents such as SMTP, POP, and IMAP. possible to send 2 bits on one wave or symbol by\ndefining four different amplitudes. Figure 3-17 shows the case where the highest-amplitude wave is\ndefined to be a symbol representing 2 bits, both 1s. The next highest amplitude is the symbol defined\nto mean first a 1 and then a 0, and so on.\nKEY TERMS\napplication architecture\napplication logic\nApplication security\nbody\nclient-based architecture\nclient\u2013server architectures\ncloud-based architecture\ncloud computing\ncloud providers\ndata access logic\ndata storage\ndesktop videoconferencing\ndistribution list\nemail\nH.320\nH.323\nHardware as a Service\nheader\nhost-based architectures\nHTTP request\nHTTP response\nhybrid cloud strategy\nHypertext Markup Language (HTML)\nHypertext Transfer Protocol (HTTP)\nInfrastructure as a Service (IaaS)\nInternet Message Access Protocol (IMAP)\nInternet\nmail transfer agent\nmail user agent\nmiddleware\nMPEG-2\nMultipurpose Internet Mail Extension (MIME)\nmultitenancy", "source": "Page 76", "chapter_title": "Chapter 11"}
{"id": "63911822795f-0", "text": "n-tier architecture\nPlatform as a Service (PaaS)\nPost Office Protocol (POP)\npresentation logic\nprotocol\npure strategy\nrequest body\nrequest header\nrequest line\nresponse body\nresponse header\nresponse status\nscalability\nserver farm\nservices logic\nSimple Mail Transfer Protocol (SMTP)\nsoftware as a service (SaaS)\nSQL injection\nstorage area network\nTelnet\nthick-client\nthin client\nthree-tier architecture\ntwo-tier architecture\nuniform resource locator (URL)\nVideoconferencing\nWeb browser\nWeb server\nWebcasting\nQUESTIONS\n1. What are the different types of application architectures?\n2. Describe the five basic functions of an application software package.\n3. What are the advantages and disadvantages of host-based networks versus client\u2013server networks?\n4. What is middleware, and what does it do?\n5. Suppose your organization was contemplating switching from a host-based architecture to client\u2013\nserver. What problems would you foresee?\n6. Which is less expensive: host-based networks or client\u2013server networks? Explain.\n7. Compare and contrast two-tier, three-tier, and n-tier client\u2013server architectures. What are the\ntechnical differences, and what advantages and disadvantages does each offer?", "source": "Page 77", "chapter_title": "Chapter 11"}
{"id": "40a29fb3a56b-0", "text": "8. How does a thin client differ from a thick client?\n9. What are the benefits of cloud computing?\n10. Compare and contrast the three cloud computing models.\n11. For what is HTTP used? What are its major parts?\n12. For what is HTML used?\n13. Describe how a Web browser and Web server work together to send a Web page to a user.\n14. Can a mail sender use a two-tier architecture to send mail to a receiver using a three-tier\narchitecture? Explain.\n15. Describe how mail user agents and mail transfer agents work together to transfer mail messages.\n16. What roles do SMTP, POP, and IMAP play in sending and receiving email on the Internet?\n17. What are the major parts of an email message?\n18. What is Telnet, and why is it useful?\n19. What is cloud computing?\n20. Explain how videoconferencing works.\n21. Which of the common application architectures for email (two-tier client\u2013server, Web-based) is\n\u201cbest\u201d? Explain.\n22. Some experts argue that thin-client client\u2013server architectures are really host-based architectures in\ndisguise and suffer from the same old problems. Do you agree? Explain.\nEXERCISES\nA. Investigate the use of the major architectures by a local organization (e.g., your university). Which\narchitecture(s) does it use most often and what does it see itself doing in the future? Why?\nB. What are the costs of thin-client versus thick-client architectures? Search the Web for at least two\ndifferent studies and be sure to report your sources. What are the likely reasons for the differences\nbetween the two?\nC. Investigate which companies are the most reliable cloud computing providers for small business.\nD. What application architecture does your university use for email? Explain.", "source": "Page 78", "chapter_title": "Chapter 11"}
{"id": "f90368fd6257-1", "text": "D. What application architecture does your university use for email? Explain.\nE. Investigate the options for having your private cloud as an individual. Hint: Try the Apple website.\nMINICASES\nI. Deals-R-Us Brokers (Part 1) Fred Jones, a distant relative of yours and president of Deals-R-Us\nBrokers (DRUB), has come to you for advice. DRUB is a small brokerage house that enables its clients\nto buy and sell stocks over the Internet, as well as place traditional orders by phone or fax. DRUB has\njust decided to offer a set of stock analysis tools that will help its clients more easily pick winning\nstocks, or so Fred tells you. Fred\u2019s information systems department has presented him with two\nalternatives for developing the new tools. The first alternative will have a special tool developed in\nC++ that clients will download onto their computers to run. The tool will communicate with the\nDRUB server to select data to analyze. The second alternative will have the C++ program running on\nthe server, the client will use his or her browser to interact with the server.\na. Classify the two alternatives in terms of what type of application architecture they use.\nb. Outline the pros and cons of the two alternatives and make a recommendation to Fred about\nwhich is better.\nII. Deals-R-Us Brokers (Part 2) Fred Jones, a distant relative of yours and president of Deals-R-Us\nBrokers (DRUB), has come to you for advice. DRUB is a small brokerage house that enables its clients", "source": "Page 78", "chapter_title": "Chapter 11"}
{"id": "09685334906c-0", "text": "to buy and sell stocks over the Internet, as well as place traditional orders by phone or fax. DRUB has\njust decided to install a new email package. The IT department offered Fred two solutions. First, it\ncould host the email in-house using Microsoft Exchange Server. The second solution would be to use\none of the cloud-based providers and completely outsource the company email. The IT department\nalso explained to Fred that both solutions would allow users to access email on their desktops and\nlaptops and also on their smart devices.\na. Briefly explain to Fred, in layperson\u2019s terms, the differences between the two.\nb. Outline the pros and cons of the two alternatives and make a recommendation to Fred about\nwhich is better.\nIII. Accurate Accounting Diego Lopez is the managing partner of Accurate Accounting, a small\naccounting firm that operates a dozen offices in California. Accurate Accounting provides audit and\nconsulting services to a growing number of small- and medium-sized firms, many of which are high\ntechnology firms. Accurate Accounting staff typically spend many days on-site with clients during\ntheir consulting and audit projects but has increasingly been using email to work with clients. Now,\nmany firms are pushing Accurate Accounting to adopt videoconferencing. Diego is concerned about\nwhat videoconferencing software and hardware to install. \u201cWhy can\u2019t we just use email as this works\nso well. I am concerned that videoconferencing will make things much more complicated. Can you\noffer something to ease my concerns?\u201d he asks. \u201cWill my new video-conferencing software and\nhardware work as simply as email?\u201d Prepare a response to his questions.\nIV. Ling Galleries Howard Ling is a famous artist with two galleries in Hawaii. Many of his paintings\nand prints are sold to tourists who visit Hawaii from Hong Kong and Japan. He paints 6 to 10 new", "source": "Page 79", "chapter_title": "Chapter 11"}
{"id": "9f738a5295f8-1", "text": "paintings a year, which sell for $50,000 each. The real money comes from the sales of prints; a\npopular painting will sell 1,000 prints at a retail price of $1,500 each. Some prints sell very quickly,\nwhile others do not. As an artist, Howard paints what he wants to paint. As a businessman, Howard\nalso wants to create art that sells well. Howard visits each gallery once a month to talk with clients,\nbut enjoys talking with the gallery staff on a weekly basis to learn what visitors say about his work and\nto get ideas for future work. Howard has decided to open two new galleries, one in Hong Kong and\none in Tokyo. How can the Internet help Howard with the two new galleries?\nTECH UPDATES\nPick one of these topics to investigate.\nTopic A: Email Spoofing and Phishing Email\nEmail spoofing is the forgery of an email header so that the message appears to have originated from\nsomeone or somewhere other than the actual source. Email spoofing is a tactic used in phishing and spam\ncampaigns because people are more likely to open an email when they think it has been sent by a\nlegitimate source. Look up videos on how to spoof email and after consulting with your instructor, spoof\nand email that you send to your classmates. Phishing email is the fraudulent practice of sending emails\npurporting to be from reputable companies in order to induce individuals to reveal personal information,\nsuch as passwords and credit card numbers. While some phishing attacks are easy to spot, others are quite\nsophisticated. What techniques can we apply to not fall for phishing. What to do if we accidentally fall for\nphishing.\nTopic B: SQL Injection\nSQL Injection (SQLi) refers to an injection attack wherein an attacker can execute malicious SQL", "source": "Page 79", "chapter_title": "Chapter 11"}
{"id": "7fb9da2530c9-2", "text": "SQL Injection (SQLi) refers to an injection attack wherein an attacker can execute malicious SQL\nstatements (also commonly referred to as a malicious payload) that control a web application\u2019s database\nserver (also commonly referred to as a Relational Database Management System\u2014RDBMS). Navigate to\nhttp://hak.me (a great environment to safely try out hacking techniques). Sign up for an account, start a\nhackme sandbox. Search for U-Hack-It basic exploits tutorial. Explore SQL Injecting and prepare to\nexplain it to your classmates.\nDeliverables", "source": "Page 79", "chapter_title": "Chapter 11"}
{"id": "6e2a59785c6e-0", "text": "Your job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title slide\n2. Short description of topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along\n5. How does it relate to material covered in class so far (and in the future)\n6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 2A\nTracing Your Email\nMost email today is spam, unwanted commercial email, or phishing, fake email designed to separate you\nfrom your money. Criminals routinely send fake emails that try to get you to tell them your log-in\ninformation for your bank or your PayPal account, so they can steal the information, log-in as you, and\nsteal your money.\nIt is very easy to fake a return address on an email, so simply looking to make sure that an email has a\nvalid sender is not sufficient to ensure that the email was actually sent by the person or company that\nclaims to have sent it. However, every SMTP email packet contains information in its header about who\nactually sent the email. You can read this information yourself, or you can use a tool designed to simplify\nthe process for you. The objective of this Activity is for you to trace an email you have received to see if the\nsending address on the email is actually the organization that sent it.\nThere are many tools you can use to trace your email. We like a tool called eMail Tracker Pro, which has a\nfree version that lasts 15 days.", "source": "Page 80", "chapter_title": "Chapter 11"}
{"id": "71b4ea6ddca9-1", "text": "free version that lasts 15 days.\n1. Go to www.emailtrackerpro.com and download and install eMail Tracker Pro.\n2. Log-in to your email and find an email message you want to trace. I recently received an email\nsupposedly from Wachovia Bank; the sender\u2019s email address was aw-login@wachovia.com.\n3. After you open the email, find the option that enables you to view the Internet header or source of the\nmessage (in Microsoft Outlook, click the Options tab and look at the bottom of the box that pops up).\nFigure 2-18 shows the email I received and how to find the SMTP header (which Outlook calls the\nInternet header). Copy the entire SMTP header to the clip-board.\n4. Start eMail Tracker Pro. Select Trace an email, and paste the SMTP header into the box provided.\nClick Trace to start the trace.\n5. It may take up to 30 seconds to trace the email, so be patient. Figure 2-19 shows the results from the\nemail I received. The email supposedly from Wachovia Bank was actually from a company named\nMusser and Kouri Law whose primary contact is Musser Ratliff, CPA, which uses SBC in Plano,\nTexas, as its Internet service provider. We suspect that someone broke into this company\u2019s network\nand used their email server without permission, or fraudulently used this company\u2019s name and\ncontact information on its domain registration.\nDeliverables\nTrace one email. Print the original email message and the trace results.", "source": "Page 80", "chapter_title": "Chapter 11"}
{"id": "99987a611d79-0", "text": "FIGURE 2-18 Viewing the SMTP packet header", "source": "Page 81", "chapter_title": "Chapter 11"}
{"id": "8a5d8a753f89-0", "text": "FIGURE 2-19 Viewing the source of the SMTP packet\nSource: http://www.visualware.com/contact.html\nHANDS-ON ACTIVITY 2B\nSeeing SMTP and POP PDUs\nWe\u2019ve discussed about how messages are transferred using layers and the different protocol data units\n(PDUs) used at each layer. The objective of this Activity is for you to see the different PDUs in the\nmessages that you send. To do this, we\u2019ll use Wireshark, which is one of the world\u2019s foremost network\nprotocol analyzers, and is the de facto standard that most professional and education institutions use\ntoday. It is used for network troubleshooting, network analysis, software and communications protocol\ndevelopment, and general education about how networks work. Wireshark enables you to see all messages\nsent by your computer and may also let you see the messages sent by other users on your LAN (depending\non how your LAN is configured).\nFor this activity, you can capture your own SMTP and POP packets using Wireshark, or use two files that\nwe\u2019ve created by capturing SMTP and POP packets. We\u2019ll assume you\u2019re going to use our files. If you\u2019d like", "source": "Page 82", "chapter_title": "Chapter 11"}
{"id": "18fc2d80aa42-0", "text": "to capture your own packets, read Hands-On Activity 1B in Chapter 1 and use your two-tier email client to\ncreate and send an email message instead of your Web browser. If you\u2019d like to use our files, go to the\nwebsite for this book and download the two files: SMTP Capture.pkt and POP3 Capture.pkt.\nFIGURE 2-20 SMTP packets in Wireshark\nPart 1: SMTP\n1. Start Wireshark and either capture your SMTP packets or open the file called SMTP Capture.pkt.\n2. We used the email software on our client computer to send an email message to our email server.\nFigure 2-20 shows the packets we captured that were sent to and from the client computer (called\n192.168.1.100) and the server (128.196.40.4) to send this message from the client to the server. The\nfirst few packets are called the handshake, as the client connects to the server and the server\nacknowledges it is ready to receive a new email message.", "source": "Page 83", "chapter_title": "Chapter 11"}
{"id": "bdd36abcb9b1-0", "text": "3. Packet 8 is the start of the email message that identifies the sender. The next packet from the client\n(packet 10) provides the recipient address and then the email message starts with the DATA\ncommand (packet 12) and is spread over several packets (14, 15, and 17) because it is too large to fit in\none Ethernet frame. (Remember that the sender\u2019s transport layer breaks up large messages into\nseveral smaller TCP segments for transmission and the receiver\u2019s transport layer reassembles the\nsegments back into the one SMTP message.)\n4. Packet 14 contains the first part of the message that the user wrote. It\u2019s not that easy to read, but by\nlooking in the bottom window, you can see what the sender wrote.\nDeliverables\n1. List the information in the SMTP header (to, from, date, subject, message ID#).\n2. Look through the packets to read the user\u2019s message. List the user\u2019s actual name (not his or her\nemail address), his or her birth date, and his or her SSN.\n3. Some experts believe that sending an email message is like sending a postcard. Why? How secure\nis SMTP email? How could security be improved?\nPart 2: POP\n1. Start Wireshark and either capture your SMTP packets or open the file called POP3 Capture.pkt.\n(Note: Depending on the version of Wireshark you are using, the file extension may be pkt or pcap.)\n2. We used the email software on our client computer to read an email message that was our email\nserver. Figure 2-21 shows the packets we captured that were sent to and from the client computer\n(called 128.196.239.91) and the server (128.192.40.4) to send an email message from the server to the", "source": "Page 84", "chapter_title": "Chapter 11"}
{"id": "86134864dca5-1", "text": "client. The first few packets are called the handshake, as the client logs in to the server and the server\naccepts the log-in.\n3. Packet 12 is the POP STAT command (status) that asks the server to show the number of email\nmessages in the user\u2019s mailbox. The server responds in packet 13 and tells the client there is one\nmessage.\n4. Packet 16 is the POP LIST command that asks the server to send the client a summary of email\nmessages, which it does in packet 17.\n5. Packet 18 is the POP RETR command (retrieve) that asks the server to send message 1 to the client.\nPackets 20, 22, and 23 contain the email message. It\u2019s not that easy to read, but by looking in the\nbottom window for packet 20, you can see what the sender wrote. You can also expand the POP\npacket in the middle packet detail window (by clicking on the + box in front of it), which is easier to\nread.\nDeliverables\n1. Packets 5 through 11 are the log-in process. Can you read the user id and passwords? Why or why\nnot?\n2. Look through the packets to read the user\u2019s message. List the user\u2019s actual name (not his or her\nemail address), his or her birth date, and his or her SSN.", "source": "Page 84", "chapter_title": "Chapter 11"}
{"id": "a80b0f07ae33-0", "text": "FIGURE 2-21 POP packets in Wireshark", "source": "Page 85", "chapter_title": "Chapter 11"}
{"id": "f033b6e1505d-0", "text": "CHAPTER 3\nPHYSICAL LAYER\nThe physical layer (also called layer 1) is the physical connection between the computers and/or devices in\nthe network. This chapter examines how the physical layer operates. It describes the most commonly used\nmedia for network circuits and explains the basic technical concepts of how data are actually transmitted\nthrough the media. Three different types of transmission are described: digital transmission of digital\ncomputer data, analog transmission of digital computer data, and digital transmission of analog voice\ndata. You do not need an engineering-level understanding of the topics to be an effective user and\nmanager of data communication applications. It is important, however, that you understand the basic\nconcepts, so this chapter is somewhat technical.\nOBJECTIVES\nBe familiar with the different types of network circuits and media\nUnderstand the digital transmission of digital data\nUnderstand the analog transmission of digital data\nUnderstand the digital transmission of analog data\nBe familiar with analog and digital modems\nBe familiar with multiplexing\nOUTLINE\n3.1 Introduction\n3.2 Circuits\n3.2.1 Circuit Configuration\n3.2.2 Data Flow\n3.2.3 Multiplexing\n3.3 Communication Media\n3.3.1 Twisted-Pair Cable\n3.3.2 Coaxial Cable\n3.3.3 Fiber-Optic Cable\n3.3.4 Radio\n3.3.5 Microwave\n3.3.6 Satellite\n3.3.7 Media Selection\n3.4 Digital Transmission of Digital Data\n3.4.1 Coding\n3.4.2 Transmission Modes\n3.4.3 Digital Transmission\n3.4.4 How Ethernet Transmits Data\n3.5 Analog Transmission of Digital Data", "source": "Page 86", "chapter_title": "Chapter 11"}
{"id": "7919c818c5ec-0", "text": "3.5.1 Modulation\n3.5.2 Capacity of a Circuit\n3.5.3 How Modems Transmit Data\n3.6 Digital Transmission of Analog Data\n3.6.1 Translating from Analog to Digital\n3.6.2 How Telephones Transmit Voice Data\n3.6.3 How Instant Messenger Transmits Voice Data\n3.6.4 Voice over Internet Protocol (VoIP)\n3.7 Implications for Cyber Security\nSummary\n3.1 INTRODUCTION\nThis chapter examines how the physical layer operates. The physical layer is the network hardware\nincluding servers, clients, and circuits, but in this chapter, we focus on the circuits and on how clients and\nservers transmit data through them. The circuits are usually a combination of both physical media (e.g.,\ncables, wireless transmissions) and special-purpose devices that enable the transmissions to travel\nthrough the media. Special-purpose devices such as switches and routers are discussed in Chapters 6 and\n8.\nThe word circuit has two very different meanings in networking, and sometimes it is hard to understand\nwhich meaning is intended. Sometimes, we use the word circuit to refer to the physical circuit\u2014the\nactual wire\u2014used to connect two devices. In this case, we are referring to the physical media that carry the\nmessage we transmit, such as the twisted-pair wire used to connect a computer to the LAN in an office. In\nother cases, we are referring to a logical circuit used to connect two devices, which refers to the\ntransmission characteristics of the connection, such as when we say a company has a T1 connection into\nthe Internet. In this case, T1 refers not to the physical media (i.e., what type of wire is used) but rather to\nhow fast data can be sent through the connection. Often, each physical circuit is also a logical circuit, but", "source": "Page 87", "chapter_title": "Chapter 11"}
{"id": "1780f091928b-1", "text": "sometimes it is possible to have one physical circuit\u2014one wire\u2014carry several separate logical circuits, or\nto have one logical circuit travel over several physical circuits.\nThere are two fundamentally different types of data that can flow through the circuit: digital and analog.\nComputers produce digital data that are binary, either on or off, 0 or 1. In contrast, telephones produce\nanalog data whose electrical signals are shaped like the sound waves they transfer; they can take on any\nvalue in a wide range of possibilities, not just 0 or 1.\nData can be transmitted through a circuit in the same form they are produced. Most computers, for\nexample, transmit their digital data through digital circuits to printers and other attached devices.\nLikewise, analog voice data can be transmitted through telephone networks in analog form. In general,\nnetworks designed primarily to transmit digital computer data tend to use digital transmission, and\nnetworks designed primarily to transmit analog voice data tend to use analog transmission (at least for\nsome parts of the transmission).\nData can be converted from one form into the other for transmission over network circuits. For example,\ndigital computer data can be transmitted over an analog telephone circuit by using a modem. A modem\nat the sender\u2019s computer translates the computer\u2019s digital data into analog data that can be transmitted\nthrough the voice communication circuits, and a second modem at the receiver\u2019s end translates the analog\ntransmission back into digital data for use by the receiver\u2019s computer.\nLikewise, it is possible to translate analog voice data into digital form for transmission over digital\ncomputer circuits using a device called a codec. Once again, there are two codecs, one at the sender\u2019s end\nand one at the receiver\u2019s end. Why bother to translate voice into digital? The answer is that digital\ntransmission is \u201cbetter\u201d than analog transmission. Specifically, digital transmission offers five key benefits\nover analog transmission:", "source": "Page 87", "chapter_title": "Chapter 11"}
{"id": "36e6ce143e3d-0", "text": "Digital transmission produces fewer errors than analog transmission. Because the transmitted data\nare binary (only two distinct values), it is easier to detect and correct errors.\nDigital transmission permits higher maximum transmission rates. Fiber-optic cable, for example, is\ndesigned for digital transmission.\nDigital transmission is more efficient. It is possible to send more data through a given circuit using\ndigital rather than analog transmission.\nDigital transmission is more secure because it is easier to encrypt.\nFinally, and most importantly, integrating voice, video, and data on the same circuit is far simpler\nwith digital transmission.\nFor these reasons, most long-distance telephone circuits built by telephone companies and other common\ncarriers over the past decades use digital transmission. In the future, most transmissions (voice, data, and\nvideo) will be sent digitally.\nRegardless of whether digital or analog transmission is used, transmission requires the sender and\nreceiver to agree on two key parameters. First, they have to agree on the symbols that will be used: What\npattern of electricity, light, or radio wave will be used to represent a 0 and a 1. Once these symbols are set,\nthe sender and receiver have to agree on the symbol rate: How many symbols will be sent over the\ncircuit per second? Analog and digital transmissions are different, but both require a commonly agreed on\na set of symbols and a symbol rate.\nIn this chapter, we first describe the basic types of circuits and examine the different media used to build\ncircuits. Then we explain how data are actually sent through these media using digital and analog\ntransmissions.\n3.2 CIRCUITS\n3.2.1 Circuit Configuration\nCircuit configuration is the basic physical layout of the circuit. There are two fundamental circuit\nconfigurations: point-to-point and multipoint. In practice, most complex computer networks have many", "source": "Page 88", "chapter_title": "Chapter 11"}
{"id": "9b703bb92c46-1", "text": "configurations: point-to-point and multipoint. In practice, most complex computer networks have many\ncircuits, some of which are point-to-point and some of which are multipoint.\nFigure 3-1 illustrates a point-to-point circuit, which is so named because it goes from one point to\nanother (e.g., one computer to another computer). These circuits sometimes are called dedicated circuits\nbecause they are dedicated to the use of these two computers. This type of configuration is used when\ncomputers generate enough data to fill the capacity of the communication circuit. When an organization\nbuilds a network using point-to-point circuits, each computer has its own circuit running from itself to the\nother computers. This can get very expensive, particularly if there is some distance between the\ncomputers. Despite the cost, point-to-point circuits are used regularly in modern wired networks to\nconnect clients to switches, switches to switches and routers, and routers to routers. We will discuss in\ndetail these circuits in Chapter 7.\nFigure 3-2 shows a multipoint circuit (also called a shared circuit). In this configuration, many\ncomputers are connected to the same circuit. This means that each must share the circuit with the others.\nThe disadvantage is that only one computer can use the circuit at a time. When one computer is sending\nor receiving data, all others must wait. The advantage of multipoint circuits is that they reduce the amount\nof cable required and typically use the available communication circuit more efficiently. Imagine the\nnumber of circuits that would be required if the network in Figure 3-2 was designed with separate point-\nto-point circuits. For this reason, multipoint configurations are cheaper than point-to-point circuits. Thus,\nmultipoint circuits typically are used when each computer does not need to continuously use the entire\ncapacity of the circuit or when building point-to-point circuits are too expensive. Wireless circuits are", "source": "Page 88", "chapter_title": "Chapter 11"}
{"id": "a819e71ed2d1-2", "text": "capacity of the circuit or when building point-to-point circuits are too expensive. Wireless circuits are\nalmost always multipoint circuits because multiple computers use the same radio frequencies and must\ntake turns transmitting.", "source": "Page 88", "chapter_title": "Chapter 11"}
{"id": "4f6c295e0c65-0", "text": "FIGURE 3-1 Point-to-point circuit\nFIGURE 3-2 Multipoint circuit", "source": "Page 89", "chapter_title": "Chapter 11"}
{"id": "62e7d7466681-0", "text": "FIGURE 3-3 Simplex, half-duplex, and full-duplex transmissions\n3.2.2 Data Flow\nCircuits can be designed to permit data to flow in one direction or in both directions. Actually, there are\nthree ways to transmit: simplex, half-duplex, and full-duplex (Figure 3-3). Simplex transmission is\none-way transmission, such as that with radios and TVs.\nHalf-duplex transmission is a two-way transmission, but you can transmit in only one direction at a\ntime. A half-duplex communication link is similar to a walkie-talkie link; only one computer can transmit\nat a time. Computers use control signals to negotiate that will send and that will receive data. The amount\nof time half-duplex communication takes to switch between sending and receiving is called turnaround\ntime (also called retrain time or reclocking time). The turnaround time for a specific circuit can be\nobtained from its technical specifications (often between 20 and 50 milliseconds). Europeans sometimes\nuse the term simplex circuit to mean a half-duplex circuit.\nWith full-duplex transmission, you can transmit in both directions simultaneously, with no\nturnaround time.\nHow do you choose which data flow method to use? Obviously, one factor is the application. If data always\nneed to flow only in one direction (e.g., from a remote sensor to a host computer), then simplex is\nprobably the best choice. In most cases, however, data must flow in both directions.\nThe initial temptation is to presume that a full-duplex channel is best; however, each circuit has only so\nmuch capacity to carry data. Creating a full-duplex circuit means that the circuit offers full capacity both\nways simultaneously. In some cases, it makes more sense to build a set of simplex circuits in the same way", "source": "Page 90", "chapter_title": "Chapter 11"}
{"id": "d936574efb6c-1", "text": "a set of one-way streets can increase the speed of traffic. In other cases, a half-duplex circuit may work\nbest. For example, terminals connected to mainframes often transmit data to the host, wait for a reply,\ntransmit more data, and so on, in a turn-taking process; usually, traffic does not need to flow in both", "source": "Page 90", "chapter_title": "Chapter 11"}
{"id": "fb4f71c28805-0", "text": "directions simultaneously. Such a traffic pattern is ideally suited to half-duplex circuits.\n3.2.3 Multiplexing\nMultiplexing means to break one high-speed physical communication circuit into several lower-speed\nlogical circuits so that many different devices can simultaneously use it but still \u201cthink\u201d that they have\ntheir own separate circuits (the multiplexer is \u201ctransparent\u201d). It is multiplexing without multiplexing, the\nInternet would have collapsed in the 1990s.\nFIGURE 3-4 Multiplexed circuit\nMultiplexing often is done in multiples of 4 (e.g., 8, 16). Figure 3-4 shows a four-level multiplexed circuit.\nNote that two multiplexers are needed for each circuit: one to combine the four original circuits into the\none multiplexed circuit and one to separate them back into the four separate circuits.\nThe primary benefit of multiplexing is to save money by reducing the amount of cable or the number of\nnetwork circuits that must be installed. For example, if we did not use multiplexers in Figure 3-4, we\nwould need to run four separate circuits from the clients to the server. If the clients were located close to\nthe server, this would be inexpensive. However, if they were located several miles away, the extra costs\ncould be substantial.\nThere are four types of multiplexing: frequency division multiplexing (FDM), time-division\nmultiplexing (TDM), statistical time-division multiplexing (STDM), and wavelength division\nmultiplexing (WDM).\nFDM can be described as dividing the circuit \u201chorizontally\u201d so that many signals can travel a single\ncommunication circuit simultaneously. The circuit is divided into a series of separate channels, each\ntransmitting on a different frequency, much like a series of different radio or TV stations. All signals", "source": "Page 91", "chapter_title": "Chapter 11"}
{"id": "e40314894ffb-1", "text": "exist in the media at the same time, but because they are on different frequencies, they do not interfere\nwith each other.\nTDM shares a communication circuit among two or more computers by having them take turns, dividing\nthe circuit vertically, so to speak.\nSTDM is the exception to the rule that the capacity of the multiplexed circuit must equal the sum of the\ncircuits it combines. STDM allows more terminals or computers to be connected to a circuit than does\nFDM or TDM. If you have four computers connected to a multiplexer and each can transmit at 64 kbps,\nthen you should have a circuit capable of transmitting 256 kbps (4 \u00d7 64 kbps). However, not all computers\nwill be transmitting continuously at their maximum transmission speed. Users typically pause to read\ntheir screens or spend time typing at lower speeds. Therefore, you do not need to provide a speed of 256\nkbps on this multiplexed circuit. If you assume that only two computers will ever transmit at the same", "source": "Page 91", "chapter_title": "Chapter 11"}
{"id": "3636a53f31d3-0", "text": "time, 128 kbps will be enough. STDM is called statistical because the selection of transmission speed for\nthe multiplexed circuit is based on a statistical analysis of the usage requirements of the circuits to be\nmultiplexed.\nWDM is a version of FDM used in fiber-optic cables. When fiber-optic cables were first developed, the\ndevices attached to them were designed to use only one color of light generated by a laser or LED.\nLight has different frequencies (i.e., colors), so rather than building devices to transmit using only one\ncolor, why not send multiple signals, each in a different frequency, through the same fiber-optic cable? By\nsimply attaching different devices that could transmit in the full spectrum of light rather than just one\nfrequency, the capacity of the existing fiber-optic cables could be dramatically increased, with no change\nto the physical cables themselves.\nMANAGEMENT FOCUS 3-1\nStructured Cabling EIA/TIA 568-B\nIn 1995, the Telecommunications Industry Association (TIA) and Electronic Industries Alliance\n(EIA) came up with the first standard to create structured cabling, called TIA/EIA 568-A. This\nstandard defined the minimum requirements for internal telecommunications wiring within\nbuildings and between buildings on one campus. This standard was updated and changed many\ntimes, and today the accepted standard is TIA/EIA 568-B, which came out in 2002. This standard\nhas six subsystems:\n1. Building entrance: the point where external cabling and wireless connects to the internal\nbuilding wiring and equipment room\n2. Equipment room (ER): the room where network servers and telephone equipment would be\nstored\n3. Telecommunications closet: the room that contains the cable termination points and the\ndistribution frames\n4. Backbone cabling: the cabling that interconnects telecommunication closets, equipment", "source": "Page 92", "chapter_title": "Chapter 11"}
{"id": "a7a4e41b12fd-1", "text": "4. Backbone cabling: the cabling that interconnects telecommunication closets, equipment\nrooms, and building entrances within a building; also, this refers to cabling between buildings\n5. Horizontal cabling: the cabling that runs from the telecommunications closet to each LAN\n6. Work area: the cabling where the computers, printers, patch cables, jacks, and so on, are\nlocated\nThis standard describes what the master cabling document should look like (which would describe\neach of the six areas discussed previously) and applies for both twisted-pair and fiber-optic cabling.\nMANAGEMENT FOCUS 3-2\nUndersea Fiber-Optic Cables\nPerhaps you were wondering what happens when you send an email from the United States to\nEurope. How is your email transmitted from one continent to another? It most likely travels through\none of the submarine cables that connect America and Europe. A neat interactive submarine cable\nmap can be found at http://www. submarinecablemap.com/.\nThis map shows you each cable\u2019s name, ready-for- service (RFS) date, length, owners, website (if\nany), and landing points. Each cable on this map has a capacity of at least 5 Gbps.\nActually, the first submarine telecommunication cable was laid in the 1850s and carried telegraphy\ntraffic. Today, we use fiber-optic cable that carries phone, Internet, and private data as digital data.", "source": "Page 92", "chapter_title": "Chapter 11"}
{"id": "45b6ced89b17-0", "text": "So now you may ask yourself, how do these cables get laid on the seabed? Submarine cables are laid\nusing special cable-layer ships\u2014these are factories that produce the cable on board and then have\nequipment to lay and bury the cable. The cable-layer ships get as close as possible to the shore where\nthe cable will be connected. A messenger line is sent out from the ship using a workboat that takes it\nto the shore.\nOnce the cable is secured onshore, the installation process under the sea can begin. A 30-ton sea\nplow with the cable in it (think about a needle and thread) is then tossed overboard and lands on the\nseabed. The plow then buries the cable under the sea bed at a required burial depth (up to 3 meters).\nThe simultaneous lay-and-bury of the cable continues until an agreed position, after which the cable\nis surface laid until reaching its destination. Here is a video that illustrates this:\nhttps://www.youtube.com/watch?v=Gsoo_BOwrrM\nOne technology that you may have come across that uses multiplexing is DSL. DSL stands for digital\nsubscriber line, and it allows for simultaneous transmission of voice (phone calls), data going to the\nInternet (called upstream data), and data coming to your house from the Internet (called downstream\ndata). With DSL, a DSL modem is installed at the customer\u2019s home or office, and another DSL modem is\ninstalled at the telephone company switch closet. The modem is first an FDM device that splits the\nphysical circuit into three logical circuits (phone, upstream data, and downstream data). TDM is then\nused within the two data channels to provide a set of one or more individual channels that can be used to\ncarry different data. A combination of amplitude and phase modulation is used in the data circuits to", "source": "Page 93", "chapter_title": "Chapter 11"}
{"id": "23798e8c1109-1", "text": "carry different data. A combination of amplitude and phase modulation is used in the data circuits to\nprovide the desired data rate. You will learn more about DSL in Chapter 10.\n3.3 COMMUNICATION MEDIA\nThe medium (or media, if there is more than one) is the physical matter or substance that carries the voice\nor data transmission. Many different types of transmission media are currently in use, such as copper\n(wire), glass or plastic (fiber-optic cable), or air (radio, microwave, or satellite). There are two basic types\nof media. Guided media are those in which the message flows through a physical medium such as a\ntwisted-pair wire, coaxial cable, or fiber-optic cable; the medium \u201cguides\u201d the signal. Wireless media\nare those in which the message is broadcast through the air, such as microwave or satellite.\nIn many cases, the circuits used in WANs are provided by the various common carriers who sell usage of\nthem to the public. We call the circuits sold by the common carrier communication services. Chapter 9\ndescribes the specific services available in North America. The following sections describe the medium\nand the basic characteristics of each circuit type, in the event you were establishing your own physical\nnetwork, whereas Chapter 9 describes how the circuits are packaged and marketed for purchase or lease\nfrom a common carrier. If your organization has leased a circuit from a common carrier, you are probably\nless interested in the media used and more interested in whether the speed, cost, and reliability of the\ncircuit meet your needs.\n3.3.1 Twisted-Pair Cable\nOne of the most commonly used types of guided media is twisted-pair cable, insulated pairs of wires\nthat can be packed quite close together (Figure 3-5). The wires usually are twisted to minimize the", "source": "Page 93", "chapter_title": "Chapter 11"}
{"id": "a720687bdc1d-2", "text": "electromagnetic interference between one pair and any other pair in the bundle. Your house or apartment\nprobably has a set of two twisted-pair wires (i.e., four wires) from it to the telephone company network.\nOne pair is used to connect your telephone; the other pair is a spare that can be used for a second\ntelephone line. The twisted-pair cable used in LANs are usually packaged as four sets of pairs, as shown in\nFigure 3-5, whereas bundles of several thousand wire pairs are placed under city streets and in large\nbuildings. The specific types of twisted-pair cable used in LANs, such as Cat 5e and Cat 6, are discussed in\nChapter 7.\n3.3.2 Coaxial Cable\nCoaxial cable is a type of guided medium that is quickly disappearing (Figure 3-6). Coaxial cable has a\ncopper core (the inner conductor) with an outer cylindrical shell for insulation. The outer shield, just", "source": "Page 93", "chapter_title": "Chapter 11"}
{"id": "f8187dda8b29-0", "text": "under the shell, is the second conductor. Because they have additional shielding provided by their\nmultiple layers of material, coaxial cables are less prone to interference and errors than basic low-cost\ntwisted-pair wires. Coaxial cables cost about three times as much as twisted-pair wires but offer few\nadditional benefits other than better shielding. One can also buy specially shielded twisted-pair wire that\nprovides the same level of quality as coaxial cable but at half its cost. For this reason, few companies are\ninstalling coaxial cable today, although some still continue to use an existing coaxial cable that was\ninstalled years ago.\nFIGURE 3-5 Category 5e twisted-pair wire\nFIGURE 3-6 Coaxial cables. Thinnet and Thicknet Ethernet cables (right)\u2014(1) center core, (2) dielectric\ninsulator, (3) metallic shield, (4) plastic jacket and a cross-sectional view (left)\n3.3.3 Fiber-Optic Cable\nAlthough twisted pair is the most common type of guided medium, fiber-optic cable also is becoming\nwidely used. Instead of carrying telecommunication signals in the traditional electrical form, this\ntechnology uses high-speed streams of light pulses from lasers or LEDs (light-emitting diodes) that carry\ninformation inside hair-thin strands of glass called optical fibers. Figure 3-7 shows a fiber-optic cable and\ndepicts the optical core, the cladding (metal coating), and how light rays travel in optical fibers.\nThe earliest fiber-optic systems were multimode, meaning that the light could reflect inside the cable at\nmany different angles. Multimode cables are plagued by excessive signal weakening (attenuation) and", "source": "Page 94", "chapter_title": "Chapter 11"}
{"id": "0febad5265b1-0", "text": "dispersion (spreading of the signal so that different parts of the signal arrive at different times at the\ndestination). For these reasons, early multimode fiber was usually limited to about 500 meters. Graded-\nindex multimode fiber attempts to reduce this problem by changing the refractive properties of the glass\nfiber so that as the light approaches the outer edge of the fiber, it speeds up, which compensates for the\nslightly longer distance it must travel compared with light in the center of the fiber. Therefore, the light in\nthe center is more likely to arrive at the same time as the light that has traveled at the edges of the fiber.\nThis increases the effective distance to just under 1,000 meters.\nFIGURE 3-7 Fiber-optic cable\nSingle-mode fiber-optic cables transmit a single direct beam of light through a cable that ensures the light\nreflects in only one pattern, in part because the core diameter has been reduced from 50 microns to about\n5\u201310 microns. This smaller-diameter core allows the fiber to send a more concentrated light beam,\nresulting in faster data transmission speeds and longer distances, often up to 100 kilometers. However,\nbecause the light source must be perfectly aligned with the cable, single-mode products usually use lasers\n(rather than the LEDs used in multimode systems) and therefore are more expensive.\nFiber-optic technology is a revolutionary departure from the traditional copper wires of twisted-pair cable\nor coaxial cable. One of the main advantages of fiber optics is that it can carry huge amounts of\ninformation at extremely fast data rates. This capacity makes it ideal for the simultaneous transmission of\nvoice, data, and image signals. In most cases, fiber-optic cable works better under harsh environmental\nconditions than do its metallic counterparts. It is not as fragile or brittle, it is not as heavy or bulky, and it", "source": "Page 95", "chapter_title": "Chapter 11"}
{"id": "d88fcc078b87-1", "text": "is more resistant to corrosion. Also, in case of fire, an optical fiber can withstand higher temperatures\nthan can copper wire. Even when the outside jacket surrounding the optical fiber has melted, a fiber-optic\nsystem still can be used.\n3.3.4 Radio\nOne of the most commonly used forms of wireless media is radio; when people used the term wireless,\nthey usually mean radio transmission. When you connect your laptop into the network wirelessly, you\nare using radio transmission. Radio data transmission uses the same basic principles as standard radio\ntransmission. Each device or computer on the network has a radio receiver/transmitter that uses a\nspecific frequency range that does not interfere with commercial radio stations. The transmitters are very\nlow power, designed to transmit a signal only a short distance, and are often built into portable computers\nor handheld devices such as phones and personal digital assistants. Wireless technologies for LAN\nenvironments, such as IEEE 802.1x, are discussed in more detail in Chapter 7.\nMANAGEMENT FOCUS 3-3\nBoingo Hot Spots Around the World", "source": "Page 95", "chapter_title": "Chapter 11"}
{"id": "258b94cc4ea3-0", "text": "Perhaps you have come across Boingo while trying to find a wireless connection in an airport\nbetween flights. Boingo is a wireless Internet service provider (WISP) that is different than many\nfree wifi connections that you can get at airports or coffee shops because it offers a secure connection\n(specifically, a VPN or WPA service that can be configured on your device, but more about this in\nChapter 11). This secure connection is now offered in 7,000 U.S. locations and 13,000 international\nlocations and as in-flight wifi on some international carriers.\nTheir monthly rates start at $9.95 for mobile devices and $39 for global access for 4 devices and\n2,000 minutes. Boingo also offers 1-, 2-, and 3-hour plans in case you don\u2019t travel frequently and\ndon\u2019t need a monthly subscription. To find Boingo hot spots, you need to download an app on your\nphone or laptop, and the app will alert you if there is an available wifi connection in your area. The\napp will even chart a graph that will show you signal strength in real-time.\nSources: Adapted from Boingo.com, cnet.com\n3.3.5 Microwave\nMicrowave transmission is an extremely high-frequency radio communication beam that is\ntransmitted over a direct line-of-sight path between any two points. As its name implies, a microwave\nsignal is an extremely short wavelength, thus the word micro-wave. Microwave radio transmissions\nperform the same functions as cables. For example, point A communicates with point B via a through-the-\nair microwave transmission path, instead of a copper wire cable. Because microwave signals approach the\nfrequency of visible light waves, they exhibit many of the same characteristics as light waves, such as\nreflection, focusing, or refraction. As with visible light waves, microwave signals can be focused into", "source": "Page 96", "chapter_title": "Chapter 11"}
{"id": "6f4898ebb40d-1", "text": "narrow, powerful beams that can be projected over long distances. Just as a parabolic reflector focuses a\nsearchlight into a beam, a parabolic reflector also focuses a high-frequency microwave into a narrow\nbeam. Towers are used to elevate the radio antennas to account for the earth\u2019s curvature and maintain a\nclear line-of-sight path between the two parabolic reflectors (see Figure 3-8).\nThis transmission medium is typically used for long-distance data or voice transmission. It does not\nrequire the laying of any cable, because long-distance antennas with microwave repeater stations can be\nplaced approximately 25\u201350 miles apart. A typical long-distance antenna might be 10 feet wide, although,\nover shorter distances in the inner cities, the dish antennas can be less than 2 feet in diameter. The\nairwaves in larger cities are becoming congested because so many microwave dish antennas have been\ninstalled that they interfere with one another.\n3.3.6 Satellite\nSatellite transmission is similar to microwave transmission, except instead of transmission involving\nanother nearby microwave dish antenna, it involves a satellite many miles up in space. Figure 3-9 depicts\na geosynchronous satellite. Geosynchronous means that the satellite remains stationary over one point on\nthe earth. One disadvantage of satellite transmission is the propagation delay that occurs because the\nsignal has to travel out into space and back to earth, a distance of many miles that even at the speed of\nlight can be noticeable. Low earth orbit (LEO) satellites are placed in lower orbits to minimize\npropagation delay. Satellite transmission is sometimes also affected by raindrop attenuation when\nsatellite transmissions are absorbed by heavy rain. It is not a major problem, but engineers need to work\naround it.", "source": "Page 96", "chapter_title": "Chapter 11"}
{"id": "c734261df393-0", "text": "FIGURE 3-8 A microwave tower. The round antennas are microwave antennas and the straight antennas\nare cell phone antennas", "source": "Page 97", "chapter_title": "Chapter 11"}
{"id": "2e7316cf1539-0", "text": "FIGURE 3-9 Satellites in operation\nMANAGEMENT FOCUS 3-4\nSatellite Communications Improve Performance\nBoyle Transportation hauls hazardous materials nation-wide for both commercial customers and the\ngovernment, particularly the U.S. Department of Defense. The Department of Defense recently\nmandated that hazardous materials contractors use mobile communications systems with up-to-the-\nminute monitoring when hauling the department\u2019s hazardous cargoes.\nAfter looking at the alternatives, Boyle realized that it would have to build its own system. Boyle\nneeded a relational database at its operations center that contained information about customers,\npickups, deliveries, truck location, and truck operating status. Data are distributed from this\ndatabase via satellite to an antenna on each truck. Now, at any time, Boyle can notify the designated\ntruck to make a new pickup via the bidirectional satellite link and record the truck\u2019s\nacknowledgment.\nEach truck contains a mobile data terminal connected to the satellite network. Each driver uses a\nkeyboard to enter information, which transmits the location of the truck. These satellite data are\nreceived by the main offices via a leased line from the satellite earth station. This system increased", "source": "Page 98", "chapter_title": "Chapter 11"}
{"id": "b43ee0a88ba2-0", "text": "productivity by an astounding 80% over 2 years; administration costs increased by only 20%.\nInterested in finding out more about how satellite communication works? Watch this video:\nhttps://www.youtube.com/watch?v=hXa3bTcIGPU\n3.3.7 Media Selection\nWhich media are best? It is hard to say, particularly when manufacturers continue to improve various\nmedia products. Several factors are important in selecting media.\nThe type of network is one major consideration. Some media are used only for WANs (microwaves\nand satellite), whereas others typically are not (twisted pair, coaxial cable, and radio), although we\nshould note that some old WAN networks still use twisted-pair cable. Fiber-optic cable is unique in\nthat it can be used for virtually any type of network.\nCost is always a factor in any business decision. Costs are always changing as new technologies are\ndeveloped and competition among vendors drives prices down. Among the guided media, twisted-\npair wire is generally the cheapest, coaxial cable is somewhat more expensive, and fiber-optic cable is\nthe most expensive. The cost of wireless media is generally driven more by distance than any other\nfactor. For very short distances (several hundred meters), radio is the cheapest; for moderate\ndistances (several hundred miles), microwave is the cheapest; and for long distances, satellite is the\ncheapest.\nTransmission distance is a related factor. Twisted-pair wire coaxial cable and radio can transmit data\nonly a short distance before the signal must be regenerated. Twisted-pair wire and radio typically can\ntransmit up to 100\u2013300 meters and coaxial cable typically between 200 and 500 meters. Fiber optics\ncan transmit up to 75 miles, and new types of fiber-optic cable can reach more than 600 miles.", "source": "Page 99", "chapter_title": "Chapter 11"}
{"id": "f66492ea7236-1", "text": "Security is primarily determined by whether the media are guided or wireless. Wireless media (radio,\nmicrowave, and satellite) are the least secure because their signals are easily intercepted. Guided\nmedia (twisted pair, coaxial, and fiber optics) are more secure, with fiber optics being the most\nsecure.\nError rates are also important. Wireless media are most susceptible to interference and thus have the\nhighest error rates. Among the guided media, fiber optics provides the lowest error rates, coaxial\ncable the next best, and twisted-pair cable the worst, although twisted-pair cable is generally better\nthan the wireless media.\nTransmission speeds vary greatly among the different media. It is difficult to quote specific speeds for\ndifferent media because transmission speeds are constantly improving and because they vary within\nthe same type of media, depending on the specific type of cable and the vendor. In general, twisted-\npair cable and coaxial cable can provide data rates of between 1 Mbps (1 million bits per second) and 1\nGbps (1 billion bits per second), whereas fiber-optic cable ranges between 1 Gbps and 40 Gbps. Radio,\nmicrowave, and satellite generally provide 10\u2013100 Mbps.\n3.4 DIGITAL TRANSMISSION OF DIGITAL DATA\nAll computer systems produce binary data. For these data to be understood by both the sender and\nreceiver, both must agree on a standard system for representing the letters, numbers, and symbols that\ncompose messages. The coding scheme is the language that computers use to represent data.\n3.4.1 Coding\nA character is a symbol that has a common, constant meaning. A character might be the letter A or B, or it\nmight be a number such as 1 or 2. Characters also may be special symbols such as ? or &. Characters in", "source": "Page 99", "chapter_title": "Chapter 11"}
{"id": "7cf4bb1c02a8-2", "text": "data communications, as in computer systems, are represented by groups of bits that are binary zeros (0)\nand ones (1). The groups of bits representing the set of characters that are the \u201calphabet\u201d of any given\nsystem are called a coding scheme, or simply a code.\nA byte is a group of consecutive bits that is treated as a unit or character. One byte normally is composed", "source": "Page 99", "chapter_title": "Chapter 11"}
{"id": "8848ec108faf-0", "text": "of 8 bits and usually represents one character; however, in data communications, some codes use 5, 6, 7,\n8, or 9 bits to represent a character. For example, a representation of the character A by a group of 8 bits\n(say, 01 000 001) is an example of coding.\nThere are three predominant coding schemes in use today. United States of America Standard Code for\nInformation Interchange (USASCII, or, more commonly, ASCII) is the most popular code for data\ncommunications and is the standard code on most microcomputers. There are two types of ASCII; one is a\n7-bit code that has 128 valid character combinations, and the other is an 8-bit code that has 256\ncombinations. The number of combinations can be determined by taking the number 2 and raising it to\nthe power equal to the number of bits in the code because each bit has two possible values, a 0 or a 1. In\nthis case 27 = 128 characters or 28 = 256 characters.\nA second commonly used coding scheme is ISO 8859, which is standardized by the International\nStandards Organization. ISO 8859 is an 8-bit code that includes the ASCII codes plus non-English letters\nused by many European languages (e.g., letters with accents). If you look closely at Figure 2.21, you will\nsee that HTML often uses ISO 8859.\nUnicode is the other commonly used coding scheme. There are many different versions of Unicode. UTF-\n8 is an 8-bit version, which is very similar to ASCII. UTF-16, which uses 16 bits per character (i.e., 2 bytes,\ncalled a \u201cword\u201d), is used by Windows. By using more bits, UTF-16 can represent many more characters", "source": "Page 100", "chapter_title": "Chapter 11"}
{"id": "c15176db7426-1", "text": "beyond the usual English or Latin characters, such as Cyrillic or Chinese.\nWe can choose any pattern of bits we like to represent any character we like, as long as all computers\nunderstand what each bit pattern represents. Figure 3-10 shows the 8-bit binary bit patterns used to\nrepresent a few of the characters we use in ASCII.", "source": "Page 100", "chapter_title": "Chapter 11"}
{"id": "7bb5536030c2-0", "text": "FIGURE 3-10 Binary numbers used to represent different characters using ASCII\n3.4.2 Transmission Modes\nParallel transmission is the way the internal transfer of binary data takes place inside a computer. If\nthe internal structure of the computer is 8 bit, then all 8 bits of the data element are transferred between\nthe main memory and the central processing unit simultaneously on 8 separate connections. The same is\ntrue of computers that use a 32-bit structure; all 32 bits are transferred simultaneously on 32 connections.\nTECHNICAL FOCUS 3-1\nBASIC ELECTRICITY\nThere are two general categories of electrical current: direct current and alternating current. Current\nis the movement or flow of electrons, normally from positive (+) to negative (\u2212). The plus (+) or\nminus (\u2212) measurements are known as polarity. Direct current (DC) travels in only one direction,", "source": "Page 101", "chapter_title": "Chapter 11"}
{"id": "640b6cede640-0", "text": "whereas alternating current (AC) travels first in one direction and then in the other direction.\nA copper wire transmitting electricity acts like a hose transferring water. We use three common\nterms when discussing electricity. Voltage is defined as electrical pressure\u2014the amount of electrical\nforce pushing electrons through a circuit. In principle, it is the same as pounds per square inch in a\nwater pipe. Amperes (amps) are units of electrical flow or volume. This measure is analogous to\ngallons per minute for water. The watt is the fundamental unit of electrical power. It is a rate unit,\nnot a quantity. You obtain the wattage by multiplying the volts by the amperes. Want to learn more?\nHere is an introductory video about electricity: https://www.youtube.com/watch?v=EJe AuQ7pkpc.\nFigure 3-11 shows how all 8 bits of one character could travel down a parallel communication circuit. The\ncircuit is physically made up of eight separate wires, wrapped in one outer coating. Each physical wire is\nused to send 1 bit of the 8-bit character. However, as far as the user is concerned (and the network for that\nmatter), there is only one circuit; each of the wires inside the cable bundle simply connects to a different\npart of the plug that connects the computer to the bundle of wire.\nFIGURE 3-11 Parallel transmission of an 8-bit code\nFIGURE 3-12 Serial transmission of an 8-bit code\nSerial transmission means that a stream of data is sent over a communication circuit sequentially in a\nbit-by-bit fashion, as shown in Figure 3-12. In this case, there is only one physical wire inside the bundle,\nand all data must be transmitted over that one physical wire. The transmitting device sends one bit, then a", "source": "Page 102", "chapter_title": "Chapter 11"}
{"id": "b747774a4939-1", "text": "second bit, and so on, until all the bits are transmitted. It takes n iterations or cycles to transmit n bits.\nThus, serial transmission is considerably slower than parallel transmission\u2014eight times slower in the case\nof 8-bit ASCII (because there are 8 bits). Compare Figure 3-12 with Figure 3-11.\n3.4.3 Digital Transmission\nDigital transmission is the transmission of binary electrical or light pulses in that it only has two\npossible states, a 1 or a 0. The most commonly encountered voltage levels range from a low of +3/\u22123 to a", "source": "Page 102", "chapter_title": "Chapter 11"}
{"id": "7542d1c6b384-0", "text": "high of +24/\u221224 volts. Digital signals are usually sent over wire of no more than a few thousand feet in\nlength.\nAll digital transmission techniques require a set of symbols (to define how to send a 1 and a 0) and the\nsymbol rate (how many symbols will be sent per second). Figure 3-13 shows five types of digital\ntransmission techniques. With unipolar signaling, the voltage is always positive or negative (like a DC\ncurrent). Figure 3-13 illustrates a unipolar technique in which a signal of 0 volts (no current) is used to\ntransmit a zero and a signal of +5 volts is used to transmit a 1.\nAn obvious question at this point is this: If 0 volts means a zero, how do you send no data? This is\ndiscussed in detail in Chapter 4. For the moment, we will just say that there are ways to indicate when a\nmessage starts and stops, and when there are no messages to send, the sender and receiver agree to ignore\nany electrical signal on the line.\nTo successfully send and receive a message, both the sender and receiver have to agree on how often the\nsender can transmit data\u2014that is, on the symbol rate. For example, if the symbol rate on a circuit is 64\nkilo Hertz (kHz) (64,000 symbols per second), then the sender changes the voltage on the circuit once\nevery 1/64,000 of a second and the receiver must examine the circuit every 1/64,000 of a second to read the\nincoming data.\nIn bipolar signaling, the ones and zeros vary from a plus voltage to a minus voltage (like an AC current).\nThe first bipolar technique illustrated in Figure 3-13 is called nonreturn to zero (NRZ) because the voltage", "source": "Page 103", "chapter_title": "Chapter 11"}
{"id": "0e9f4359ece8-1", "text": "alternates from +5 volts (a symbol indicating a 1) to \u22125 volts (a symbol indicating a 0) without ever\nreturning to 0 volts. The second bipolar technique in this figure is called return to zero (RZ) because it\nalways returns to 0 volts after each bit before going to +5 volts (the symbol for a 1) or \u22125 volts (the symbol\nfor a 0). The third bipolar technique is called alternate mark inversion (AMI) because a 0 is always sent\nusing 0 volts, but 1s alternate between +5 volts and \u22125 volts. AMI is used on T1 and T3 circuits. In Europe,\nbipolar signaling sometimes is called double current signaling because you are moving between a positive\nand negative voltage potential.", "source": "Page 103", "chapter_title": "Chapter 11"}
{"id": "e63f3f687972-0", "text": "FIGURE 3-13 Unipolar, bipolar, and Manchester signals (digital)\nIn general, bipolar signaling experiences fewer errors than unipolar signaling because the symbols are\nmore distinct. Noise or interference on the transmission circuit is less likely to cause the bipolar\u2019s +5 volts\nto be misread as a \u22125 volts than it is to cause the unipolar\u2019s 0 volts to be misread as a +5 volts. This is\nbecause changing the polarity of a current (from positive to negative, or vice versa) is more difficult than\nchanging its magnitude.\n3.4.4 How Ethernet Transmits Data\nThe most common technology used in LANs is Ethernet; if you are working in a computer lab on campus,\nyou are most likely using Ethernet. Ethernet uses digital transmission over either serial or parallel\ncircuits, depending on which version of Ethernet you use. One version of Ethernet that uses serial\ntransmission requires 1/10,000,000 of a second to send one symbol; that is, it transmits 10 million\nsymbols (each of 1 bit) per second. This gives a data rate of 10 Mbps, and if we assume that there are 8 bits", "source": "Page 104", "chapter_title": "Chapter 11"}
{"id": "db625407a1f9-0", "text": "in each character, this means that about 1.25 million characters can be transmitted per second in the\ncircuit.\nEthernet uses Manchester encoding, which is a special type of bipolar signaling in which the signal is\nchanged from high to low or from low to high in the middle of the signal. A change from high to low is\nused to represent a 0, whereas the opposite (a change from low to high) is used to represent a 1 (see Figure\n3-13). Manchester encoding is less susceptible to having errors go undetected because if there is no\ntransition in midsignal, the receiver knows that an error must have occurred.\n3.5 ANALOG TRANSMISSION OF DIGITAL DATA\nTelephone networks were originally built for human speech rather than for data. They were designed to\ntransmit the electrical representation of sound waves, rather than the binary data used by computers.\nThere are many occasions when data need to be transmitted over a voice communications network. Many\npeople working at home still use a modem over their telephone line to connect to the Internet.\nThe telephone system (commonly called POTS for plain old telephone service) enables voice\ncommunication between any two telephones within its network. The telephone converts the sound waves\nproduced by the human voice at the sending end into electrical signals for the telephone network. These\nelectrical signals travel through the network until they reach the other telephone and are converted back\ninto sound waves.\nAnalog transmission occurs when the signal sent over the transmission media continuously varies\nfrom one state to another in a wave-like pattern much like the human voice. Modems translate the digital\nbinary data produced by computers into the analog signals required by voice transmission circuits. One\nmodem is used by the transmitter to produce the analog signals and a second by the receiver to translate\nthe analog signals back into digital signals.", "source": "Page 105", "chapter_title": "Chapter 11"}
{"id": "c4a8a0de6d19-1", "text": "the analog signals back into digital signals.\nThe sound waves transmitted through the voice circuit have three important characteristics (see Figure 3-\n14). The first is the height of the wave, called amplitude. Amplitude is measured in decibels (dB). Our\nears detect amplitude as the loudness or volume of sound. Every sound wave has two parts, half above the\nzero amplitude point (i.e., positive) and half below (i.e., negative), and both halves are always the same\nheight.\nThe second characteristic is the length of the wave, usually expressed as the number of waves per second,\nor frequency. Frequency is expressed in hertz (Hz). Our ears detect frequency as the pitch of the sound.\nFrequency is the inverse of the length of the sound wave so that a high frequency means that there are\nmany short waves in a 1-second interval, whereas a low frequency means that there are fewer (but longer)\nwaves in 1 second.\nThe third characteristic is the phase, which refers to the direction in which the wave begins. The phase is\nmeasured in the number of degrees (\u00b0 ). The wave in Figure 3-14 starts up and to the right, which is\ndefined as a 0\u00b0 phase wave. Waves can also start down and to the right (a 180\u00b0 phase wave), and in\nvirtually any other part of the sound wave.\n3.5.1 Modulation\nWhen we transmit data through the telephone lines, we use the shape of the sound waves we transmit (in\nterms of amplitude, frequency, and phase) to represent different data values. We do this by transmitting a\nsimple sound wave through the circuit (called the carrier wave) and then changing its shape in different\nways to represent a 1 or a 0. Modulation is the technical term used to refer to these \u201cshape changes.\u201d", "source": "Page 105", "chapter_title": "Chapter 11"}
{"id": "702a9c6f7f11-2", "text": "There are three fundamental modulation techniques: amplitude modulation (AM), frequency\nmodulation, and phase modulation. Once again, the sender and receiver have to agree on what symbols\nwill be used (what amplitude, frequency, and phase will represent a 1 and a 0) and on the symbol rate\n(how many symbols will be sent per second).", "source": "Page 105", "chapter_title": "Chapter 11"}
{"id": "3a950eec06f1-0", "text": "FIGURE 3-14 Sound wave\nFIGURE 3-15 Amplitude modulation\nFIGURE 3-16 Frequency modulation\nBasic Modulation With AM (also called amplitude shift keying [ASK]), the amplitude or height of\nthe wave is changed. One amplitude is the symbol defined to be 0, and another amplitude is the symbol\ndefined to be a 1. In the AM shown in Figure 3-15, the highest amplitude symbol (tallest wave) represents\na binary 1 and the lowest amplitude symbol represents a binary 0. In this case, when the sending device\nwants to transmit a 1, it would send a high-amplitude wave (i.e., a loud signal). AM is more susceptible to\nnoise (more errors) during transmission than is frequency modulation (FM) or phase modulation.\nFM (also called frequency shift keying [FSK]) is a modulation technique whereby each 0 or 1 is\nrepresented by a number of waves per second (i.e., a different frequency). In this case, the amplitude does", "source": "Page 106", "chapter_title": "Chapter 11"}
{"id": "ad1f3658aaac-0", "text": "not vary. One frequency (i.e., a certain number of waves per second) is the symbol defined to be a 1, and a\ndifferent frequency (a different number of waves per second) is the symbol defined to be a 0. In Figure 3-\n16, the higher frequency wave symbol (more waves per time period) equals a binary 1, and the lower\nfrequency wave symbol equals a binary 0.\nPhase modulation (PM) (also called phase-shift keying [PSK]) is the most difficult to understand.\nPhase refers to the direction in which the wave begins. Until now, the waves we have shown start by\nmoving up and to the right (this is called a 0 \u00b0 phase wave). Waves can also start down and to the right.\nThis is called a phase of 180\u00b0. With phase modulation, one phase symbol is defined to be a 0 and the other\nphase symbol is defined to be a 1. Figure 3-17 shows the case where a phase of 0\u00b0 symbol is defined to be a\nbinary 0 and a phase of 180\u00b0 symbol is defined to be a binary 1.\nFIGURE 3-17 Phase modulation\nFIGURE 3-18 Two-bit amplitude modulation\nSending Multiple Bits Simultaneously Each of the three basic modulation techniques (AM, FM, and\nPM) can be refined to send more than 1 bit at one time. For example, basic AM sends 1 bit per wave (or\nsymbol) by defining two different amplitudes, one for a 1 and one for a 0. It is possible to send 2 bits on\none wave or symbol by defining four different amplitudes. Figure 3-18 shows the case where the highest-\namplitude wave is defined to be a symbol representing 2 bits, both 1s. The next highest amplitude is the", "source": "Page 107", "chapter_title": "Chapter 11"}
{"id": "95bb5dd99e6d-1", "text": "symbol defined tomean first a 1 and then a 0, and so on.\nThis technique could be further refined to send 3 bits at the same time by defining eight different symbols,\neach with different amplitude levels or 4 bits by defining 16 symbols, each with different amplitude levels,\nand so on. At some point, however, it becomes very difficult to differentiate between the different\namplitudes. The differences are so small that even a small amount of noise could destroy the signal.\nThis same approach can be used for FM and PM. Two bits could be sent on the same symbol by defining", "source": "Page 107", "chapter_title": "Chapter 11"}
{"id": "f7c41f8e2d96-0", "text": "four different frequencies, one for 11, one for 10, and so on, or by defining four phases (0\u00b0, 90\u00b0, 180\u00b0, and\n270\u00b0). Three bits could be sent by defining symbols with eight frequencies or eight phases (0\u00b0, 45\u00b0, 90\u00b0,\n135\u00b0, 180\u00b0, 225\u00b0, 270\u00b0, and 315\u00b0). These techniques are also subject to the same limitations as AM; as the\nnumber of different frequencies or phases becomes larger, it becomes difficult to differentiate among\nthem.\nIt is also possible to combine modulation techniques\u2014that is, to use AM, FM, and PM techniques on the\nsame circuit. For example, we could combine AM with four defined amplitudes (capable of sending 2 bits)\nwith FM with four defined frequencies (capable of sending 2 bits) to enable us to send 4 bits on the same\nsymbol.\nOne popular technique is quadrature amplitude modulation (QAM). QAM involves splitting the\nsymbol into eight different phases (3 bits) and two different amplitudes (1 bit), for a total of 16 different\npossible values. Thus, one symbol in QAM can represent 4 bits, while 256-QAM sends 8 bits per symbol.\n64-QAM and 256-QAM are commonly used in digital TV services and cable modem Internet services.\nBit Rate versus Baud Rate versus Symbol Rate The terms bit rate (i.e., the number bits per second\ntransmitted) and baud rate are used incorrectly much of the time. They often are used interchangeably,\nbut they are not the same. In reality, the network designer or network user is interested in bits per second\nbecause it is the bits that are assembled into characters, characters into words and, thus, business\ninformation.", "source": "Page 108", "chapter_title": "Chapter 11"}
{"id": "e1f51706eef4-1", "text": "information.\nA bit is a unit of information. A baud is a unit of signaling speed used to indicate the number of times per\nsecond the signal on the communication circuit changes. Because of the confusion over the term baud\nrate among the general public, ITU-T now recommends the term baud rate be replaced by the term\nsymbol rate. The bit rate and the symbol rate (or baud rate) are the same only when 1 bit is sent on each\nsymbol. For example, if we use AM with two amplitudes, we send 1 bit on one symbol. Here, the bit rate\nequals the symbol rate. However, if we use QAM, we can send 4 bits on every symbol; the bit rate would\nbe four times the symbol rate. If we used 64-QAM, the bit rate would be six times the symbol rate.\nVirtually all of today\u2019s modems send multiple bits per symbol.\n3.5.2 Capacity of a Circuit\nThe data capacity of a circuit is the fastest rate at which you can send your data over the circuit in terms of\nthe number of bits per second. The data rate (or bit rate) is calculated by multiplying the number of bits\nsent on each symbol by the maximum symbol rate. As we discussed in the previous section, the number of\nbits per symbol depends on the modulation technique (e.g., QAM sends 4 bits per symbol).\nThe maximum symbol rate in any circuit depends on the bandwidth available and the signal-to-noise ratio\n(the strength of the signal compared with the amount of noise in the circuit). The bandwidth is the\ndifference between the highest and the lowest frequencies in a band or set of frequencies. The range of\nhuman hearing is between 20 and 14,000 Hz, so its bandwidth is 13,880 Hz. The maximum symbol rate", "source": "Page 108", "chapter_title": "Chapter 11"}
{"id": "59e40ae8a816-2", "text": "for analog transmission is usually the same as the bandwidth as measured in hertz. If the circuit is very\nnoisy, the maximum symbol rate may fall as low as 50% of the bandwidth. If the circuit has very little\nnoise, it is possible to transmit at rates up to the bandwidth.\nDigital transmission symbol rates can reach as high as two times the bandwidth for techniques that have\nonly one voltage change per symbol (e.g., NRZ). For digital techniques that have two voltage changes per\nsymbol (e.g., RZ, Manchester), the maximum symbol rate is the same as the bandwidth.\nStandard telephone lines provide a bandwidth of 4,000 Hz. Under perfect circumstances, the maximum\nsymbol rate is therefore about 4,000 symbols per second. If we were to use basic AM (1 bit per symbol),\nthe maximum data rate would be 4,000 bits per second (bps). If we were to use QAM (4 bits per\nsymbol), the maximum data rate would be 4 bits per symbol \u00d7 4,000 symbols per second = 16,000 bps. A\ncircuit with a 10 MHz bandwidth using 64-QAM could provide up to 60 Mbps.\n3.5.3 How Modems Transmit Data\nThe modem (an acronym for modulator/demodulator) takes the digital data from a computer in the form\nof electrical pulses and converts them into the analog signal that is needed for transmission over an\nanalog voice-grade circuit. There are many different types of modems available today from dial-up", "source": "Page 108", "chapter_title": "Chapter 11"}
{"id": "439936078e42-0", "text": "modems to cable modems. For data to be transmitted between two computers using modems, both need\nto use the same type of modem. Fortunately, several standards exist for modems, and any modem that\nconforms to a standard can communicate with any other modem that conforms to the same standard.\nA modem\u2019s data transmission rate is the primary factor that determines the throughput rate of data, but it\nis not the only factor. Data compression can increase the throughput of data over a communication link\nby literally compressing the data. V.44, the ISO standard for data compression, uses Lempel\u2013Ziv\nencoding. As a message is being transmitted, Lempel\u2013Ziv encoding builds a dictionary of two-, three-,\nand four-character combinations that occur in the message. Anytime the same character pattern reoccurs\nin the message, the index to the dictionary entry is transmitted rather than sending the actual data. The\nreduction provided by V.44 compression depends on the actual data sent but usually averages about 6:1\n(i.e., almost six times as much data can be sent per second using V.44 as without it).\n3.6 DIGITAL TRANSMISSION OF ANALOG DATA\nIn the same way that digital computer data can be sent over analog telephone networks using analog\ntransmission, analog voice data can be sent over digital networks using digital transmission. This process\nis somewhat similar to the analog transmission of digital data. A pair of special devices called codecs\n(code/decode) is used in the same way that a pair of modems are used to translate the data to send across\nthe circuit. One codec is attached to the source of the signal (e.g., a telephone or the local loop at the end\noffice) and translates the incoming analog voice signal into a digital signal for transmission across the", "source": "Page 109", "chapter_title": "Chapter 11"}
{"id": "f05a36f69482-1", "text": "office) and translates the incoming analog voice signal into a digital signal for transmission across the\ndigital circuit. A second codec at the receiver\u2019s end translates the digital data back into analog data.\n3.6.1 Translating from Analog to Digital\nAnalog voice data must first be translated into a series of binary digits before they can be transmitted over\na digital circuit. This is done by sampling the amplitude of the sound wave at regular intervals and\ntranslating it into a binary number. Figure 3-19 shows an example where eight different amplitude levels\nare used (i.e., each amplitude level is represented by 3 bits). The top diagram shows the original signal,\nand the bottom diagram shows the digitized signal.\nA quick glance will show that the digitized signal is only a rough approximation of the original signal. The\noriginal signal had a smooth flow, but the digitized signal has jagged \u201csteps.\u201d The difference between the\ntwo signals is called quantizing error. Voice transmissions using digitized signals that have a great deal\nof quantizing error sound metallic or machinelike to the ear.\nThere are two ways to reduce quantizing error and improve the quality of the digitized signal, but neither\nis without cost. The first method is to increase the number of amplitude levels. This minimizes the\ndifference between the levels (the \u201cheight\u201d of the \u201csteps\u201d) and results in a smoother signal. In Figure 3-19,\nwe could define 16 amplitude levels instead of eight levels. This would require 4 bits (rather than the\ncurrent 3 bits) to represent the amplitude, thus increasing the amount of data needed to transmit the\ndigitized signal.\nNo amount of levels or bits will ever result in perfect-quality sound reproduction, but in general, 7 bits (27", "source": "Page 109", "chapter_title": "Chapter 11"}
{"id": "e9a37602d90e-2", "text": "= 128 levels) reproduces human speech adequately. Music, on the other hand, typically uses 16 bits (216 =\n65,536 levels).\nThe second method is to sample more frequently. This will reduce the \u201clength\u201d of each \u201cstep,\u201d also\nresulting in a smoother signal. To obtain a reasonable-quality voice signal, one must sample at least twice\nthe highest possible frequency in the analog signal. You will recall that the highest frequency transmitted\nin telephone circuits is 4,000 Hz. Thus, the methods used to digitize telephone voice transmissions must\nsample the input voice signal at a minimum of 8,000 times per second. Sampling more frequently than\nthis (called oversampling) will improve signal quality. RealNetworks.com, which produces Real Audio\nand other Web-based tools, sets its products to sample at 48,000 times per second to provide higher\nquality. The iPod and most CDs sample at 44,100 times per second and use 16 bits per sample to produce\nalmost error-free music. Some other MP3 players sample less frequently and use fewer bits per sample to\nproduce smaller transmissions, but the sound quality may suffer.", "source": "Page 109", "chapter_title": "Chapter 11"}
{"id": "5f6d140018c4-0", "text": "FIGURE 3-19 Pulse amplitude modulation (PAM)\n3.6.2 How Telephones Transmit Voice Data\nWhen you make a telephone call, the telephone converts your analog voice data into a simple analog\nsignal and sends it down the circuit from your home to the telephone company\u2019s network. This process is\nalmost unchanged from the one used by Bell when he invented the telephone in 1876. With the invention\nof digital transmission, the common carriers (i.e., the telephone companies) began converting their voice\nnetworks to use digital transmission. Today, all of the common carrier networks use digital transmission,\nexcept in the local loop (sometimes called the last mile), the wires that run from your home or business\nto the telephone switch that connects your local loop into the telephone network. This switch contains a\ncodec that converts the analog signal from your phone into a digital signal.This digital signal is then sent\nthrough the telephone network until it hits the switch for the local loop for the person you are calling. This\nswitch uses its codec to convert the digital signal used inside the phone network back into the analog\nsignal needed by that person\u2019s local loop and telephone (see Figure 3-20).\nFIGURE 3-20 Pulse amplitude modulation (PAM)\nThere are many different combinations of sampling frequencies and numbers of bits per sample that\ncould be used. For example, one could sample 4,000 times per second using 128 amplitude levels (i.e., 7\nbits) or sample at 16,000 times per second using 256 levels (i.e., 8 bits).\nThe North American telephone network uses pulse code modulation (PCM). With PCM, the input\nvoice signal is sampled 8,000 times per second. Each time the input voice signal is sampled, 8 bits are", "source": "Page 111", "chapter_title": "Chapter 11"}
{"id": "01f2dcd313e8-1", "text": "generated. Therefore, the transmission speed on the digital circuit must be 64,000 bps (8 bits per sample\n\u00d7 8,000 samples per second) to transmit a voice signal when it is in digital form. Thus, the North\nAmerican telephone network is built using millions of 64 kbps digital circuits that connect via codecs to\nthe millions of miles of analog local loop circuits into the users\u2019 residences and businesses.", "source": "Page 111", "chapter_title": "Chapter 11"}
{"id": "c3e026f29b66-0", "text": "3.6.3 How Instant Messenger Transmits Voice Data\nA 64 kbps digital circuit works very well for transmitting voice data because it provides very good quality.\nThe problem is that it requires a lot of capacity.\nAdaptive differential pulse code modulation (ADPCM) is the alternative used by IM and many\nother applications that provide voice services over lower-speed digital circuits. ADPCM works in much the\nsame way as PCM. It samples incoming voice signals 8,000 times per second and calculates the same 8-\nbit amplitude value as PCM. However, instead of transmitting the 8-bit value, it transmits the difference\nbetween the 8-bit value in the last time interval and the current 8-bit value (i.e., how the amplitude has\nchanged from one time period to another). Because analog voice signals change slowly, these changes can\nbe adequately represented by using only 4 bits. This means that ADPCM can be used on digital circuits\nthat provide only 32 kbps (4 bits per sample \u00d7 8,000 samples per second = 32,000 bps).\nSeveral versions of ADPCM have been developed and standardized by the ITU-T. There are versions\ndesigned for 8 kbps circuits (which send 1 bit 8,000 times per second) and 16 kbps circuits (which send 2\nbits 8,000 times per second), as well as the original 32 kbps version. However, there is a trade-off here.\nAlthough the 32 kbps version usually provides as good a sound quality as that of a traditional voice\ntelephone circuit, the 8 and 16 kbps versions provide poorer sound quality.\n3.6.4 Voice over Internet Protocol (VoIP)\nVoice over Internet Protocol (VoIP) (pronounced as \u201cvoyp\u201d) is commonly used to transmit phone", "source": "Page 112", "chapter_title": "Chapter 11"}
{"id": "e27ec0474ac5-1", "text": "conversations over digital networks. VoIP is a relatively new standard that uses digital telephones with\nbuilt-in codecs to convert analog voice data into digital data (see Figure 3-21). Because the codec is built\ninto the telephone, the telephone transmits digital data and therefore can be connected directly into a\nlocal area network, in much the same manner as a typical computer. Because VoIP phones operate on the\nsame networks as computers, we can reduce the amount of wiring needed; with VoIP, we need to operate\nand maintain only one network throughout our offices, rather than two separate networks\u2014one for voice\nand one for data. However, this also means that data networks with VoIP phones must be designed to\noperate in emergencies (to enable 911 calls) even when the power fails; they must have uninterruptable\npower supplies (UPS) for all network circuits.\nOne commonly used VoIP standard is G.722 wideband audio, which is a version of ADPCM that operates\nat 64 kbps. It samples 8,000 times per second and produces 8 bits per sample. Because VoIP phones are\ndigital, they can also contain additional capabilities. For example, high-end VoIP phones often contain\ncomputer chips to enable them to download and install small software applications so that they can\nfunction in many ways like computers.", "source": "Page 112", "chapter_title": "Chapter 11"}
{"id": "c837ef974627-0", "text": "FIGURE 3-21 VoIP phone\n3.7 IMPLICATIONS FOR CYBER SECURITY\nWhile the physical layer (layer 1) may not seem very exciting at first sight, it offers a lot of possibilities to a\nhacker to invade a computer or a network. Therefore, the physical layer must be protected just like the\napplication layer. We refer to this type of security as physical security. If physical security, access to an\norganization\u2019s hardware on which data is stored, is jeopardized, no firewall, encryption, or any other\nsecurity measures would be able to protect the organization.\nWhere does the problem with physical security originate? Laptops, USB drives, tablets, mobile devices,\nyou name it, have the ability to easily copy data to and from and therefore allow the stealing of sensitive\ndata to be very easy. USB drives, in particular, are very problematic. Many organizations disable USB\ndrives on computers because of the potential of stealing data. Or many times, employees have good\nintentions to work on data at home, but it is very easy to lose or misplace a USB drive. Therefore, if you\nneed to use a USB drive and want to have sensitive data on it, always encrypt the data. Also, never pick up\na USB drive and plug it into your computer because it is one of the known ways how hackers get into a\ncomputer. Hackers, and unfortunately also some commercial vendors who manufacture USBs, put\nmalware on USB drives with the purpose of stealing your data or your organization\u2019s data.\nIn addition to devices that come and go from an organization, routers and servers are potential sources of\nproblems when it comes to physical security. These devices must be protected just like mobile devices. In", "source": "Page 113", "chapter_title": "Chapter 11"}
{"id": "0c91f588b216-0", "text": "the movie Ocean\u2019s Eleven, Daniel Ocean (played by George Clooney) hires professionals from all over the\ncountry to steal $150 million from a safe in one of the casinos. Among these professionals is Livingston\nDell, who is an expert in communication systems. Livingston places a USB drive on one of the routers in\nthe casino\u2019s server room and not only highjacks the 911 call but also is able to look over the shoulders of\nthe security personnel.\nPhysical security, just like security at all layers, should be a priority for organizations. An organization\nneeds to create a physical security plan, in addition to a cyber security plan, so that it can adequately\nprotect its most important asset, data. Once an organization allows and attacked to access its hardware,\nthere no security measure that will protect it.\nSUMMARY\nCircuits Networks can be configured so that there is a separate circuit from each client to the host\n(called a point-to-point configuration) or so that several clients share the same circuit (a multipoint\nconfiguration). Data can flow through the circuit in one direction only (simplex), in both directions\nsimultaneously (full-duplex), or by taking turns so that data sometimes flow in one direction and then\nin the other (half-duplex). A multiplexer is a device that combines several simultaneous low-speed\ncircuits on one higher-speed circuit so that each low-speed circuit believes it has a separate circuit. In\ngeneral, the transmission capacity of the high-speed circuit must equal or exceed the sum of the low-\nspeed circuits.\nCommunication Media Media are either guided, in that they travel through a physical cable (e.g.,\ntwisted-pair wires, coaxial cable, or fiber-optic cable), or wireless, in that they are broadcast through\nthe air (e.g., radio, microwave, or satellite). Among the guided media, fiber-optic cable can transmit", "source": "Page 114", "chapter_title": "Chapter 11"}
{"id": "9960cf51cf69-1", "text": "data the fastest with the fewest errors and offers greater security but costs the most; twisted-pair wire\nis the cheapest and most commonly used. The choice of wireless media depends more on distance\nthan on any other factor; radio is cheapest for short distances, microwave is cheapest for moderate\ndistances, and satellite is cheapest for long distances.\nDigital Transmission of Digital Data Digital transmission (also called baseband transmission) is\ndone by sending a series of electrical (or light) pulses through the media. Digital transmission is\npreferred to analog transmission because it produces fewer errors; is more efficient; permits higher\nmaximum transmission rates; is more secure; and simplifies the integration of voice, video, and data\non the same circuit. With unipolar digital transmission, the voltage changes between 0 volts to\nrepresent a binary 0 and some positive value (e.g., +15 volts) to represent a binary 1. With bipolar\ndigital transmission, the voltage changes polarity (i.e., positive or negative) to represent a 1 or a 0.\nBipolar is less susceptible to errors. Ethernet uses Manchester encoding, which is a version of\nunipolar transmission.\nAnalog Transmission of Digital Data Modems are used to translate the digital data produced by\ncomputers into the analog signals for transmission in today\u2019s voice communication circuits. Both the\nsender and receiver need to have a modem. Data are transmitted by changing (or modulating) a\ncarrier sound wave\u2019s amplitude (height), frequency (length), or phase (shape) to indicate a binary 1 or\n0. For example, in AM, one amplitude is defined to be a 1 and another amplitude is defined to be a 0.\nIt is possible to send more than 1 bit on every symbol (or wave). For example, with AM, you could", "source": "Page 114", "chapter_title": "Chapter 11"}
{"id": "03190d3c264b-2", "text": "send 2 bits on each wave by defining four amplitude levels. The capacity or maximum data rate that a\ncircuit can transmit is determined by multiplying the symbol rate (symbols per second) by the\nnumber of bits per symbol. Generally (but not always), the symbol rate is the same as the bandwidth,\nso bandwidth is often used as a measure of capacity. V.44 is a data compression standard that can be\ncombined with any of the foregoing types of modems to reduce the amount of data in the transmitted\nsignal by a factor of up to six. Thus, a V.92 modem using V.44 could provide an effective data rate of\n5,600 \u00d7 6 = 336,000 bps.\nDigital Transmission of Analog Data Because digital transmission is better, analog voice data\nare sometimes converted to digital transmission. PCM is the most commonly used technique. PCM\nsamples the amplitude of the incoming voice signal 8,000 times per second and uses 8 bits to\nrepresent the signal. PCM produces a reasonable approximation of the human voice, but more", "source": "Page 114", "chapter_title": "Chapter 11"}
{"id": "868ed1ecdc31-0", "text": "sophisticated techniques are needed to adequately reproduce more complex sounds such as music.\nKEY TERMS\nadaptive differential pulse code modulation (ADPCM)\nAmerican Standard Code for Information Interchange (ASCII)\namplitude modulation (AM)\namplitude shift keying (ASK)\namplitude\nanalog transmission\nbandwidth\nbaud rate\nbipolar\nbit rate\nbits per second (bps)\ncarrier wave\ncircuit configuration\ncircuit\ncoaxial cable\ncodec\ncoding scheme\ndata compression\ndata rate\ndigital subscriber line\ndigital transmission\nfiber-optic cable\nfrequency division multiplexing (FDM)\nFrequency modulation (FM)\nfrequency shift keying (FSK)\nfrequency\nfull-duplex transmission\nguided media\nhalf-duplex transmission\nISO 8859\nkilo Hertz (kHz)\nLempel\u2013Ziv encoding\nlocal loop\nlogical circuit\nmalware\nManchester encoding", "source": "Page 115", "chapter_title": "Chapter 11"}
{"id": "34f4b884a40e-0", "text": "microwave transmission\nmodem\nmultiplexing\nmultipoint circuit\nparallel transmission\nphase modulation (PM)\nphase\nphase-shift keying [PSK]\nphysical circuit\nplain old telephone service (POTS)\nplain old telephone service\npoint-to-point circuit\npolarity\nPOTS\npulse code modulation (PCM)\nquadrature amplitude modulation (QAM)\nquantizing error\nradio transmission\nretrain time\nsatellite transmission\nserial transmission\nsimplex transmission\nstatistical time-division multiplexing (STDM)\nswitch\nsymbol rate\ntime-division multiplexing (TDM)\nturnaround time\ntwisted-pair cable\nunicode\nunipolar\nUSB drive\nV.44\nVoice over Internet Protocol (VoIP)\nwavelength division multiplexing (WDM)\nWireless media\nQUESTIONS\n1. How does a multipoint circuit differ from a point-to-point circuit?\n2. Describe the three types of data flows.", "source": "Page 116", "chapter_title": "Chapter 11"}
{"id": "3266ca6ee52d-0", "text": "3. Describe the three types of guided media.\n4. Describe the four types of wireless media.\n5. How do analog data differ from digital data?\n6. Clearly explain the differences between analog data, analog transmission, digital data, and digital\ntransmission.\n7. Explain why most telephone company circuits are now digital.\n8. What is coding?\n9. Briefly describe three important coding schemes.\n10. How are data transmitted in parallel?\n11. What feature distinguishes serial mode from parallel mode?\n12. How does bipolar signaling differ from unipolar signaling? Why is Manchester encoding more\npopular than either?\n13. What are the three important characteristics of a sound wave?\n14. What is bandwidth? What is the bandwidth in a traditional North American telephone circuit?\n15. Describe how data could be transmitted using amplitude modulation.\n16. Describe how data could be transmitted using frequency modulation.\n17. Describe how data could be transmitted using phase modulation.\n18. Describe how data could be transmitted using a combination of modulation techniques.\n19. Is the bit rate the same as the symbol rate? Explain.\n20. What is a modem?\n21. What is quadrature amplitude modulation (QAM)?\n22. What is 64-QAM?\n23. What factors affect transmission speed?\n24. What is oversampling?\n25. Why is data compression so useful?\n26. What data compression standard uses Lempel\u2013Ziv encoding? Describe how it works.\n27. Explain how pulse code modulation (PCM) works.\n28. What is quantizing error?\n29. What is the term used to describe the placing of two or more signals on a single circuit?\n30. What is the purpose of multiplexing?\n31. How does DSL (digital subscriber line) work?", "source": "Page 117", "chapter_title": "Chapter 11"}
{"id": "24f35d682637-1", "text": "31. How does DSL (digital subscriber line) work?\n32. Of the different types of multiplexing, what distinguishes (a) Frequency division multiplexing\n(FDM)? (b) Time-division multiplexing (TDM)? (c) Statistical time-division multiplexing (STDM)?\n(d) Wavelength division multiplexing (WDM)?\n33. What is the function of inverse multiplexing (IMUX)?\n34. If you were buying a multiplexer, would you choose TDM or FDM? Why?\n35. Some experts argue that modems may soon become obsolete. Do you agree? Why or why not?\n36. What is the maximum capacity of an analog circuit with a bandwidth of 4,000 Hz using QAM?\n37. What is the maximum data rate of an analog circuit with a 10-MHz bandwidth using 64-QAM and\nV.44?\n38. What is the capacity of a digital circuit with a symbol rate of 10 MHz using Manchester encoding?", "source": "Page 117", "chapter_title": "Chapter 11"}
{"id": "0dc755002acb-0", "text": "39. What is the symbol rate of a digital circuit providing 100 Mbps if it uses bipolar NRz signaling?\n40. What is VoIP?\nEXERCISES\nA. Investigate the costs of dumb terminals, network computers, minimally equipped personal\ncomputers, and top-of-the-line personal computers. Many equipment manufacturers and resellers\nare on the Web, so it\u2019s a good place to start looking.\nB. Investigate the different types of cabling used in your organization and where they are used (e.g.,\nLAN, backbone network).\nC. Three terminals (T1, T2, T3) are to be connected to three computers (C1, C2, C3) so that T1 is connected\nto C1, T2 to C2 and T3 to C3. All are in different cities. T1 and C1 are 1,500 miles apart, as are T2 and C2,\nand T3 and C3. The points T1, T2, and T3 are 25 miles apart, and the points C1, C2, and C3 also are 25\nmiles apart. If telephone lines cost $1 per mile, what is the line cost for three?\nD. Investigate different types of satellite communication services that are provided today.\nE. Draw how the bit pattern 01101100 would be sent using\na. Single-bit AM\nb. Single-bit FM\nc. Single-bit PM\nd. Two-bit AM (i.e., four amplitude levels)\ne. Two-bit FM (i.e., four frequencies)\nf. Two-bit PM (i.e., four different phases)\ng. Single-bit AM combined with single-bit FM\nh. Single-bit AM combined with single-bit PM\ni. Two-bit AM combined with two-bit PM", "source": "Page 118", "chapter_title": "Chapter 11"}
{"id": "9855a64a66b5-1", "text": "i. Two-bit AM combined with two-bit PM\nF. If you had to download a 20-page paper of 400 k (bytes) from your professor, approximately how\nlong would it take to transfer it over the following circuits? Assume that control characters add an\nextra 10% to the message.\na. Dial-up modem at 33.6 kbps\nb. Cable modem at 384 kbps\nc. Cable modem at 1.5 Mbps\nd. If the modem includes V.44 data compression with a 6:1 data compression ratio, what is the data\nrate in bits per second you would actually see in choice c?\nMINICASES\nI. Eureka! (Part 1) Eureka! is a telephone- and Internet-based concierge service that specializes in\nobtaining things that are hard to find (e.g., Super Bowl tickets, first-edition books from the 1500s,\nFaberg\u00e9 eggs). It currently employs 60 staff members who collectively provide 24-hour coverage\n(over three shifts). They answer the phones and respond to requests entered on the Eureka! website.\nMuch of their work is spent on the phone and on computers searching on the Internet. The company\nhas just leased a new office building and is about to wire it. What media would you suggest the\ncompany install in its office and why?\nII. Eureka! (Part 2) Eureka! is a telephone- and Internet-based concierge service that specializes in\nobtaining things that are hard to find (e.g., Super Bowl tickets, first-edition books from the 1500s,\nFaberg\u00e9 eggs). It currently employs 60 staff members who work 24 hours per day (over three shifts).", "source": "Page 118", "chapter_title": "Chapter 11"}
{"id": "f9b8892583e2-0", "text": "Staff answer the phone and respond to requests entered on the Eureka! website. Much of their work\nis spent on the phone and on computers searching on the Internet. What type of connections should\nEureka! consider from its offices to the outside world, in terms of phone and Internet? Outline the\npros and cons of each alternative below and make a recommendation. The company has three\nalternatives:\n1. Should the company use standard voice lines but use DSL for its data ($40 per month per line for\nboth services)?\n2. Should the company separate its voice and data needs, using standard analog services for voice\nbut finding some advanced digital transmission services for data ($40 per month for each voice\nline and $300 per month for a circuit with 1.5 Mbps of data)?\n3. Should the company search for all digital services for both voice and data ($60 per month for an\nall-digital circuit that provides two phone lines that can be used for two voice calls, one voice call\nand one data call at 64 kbps, or one data call at 128 kbps)?\nIII. Eureka! (Part 3) Eureka! is a telephone- and Internet-based concierge service that specializes in\nobtaining things that are hard to find (e.g., Super Bowl tickets, first-edition books from the 1500s,\nFaberg\u00e9 eggs). It currently employees 60 staff members who work 24 hours per day (over three\nshifts). Staff members answer phone calls and respond to requests entered on the Eureka! website.\nCurrently, each staff member has a desktop PC with two monitors and a twisted pair connection\n(Cat5e) that offers speeds up to 100 Mbps. Some employees made a suggestion to the CEO of Eureka!\nto upgrade their connection to a fiber-optic cable that can provide speeds up to 1 Gbps. What do you", "source": "Page 119", "chapter_title": "Chapter 11"}
{"id": "6869e223437d-1", "text": "think about this idea? How easy (difficult) is it to change wiring from twisted pair to fiber optic? Can\nwe use the same network cards in the PCs, or do we need to change them? How much would this\nchange cost?\nIV. (Speedy Package) Speedy Package is a same-day package delivery service that operates in Chicago.\nEach package has a shipping label that is attached to the package and is also electronically scanned\nand entered into Speedy\u2019s data network when the package is picked up and when it is delivered. The\nelectronic labels are transmitted via a device that operates on a cell phone network. (1) Assuming that\neach label is 1,000 bytes long, how long does it take to transmit one label over the cell network,\nassuming that the cell phone network operates at 144 kbps (144,000 bits per second) and that there\nare 8 bits in a byte? and (2) if speedy were to upgrade to the new, faster digital phone network that\ntransmits data at 200 kbps (200,000 bits per second), how long would it take to transmit a label?\nV. (Boingo) Reread Management Focus 3.2. What other alternatives can travelers consider? How is\nBoingo different from other companies offering hot spots, such as T-Mobile or AT&T?\nTECH UPDATES\nIn every chapter, we will offer a couple of ideas to investigate.\nTopic A: Satellite Communication\nYou decided to take a cruise during your spring break, but know that you will need to connect to the\ninternet to check your grade in this class. Being in the middle of the sea will not allow you to use your\n\u201cland\u201d Internet connection, you will have to use satellite communication. Who are the current satellite\ncommunication vendors? How does this technology work? Which providers are used by the military?", "source": "Page 119", "chapter_title": "Chapter 11"}
{"id": "87f397599013-2", "text": "communication vendors? How does this technology work? Which providers are used by the military?\nInvestigate the different providers, their services, infrastructure, and cost structure.\nTopic B: Fiber Optic Cables\nImagine that you are calling your relative who lives in Australia. You can connect using a variety of\napplications (WhatsApp, Facebook, Skype, just to name a few). You can make a video call because of the\nexisting network of undersea fiber-optic cables. Is there a map of this network? What\u2019s inside an under\nthe sea fiber optic wire? How do they lay these wires? Who are the main vendors? Explore this topic, and\ncompile your research.", "source": "Page 119", "chapter_title": "Chapter 11"}
{"id": "6d6358383f61-0", "text": "Deliverables\nYour job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title Slide\n2. Short description of the topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use a lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along\n5. How does it relate to material covered in class so far (and in the future)\n6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 3A\nLooking Inside Your Cable\nOne of the most commonly used types of local network cable is Category 5 unshielded twisted-pair cable,\ncommonly called \u201cCat 5.\u201d Cat 5 (and an enhanced version called Cat 5e) are used in Ethernet LANs. If you\nhave installed a LAN in your house or apartment, you probably used Cat 5 or Cat 5e.\nFigure 3-22 shows a picture of a typical Cat 5 cable. Each end of the cable has a connector called an RJ-45\nconnector that enables the cable to be plugged into a computer or network device. If you look closely at\nthe connector, you will see there are eight separate \u201cpins.\u201d You might think that this would mean the Cat 5\ncan transmit data in parallel, but it doesn\u2019t do this. Cat 5 is used for serial transmission.\nFIGURE 3-22 Cat 5 cable", "source": "Page 120", "chapter_title": "Chapter 11"}
{"id": "a4a88f89a2bc-0", "text": "FIGURE 3-23 Inside a Cat 5 cable\nIf you have an old Cat 5 cable (or are willing to spend a few dollars to buy cheap cable), it is simple to take\nthe connector off. Simply take a pair of scissors and cut through the cable a few inches from the connector.\nFigure 3-23 shows the same Cat 5 cable with the connector cut off. You can see why twisted pair is called\ntwisted pair: a single Cat 5 cable contains four separate sets of twisted-pair wires for a total of eight wires.\nUnfortunately, this picture is in black and white so it is hard to see the different colors of the eight wires\ninside the cable. Figure 3-24 lists the different colors of the wires and what they are used for under the\nEIA/TIA 568B standard (the less common 568A standard uses the pins in different ways). One pair of\nwires (connected to pins 1 and 2) is used to transmit data from your computer into the network. When\nyour computer transmits, it sends the same data on both wires; pin 1 (transmit+) transmits the data\nnormally and pin 2 (transmit\u2212) transmits the same data with reversed polarity. This way, if an error\noccurs, the hardware will likely detect a different signal on the two cables. For example, if there is a\nsudden burst of electricity with a positive polarity (or a negative polarity), it will change only one of the\ntransmissions from negative to positive (or vice versa) and leave the other transmission unchanged.\nElectrical pulses generate a magnetic field that has very bad side effects on the other wires. To minimize\nthis, the two transmit wires are twisted together so that the other wires in the cable receive both a positive\nand a negative polarity magnetic field from the wires twisted around each other, which cancel each other", "source": "Page 121", "chapter_title": "Chapter 11"}
{"id": "8bfd7f6e4ba9-1", "text": "and a negative polarity magnetic field from the wires twisted around each other, which cancel each other\nout.\nFigure 3-24 also shows a separate pair of wires for receiving transmissions from the network (pin 3\n[receive+] and pin 6 [receive\u2212]). These wires work exactly the same way as transmit+ and transmit\u2212 but\nare used by the network to send data to your computer. You\u2019ll notice that they are also twisted together in\none pair of wires, even though they are not side by side on the connector.\nFigure 3-24 shows the pin functions from the viewpoint of your computer. If you think about it, you\u2019ll\nquickly realize that the pin functions at the network end of the cable are reversed; that is, pin 1 is receive+\nbecause it is the wire that the network uses to receive the transmit+ signal from your computer. Likewise,\npin 6 at the network end is the transmit\u2212 wire because it is the wire on which your computer receives the\nreversed data signal.\nThe separate set of wires for transmitting and receiving means that Cat 5 is designed for full-duplex\ntransmission. It can send and receive at the same time because one set of wires is used for sending data\nand one set is used for receiving data. However, Cat 5 is not often used this way. Most hardware that uses\nCat 5 is designed to operate in a half-duplex mode, even though the cable itself is capable of full-duplex.", "source": "Page 121", "chapter_title": "Chapter 11"}
{"id": "b62d9f67ca95-0", "text": "FIGURE 3-24 Pin connection for Cat 5 at the computer end\nYou\u2019ll also notice that the other four wires in the cable are not used. Yes, that\u2019s right; they are simply\nwasted.\nDeliverable\nFind a Cat 5 or Cat 5e cable and record what color wires are used for each pin.\nHANDS-ON ACTIVITY 3B\nMaking MP3 Files\nMP3 files are good examples of analog-to-digital conversion. It is simple to take an analog signal\u2014such as\nyour voice\u2014 and convert it into a digital file for transmission or playback. In this activity, we will show you\nhow to record your voice and see how different levels of digital quality affect the sound.\nFirst, you need to download a sound editor and MP3 converter. One very good sound editor is Audacity\u2014\nand it\u2019s free. Go to audacity.sourceforge.net and download and install the audacity software. You will also\nneed the plug-in called LAME (an MP3 encoder), which is also free and available at lame.sourceforge.net.\nUse Audacity to record music or your voice (you can use a cheap microphone). Audacity records in very\nhigh quality, but will produce MP3 files in whatever quality level you choose.\nOnce you have the file recorded, you can edit the Preferences to change the File Format to use in saving\nthe MP3 file. Audacity/LAME offers a wide range of qualities. Try recording at least three different quality\nlevels. For example, for high quality, you could use 320 kbps, which means the recording uses 320 kbps of\ndata per second. In other words, the number of samples per second times the number of bits per sample\nequals 320 kbps. For regular quality, you could use 128 kbps. For low quality, you could use 16 kbps.", "source": "Page 122", "chapter_title": "Chapter 11"}
{"id": "c99586208f82-1", "text": "Create each of these files and listen to them to hear the differences in quality produced by the quantizing\nerror. The differences should be most noticeable for music. A recording at 24 kbps is often adequate for\nvoice, but music will require a better quality encoding.\nDeliverable\n1. Produce three MP3 files of the same music or voice recording at three different quality levels.\n2. List the size of each file.", "source": "Page 122", "chapter_title": "Chapter 11"}
{"id": "72b02c2b7a8b-0", "text": "3. Listen to each file and describe the quality differences you hear (if any).\nHANDS-ON ACTIVITY 3C\nMaking a Cat 5e Patch Cable\nA patch cable is a cable that runs a short distance (usually less than 10 feet) that connects a device into a\nwall jack, a patch panel jack, or a device. If you have a desktop computer, you\u2019re using a patch cable to\nconnect it into your Ethernet LAN. Patch cables are relatively inexpensive (usually $10 or less), but\ncompared to the cost of their materials, they are expensive (the materials usually cost less than $1).\nBecause it is relatively easy to make a patch cable, many companies make their own in order to save\nmoney.\nTo make your own patch cable, you will need a crimper, some Cat 5e cable, two RJ45 connectors, and a\ncable tester (optional) (see Figure 3-25).\n1. Using the cutter on the crimping tool, cut the desired length of Cat 5e cable.\n2. Insert the end of the cable into the stripper and gently press on the cable while rotating it to remove\nthe outer insulation of the cable. Be careful not to cut the twisted pairs inside. After removing the\nouter insulation, visually inspect the twisted pairs for damage. Do this on both ends of your cable. If\nany of the cables are damaged, you need to cut them and start over.\n3. Untwist the twisted pairs and straighten them. Once they are straightened, put them into this order:\norange-white, orange, green-white, blue, blue-white, green, brown-white, brown.\n4. Hold the cable in your right hand; the orange-white wire should be closest to you. Hold the RJ45\nconnector in your left hand with the little \u201chandle\u201d on the bottom.", "source": "Page 123", "chapter_title": "Chapter 11"}
{"id": "28be8e59286d-1", "text": "connector in your left hand with the little \u201chandle\u201d on the bottom.\nFIGURE 3-25 Tools and materials for making a patch cable\n5. Insert the wires inside the connector all the way to the end\u2014you should be able to see the colors of", "source": "Page 123", "chapter_title": "Chapter 11"}
{"id": "c20dc72fc011-0", "text": "the wires when you look at the front of the connector. Make sure that the wires don\u2019t change order.\nThe white insulation should be about 1/3 of the way inside the connector. (If you used the stripper on\nthe tool properly, the length of the wires will be exactly as needed to fit the RJ45 connector.)\n6. Now you are ready to crimp the connector. Insert the RJ45 connector to the crimper and press really\nhard. This will push the gold contacts on the connector onto the twisted pairs.\n7. Crimp the other end of the cable by repeating steps 4 through 7.\n8. The final step is to test your cable. Turn on the cable tester and insert both ends of the patch cable\ninto the tester. If you see the flashing light going down the indicators 1 through 8, not skipping any\nnumber or changing the order, you made a fully functional patch cable. If you don\u2019t have a cable\ntester, you can use the cable to connect your computer into an Ethernet LAN. If you\u2019re able to use the\nLAN, the cable is working.\nDeliverable\nA working patch cable.", "source": "Page 124", "chapter_title": "Chapter 11"}
{"id": "14f401c878d8-0", "text": "CHAPTER 4\nDATA LINK LAYER\nThe data link layer (also called layer 2) is responsible for moving a message from one computer or\nnetwork device to the next computer or network device in the overall path from the sender or receiver. It\ncontrols the way messages are sent on the physical media. Both the sender and receiver have to agree on\nthe rules, or protocols, that govern how they will communicate with each other. A data link protocol\ndetermines who can transmit at what time, where a message begins and ends, and how a receiver\nrecognizes and corrects a transmission error. In this chapter, we discuss these processes as well as several\nimportant sources of errors.\nOBJECTIVES\nUnderstand the role of the data link layer\nBecome familiar with two basic approaches to controlling access to the media\nBecome familiar with common sources of error and their prevention\nUnderstand three common error detection and correction methods\nBecome familiar with several commonly used data link protocols\nOUTLINE\n4.1 Introduction\n4.2 Media Access Control\n4.2.1 Contention\n4.2.2 Controlled Access\n4.2.3 Relative Performance\n4.3 Error Control\n4.3.1 Sources of Errors\n4.3.2 Error Prevention\n4.3.3 Error Detection\n4.3.4 Error Correction via Retransmission\n4.3.5 Forward Error Correction\n4.3.6 Error Control in Practice\n4.4 Data Link Protocols\n4.4.1 Asynchronous Transmission\n4.4.2 Synchronous Transmission\n4.5 Transmission Efficiency\n4.6 Implications for Cyber Security\nSummary\n4.1 INTRODUCTION\nIn Chapter 1, we introduced the concept of layers in data communications. The data link layer sits between", "source": "Page 125", "chapter_title": "Chapter 11"}
{"id": "01560622ae51-0", "text": "the physical layer (hardware such as the circuits, computers, and multiplexers described in Chapter 3) and\nthe network layer (which performs addressing and routing, as described in Chapter 5).\nThe data link layer is responsible for sending and receiving messages to and from other computers. Its job\nis to reliably move a message from one computer over one circuit to the next computer where the message\nneeds to go.\nThe data link layer performs two main functions and therefore is often divided into two sublayers. The\nfirst sublayer (called the logical link control [LLC] sublayer) is the data link layer\u2019s connection to the\nnetwork layer above it. At the sending computer, the LLC sublayer software is responsible for\ncommunicating with the network layer software (e.g., Internet Protocol (IP)) and for taking the network\nlayer Protocol Data Unit (PDU)\u2014usually an IP packet\u2014and surrounding it with a data link layer PDU\u2014\noften an Ethernet frame. At the receiving computer, the LLC sublayer software removes the data link layer\nPDU and passes the message it contains (usually an IP packet) to the network layer software.\nThe second sublayer (called the media access control [MAC] sublayer) controls the physical\nhardware. The MAC sublayer software at the sending computer controls how and when the physical layer\nconverts bits into the physical symbols that are sent down the circuit. At the receiving computer, the MAC\nsublayer software takes the data link layer PDU from the LLC sublayer, converts it into a stream of bits,\nand controls when the physical layer actually transmits the bits over the circuit. At the receiving\ncomputer, the MAC sublayer receives a stream of bits from the physical layer and translates it into a\ncoherent PDU, ensures that no errors have occurred in transmission, and passes the data link layer PDU\nto the LLC sublayer.", "source": "Page 126", "chapter_title": "Chapter 11"}
{"id": "e412c808c1de-1", "text": "to the LLC sublayer.\nBoth the sender and receiver have to agree on the rules or protocols that govern how their data link layers\nwill communicate with each other. A data link protocol performs three functions:\nControls when computers transmit (media access control)\nDetects and corrects transmission errors (error control)\nIdentifies the start and end of a message by using a PDU (message delineation)\n4.2 MEDIA ACCESS CONTROL\nMedia access control refers to the need to control when computers transmit. With point-to-point full-\nduplex configurations, media access control is unnecessary because there are only two computers on the\ncircuit, and full-duplex permits either computer to transmit at any time.\nMedia access control becomes important when several computers share the same communication circuit,\nsuch as a point-to-point configuration with a half-duplex configuration that requires computers to take\nturns or a multipoint configuration in which several computers share the same circuit. Here, it is critical\nto ensure that no two computers attempt to transmit data at the same time\u2014but if they do, there must be\na way to recover from the problem. There are two fundamental approaches to media access control:\ncontention and controlled access.\n4.2.1 Contention\nWith contention, computers wait until the circuit is free (i.e., no other computers are transmitting) and\nthen transmit whenever they have data to send. Contention is commonly used in Ethernet\u2014Local Area\nNetworks (LANs).\nAs an analogy, suppose that you are talking with some friends. People listen, and if no one is talking, they\ncan talk. If you want to say something, you wait until the speaker is done and then you try to talk. Usually,\npeople yield to the first person who jumps in at the precise moment the previous speaker stops.", "source": "Page 126", "chapter_title": "Chapter 11"}
{"id": "73013561fe71-2", "text": "people yield to the first person who jumps in at the precise moment the previous speaker stops.\nSometimes, two people attempt to talk at the same time, so there must be some technique to continue the\nconversation after such a verbal collision occurs.\n4.2.2 Controlled Access\nWith controlled access, one device controls the circuit and determines which clients can transmit at\nwhat time. There are two commonly used controlled access techniques: access requests and polling.", "source": "Page 126", "chapter_title": "Chapter 11"}
{"id": "33887495906e-0", "text": "With the access request technique, client computers that want to transmit send a request to transmit to\nthe device that is controlling the circuit (e.g., the wireless access point). The controlling device grants\npermission for one computer at a time to transmit. When one computer has permission to transmit, all\nother computers wait until that computer has finished, and then, if they have something to transmit, they\nuse a contention technique to send an access request.\nThe access request technique is like a classroom situation in which the instructor calls on the students\nwho raise their hands. The instructor acts as the controlling access point. When they want to talk,\nstudents raise their hands and the instructor recognizes them so they can contribute. When they have\nfinished, the instructor again takes charge and allows someone else to talk. And of course, just like in a\nclassroom, the wireless access point can choose to transmit whenever it likes.\nPolling is the process of sending a signal to a client computer that permits it to transmit. With polling,\nthe clients store all messages that need to be transmitted. Periodically, the controlling device (e.g., a\nwireless access point) polls the client to see if it has data to send. If the client has data to send, it does so.\nIf the client has no data to send, it responds negatively, and the controller asks another client if it has data\nto send.\nThere are several types of polling. With roll-call polling, the controller works consecutively through a\nlist of clients, first polling client 1, then client 2, and so on, until all are polled. Roll-call polling can be\nmodified to select clients in priority so that some get polled more often than others. For example, one", "source": "Page 127", "chapter_title": "Chapter 11"}
{"id": "2bb2a90bfded-1", "text": "could increase the priority of client 1 by using a polling sequence such as 1, 2, 3, 1, 4, 5, 1, 6, 7, 1, 8, 9.\nTypically, roll-call polling involves some waiting because the controller has to poll a client and then wait\nfor a response. The response might be an incoming message that was waiting to be sent, a negative\nresponse indicating nothing is to be sent, or the full \u201ctime-out period\u201d may expire because the client is\ntemporarily out of service (e.g., it is malfunctioning or the user has turned it off). Usually, a timer \u201ctimes\nout\u201d the client after waiting several seconds without getting a response. If some sort of fail-safe time-out is\nnot used, the circuit poll might lock up indefinitely on an out-of-service client.\nWith hub polling (often called token passing), one device starts the poll and passes it to the next\ncomputer on the multipoint circuit, which sends its message and passes the poll to the next. That\ncomputer then passes the poll to the next, and so on, until it reaches the first computer, which restarts the\nprocess again.\n4.2.3 Relative Performance\nWhich media access control approach is best: controlled access or contention? There is no simple answer.\nThe key consideration is throughput\u2014which approach will permit the most amount of user data to be\ntransmitted through the network.\nIn general, contention approaches work better than controlled approaches for small networks that have\nlow usage. In this case, each computer can transmit when necessary, without waiting for permission.\nBecause the usage is low, there is little chance of a collision. In contrast, computers in a controlled access\nenvironment must wait for permission, so even if no other computer needs to transmit, they must wait for\nthe poll.", "source": "Page 127", "chapter_title": "Chapter 11"}
{"id": "9657c8c8f8a6-2", "text": "the poll.\nThe reverse is true for large networks with high usage: Controlled access works better. In high-volume\nnetworks, many computers want to transmit, and the probability of a collision using contention is high.\nCollisions are very costly in terms of throughput because they waste circuit capacity during the collision\nand require both computers to retransmit later. Controlled access prevents collisions and makes more\nefficient use of the circuit, and although response time does increase, it does so more gradually (Figure 4-\n1).\nThe key to selecting the best access control technique is to find the crossover point between controlled and\ncontention. Although there is no one correct answer, because it depends on how many messages the\ncomputers in the network transmit, most experts believe that the crossover point is often around 20\ncomputers (lower for busy computers, higher for less-busy computers). For this reason, when we build\nshared multipoint circuits like those often used in LANs or wireless LANs, we try to put no more than 20\ncomputers on any one shared circuit.", "source": "Page 127", "chapter_title": "Chapter 11"}
{"id": "a55c3d6029e6-0", "text": "FIGURE 4-1 Relative response times\n4.3 ERROR CONTROL\nBefore learning the control mechanisms that can be implemented to protect a network from errors, you\nshould realize that there are human errors and network errors. Human errors, such as a mistake in\ntyping a number, usually are controlled through the application program. Network errors, such as those\nthat occur during transmission, are controlled by the network hardware and software.\nThere are two categories of network errors: corrupted data (data that have been changed) and lost data.\nNetworks should be designed to (1) prevent, (2) detect, and (3) correct both corrupted data and lost data.\nWe begin by examining the sources of errors and how to prevent them and then turn to error detection\nand correction.\nNetwork errors are a fact of life in data communications networks. Depending on the type of circuit, they\nmay occur every few hours, minutes, or seconds because of noise on the lines. No network can eliminate\nall errors, but most errors can be prevented, detected, and corrected by proper design. Inter-Exchange\nCarriers (IXCs) that provide data transmission circuits provide statistical measures specifying typical\nerror rates and the pattern of errors that can be expected on the circuits they lease. For example, the\nerror rate might be stated as 1 in 500,000, meaning there is 1 bit in error for every 500,000 bits\ntransmitted.\nNormally, errors appear in bursts. In a burst error, more than 1 data bit is changed by the error-causing\ncondition. In other words, errors are not uniformly distributed in time. Although an error rate might be\nstated as 1 in 500,000, errors are more likely to occur as 100 bits every 50,000,000 bits. The fact that", "source": "Page 128", "chapter_title": "Chapter 11"}
{"id": "2c2b349690f8-1", "text": "errors tend to be clustered in bursts rather than evenly dispersed is both good and bad. If the errors were\nnot clustered, an error rate of 1 bit in 500,000 would make it rare for 2 erroneous bits to occur in the same\ncharacter. Consequently, simple character-checking schemes would be effective at detecting errors. When\nerrors are more or less evenly distributed, it is not difficult to grasp the meaning even when the error rate\nis high, as it is in this sentence (1 character in 20). But burst errors are the rule rather than the exception,\noften obliterating 100 or more bits at a time. This makes it more difficult to recover the meaning, so more", "source": "Page 128", "chapter_title": "Chapter 11"}
{"id": "1dbcae6b03fb-0", "text": "reliance must be placed on error detection and correction methods. The positive side is that there are long\nperiods of error-free transmission, meaning that very few messages encounter errors.\n4.3.1 Sources of Errors\nLine noise and distortion can cause data communication errors. The focus in this section is on electrical\nmedia such as twisted pair wire and coaxial cable because they are more likely to suffer from noise than\nare optical media such as fiber-optic cable. In this case, noise is undesirable electrical signals (for fiber-\noptic cable, it is undesirable light). Noise is introduced by equipment or natural disturbances, and it\ndegrades the performance of a communication circuit. Noise manifests itself as extra bits, missing bits, or\nbits that have been \u201cflipped\u201d (i.e., changed from 1 to 0 or vice versa). Figure 4-2 summarizes the major\nsources of error and ways to prevent them. The first six sources listed there are the most important; the\nlast three are more common in analog rather than digital circuits.\nFIGURE 4-2 Sources of errors and ways to minimize them\nWhite noise or Gaussian noise (the familiar background hiss or static on radios and telephones) is\ncaused by the thermal agitation of electrons and therefore is inescapable. Even if the equipment were\nperfect and the wires were perfectly insulated from any and all external interference, there still would be\nsome white noise. White noise usually is not a problem unless it becomes so strong that it obliterates the\ntransmission. In this case, the strength of the electrical signal is increased so it overpowers the white\nnoise; in technical terms, we increase the signal-to-noise ratio.\nImpulse noise (sometimes called spikes) is the primary source of errors in data communications. It is", "source": "Page 129", "chapter_title": "Chapter 11"}
{"id": "b230c911c878-1", "text": "heard as a click or a crackling noise and can last as long as 1/100 of a second. Such a click does not really\naffect voice communications, but it can obliterate a group of data, causing a burst error. At 1.5 Mbps,\n15,000 bits would be changed by a spike of 1/100 of a second. Some of the sources of impulse noise are\nvoltage changes in adjacent lines, lightning flashes during thunderstorms, fluorescent lights, and poor\nconnections in circuits.\nCross-talk occurs when one circuit picks up signals in another. A person experiences cross-talk during\ntelephone calls when she or he hears other conversations in the background. It occurs between pairs of\nwires that are carrying separate signals, in multiplexed links carrying many discrete signals, or in\nmicrowave links in which one antenna picks up a minute reflection from another antenna. Cross-talk\nbetween lines increases with increased communication distance increased proximity of the two wires,\nincreased signal strength, and higher-frequency signals. Wet or damp weather can also increase cross-\ntalk. Like white noise, cross-talk has such a low signal strength that it normally is not bothersome.\nEchoes are the result of poor connections that cause the signal to reflect back to the transmitting\nequipment. If the strength of the echo is strong enough to be detected, it causes errors. Echoes, like cross-\ntalk and white noise, have such a low signal strength that they normally are not bothersome. Echoes can\nalso occur in fiber-optic cables when connections between cables are not properly aligned.\nAttenuation is the loss of power a signal suffers as it travels from the transmitting computer to the\nreceiving computer. Some power is absorbed by the medium or is lost before it reaches the receiver. As the", "source": "Page 129", "chapter_title": "Chapter 11"}
{"id": "beb958d8c0f4-0", "text": "medium absorbs power, the signal becomes weaker, and the receiving equipment has less and less chance\nof correctly interpreting the data. This power loss is a function of the transmission method and circuit\nmedium. High frequencies lose power more rapidly than do low frequencies during transmission, so the\nreceived signal can thus be distorted by unequal loss of its component frequencies. Attenuation increases\nas frequency increases or as the diameter of the wire decreases.\nIntermodulation noise is a special type of cross-talk. The signals from two circuits combine to form a\nnew signal that falls into a frequency band reserved for another signal. This type of noise is similar to\nharmonics in music. On a multiplexed line, many different signals are amplified together, and slight\nvariations in the adjustment of the equipment can cause intermodulation noise. A maladjusted modem\nmay transmit a strong frequency tone when not transmitting data, thus producing this type of noise.\nIn general, errors are more likely to occur in wireless, microwave, or satellite transmission than in\ntransmission through cables. Therefore, error detection is more important when using radiated media\nthan guided media. Impulse noise is the most frequent cause of errors in today\u2019s networks. Unfortunately,\nas the next section describes, it could be very difficult to determine what caused this type of error.\n4.3.2 Error Prevention\nObviously, error prevention is very important. There are many techniques to prevent errors (or at least\nreduce them), depending on the situation. Shielding (protecting wires by covering them with an insulating\ncoating) is one of the best ways to prevent impulse noise, cross-talk, and intermodulation noise. Many\ndifferent types of wires and cables are available with different amounts of shielding. In general, the\ngreater the shielding, the more expensive the cable and the more difficult it is to install.", "source": "Page 130", "chapter_title": "Chapter 11"}
{"id": "abf9192862e6-1", "text": "greater the shielding, the more expensive the cable and the more difficult it is to install.\nMoving cables away from sources of noise (especially power sources) can also reduce impulse noise,\ncross-talk, and intermodulation noise. For impulse noise, this means avoiding lights and heavy\nmachinery. Locating communication cables away from power cables is always a good idea. For cross-talk,\nthis means physically separating the cables from other communication cables.\nCross-talk and intermodulation noise is often caused by improper multiplexing. Changing multiplexing\ntechniques (e.g., from FDM [Frequency Division Multiplexing] to TDM [Time Division Multiplexing]) or\nchanging the frequencies or size of the guardbands in FDM can help.\nMany types of noise (e.g., echoes, white noise) can be caused by poorly maintained equipment or poor\nconnections and splices among cables. This is particularly true for echo in fiber-optic cables, which is\nalmost always caused by poor connections. The solution here is obvious: Tune the transmission\nequipment and redo the connections.\nTo avoid attenuation, telephone circuits have repeaters or amplifiers spaced throughout their length.\nThe distance between them depends on the amount of power lost per unit length of the transmission line.\nAn amplifier takes the incoming signal, increases its strength, and retransmits it on the next section of the\ncircuit. They are typically used on analog circuits such as the telephone company\u2019s voice circuits. The\ndistance between the amplifiers depends on the amount of attenuation, although 1- to 10-mile intervals\nare common. On analog circuits, it is important to recognize that the noise and distortion are also\namplified, along with the signal. This means some noise from a previous circuit is regenerated and\namplified each time the signal is amplified.\nMANAGEMENT FOCUS 4-1\nFinding the Source of Impulse Noise", "source": "Page 130", "chapter_title": "Chapter 11"}
{"id": "77acf1e4c943-2", "text": "MANAGEMENT FOCUS 4-1\nFinding the Source of Impulse Noise\nSeveral years ago, the University of Georgia radio station received FCC (Federal Communications\nCommission) approval to broadcast using a stronger signal. Immediately after the station started\nbroadcasting with the new signal, the campus backbone network (BN) became unusable because of\nimpulse noise. It took 2 days to link the impulse noise to the radio station, and when the radio\nstation returned to its usual broadcast signal, the problem disappeared.\nHowever, this was only the first step in the problem. The radio station wanted to broadcast at full", "source": "Page 130", "chapter_title": "Chapter 11"}
{"id": "0ead1f101d73-0", "text": "strength, and there was no good reason for why the stronger broadcast should affect the BN in this\nway. After 2 weeks of effort, the problem was discovered. A short section of the BN ran above ground\nbetween two buildings. It turned out that the specific brand of outdoor cable we used was\nparticularly tasty to squirrels. They had eaten the outer insulating coating off of the cable, making it\nact like an antenna to receive the radio signals. The cable was replaced with a steel-coated armored\ncable so the squirrels could not eat the insulation. Things worked fine when the radio station\nreturned to its stronger signal.\nRepeaters are commonly used on digital circuits. A repeater receives the incoming signal, translates it into\na digital message, and retransmits the message. Because the message is recreated at each repeater, noise,\nand distortion from the previous circuit are not amplified. This provides a much cleaner signal and results\nin a lower error rate for digital circuits.\n4.3.3 Error Detection\nIt is possible to develop data transmission methodologies that give very high error-detection\nperformance. The only way to do error detection is to send extra data with each message. These error-\ndetection data are added to each message by the data link layer of the sender based on some mathematical\ncalculations performed on the message (in some cases, error-detection methods are built into the\nhardware itself). The receiver performs the same mathematical calculations on the message it receives and\nmatches its results against the error-detection data that were transmitted with the message. If the two\nmatch, the message is assumed to be correct. If they don\u2019t match, an error has occurred.\nIn general, the larger the amount of error-detection data sent, the greater the ability to detect an error.\nHowever, as the amount of error-detection data is increased, the throughput of useful data is reduced,", "source": "Page 131", "chapter_title": "Chapter 11"}
{"id": "e05ed1b4c3df-1", "text": "because more of the available capacity is used to transmit these error-detection data and less is used to\ntransmit the actual message itself. Therefore, the efficiency of data throughput varies inversely as the\ndesired amount of error detection is increased.\nThree well-known error-detection methods are parity checking, checksum, and cyclic redundancy\nchecking.\nParity Checking\nOne of the oldest and simplest error-detection methods is parity. With this technique, one additional bit\nis added to each byte in the message. The value of this additional parity bit is based on the number of 1s\nin each byte transmitted. This parity bit is set to make the total number of 1s in the byte (including the\nparity bit) either an even number or an odd number. Figure 4-3 gives an example.\nA little thought will convince you that any single error (a switch of a 1 to a 0, or vice versa) will be detected\nby parity, but it cannot determine which bit was in error. You will know an error occurred, but not what\nthe error was. But if two bits are switched, the parity check will not detect any error. It is easy to see that\nparity can detect errors only when an odd number of bits have been switched; any even number of errors\ncancel one another out. Therefore, the probability of detecting an error, given that one has occurred, is\nonly about 50%. Many networks today do not use parity because of its low error-detection rate. When\nparity is used, protocols are described as having odd parity or even parity.", "source": "Page 131", "chapter_title": "Chapter 11"}
{"id": "7d5e7a3f7f15-0", "text": "FIGURE 4-3 Using parity for error detection\nChecksum\nWith the checksum technique, a checksum (typically 1 byte) is added to the end of the message. The\nchecksum is calculated by adding the decimal value of each character in the message, dividing the sum by\n255, and using the remainder as the checksum. The receiver calculates its own checksum in the same way\nand compares it with the transmitted checksum. If the two values are equal, the message is presumed to\ncontain no errors. The use of checksum detects close to 95% of the errors for multiple-bit burst errors.\nCyclic Redundancy Check\nOne of the most popular error-checking schemes is the cyclic redundancy check (CRC). It adds 8, 16,\n24, or 32 bits to the message. With CRC, a message is treated as one long binary number, which is divided\nby a preset number, and the remainder is used as the CRC code. The preset number is chosen so that the\nremainder will be either 8 bits, 16 bits, 24 bits, or 32 bits. The receiving hardware divides the received\nmessage by the same preset number, which generates a remainder. The receiving hardware checks if the\nreceived CRC matches the locally generated remainder. If it does not, the message is assumed to be in\nerror. In practice, the CRC algorithm is implemented using binary logic on a bit-by-bit basis to simplify\nmemory requirements.\nCRC performs quite well. The most commonly used CRC codes are CRC-16 (a 16-bit version), CRC-CCITT\n(another 16-bit version), and CRC-32 (a 32-bit version). The probability of detecting an error is 100% for\nall errors of the same length as the CRC or less. For example, CRC-16 is guaranteed to detect errors if 16 or", "source": "Page 132", "chapter_title": "Chapter 11"}
{"id": "19185d18e561-1", "text": "fewer bits are affected. If the burst error is longer than the CRC, then CRC is not perfect but is close to it.\nCRC-16 will detect about 99.998% of all burst errors longer than 16 bits, whereas CRC-32 will detect about\n99.99999998% of all burst errors longer than 32 bits.\n4.3.4 Error Correction via Retransmission\nOnce an error has been detected, it must be corrected. The simplest, most effective, least expensive, and\nmost commonly used method for error correction is retransmission. Interestingly, the transport layer\n(layer 3) is responsible for retransmission, and we will discuss the details of it in Chapter 5.\n4.3.5 Forward Error Correction\nForward error correction uses codes containing sufficient redundancy to prevent errors by detecting\nand correcting them at the receiving end without retransmission of the original message. The redundancy,\nor extra bits required, varies with different schemes. It ranges from a small percentage of extra bits to\n100% redundancy, with the number of error-detecting bits roughly equaling the number of data bits. One", "source": "Page 132", "chapter_title": "Chapter 11"}
{"id": "cf64f7001b76-0", "text": "of the characteristics of many error-correcting codes is that there must be a minimum number of error-\nfree bits between bursts of errors.\nForward error correction is commonly used in satellite transmission. A round trip from the earth station\nto the satellite and back includes a significant delay. Error rates can fluctuate depending on the condition\nof equipment, sunspots, or the weather. Indeed, some weather conditions make it impossible to transmit\nwithout some errors, making forward error correction essential. Compared with satellite equipment costs,\nthe additional cost of forward error correction is insignificant.\nTECHNICAL FOCUS 4-1\nHow Forward Error Correction Works\nTo see how error-correcting codes work, consider the example of a forward error-checking code in\nFigure 4-4, called a Hamming code, after its inventor, R. W. Hamming. This code is a very simple\napproach, capable of correcting 1-bit errors. More sophisticated techniques (e.g., Reed\u2013Solomon)\nare commonly used today, but this will give you a sense of how they work.\nThe Hamming code associates even parity bits with unique combinations of data bits. With a 4-data-\nbit code as an example, a character might be represented by the data-bit configuration 1010. Three\nparity bits, P1, P2, and P4, are added, resulting in a 7-bit code, shown in the upper half of Figure 4-6.\nNotice that the data bits (D3, D5, D6, D7) are 1010 and the parity bits (P1, P2, P4) are 101.\nAs depicted in the upper half of Figure 4-6, parity bit P1 applies to data bits D3, D5, and D7. Parity bit", "source": "Page 133", "chapter_title": "Chapter 11"}
{"id": "dee8f018be7b-1", "text": "P2 applies to data bits D3, D6, and D7. Parity bit P4 applies to data bits D5, D6, and D7. For example,\nin which D3, D5, D6, D7 = 1010, P1 must equal 1 because there is only a single 1 among D3, D5, and D7\nand parity must be even. Similarly, P2 must be 0 because D3 and D6 are 1s. P4 is 1 because D6 is the\nonly 1 among D5, D6, and D7.\nNow, assume that during the transmission, data bit D7 is changed from a 0 to a 1 by line noise.\nBecause this data bit is being checked by P1, P2, and P4, all three parity bits now show odd parity\ninstead of the correct even parity. D7 is the only data bit that is monitored by all three parity bits;\ntherefore, when D7 is in error, all three parity bits show an incorrect parity. In this way, the receiving\nequipment can determine which bit was in error and reverse its state, thus correcting the error\nwithout retransmission.\nThe lower half of the figure is a table that determines the location of the bit in error. A 1 in the table\nmeans that the corresponding parity bit indicates a parity error. Conversely, a 0 means that the\nparity check is correct. These 0s and 1s form a binary number that indicates the numeric location of\nthe erroneous bit. In the previous example, P1, P2, and P4 checks all failed, yielding 111, or a decimal\n7, the subscript of the erroneous bit.\n4.3.6 Error Control in Practice", "source": "Page 133", "chapter_title": "Chapter 11"}
{"id": "ec1c868e489c-2", "text": "7, the subscript of the erroneous bit.\n4.3.6 Error Control in Practice\nIn the Open Systems Interconnection (OSI) model (see Chapter 1), error control is defined to be a layer-2\nfunction\u2014it is the responsibility of the data link layer. However, in practice, we have moved away from\nthis. Most network cables\u2014especially LAN cables\u2014are very reliable, and errors are far less common than\nthey were in the 1980s.\nTherefore, most data link layer software used in LANs (i.e., Ethernet) is configured to detect errors, but\nnot correct them. Any time a packet with an error is discovered, it is simply discarded. Wireless LANs and\nsome Wide Area Networks (WANs), where errors are more likely, still perform both error detection and\nerror correction.\nThe implication from this is that error correction must be performed at higher layers (see Chapter 5,\nSection 5.3.3, for more information). This is commonly done by the transport layer using continuous\nautomatic repeat reQuest (ARQ), as we shall see in the next chapter. The transport layer must be", "source": "Page 133", "chapter_title": "Chapter 11"}
{"id": "22746931f0ae-0", "text": "able to detect lost packets (i.e., those that have been discarded) and request the sender to retransmit\nthem.\nFIGURE 4-4 Hamming code for forward error correction\n4.4 DATA LINK PROTOCOLS\nIn this section, we outline several commonly used data link layer protocols, which are summarized in\nFigure 4-5. Here, we focus on message delineation, which indicates where a message starts and stops, and\nthe various parts or fields within the message. For example, you must clearly indicate which part of a\nmessage or packet of data is the error-control portion; otherwise, the receiver cannot use it properly to\ndetermine if an error has occurred. The data link layer performs this function by adding a PDU to the\npacket it receives from the network layer. This PDU is called a frame.", "source": "Page 134", "chapter_title": "Chapter 11"}
{"id": "a6521f16a88c-0", "text": "FIGURE 4-5 Protocol summary\n4.4.1 Asynchronous Transmission\nAsynchronous transmission is often referred to as start\u2013stop transmission because the transmitting\ncomputer can transmit a character whenever it is convenient, and the receiving computer will accept that\ncharacter. It is typically used on point-to-point full-duplex circuits (i.e., circuits that have only two\ncomputers on them), so media access control is not a concern. If you use VT100 protocol or connect to a\nUNIX or Linux computer using Telnet, chances are you are using asynchronous transmission.\nWith asynchronous transmission, each character is transmitted independently of all other characters. To\nseparate the characters and synchronize transmission, a start bit and a stop bit are put on the front and\nback of each individual character. For example, if we are using 7-bit ASCII with even parity, the total\ntransmission is 10 bits for each character (1 start bit, 7 bits for the letter, 1 parity bit, and 1 stop bit).\nThe start bit and stop bit are the opposite of each other. Typically, the start bit is a 0 and the stop bit is a 1.\nThere is no fixed distance between characters because the terminal transmits the character as soon as it is\ntyped, which varies with the speed of the typist. The recognition of the start and stop of each message\n(called synchronization) takes place for each individual character because the start bit is a signal that\ntells the receiver to start sampling the incoming bits of a character so the data bits can be interpreted into\ntheir proper character structure. A stop bit informs the receiver that the character has been received and\nresets it for recognition of the next start bit.\nWhen the sender is waiting for the user to type the next character, no data are sent; the communication", "source": "Page 135", "chapter_title": "Chapter 11"}
{"id": "ddc6e2cd9ca0-1", "text": "circuit is idle. This idle time really is artificial\u2014some signal always must be sent down the circuit. For\nexample, suppose that we are using a unipolar digital signaling technique where +5 volts indicates a 1 and\n0 volts indicates a 0 (see Chapter 3). Even if we send 0 volts, we are still sending a signal, a 0 in this case.\nAsynchronous transmission defines the idle signal (the signal that is sent down the circuit when no data\nare being transmitted) as the same as the stop bit. When the sender finishes transmitting a letter and is\nwaiting for more data to send, it sends a continuous series of stop bits. Figure 4-6 shows an example of\nasynchronous transmission. Some older protocols have two stop bits instead of the traditional single stop\nbit. The use of both a start bit and a stop bit is changing; some protocols have eliminated the stop bit\naltogether.\n4.4.2 Synchronous Transmission\nWith synchronous transmission, all the letters or data in one group of data are transmitted at one\ntime as a block of data. This block of data is called a frame. For example, a terminal or a personal\ncomputer will save all the keystrokes typed by the user and transmit them only when the user presses a\nspecial \u201ctransmit\u201d key. In this case, the start and end of the entire frame must be marked, not the start and\nend of each letter. Synchronous transmission is often used on both point-to-point and multipoint circuits.\nFor multipoint circuits, each packet must include a destination address and a source address, and media\naccess control is important.", "source": "Page 135", "chapter_title": "Chapter 11"}
{"id": "c0271b2d1750-0", "text": "FIGURE 4-6 Asynchronous transmission. ASCII = United States of America Standard Code for\nInformation Interchange\nThe start and end of each frame (synchronization) sometimes are established by adding synchronization\ncharacters (SYN) to the start of the frame. Depending on the protocol, there may be anywhere from one to\neight SYN characters. After the SYN characters, the transmitting computer sends a long stream of data\nthat may contain thousands of bits. Knowing what code is being used, the receiving computer counts off\nthe appropriate number of bits for the first character, assumes that this is the first character, and passes it\nto the computer. It then counts off the bits for the second character, and so on.\nIn summary, asynchronous data transmission means each character is transmitted as a totally\nindependent entity with its own start and stop bits to inform the receiving computer that the character is\nbeginning and ending. Synchronous transmission means that whole blocks of data are transmitted as\nframes after the sender and the receiver have been synchronized.\nThere are many protocols for synchronous transmission. We discuss four commonly used synchronous\ndata link protocols.\nSynchronous Data Link Control\nSynchronous data link control (SDLC) is a mainframe protocol developed by IBM in 1972 that is still in\nuse today. It uses a controlled-access media access protocol. If you use a 3270 protocol, you\u2019re using\nSDLC.\nFigure 4-7 shows a typical SDLC frame. Each SDLC frame begins and ends with a special bit pattern\n(01111110), known as the flag. The address field identifies the destination. The length of the address field\nis usually 8 bits but can be set at 16 bits; all computers on the same network must use the same length.\nThe control field identifies the kind of frame that is being transmitted, either information or supervisory.", "source": "Page 136", "chapter_title": "Chapter 11"}
{"id": "d4e5a25cc10f-1", "text": "The control field identifies the kind of frame that is being transmitted, either information or supervisory.\nAn information frame is used for the transfer and reception of messages, frame numbering of contiguous\nframes, and the like. A supervisory frame is used to transmit acknowledgments (ACKs) and negative\nacknowledgment (NAKs). The message field is of variable length and is the user\u2019s message. The frame\ncheck sequence field is a 32-bit CRC code (some older versions use a 16-bit CRC).\nHigh-Level Data Link Control\nHigh-level data link control (HDLC) is a formal standard developed by the ISO often used in WANs.\nHDLC is essentially the same as SDLC, except that the address and control fields can be longer. HDLC\nalso has several additional benefits that are beyond the scope of this book, such as a larger sliding\nwindow for continuous ARQ. It uses a controlled-access media access protocol. One variant, Link\nAccess Protocol-Balanced (LAP-B), uses the same structure as HDLC but is a scaled-down version of\nHDLC (i.e., provides fewer of those benefits mentioned that are \u201cbeyond the scope of this book\u201d). A\nversion of HDLC called Cisco HDLC (cHDLC) includes a network protocol field. cHDLC and HDLC have\ngradually replaced SDLC.\nEthernet\nEthernet is a very popular LAN protocol, conceived by Bob Metcalfe in 1973 and developed jointly by\nDigital, Intel, and Xerox in the 1970s. Since then, Ethernet has been further refined and developed into a\nformal standard called IEEE 802.3ac. There are several versions of Ethernet in use today. Ethernet uses\na contention media access protocol.", "source": "Page 136", "chapter_title": "Chapter 11"}
{"id": "a0fa97d1d3b0-0", "text": "There are several standard versions of Ethernet. Figure 4-8 shows an Ethernet 803.3ac frame. The frame\nstarts with a 7-byte preamble, which is a repeating pattern of ones and zeros (10101010). This is followed\nby a start of frame delimiter, which marks the start of the frame. The destination address specifies the\nreceiver, whereas the source address specifies the sender. The length indicates the length in 8-bit bytes of\nthe message portion of the frame. The VLAN tag field is an optional 4-byte address field used by virtual\nLANs (VLANs), which are discussed in Chapter 7. The Ethernet frame uses this field only when VLANs are\nin use; otherwise, the field is omitted, and the length field immediately follows the source address field.\nWhen the VLAN tag field is in use, the first 2 bytes are set to the number 24,832 (hexadecimal 81-00),\nwhich is obviously an impossible packet length. When Ethernet sees this length, it knows that the VLAN\ntag field is in use. When the length is some other value, it assumes that VLAN tags are not in use and that\nthe length field immediately follows the source address field. The DSAP and SSAP are used to pass control\ninformation between the sender and the receiver. These are often used to indicate the type of network\nlayer protocol the packet contains (e.g., TCP/IP or IPX/SPX, as described in Chapter 5). The control field\nis used to hold the frame sequence numbers and ACKs and NAKs used for error control, as well as to\nenable the data link layers of communicating computers to exchange other control information. The last 2\nbits in the first byte are used to indicate the type of control information being passed and whether the", "source": "Page 137", "chapter_title": "Chapter 11"}
{"id": "ec09de55977c-1", "text": "bits in the first byte are used to indicate the type of control information being passed and whether the\ncontrol field is 1 or 2 bytes (e.g., if the last 2 bits of the control field are 11, then the control field is 1 byte in\nlength). In most cases, the control field is 1-byte long. The maximum length of the message is about 1,500\nbytes. The frame ends with a CRC-32 frame check sequence used for error detection.\nFIGURE 4-7 SDLC (synchronous data link control) frame layout\nFIGURE 4-8a Ethernet 802.3ac frame layout\nEthernet II is another commonly used version of Ethernet. Like SDLC, it uses a preamble to mark the\nstart of the frame. It has the same source and destination address format as Ethernet 802.3ac. The type\nfield is used to specify an ACK frame or the type of network layer packet the frame contains (e.g., IP). The\ndata and frame check sequence fields are the same as Ethernet 802.3ac. Ethernet II has an unusual way of\nmarking the end of a frame. It uses bipolar signaling to send 1s (positive voltage) and 0s (negative voltage)\n(see Chapter 3). When the frame ends, the sending computer transmits no signal for 96 bits (i.e., neither a\n0 nor a 1). After these 96 bits have been on no signal, the sending computer then transmits the next frame,\nwhich starts with a preamble, and so on. It is possible that in the time that the computer is sending no\nsignal, some other computer could jump in and begin transmitting. In fact, this 96-bit pause is designed\nto prevent any one computer from monopolizing the circuit. Figure 4-8 shows an Ethernet II frame.", "source": "Page 137", "chapter_title": "Chapter 11"}
{"id": "7e888c9384e2-2", "text": "Newer versions of these two types of Ethernet permit jumbo frames with up to 9,000 bytes of user data in\nthe message field. Some vendors are experimenting with super jumbo frames that can hold up to 64,000\nbytes. Jumbo frames are common for some types of Ethernet such as gigabit Ethernet (see Chapter 6).\nPoint-to-Point Protocol\nPoint-to-Point Protocol (PPP) was developed in the early 1990s and is often used in WANs. It is\ndesigned to transfer data over a point-to-point circuit but provides an address so that it can be used on\nmultipoint circuits. Figure 4-9 shows the basic layout of a PPP frame, which is very similar to an SDLC or\nHDLC frame. The frame starts with a flag and has a 1-byte address (which is not used on point-to-point\ncircuits). The control field is typically not used. The protocol field indicates what type of data packet the\nframe contains (e.g., an IP packet). The data field is variable in length and may be up to 1,500 bytes. The\nframe check sequence is usually a CRC-16 but can be a CRC-32. The frame ends with a flag.", "source": "Page 137", "chapter_title": "Chapter 11"}
{"id": "e134377d4c52-0", "text": "FIGURE 4-8b Ethernet II frame layout\nFIGURE 4-9 PPP frame layout\nA Day in the Life: Network Support Technician\nWhen a help call arrives at the help desk, the help desk staff (first-level support) spends up to 10\nminutes attempting to solve the problem. If they can\u2019t, then the problem is passed to the second-\nlevel support, the network support technician.\nA typical day in the life of a network support technician starts by working on computers from the day\nbefore. Troubleshooting usually begins with a series of diagnostic tests to eliminate hardware\nproblems. The next step, for a laptop, is to remove the hard disk and replace it with a hard disk\ncontaining a correct standard image. If the computer passes those tests, then the problem is usually\nthe software. Then the fun begins.\nOnce a computer has been fixed, it is important to document all the hardware and/or software\nchanges to help track problem computers or problem software. Sometimes, a problem is new but\nrelatively straightforward to correct once it has been diagnosed. In this case, the technician will\nchange the standard support process followed by the technicians working at the help desk to catch\nthe problem before it is escalated to the network support technicians. In other cases, a new entry is\nmade into the organization\u2019s technical support knowledge base so that if another technician (or user)\nencounters the problem, it is easier for him or her to diagnose and correct the problem. About 10% of\nthe network technician\u2019s time is spent documenting solutions to problems.\nNetwork support technicians also are the ones who manage new inventory and set up and configure\nnew computers as they arrive from the manufacturer. In addition, they are responsible for deploying\nnew software and standard desktop images across the network. Many companies also set aside\nstandard times for routine training; in our case, every Friday, several hours are devoted to regular", "source": "Page 138", "chapter_title": "Chapter 11"}
{"id": "8567c7b2413e-1", "text": "standard times for routine training; in our case, every Friday, several hours are devoted to regular\ntraining.\nSource: With thanks to Doug Strough.\n4.5 TRANSMISSION EFFICIENCY\nOne objective of a data communication network is to move the highest possible volume of accurate\ninformation through the network. The higher the volume, the greater the resulting network\u2019s efficiency\nand the lower the cost. Network efficiency is affected by characteristics of the circuits such as error rates\nand maximum transmission speed, as well as by the speed of transmitting and receiving equipment, the\nerror-detection and control methodology, and the protocol used by the data link layer.\nEach protocol we discussed uses some bits or bytes to delineate the start and end of each message and to\ncontrol error. These bits and bytes are necessary for the transmission to occur, but they are not part of the\nmessage. They add no value to the user, but they count against the total number of bits that can be", "source": "Page 138", "chapter_title": "Chapter 11"}
{"id": "6ef0f1db53d4-0", "text": "transmitted.\nEach communication protocol has both information bits and overhead bits. Information bits are those\nused to convey the user\u2019s meaning. Overhead bits are used for purposes such as error checking and\nmarking the start and end of characters and packets. A parity bit used for error checking is an overhead\nbit because it is not used to send the user\u2019s data; if you did not care about errors, the overhead error\nchecking bit could be omitted and the users could still understand the message.\nTransmission efficiency is defined as the total number of information bits (i.e., bits in the message\nsent by the user) divided by the total bits in transmission (i.e., information bits plus overhead bits). For\nexample, let\u2019s calculate the transmission efficiency of asynchronous transmission. Assume that we are\nusing 7-bit ASCII. We have 1 bit for parity, plus 1 start bit and 1 stop bit. Therefore, there are 7 bits of\ninformation in each letter, but the total bits per letter is 10 (7 + 3). The efficiency of the asynchronous\ntransmission system is 7 bits of information divided by 10 total bits or 70%.\nIn other words, with asynchronous transmission, only 70% of the data rate is available for the user; 30% is\nused by the transmission protocol. If we have a communication circuit using a dial-up modem receiving\n56 Kbps, the user sees an effective data rate (or throughput) of 39.2 Kbps. This is very inefficient.\nWe can improve efficiency by reducing the number of overhead bits in each message or by increasing the\nnumber of information bits. For example, if we remove the stop bits from the asynchronous transmission,\nefficiency increases to or 77.8%. The throughput of a dial-up modem at 56 Kbps would increase 43.6", "source": "Page 139", "chapter_title": "Chapter 11"}
{"id": "d09e9fbe4783-1", "text": "Kbps, which is not great but is at least a little better.\nThe same basic formula can be used to calculate the efficiency of synchronous transmission. For example,\nsuppose that we are using SDLC. The number of information bits is calculated by determining how many\ninformation characters are in the message. If the message portion of the frame contains 100 information\ncharacters and we are using an 8-bit code, then there are 100 \u00d7 8 = 800 bits of information. The total\nnumber of bits is the 800 information bits plus the overhead bits that are inserted for delineation and\nerror control. Figure 4-9 shows that SDLC has a beginning flag (8 bits), an address (8 bits), a control field\n(8 bits), a frame check sequence (assume that we use a CRC-32 with 32 bits), and an ending flag (8 bits).\nThis is a total of 64 overhead bits; thus, efficiency is 800/(800 + 64) = 92.6%. If the circuit provides a\ndata rate of 56 Kbps, then the effective data rate available to the user is about 51.9 Kbps.\nThis example shows that synchronous networks usually are more efficient than asynchronous networks\nand that some protocols are more efficient than others. The longer the message (1,000 characters as\nopposed to 100), the more efficient the protocol. For example, suppose that the message in the SDLC\nexample contained 1,000 bytes. The efficiency here would be 99.2% or 8000/(8000 + 64), giving an\neffective data rate of about 55.6 Kbps.\nThe general rule is that the larger the message field, the more efficient the protocol. So why not have\n10,000-byte or even 100,000-byte packets to really increase the efficiency? The answer is that anytime a", "source": "Page 139", "chapter_title": "Chapter 11"}
{"id": "06a6a6201f4f-2", "text": "frame is received containing an error, the entire frame must be retransmitted. Thus, if an entire file is sent\nas one large packet (e.g., 100 K) and 1 bit is received in error, all 100,000 bytes must be sent again.\nClearly, this is a waste of capacity. Furthermore, the probability that a frame contains an error increases\nwith the size of the frame; larger frames are more likely to contain errors than are smaller ones, simply\nbecause of the laws of probability.\nThus, in designing a protocol, there is a trade-off between large and small frames. Small frames are less\nefficient but are less likely to contain errors and cost less (in terms of circuit capacity) to retransmit if\nthere is an error (Figure 4-10).\nThroughput is the total number of information bits received per second, after taking into account the\noverhead bits and the need to retransmit frames containing errors. Generally speaking, small frames\nprovide better throughput for circuits with more errors, whereas larger frames provide better throughput\nin less-error-prone networks. Fortunately, in most real networks, the curve shown in Figure 4-10 is very\nflat on top, meaning that there is a range of frame sizes that provide almost optimum performance. Frame\nsizes vary greatly among different networks, but the ideal frame size tends to be between 2,000 and\n10,000 bytes.", "source": "Page 139", "chapter_title": "Chapter 11"}
{"id": "574b3dda3ca4-0", "text": "FIGURE 4-10 Frame size effects on throughput\nSo why are the standard sizes of Ethernet frames about 1,500 bytes? Because Ethernet was standardized\nmany years ago when errors were more common. Jumbo and super jumbo frame sizes emerged from\nhigher speed, highly error-free fiber-optic networks.\nMANAGEMENT FOCUS 4-2\nSleuthing for the Right Frame Size\nOptimizing performance in a network, particularly a client-server network, can be difficult because\nfew network managers realize the importance of the frame size. Selecting the right\u2014or the wrong\u2014\nframe size can have greater effects on performance than anything you might do to the server.\nStandard Commercial, a multinational tobacco and agricultural company, noticed a decrease in\nnetwork performance when they upgraded to a new server. They tested the effects of using frame\nsizes between 500 bytes and 32,000 bytes. In their tests, a frame size of 512 bytes required a total of\n455,000 bytes transmitted over their network to transfer the test messages. In contrast, the 32,000-\nbyte frames were far more efficient, cutting the total data by 44% to 257,000 bytes.\nHowever, the problem with 32,000-byte frames was a noticeable response time delay because\nmessages were saved until the 32,000-byte frames were full before transmitting.\nThe ideal frame size depends on the specific application and the pattern of messages it generates.\nFor Standard Commercial, the ideal frame size appeared to be between 4,000 and 8,000 bytes.\nUnfortunately, not all network software packages enable network managers to fine-tune frame sizes\nin this way.\nSource: Adapted from \u201cSleuthing for the Right Packet Size,\u201d Info-World, January 16, 1995.", "source": "Page 140", "chapter_title": "Chapter 11"}
{"id": "d174cd617df9-0", "text": "4.6 IMPLICATIONS FOR CYBER SECURITY\nOne of the main responsibilities of the data link layer is to determine who can transmit at what time and\nensure that the message is delivered to the correct computer. The data link layer uses the MAC address\n(a.k.a. physical address) to recognize the source and destination addresses (see Figures 4-8a and 4-8b) of\ntwo computers that communicate with each other. If you want to allow only certain computers to connect\nto your network, you can use MAC address filtering. MAC address filtering will create a list of MAC\naddresses that are allowed to connect to a Wi-Fi network or to a switch in corporate networks. This\nfeature allows for some degree of security.\nHowever, MAC address filtering can offer a false sense of security because of MAC address spoofing. The\nMAC address is assigned to a computer network interface card in a factory and is therefore hardcoded on\nthe network interface card (NIC) and cannot be changed. MAC address spoofing is a software-enabled\ntechnique that can change the hardcoded MAC address to any MAC address and thus overcome MAC\naddress filtering. There are many tutorials on how to spoof a MAC address; here is one that does a good\njob explaining it: https://www.youtube.com/watch?v=ePtCvwmNhb4. Keep in mind that while MAC\naddress spoofing is not illegal, what you do with it may be.\nSUMMARY\nMedia Access Control Media access control refers to controlling when computers transmit. There\nare three basic approaches. With roll-call polling, the server polls client computers to see if they have\ndata to send; computers can transmit only when they have been polled. With hub polling or token\npassing, the computers themselves manage when they can transmit by passing a token to one other;\nno computer can transmit unless it has the token. With contention, computers listen and transmit", "source": "Page 141", "chapter_title": "Chapter 11"}
{"id": "cc60ddef02ce-1", "text": "no computer can transmit unless it has the token. With contention, computers listen and transmit\nonly when no others are transmitting. In general, contention approaches work better for small\nnetworks that have low levels of usage, whereas polling approaches work better for networks with\nhigh usage.\nSources and Prevention of Error Errors occur in all networks. Errors tend to occur in groups (or\nbursts) rather than 1 bit at a time. The primary sources of errors are impulse noises (e.g., lightning),\ncross-talk, echo, and attenuation. Errors can be prevented (or at least reduced) by shielding the\ncables; moving cables away from sources of noise and power sources; using repeaters (and, to a lesser\nextent, amplifiers); and improving the quality of the equipment, media, and their connections.\nError Detection and Correction All error-detection schemes attach additional error-detection\ndata, based on a mathematical calculation, to the user\u2019s message. The receiver performs the same\ncalculation on incoming messages, and if the results of this calculation do not match the error-\ndetection data on the incoming message, an error has occurred. Parity, checksum, and CRC are the\nmost common error-detection schemes. The most common error-correction technique is simply to\nask the sender to retransmit the message until it is received without error. A different approach,\nforward error correction, includes sufficient information to allow the receiver to correct the error in\nmost cases without asking for a retransmission.\nMessage Delineation Message delineation means to indicate the start and end of a message.\nAsynchronous transmission uses start and stop bits on each letter to mark where they begin and end.\nSynchronous techniques (e.g., SDLC, HDLC, Ethernet, PPP) group blocks of data together into\nframes that use special characters or bit patterns to mark the start and end of entire messages.", "source": "Page 141", "chapter_title": "Chapter 11"}
{"id": "30870c53eeb4-2", "text": "frames that use special characters or bit patterns to mark the start and end of entire messages.\nTransmission Efficiency and Throughput Every protocol adds additional bits to the user\u2019s\nmessage before sending it (e.g., for error detection). These bits are called overhead bits because they\nadd no value to the user; they simply ensure correct data transfer. The efficiency of a transmission\nprotocol is the number of information bits sent by the user divided by the total number of bits\ntransferred (information bits plus overhead bits). Synchronous transmission provides greater\nefficiency than does asynchronous transmission. In general, protocols with larger frame sizes provide\ngreater efficiency than do those with small frame sizes. The drawback to large frame sizes is that they\nare more likely to be affected by errors and thus require more retransmission. Small frame sizes are\ntherefore better suited to error-prone circuits, and large frames to error-free circuits.", "source": "Page 141", "chapter_title": "Chapter 11"}
{"id": "60728c7ce537-0", "text": "KEY TERMS\naccess request\nacknowledgment (ACK)\namplifiers\nasynchronous transmission\nattenuation\nAutomatic Repeat reQuest (ARQ)\nburst error\nchecksum\ncontention\ncontinuous ARQ\ncontrolled access\ncross-talk\ncyclic redundancy check (CRC)\necho\nefficiency\nerror detection\nerror prevention\nerror rates\nEthernet (IEEE 802.3)\neven parity\nforward error correction\nframe\nGaussian noise\nHamming code\nhigh-level data link control (HDLC)\nhub polling\nimpulse noise\ninformation bits\nintermodulation noise\nline noise\nLink Access Protocol-Balanced (LAP-B)\nlogical link control [LLC] sublayer\nmedia access control\nmedia access control [MAC] sublayer\nMAC address\nMAC address filtering\nMAC address spoofing\nnegative acknowledgment (NAKs)", "source": "Page 142", "chapter_title": "Chapter 11"}
{"id": "693d09460458-0", "text": "odd parity\noverhead bits\nparity bit\nparity check\nPoint-to-Point Protocol (PPP)\npolling\nrepeater\nrepeaters\nroll-call polling\nsliding window\nstart bit\nstop bit\nsynchronization\nsynchronous transmission\nthroughput\ntoken passing\ntransmission efficiency\nwhite noise\nQUESTIONS\n1. What does the data link layer do?\n2. What is media access control, and why is it important?\n3. Under what conditions is media access control unimportant?\n4. Compare and contrast roll-call polling, hub polling (or token passing), and contention.\n5. Which is better, controlled access or contention? Explain.\n6. Define two fundamental types of errors.\n7. Errors normally appear in _____, which is when more than 1 data bit is changed by the error-\ncausing condition.\n8. Is there any difference in the error rates of lower-speed lines and higher-speed lines?\n9. Briefly define noise.\n10. Describe four types of noise. Which one is likely to pose the greatest problem to network managers?\n11. How do amplifiers differ from repeaters?\n12. What are the three ways of reducing errors and the types of noise they affect?\n13. Describe three approaches to detecting errors, including how they work, the probability of detecting\nan error, and any other benefits or limitations.\n14. Briefly describe how even parity and odd parity work.\n15. Briefly describe how checksum works.\n16. How does CRC work?\n17. How does forward error-correction work? How is it different from other error-correction methods?\n18. Under what circumstances is forward error correction desirable?", "source": "Page 143", "chapter_title": "Chapter 11"}
{"id": "9c0bb03b1414-0", "text": "19. Briefly describe how continuous ARQ works.\n20. Which is the simplest (least sophisticated) protocol described in this chapter? How does it work?\n21. Describe the frame layouts for SDLC, Ethernet, and PPP.\n22. What is transmission efficiency?\n23. How do information bits differ from overhead bits?\n24. Are stop bits necessary in asynchronous transmission? Explain by using a diagram.\n25. During the 1990s, there was intense competition between two technologies (10-Mbps Ethernet and\n16-Mbps token ring) for the LAN market. Ethernet was promoted by a consortium of vendors,\nwhereas token ring was primarily an IBM product, even though it was standardized. Ethernet won,\nand no one talks about token ring anymore. Token ring used a hub-polling-based approach. Outline a\nnumber of reasons why Ethernet might have won.\nHint: The reasons were both technical and business.\n26. Under what conditions does a data link layer protocol need an address?\n27. Are large frame sizes better than small frame sizes? Explain.\n28. What media access control technique does your class use?\n29. Show how the word \u201cHI\u201d would be sent using asynchronous transmission using even parity (make\nassumptions about the bit patterns needed). Show how it would be sent using Ethernet.\nEXERCISES\nA. Draw how a series of four separate messages would be successfully sent from one computer to\nanother if the first message were transferred without error, the second were initially transmitted with\nan error, the third were initially lost, and the ACK for the fourth were initially lost.\nB. How efficient would a 6-bit code be in asynchronous transmission if it had 1 parity bit, 1 start bit, and\n2 stop bits? (Some old equipment uses 2 stop bits.)", "source": "Page 144", "chapter_title": "Chapter 11"}
{"id": "eebd11bf31fa-1", "text": "2 stop bits? (Some old equipment uses 2 stop bits.)\nC. What is the transmission rate of information bits (TRIB) if you use ASCII (8 bits plus 1 parity bit), a\n1,000-character frame, 56 Kbps modem transmission speed, 20 control characters per frame, an\nerror rate of 1%, and a 30-millisecond turnaround time? What is the TRIB if you add a half-second\ndelay to the turnaround time because of satellite delay?\nD. Search the Web to find a software vendor that sells a package that supports each of the following\nprotocols: SDLC, HDLC, Ethernet, and PPP (i.e., one package that supports SDLC, another [or the\nsame] for HDLC, and so on).\nE. Investigate the network at your organization (or a service offered by an IXC) to find out the average\nerror rates.\nF. What is the efficiency if a 100-byte file is transmitted using Ethernet? A 10,000-byte file?\nG. What is the propagation delay on a circuit using a LEO satellite orbiting 500 miles above the earth if\nthe speed of the signal is 186,000 miles per second? If the satellite is 22,000 miles above the earth?\nH. Suppose that you are going to connect the computers in your house or apartment. What media would\nyou use? Why? Would this change if you were building a new house?\nMINICASES\nI. Smith, Smith, Smith, and Smith Smith, Smith, Smith, and Smith is a regional accounting firm\nthat is putting up a new headquarters building. The building will have a backbone network that\nconnects eight LANs (two on each floor). The company is very concerned with network errors. What\nadvice would you give regarding the design of the building and network cable planning that would", "source": "Page 144", "chapter_title": "Chapter 11"}
{"id": "345a336c2125-2", "text": "advice would you give regarding the design of the building and network cable planning that would\nhelp reduce network errors?", "source": "Page 144", "chapter_title": "Chapter 11"}
{"id": "cbea3afe1039-0", "text": "II. Worldwide Charity Worldwide Charity is a charitable organization whose mission is to improve\neducation levels in developing countries. In each country where it is involved, the organization has a\nsmall headquarters and usually 5\u201310 offices in outlying towns. Staff members communicate with one\nanother via email on older computers donated to the organization. Because Internet service is not\nreliable in many of the towns in these countries, the staff members usually phone headquarters and\nuse a very simple Linux email system that uses a server-based network architecture. They also upload\nand download files. What range of frame sizes is likely to be used?\nIII. Industrial Products Industrial Products is a small light-manufacturing firm that produces a\nvariety of control systems for heavy industry. It has a network that connects its office building and\nwarehouse that has functioned well for the last year, but over the past week, users have begun to\ncomplain that the network is slow. Clarence Hung, the network manager, did a quick check of the\nnumber of orders over the past week and saw no real change, suggesting that there has been no major\nincrease in network traffic. What would you suggest that Clarence do next?\nIV. Alpha Corp. Alpha Corp. is trying to decide the size of the connection it needs to the Internet. The\ncompany estimates that it will send and receive a total of about 1,000 emails per hour and that each\nemail message is about 1,500 bytes in size. The company also estimates that it will send and receive a\ntotal of about 3,000 Web pages per hour and that each page is about 40,000 bytes in size. (1) Without\nconsidering transmission efficiency, how large an Internet connection would you recommend in\nterms of bits per second (assuming that each byte is 8 bits in length)? (2) Assuming they use a", "source": "Page 145", "chapter_title": "Chapter 11"}
{"id": "b50451d25999-1", "text": "synchronous data link layer protocol with an efficiency of about 90%, how large an Internet\nconnection would you recommend? (3) Suppose that Alpha wants to be sure that its Internet\nconnection will provide sufficient capacity the next 2 years. How large an Internet connection would\nyou recommend?\nTECH UPDATES\nIn every chapter, we will offer a couple of ideas to investigate.\nTopic A: MAC Address Filtering\nMAC address filtering enforces access control and is used to enhance the security of not only wireless\nnetworks but also wired networks. How can one set up MAC address filtering on a home wireless router?\nProvide a step-by-step tutorial on how to do this. Show, that when you implement MAC address filtering\nonly computers that are listed can access the network. Investigate whether MAC address filtering is done\non large networks. For example, you could talk to a network administrator (e.g., at your college or\nuniversity) and ask them whether they use MAC address filtering and why.\nTopic B: ARP Spoofing\nARP spoofing is a technique that allows an attacker to gain access to a network that he/she would not be\nable to access otherwise. But, how difficult is it to change a MAC address (in software)? Create a step-by-\nstep tutorial on how to change a computer\u2019s MAC address. What would one have to do to change the MAC\naddress on an iPhone? Have fun!\nDeliverables\nYour job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title Slide\n2. Short description of the topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use a lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along", "source": "Page 145", "chapter_title": "Chapter 11"}
{"id": "816c9d94d049-2", "text": "your audience can follow along\n5. How does it relate to material covered in class so far (and in the future)", "source": "Page 145", "chapter_title": "Chapter 11"}
{"id": "5048057f672b-0", "text": "6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 4A\nCapturing Packets on Your Network\nIn this chapter, we discussed several data link layer protocols, such as SDLC and Ethernet. The objective\nof this activity is for you to see the data link layer frames in action on your network.\nWireshark is one of the many tools that permit users to examine the frames in their network. It is called a\npacket sniffer because it enables you to see inside the frames and packets that your computer sends, as\nwell as the frames and packets sent by other users on your LAN. In other words, you can eavesdrop on the\nother users on your LAN to see what websites they visit and even the email they send. We don\u2019t\nrecommend using it for this reason, but it is important that you understand that someone else could be\nusing Ethereal to sniff your packets to see and record what you are doing on the Internet.\n1. Use your browser to connect to www.wireshark.org and download and install the Wireshark software.\n2. When you start Wireshark, you will see a screen like that in Figure 4-11, minus the two smaller\nwindows on top.\na. Click Capture\nb. Click Interfaces\nc. Click the Capture button beside your Wireshark connection (wireless LAN or traditional LAN).\n3. Wireshark will capture all packets moving through your LAN. To make sure you have something to\nsee, open your Web browser and visit one or two websites. After you have captured packets for 30\u201360\nseconds, return to Wireshark and click Stop.", "source": "Page 146", "chapter_title": "Chapter 11"}
{"id": "b2ef45e489dd-0", "text": "FIGURE 4-11 Capturing packets with Wireshark\n4. Figure 4-12 shows the packets captured on my home network. The top window in Wireshark displays\nthe complete list of packets in chronological order. Each packet is numbered; I\u2019ve scrolled the\nwindow, so the first packet shown is packet 11. Wireshark lists the time, the source IP address, the\ndestination IP address, the protocol, and some additional information about each packet. The IP\naddresses will be explained in more detail in the next chapter.\nFor the moment, look at packet number 16, the second HTTP packet from the top. I\u2019ve clicked on this\npacket, so the middle window shows the inside of the packet. The first line in this second window says the\nframe (or packet if you prefer) is 1091 bytes long. It contains an Ethernet II packet, an Internet Protocol\n(IP) packet, a Transmission Control Protocol (TCP) packet, and a Hypertext Transfer Protocol (HTTP)\npacket. Remember in Chapter 1 that Figure 1-4 described how each packet was placed inside another\npacket as the message moved through the layers and was transmitted.\nClick on the plus sign (+) in front of the HTTP packet to expand it. Wireshark shows the contents of the\nHTTP packet. By reading the data inside the HTTP packet, you can see that this packet was an HTTP\nrequest to my.yahoo.com that contained a cookie. If you look closely, you\u2019ll see that the sending computer\nwas a Tablet PC\u2014that\u2019s some of the optional information my Web browser (Internet Explorer) included in\nthe HTTP header.\nThe bottom window in Figure 4-12 shows the exact bytes that were captured. The section highlighted in\ngray shows the HTTP packet. The numbers on the left show the data in hexadecimal format, whereas the", "source": "Page 147", "chapter_title": "Chapter 11"}
{"id": "a7ddeb6cc6d9-1", "text": "data on the right show the text version. The data before the highlighted section are the TCP packet.", "source": "Page 147", "chapter_title": "Chapter 11"}
{"id": "c23c66ed44f4-0", "text": "FIGURE 4-12 Analyzing packets with Wireshark\nFrom Chapter 2, you know that the client sends an HTTP request packet to request a Web page, and the\nWeb server sends back an HTTP response packet. Packet number 25 in the top window in Figure 4-12 is\nthe HTTP response sent back to my computer by the Yahoo! server. You can see that the destination IP\naddress in my HTTP request is the source IP address of this HTTP packet.\n5. Figure 4-12 also shows what happens when you click the plus sign (+) in front of the Ethernet II\npacket to expand it. You can see that this Ethernet packet has a destination address and source\naddress (e.g., 00:02:2d:85:cb:e0).\nDeliverables\n1. List the layer 2, 3, 4, and 5 PDUs that are used in your network to send a request to get a Web\npage.\n2. List the source and destination Ethernet addresses on the message.\n3. What value is in the Ethernet type field in this message? Why?", "source": "Page 148", "chapter_title": "Chapter 11"}
{"id": "070e1803104d-0", "text": "CHAPTER 5\nNETWORK AND TRANSPORT LAYERS\nThe network and transport layers are responsible for moving messages from end to end in a network.\nThey are so closely tied together that they are usually discussed together. The transport layer (layer 4)\nperforms three functions: linking the application layer to the network, segmenting (breaking long\nmessages into smaller packets for transmission), and session management (establishing an end-to-end\nconnection between the sender and receiver). The network layer (layer 3) performs two functions: routing\n(determining the next computer to which the message should be sent to reach the final destination) and\naddressing (finding the address of that next computer). There are several standard transport and network\nlayer protocols that specify how packets are to be organized, in the same way that there are standards for\ndata link layer packets. However, only one set of protocols is in widespread use today: the Internet\nProtocol Suite, commonly called Transmission Control Protocol/Internet Protocol (TCP/IP). This chapter\ntakes a detailed look at how TCP/IP and the other protocols in the Internet Protocol Suite work.\nOBJECTIVES\nBe aware of the TCP/IP protocols\nBe familiar with linking to the application layer, segmenting, and session management\nBe familiar with addressing\nBe familiar with routing\nUnderstand how TCP/IP works\nOUTLINE\n5.1 Introduction\n5.2 Transport and Network Layer Protocols\n5.2.1 Transmission Control Protocol (TCP)\n5.2.2 Internet Protocol (IP)\n5.3 Transport Layer Functions\n5.3.1 Linking to the Application Layer\n5.3.2 Segmenting\n5.3.3 Session Management\n5.4 Addressing\n5.4.1 Assigning Addresses\n5.4.2 Address Resolution\n5.5 Routing\n5.5.1 Types of Routing\n5.5.2 Routing Protocols", "source": "Page 149", "chapter_title": "Chapter 11"}
{"id": "b9ad3f1ba45c-1", "text": "5.5.1 Types of Routing\n5.5.2 Routing Protocols\n5.5.3 Multicasting\n5.5.4 The Anatomy of a Router\n5.6 TCP/IP Example\n5.6.1 Known Addresses", "source": "Page 149", "chapter_title": "Chapter 11"}
{"id": "d5712449f754-0", "text": "5.6.2 Unknown Addresses\n5.6.3 TCP Connections\n5.6.4 TCP/IP and Network Layers\n5.7 Implications for Cyber Security\nSummary\n5.1 INTRODUCTION\nThe transport and network layers are so closely tied together that they are almost always discussed\ntogether. For this reason, we discuss them in the same chapter. Transmission Control Protocol/Internet\nProtocol (TCP/IP) is the most commonly used set of transport and network layer protocols, so this\nchapter focuses on TCP/IP.\nThe transport layer links the application software in the application layer with the network and is\nresponsible for the end-to-end delivery of the message. The transport layer accepts outgoing messages\nfrom the application layer (e.g., Web, email, and so on, as described in Chapter 2) and segments them for\ntransmission. Figure 5-1 shows the application layer software producing a Simple Mail Transfer Protocol\n(SMTP) packet that is split into two smaller TCP segments by the transport layer. The Protocol Data Unit\n(PDU) at the transport layer is called a segment. The network layer takes the messages from the\ntransport layer and routes them through the network by selecting the best path from computer to\ncomputer through the network (and adds an IP packet). The data link layer adds an Ethernet frame and\ninstructs the physical layer hardware when to transmit. As we saw in Chapter 1, each layer in the network\nhas its own set of protocols that are used to hold the data generated by higher layers, much like a set of\nmatryoshka (nested Russian dolls).\nThe network and transport layers also accept incoming messages from the data link layer and organize\nthem into coherent messages that are passed to the application layer. For example, as in Figure 5-1, a large\nemail message might require several data link layer frames to transmit. The transport layer at the sender", "source": "Page 150", "chapter_title": "Chapter 11"}
{"id": "487caa519d0f-1", "text": "email message might require several data link layer frames to transmit. The transport layer at the sender\nwould break the message into several smaller segments and give them to the network layer to route, which\nin turn gives them to the data link layer to transmit. The network layer at the receiver would receive the\nindividual packets from the data link layer, process them, and pass them to the transport layer, which\nwould reassemble them into the one email message before giving it to the application layer.", "source": "Page 150", "chapter_title": "Chapter 11"}
{"id": "b500cd509ba7-0", "text": "FIGURE 5-1 Message transmission using layers. SMTP = Simple Mail Transfer Protocol; HTTP =\nHypertext Transfer Protocol; IP = Internet Protocol; TCP = Transmission Control Protocol\nIn this chapter, we provide a brief look at the transport and network layer protocols, before turning our\nattention to how TCP/IP works. We first examine the transport layer functions. Addressing and routing\nare performed by the transport and network layers working together, so we will discuss them together\nrather than separate them according to which part is performed by the transport layer and which by the\nnetwork layer.\n5.2 TRANSPORT AND NETWORK LAYER PROTOCOLS\nThere are different transport/network layer protocols, but one family of protocols, the Internet Protocol\nSuite, dominates. Each transport and network layer protocol performs essentially the same functions, but\neach is incompatible with the others unless there is a special device to translate between them. In this\nchapter, we focus on TCP/IP. A good overview of protocols, at all layers, is available at\nwww.protocols.com.\nThe Transmission Control Protocol/Internet Protocol (TCP/IP) was developed for the U.S.\nDepartment of Defense\u2019s Advanced Research Project Agency network (ARPANET) by Vinton Cerf and Bob\nKahn in 1974. TCP/IP is the transport/network layer protocol used on the Internet. It is the world\u2019s most\npopular protocol set, used by almost all backbone networks (BNs) and WANs. TCP/IP allows reasonably\nefficient and error-free transmission. Because it performs error checking, it can send large files across\nsometimes unreliable networks with great assurance that the data will arrive uncorrupted. TCP/IP is\ncompatible with a variety of data link protocols, which is one reason for its popularity.", "source": "Page 151", "chapter_title": "Chapter 11"}
{"id": "b541f8d2b004-0", "text": "As the name implies, TCP/IP has two parts. TCP is the transport layer protocol that links the application\nlayer to the network layer. It performs segmenting: breaking the data into smaller PDUs called segments,\nnumbering them, ensuring that each segment is reliably delivered, and putting them in the proper order\nat the destination. IP is the network layer protocol and performs addressing and routing. IP software is\nused at each of the intervening computers through which the message passes; it is IP that routes the\nmessage to the final destination. The TCP software needs to be active only at the sender and the receiver\nbecause TCP is involved only when data comes from or goes to the application layer.\n5.2.1 Transmission Control Protocol (TCP)\nA typical TCP segment has a 192-bit header (24 bytes) of control information (Figure 5-2). Among other\nfields, it contains the source and destination port identifier. The destination port tells the TCP software at\nthe destination to which application layer program the application layer packet should be sent, whereas\nthe source port tells the receiver which application layer program the packet is from. The TCP segment\nalso provides a sequence number so that the TCP software at the destination can assemble the segments\ninto the correct order and make sure that no segments have been lost.\nFIGURE 5-2 Transmission Control Protocol (TCP) segment. ACK = Acknowledgment; CRC = Cyclical\nRedundancy Check\nThe options field is optional and rarely used. Therefore, this results in a 20-byte-long TCP header. The\nheader length field is used to tell the receiver how long the TCP packet is\u2014that is, whether the options\nfield is included.\nThe Internet Protocol Suite has a second type of transport layer protocol called User Datagram\nProtocol (UDP). UDP PDUs are called datagrams. Typically, UDP is used when the sender needs to", "source": "Page 152", "chapter_title": "Chapter 11"}
{"id": "ecdd1c6baf60-1", "text": "send a single small packet to the receiver (e.g., for a domain name service (DNS) request, which we\ndiscuss later in this chapter). When there is only one small packet to be sent, the transport layer doesn\u2019t\nneed to worry about segmenting the outgoing messages or reassembling them upon receipt, so the\ntransmission can be faster. A UDP datagram has only four fields (8 bytes of over-head) plus the\napplication layer packet: source port, destination port, length, and a CRC-16. Unlike TCP, UDP does not\ncheck for lost messages, so occasionally a UDP datagram is lost and the message must be resent.\nInterestingly, it is not the transport layer that decides whether TCP or UDP is going to be used. This\ndecision is left to the engineer who is writing the application.\n5.2.2 Internet Protocol (IP)\nThe Internet Protocol (IP) is the network layer protocol. Network layer PDUs are called packets. Two\nforms of IP are currently in use. The older form is IP version 4 (IPv4), which also has a 192-bit header (24\nbytes) (Figure 5-3). This header contains the source and destination addresses, packet length, and packet\nnumber. Similar to the TCP header, the options field is rarely used, and therefore, the header is usually 20\nbytes long.\nIP version 4 is being replaced by IPv6, which has a 320-bit header (40 bytes) (Figure 5-4). The primary\nreason for the increase in the packet size is an increase in the address size from 32 bits to 128 bits. IPv6\u2019s\nsimpler packet structure makes it easier to perform routing and supports a variety of new approaches to\naddressing and routing.\nThe development of the IPv6 came about because IP addresses were being depleted on the Internet. IPv4", "source": "Page 152", "chapter_title": "Chapter 11"}
{"id": "ce285f6cd1ef-2", "text": "has a 4-byte address field, which means that there is a theoretical maximum of about 4.2 billion\naddresses. However, about 500 million of these addresses are reserved and cannot be used, and the way\naddresses were assigned in the early days of the Internet means that a small number of companies\nreceived several million addresses, even when they didn\u2019t need all of them. With the increased growth in\nInternet users and the explosion in mobile Internet devices, current estimates project that we will run out\nof IPv4 addresses sometime in 2011.", "source": "Page 152", "chapter_title": "Chapter 11"}
{"id": "58295941a215-0", "text": "Internet Protocol version 6 uses a 16-byte-long address, which provides a theoretical maximum of 3.4 \u00d7\n1038 addresses\u2014more than enough for the foreseeable future. IPv4 uses decimals to express addresses\n(e.g., 128.192.55.72), but IPv6 uses hexadecimal (base 16) like Ethernet to express addresses, which makes\nit slightly more confusing to use. Addresses are eight sets of 2-byte numbers (e.g.,\n2001:0890:0600:00d1:0000:0000:abcd:f010), but because this can be long to write, there is a IPv6\n\u201ccompressed notation\u201d that eliminates the leading zeros within each block and blocks that are all zeros.\nSo, the preceding IPv6 address could also be written as 2001:890:600:d1: :abcd:f010.\nFIGURE 5-3 Internet Protocol (IP) packet (version 4). CRC = Cyclical Redundancy Check\nFIGURE 5-4 Internet Protocol (IP) packet (version 6)\nAdoption of IPv6 has been slow. Most organizations have not felt the need to change because IPv6\nprovides few benefits other than the larger address space and requires their staff to learn a whole new\nprotocol. In most cases, the shortage of addresses on the Internet doesn\u2019t affect organizations that already\nhave Internet addresses, so there is little incentive to convert to IPv6. Most organizations that implement\nIPv6 also run IPv4, and IPv6 is not backward-compatible with IPv4, which means that all network devices\nmust be changed to understand both IPv4 and IPv6. The cost of this conversion, along with the few\nbenefits it provides to organizations that do convert, has led a number of commentators to refer to this as", "source": "Page 153", "chapter_title": "Chapter 11"}
{"id": "f54fc09289ca-1", "text": "the IPv6 \u201cmess.\u201d To encourage the move to IPv6, the U.S. government required all of its agencies to\nconvert to IPv6 on their WANs and BNs by June 2008, but the change was not completed on time.\nThe size of the message field depends on the data link layer protocol used. TCP/IP is commonly combined\nwith Ethernet. Ethernet has a maximum packet size of 1,492 bytes, so the maximum size of a TCP message\nfield if IPv4 is used is 1,492 \u2212 24 (the size of the TCP header) \u2212 24 (the size of the IPv4 header) = 1,444.\n5.3 TRANSPORT LAYER FUNCTIONS\nThe transport layer links the application software in the application layer with the network and is\nresponsible for segmenting large messages into smaller ones for transmission and for managing the\nsession (the end-to-end delivery of the message). One of the first issues facing the application layer is to\nfind the numeric network address of the destination computer. Different protocols use different methods\nto find this address. Depending on the protocol\u2014and which expert you ask\u2014finding the destination\naddress can be classified as a transport layer function, a network layer function, a data link layer function,\nor an application layer function with help from the operating system. In all honesty, understanding how\nthe process works is more important than memorizing how it is classified. The next section discusses\naddressing at the network layer and transport layer. In this section, we focus on three unique functions\nperformed by the transport layer: linking the application layer to the network layer, segmenting, and\nsession management.\n5.3.1 Linking to the Application Layer\nMost computers have many application layer software packages running at the same time. Users often\nhave Web browsers, email programs, and word processors in use at the same time on their client", "source": "Page 153", "chapter_title": "Chapter 11"}
{"id": "353c37f8ef80-2", "text": "have Web browsers, email programs, and word processors in use at the same time on their client\ncomputers. Similarly, many servers act as Web servers, mail servers, FTP servers, and so on. When the\ntransport layer receives an incoming message, the transport layer must decide to which application\nprogram it should be delivered. It makes no sense to send a Web page request to email server software.\nWith TCP, each application layer software package has a unique port address. Any message sent to a\ncomputer must tell TCP (the transport layer software) the application layer port address that is to receive", "source": "Page 153", "chapter_title": "Chapter 11"}
{"id": "134279a902f2-0", "text": "the message. Therefore, when an application layer program generates an outgoing message, it tells the\nTCP software its own port address (i.e., the source port address) and the port address at the\ndestination computer (i.e., the destination port address). These two port addresses are placed in the\nfirst two fields in the TCP segment (see Figure 5-2).\nPort addresses can be any 16-bit (2-byte) number. So, how does a client computer sending a Web request\nto a Web server know what port address to use for the Web server? Simple. On the Internet, all port\naddresses for popular services such as the Web, email, and FTP have been standardized. Anyone using a\nWeb server should set up the Web server with a port address of 80, which is called the well-known port.\nWeb browsers, therefore, automatically generate a port address of 80 for any Web page you click on. FTP\nservers use port 21, Telnet 23, SMTP 25, and so on. Network managers are free to use whatever port\naddresses they want, but if they use a nonstandard port number, then the application layer software on\nthe client must specify the correct port number.\nFIGURE 5-5 Linking to application layer services\nFigure 5-5 shows a user running three applications on the client (Internet Explorer, Outlook, and\nRealPlayer), each of which has been assigned a different port number, called a temporary port number\n(1027, 1028, and 1029, respectively). Each of these can simultaneously send and receive data to and from\ndifferent servers and different applications on the same server. In this case, we see a message sent by\nInternet Explorer on the client (port 1027) to the Web server software on the xyz.com server (port 80). We", "source": "Page 154", "chapter_title": "Chapter 11"}
{"id": "7cc93753d643-1", "text": "also see a message sent by the mail server software on port 25 to the email client on port 1028. At the\nsame time, the RealPlayer software on the client is sending a request to the music server software (port\n554) at 123.com.\n5.3.2 Segmenting\nSome messages or blocks of application data are small enough that they can be transmitted in one frame\nat the data link layer. However, in other cases, the application data in one \u201cmessage\u201d are too large and\nmust be broken into several frames (e.g., Web pages, graphic images). As far as the application layer is\nconcerned, the message should be transmitted and received as one large block of data. However, the data\nlink layer can transmit only messages of certain lengths. It is therefore up to the sender\u2019s transport layer\nto break the data into several smaller segments that can be sent by the data link layer across the circuit. At", "source": "Page 154", "chapter_title": "Chapter 11"}
{"id": "094da864cb07-0", "text": "the other end, the receiver\u2019s transport layer must receive all these separate segments and recombine them\ninto one large message.\nSegmenting means to take one outgoing message from the application layer and break it into a set of\nsmaller segments for transmission through the network. It also means to take the incoming set of smaller\nsegments from the network layer and reassemble them into one message for the application layer.\nDepending on what the application layer software chooses, the incoming packets can be either delivered\none at a time or held until all packets have arrived and the message is complete. Web browsers, for\nexample, usually request delivery of packets as they arrive, which is why your screen gradually builds a\npiece at a time. Most email software, conversely, usually requests that messages be delivered only after all\npackets have arrived and TCP has organized them into one intact message, which is why you usually don\u2019t\nsee email messages building screen by screen.\nThe TCP is also responsible for ensuring that the receiver has actually received all segments that have\nbeen sent. TCP therefore uses continuous automatic repeat request (ARQ) (see also Chapter 4).\nOne of the challenges at the transport layer is deciding how big to make the segments. Remember, we\ndiscussed packet sizes in Chapter 4. When transport layer software is set up, it is told what size segments\nit should use to make best use of its own data link layer protocols (or it chooses the default size of 536).\nHowever, it has no idea what size is best for the destination. Therefore, the transport layer at the sender\nnegotiates with the transport layer at the receiver to settle on the best segment sizes to use. This\nnegotiation is done by establishing a TCP connection between the sender and receiver.\n5.3.3 Session Management\nA session can be thought of as a conversation between two computers. When the sending computer", "source": "Page 155", "chapter_title": "Chapter 11"}
{"id": "e50363fb575e-1", "text": "A session can be thought of as a conversation between two computers. When the sending computer\nwants to send a message to the receiver, it usually starts by establishing a session with that computer. The\nsender transmits the segments in sequence until the conversation is done, and then the sender ends the\nsession. This approach to session management is called connection-oriented messaging.\nSometimes, the sender only wants to send one short information message or a request. In this case, the\nsender may choose not to start a session but just send the one quick message and move on. This approach\nis called connectionless messaging.\nConnection-Oriented Messaging\nConnection-oriented messaging sets up a TCP connection (also called a session) between the sender\nand receiver. To establish a connection, the transport layer on both the sender and the receiver must send\na SYN (synchronize) and receive a ACK (acknowledgement) segment. This process starts with the sender\n(usually a client) sending a SYN to the receiver (usually a server). The server responds with an ACK for the\nsender\u2019s/client\u2019s SYN and then sends its own SYN. SYN is usually a randomly generated number that\nidentifies a packet. The last step is when the client sends an ACK for the server\u2019s SYN. This is called the\nthree-way handshake. This process also contains the segment size negotiation and is responsible for error\ncorrection via retransmission (described in Chapter 4).\nOnce the connection is established, the segments flow between the sender and the receiver. In case of an\nerror, the receiver simply asks the sender to retransmit the message until it is received without an error.\nTCP calls this Automatic Repeat reQuest (ARQ). There are two types of ARQ: stop-and-wait and\ncontinuous.\nStop-and-Wait ARQ", "source": "Page 155", "chapter_title": "Chapter 11"}
{"id": "5fb739de84b7-2", "text": "continuous.\nStop-and-Wait ARQ\nWith stop-and-wait ARQ, the sender stops and waits for a response from the receiver after each data\npacket. After receiving a packet, the receiver sends either an acknowledgment (ACK), if the packet was\nreceived without error, or a negative acknowledgment (NAK), if the message contained an error. If it\nis an NAK, the sender resends the previous message. If it is an ACK, the sender continues with the next\nmessage. Stop-and-wait ARQ is by definition a half-duplex transmission technique (Figure 5-6).", "source": "Page 155", "chapter_title": "Chapter 11"}
{"id": "f4882580449e-0", "text": "FIGURE 5-6 Stop-and-wait ARQ (Automatic Repeat reQuest). ACK = Acknowledgment; NAK = Negative\nAcknowledgment\nContinuous ARQ\nWith continuous ARQ, the sender does not wait for an acknowledgment after sending a message; it\nimmediately sends the next one. Although the messages are being transmitted, the sender examines the\nstream of returning acknowledgments. If it receives a NAK, the sender retransmits the needed messages.\nThe packets that are retransmitted maybe only those containing an error (called Selective-Repeat ARQ\nor Link Access Protocol for Modems [LAP-M]) or maybe the first packet with an error and all those\nthat followed it (called Go-Back-N ARQ). LAP-M is better because it is more efficient.\nContinuous ARQ is by definition a full-duplex transmission technique because both the sender and the\nreceiver are transmitting simultaneously. (The sender is sending messages, and the receiver is sending\nACKs and NAKs.) Figure 5-7 illustrates the flow of messages on a communication circuit using continuous\nARQ. Continuous ARQ is sometimes called sliding window because of the visual imagery the early\nnetwork designers used to think about continuous ARQ. Visualize the sender having a set of messages to\nsend in memory stacked in order from first to last. Now imagine a window that moves through the stack\nfrom first to last. As a message is sent, the window expands to cover it, meaning that the sender is waiting\nfor an ACK for the message. As an ACK is received for a message, the window moves forward, dropping\nthe message out of the bottom of the window, indicating that it has been sent and received successfully.\nContinuous ARQ is also important in providing flow control, which means ensuring that the computer\nsending the message is not transmitting too quickly for the receiver. For example, if a client computer was", "source": "Page 156", "chapter_title": "Chapter 11"}
{"id": "a5cd2a632dd9-1", "text": "sending information too quickly for a server computer to store a file being uploaded, the server might run\nout of memory to store the file. By using ACKs and NAKs, the receiver can control the rate at which it", "source": "Page 156", "chapter_title": "Chapter 11"}
{"id": "7acfa1c811e0-0", "text": "receives information. With stop-and-wait ARQ, the receiver does not send an ACK until it is ready to\nreceive more packets. In continuous ARQ, the sender and receiver usually agree on the size of the sliding\nwindow. Once the sender has transmitted the maximum number of packets permitted in the sliding\nwindow, it cannot send any more packets until the receiver sends an ACK.\nFIGURE 5-7 Continuous ARQ (Automatic Repeat reQuest). ACK = Acknowledgment; NAK = Negative\nAcknowledgment", "source": "Page 157", "chapter_title": "Chapter 11"}
{"id": "0753ece08d4f-0", "text": "When the transmission is complete, the session is terminated using a four-way handshake. Because the\nTCP/IP connection is a full-duplex connection, each side of the session has to terminate the connection\nindependently. The sender (i.e., the client) will start by sending with a FIN to inform the receiver (i.e., the\nserver) that is finished sending data. The server acknowledges the FIN sending an ACK. Then the server\nsends a FIN to the client. The connection is successfully terminated when the server receives the ACK for\nits FIN.\nConnectionless Messaging\nConnectionless messaging means each packet is treated separately and makes its own way through\nthe network. Unlike connection-oriented routing, no connection is established. The sender simply sends\nthe packets as separate, unrelated entities, and it is possible that different packets will take different\nroutes through the network, depending on the type of routing used and the amount of traffic. Because\npackets following different routes may travel at different speeds, they may arrive out of sequence at their\ndestination. The sender\u2019s network layer, therefore, puts a sequence number on each packet, in addition to\ninformation about the message stream to which the packet belongs. The network layer must reassemble\nthem in the correct order before passing the message to the application layer.\nThe Internet Protocol Suite can operate either as connection-oriented or connectionless. When\nconnection-oriented messaging is desired, TCP is used. When connectionless messaging is desired, the\nTCP segment is replaced with a UDP packet. The UDP header is much smaller than the TCP header (only\n8 bytes).\nConnectionless is most commonly used when the application data or message can fit into one single\nmessage. One might expect, for example, that because Hypertext Transfer Protocol (HTTP) requests are\noften very short, they might use UDP connectionless rather than TCP connection-oriented messaging.", "source": "Page 158", "chapter_title": "Chapter 11"}
{"id": "92c1ebd21eb8-1", "text": "often very short, they might use UDP connectionless rather than TCP connection-oriented messaging.\nHowever, HTTP always uses TCP. All of the application layer software we have discussed so far uses TCP\n(HTTP, SMTP, FTP, Telnet). UDP is most commonly used for control messages such as addressing (DHCP\n[Dynamic Host Configuration Protocol], discussed later in this chapter), routing control messages (RIP\n[Routing Information Protocol], discussed later in this chapter), and network management (SNMP\n[Simple Network Management Protocol], discussed in Chapter 12).\nQuality of Service\nQuality of Service (QoS) routing is a special type of connection-oriented messaging in which different\nconnections are assigned different priorities. For example, video-conferencing requires fast delivery of\npackets to ensure that the images and voices appear smooth and continuous; they are very time\ndependent because delays in routing seriously affect the quality of the service provided. Email packets,\nconversely, have no such requirements. Although everyone would like to receive an email as fast as\npossible, a 10-second delay in transmitting an email message does not have the same consequences as a\n10-second delay in a videoconferencing packet.\nWith QoS routing, different classes of service are defined, each with different priorities. For example, a\npacket of videoconferencing images would likely get higher priority than would an SMTP packet with an\nemail message and thus be routed first. When the transport layer software attempts to establish a\nconnection (i.e., a session), it specifies the class of service that connection requires. Each path through the\nnetwork is designed to support a different number and mix of service classes. When a connection is\nestablished, the network ensures that no connections are established that exceed the maximum number of\nthat class on a given circuit.\nQoS routing is common in certain types of networks (e.g., ATM, as discussed in Chapter 8). The Internet", "source": "Page 158", "chapter_title": "Chapter 11"}
{"id": "f089d20f64a5-2", "text": "provides several QoS protocols that can work in a TCP/IP environment. Resource Reservation\nProtocol (RSVP) and Real-Time Streaming Protocol (RTSP) both permit application layer\nsoftware to request connections that have certain minimum data transfer capabilities. As one might\nexpect, RTSP is geared toward audio/video streaming applications, whereas RSVP is more for general\npurposes.\nBoth QoS protocols, RSVP and RTSP, are used to create a connection (or session) and request a certain\nminimum guaranteed data rate. Once the connection has been established, they use the Real-Time\nTransport Protocol (RTP) to send packets across the connection. RTP contains information about the", "source": "Page 158", "chapter_title": "Chapter 11"}
{"id": "0765b41fa469-0", "text": "sending application, a packet sequence number, and a timestamp so that the data in the RTP packet can\nbe synchronized with other RTP packets by the application layer software if needed.\nWith a name like Real-Time Transport Protocol, one would expect RTP to replace TCP and UDP at the\ntransport layer. It does not. Instead, RTP is combined with UDP. (If you read the previous paragraph\ncarefully, you noticed that RTP does not provide source and destination port addresses.) This means that\neach real-time packet is first created using RTP and then surrounded by a UDP datagram, before being\nhanded to the IP software at the network layer.\n5.4 ADDRESSING\nBefore you can send a message, you must know the destination address. It is extremely important to\nunderstand that each computer has several addresses, each used by a different layer. One address is used\nby the data link layer, another by the network layer, and still another by the application layer.\nWhen users work with application software, they typically use the application layer address. For example,\nin Chapter 2, we discussed application software that used Internet addresses (e.g., www.indiana.edu).\nThis is an application layer address (or a server name). When a user types an Internet address into a\nWeb browser, the request is passed to the network layer as part of an application layer packet formatted\nusing the HTTP protocol (Figure 2-11) (see Chapter 2).\nFIGURE 5-8 Types of addresses\nThe network layer software, in turn, uses a network layer address. The network layer protocol used on\nthe Internet is IP, so this Web address (www.indiana.edu) is translated into an IP address that is 4 bytes\nlong when using IPv4 (e.g., 129.79.127.4) (Figure 5-8). This process is similar to using a phone book to go", "source": "Page 159", "chapter_title": "Chapter 11"}
{"id": "ddc5138ec9d0-1", "text": "from someone\u2019s name to his or her phone number.\nThe network layer then determines the best route through the network to the final destination. Based on\nthis routing, the network layer identifies the data link layer address of the next computer to which the\nmessage should be sent. If the data link layer is running Ethernet, then the network layer IP address\nwould be translated into an Ethernet address. Chapter 3 shows that Ethernet addresses are 6 bytes in\nlength, so a possible address might be 00-0F-00-81-14-00 (Ethernet addresses are usually expressed in\nhexadecimal) (Figure 5-8). Data link layer addresses are needed only on multipoint circuits that have\nmore than one computer on them. For example, many WANs are built with point-to-point circuits that\nuse Point-to-Point Protocol (PPP) as the data link layer protocol. These networks do not have data link\nlayer addresses.\n5.4.1 Assigning Addresses\nIn general, the data link layer address is permanently encoded in each network card, which is why the data\nlink layer address is also commonly called the physical address or the media access control (MAC)\naddress. This address is part of the hardware (e.g., Ethernet card) and should never be changed.\nHardware manufacturers have an agreement that assigns each manufacturer a unique set of permitted\naddresses, so even if you buy hardware from different companies, it will never have the same address.\nWhenever you install a network card into a computer, it immediately has its own data link layer address\nthat uniquely identifies it from every other computer in the world.", "source": "Page 159", "chapter_title": "Chapter 11"}
{"id": "6084a322f845-0", "text": "Network layer addresses are generally assigned by software. Every network layer software package usually\nhas a configuration file that specifies the network layer address for that computer. Network managers can\nassign any network layer addresses they want. It is important to ensure that every computer on the same\nnetwork has a unique network layer address so that every network has a standards group that defines\nwhat network layer addresses can be used by each organization.\nApplication layer addresses (such as Internet domain names or Windows device names) are also assigned\nby a software configuration file. Virtually all servers have an application layer address, but most client\ncomputers do not. This is because it is important for users to easily access servers and the information\nthey contain, but there is usually little need for someone to access someone else\u2019s client computer. As with\nnetwork layer addresses, network managers can assign any application layer address they want, but a\nnetwork standards group must approve Internet domain names to ensure that no two computers on the\nInternet have the same name. Network layer addresses and Internet domain names go hand in hand, so\nthe same standards group usually assigns both (e.g., www.indiana.edu at the application layer means\n129.79.78.4 at the network layer). It is possible to have several Internet names for the same computer. For\nexample, one of the Web servers in the Kelley School of Business at Indiana University is called both\nwww.kelley.indiana.edu and www.kelley.iu.edu.\nMANAGEMENT FOCUS 5-1\nFinal Countdown for IPv4\nThe address space for IPv4 was depleted on September 24, 2015. There are no more IPv4 addresses\nleft to be assigned. The American Registry for Internet Numbers (ARIN), which is in charge of the\nIPv4 address space, is ready to help organizations that need IPv4 addresses. ARIN created a service", "source": "Page 160", "chapter_title": "Chapter 11"}
{"id": "b4e41edb1d1f-1", "text": "that allows organizations to transfer IPv4 addresses they don\u2019t need to another organization. If a\ntransfer is not available, organizations will be put on a waiting list. The reality, however, we have\nreached the inevitable end of IPv4, also called the \u201cIPcalypse\u201d by the supporters of IPv6, who can\u2019t\nwait for the world to convert to IPv6.\nSource: Adapted from American Registry for Internet Numbers. www.arin.net.\nInternet Addresses\nNo one is permitted to operate a computer on the Internet unless he or she uses approved addresses.\nICANN (Internet Corporation for Assigned Names and Numbers) is responsible for managing\nthe assignment of network layer addresses (i.e., IP addresses) and application layer addresses (e.g.,\nwww.indiana.edu). ICANN sets the rules by which new domain names (e.g., .com, .org, .ca, .uk) are\ncreated and IP address numbers are assigned to users. ICANN also directly manages a set of Internet\ndomains (e.g., .com, .org, .net) and authorizes private companies to become domain name registrars for\nthose domains. Once authorized, a registrar can approve requests for application layer addresses and\nassign IP numbers for those requests. This means that individuals and organizations wishing to register\nan Internet name can use any authorized registrar for the domain they choose, and different registrars are\npermitted to charge different fees for their registration services. Many registrars are authorized to issue\nnames and addresses in the ICANN managed domains, as well as domains in other countries (e.g., .ca, .uk,\n.au).\nSeveral application layer addresses and network layer addresses can be assigned at the same time. IP\naddresses are often assigned in groups so that one organization receives a set of numerically similar\naddresses for use on its computers. For example, Indiana University has been assigned the set of", "source": "Page 160", "chapter_title": "Chapter 11"}
{"id": "6181f43d2705-2", "text": "addresses for use on its computers. For example, Indiana University has been assigned the set of\napplication layer addresses that end in indiana.edu and iu.edu and the set of IP addresses in the 129.79.x.x\nrange (i.e., all IP addresses that start with the numbers 129.79).\nThe IP protocol defines the address space that can be used on the Internet. The address space is the total\nnumber of addresses available. In general, if a protocol uses N bits to define an address, the available\nspace is 2N (because each bit can be either 1 or 0). Specifically, IPv4 uses 32 bits (4 bytes) to define an\naddress, and therefore, the number of available addresses is 232 = 4,294, 967,296 or approximately 4.3", "source": "Page 160", "chapter_title": "Chapter 11"}
{"id": "cfb25227574a-0", "text": "billion.\nThese 4.3 billion addresses in the IPv4 address space are divided into Internet address classes.\nAlthough this terminology is considered to be old, you can still run into people who use it. Figure 5-7\nshows the address ranges for each class of addresses. There are three classes of addresses that can be\nassigned to organizations: Class A, Class B, and Class C. Addresses are assigned into a particular class by\nthe value of the first byte (the original standard used the term \u201coctet\u201d to mean a \u201cbyte,\u201d so you may see\ndocuments using the term \u201coctet\u201d). For example, Class A addresses can have any number between 1 and\n126 in the first byte.\nThe first byte can be any number from 0 to 255 (for an explanation, refer to Hands-On Activity 5C). Figure\n5-9 shows that there are some numbers in the first byte range that are not assigned to any address range.\nAn address starting with 0 is not allowed. The 127 address range is reserved for a computer to\ncommunicate with itself and is called the loopback. Loopback is used mostly by developers and system\nadministrators when testing software. Addresses starting from 224 are reserved addresses that should\nnot be used on IP networks. Addresses from 224 to 239 belong to Class D and are reserved for\nmulticasting, which is sending messages to a group of computers rather than to one computer (which is\nnormal) or every computer on a network (called broad-cast). Addresses from 240 to 254 belong to Class E\nand are reserved for experimental use. Some companies use the Class E addresses for multicasting\ninternal content in addition to the Class D addresses. Addresses starting with 255 are reserved for\nbroadcast messages (which are explained in more detail in the final section of this chapter).", "source": "Page 161", "chapter_title": "Chapter 11"}
{"id": "25cc7a1ce016-1", "text": "broadcast messages (which are explained in more detail in the final section of this chapter).\nFIGURE 5-9 IPv4 public address space\nWithin each class, there is a set of addresses that are labeled as private IPv4 address space (see Figure\n5-10). This address space can be used internally by organizations, but routers on the Internet do not route\npackets that use private addresses (they simply discard them). For this reason, private addresses are often\nused to increase security. An organization will assign private addresses to its computers so that hackers\ncan\u2019t send messages to them. However, these computers need to be able to send messages to other\ncomputers on the Internet. The organization has special devices (called NAT firewalls) that translate the\nprivate addresses on messages that these computers send into valid public addresses for use on the\nInternet. We talk more about NAT firewalls and the use of private addresses in Chapter 11. The computer\nyou\u2019re using right now probably has a private IP address (see Hands-On Activity 5A).\nFigure 5-8 also shows how the newer terminology classless addressing is used. Classless addressing\nuses a slash to indicate the address range (it\u2019s also called slash notation). For example, 128.192.1.0 is a\nClass B address, so the first 2 bytes (16 bits) are to be used for the network address and the next 2 bytes\n(third and fourth bytes) are allocated for host addresses. Using the slash notation, one would identify this\nnetwork as 128.192.1.0/16. However, a network administrator may decide that rather than allocating 16\nbits for the network, it would be more beneficial to allocate 24 bits, and the remaining 8 bits would be", "source": "Page 161", "chapter_title": "Chapter 11"}
{"id": "1d2aa945af75-2", "text": "used for clients. Therefore, the network would be identified as 128.192.1.0/24. We discuss more about bit\nallocation for a network and hosts when we discuss subnetting.\nOne of the problems with the current address system is that the Internet is quickly running out of\naddresses. Although the 4-byte address of IPv4 provides more than 4 billion possible addresses, the fact\nthat they are assigned in sets significantly limits the number of usable addresses. For example, the address\nrange owned by Indiana University includes about 65,000 addresses, but the university will probably not\nuse all of them.", "source": "Page 161", "chapter_title": "Chapter 11"}
{"id": "1a335bf1beb2-0", "text": "FIGURE 5-10 IPv4 private address space\nThe IP address shortage was one of the reasons behind the development of IPv6, discussed previously.\nOnce IPv6 is in wide use, the current Internet address system will be replaced by a totally new system\nbased on 16-byte addresses. Most experts expect that all the current 4-byte addresses will simply be\nassigned an arbitrary 12-byte prefix (e.g., all zeros) so that the holders of the current addresses can\ncontinue to use them.\nSubnets\nEach organization must assign the IP addresses it has received to specific computers on its networks. To\nmake the IP address assignment more functional, we use an addressing hierarchy. The first part of the\naddress defines the network, and the second part of the address defines a particular computer or host on\nthe network. However, it is not efficient to assign every computer to the same network. Rather,\nsubnetworks or subnets are designed on the network that subdivide the network into logical pieces. For\nexample, suppose that a university has just received a set of addresses starting with 128.192.x.x. It is\ncustomary to assign all the computers in the same LAN numbers that start with the same first three digits,\nso the business school LAN might be assigned 128.192.56.x, which means that all the computers in that\nLAN would have IP numbers starting with those numbers (e.g., 128.192.56.4, 128.192.56.5, and so on)\n(Figure 5-11). The subnet ID for this LAN then is 128.192.56. Two addresses on this subnet cannot be\nassigned as IP address to any computer. The first address is 128.192.56.0, and this is the network address.", "source": "Page 162", "chapter_title": "Chapter 11"}
{"id": "908564888d61-1", "text": "The second address is 128.192.56.255, which is the broadcast address. The computer science LAN might\nbe assigned 128.192.55.x, and similarly, all the other LANs at the university and the BN that connects\nthem would have a different set of numbers. Similar to the business school LAN, the computer science\nLAN would have a subnet ID 128.192.55. Thus, 128.192.55.0 and 128.192.55.255 cannot be assigned to any\ncomputer on this network because they are reserved for the network address and broadcast address.", "source": "Page 162", "chapter_title": "Chapter 11"}
{"id": "2b3079ac5212-0", "text": "FIGURE 5-11 Address subnets\nRouters connect two or more subnets so they have a separate address on each subnet. Without routers,\nthe two subnets would not be able to communicate. The routers in Figure 5-11, for example, have two\naddresses each because they connect two subnets and must have one address in each subnet.", "source": "Page 163", "chapter_title": "Chapter 11"}
{"id": "444529bf2c08-0", "text": "Although it is customary to use the first 3 bytes of the IP address to indicate different subnets, it is not\nrequired. Any portion of the IP address can be designated as a subnet by using a subnet mask. Every\ncomputer in a TCP/IP network is given a subnet mask to enable it to determine which computers are on\nthe same subnet (i.e., LAN) that it is on and which computers are outside of its subnet. Knowing whether\na computer is on your subnet is very important for message routing, as we shall see later in this chapter.\nFor example, a network could be configured so that the first 2 bytes indicated a subnet (e.g., 128.184.x.x),\nso all computers would be given a subnet mask giving the first 2 bytes as the subnet indicator. This would\nmean that a computer with an IP address of 128.184.22.33 would be on the same subnet as 128.184.78.90.\nIP addresses are binary numbers, so partial bytes can also be used as subnets. For example, we could\ncreate a subnet that has IP addresses between 128.184.55.1 and 128.184.55.127 and another subnet with\naddresses between 128.184.55.128 and 128.184.55.254.\nDynamic Addressing\nTo this point, we have said that every computer knows its network layer address from a configuration file\nthat is installed when the computer is first attached to the network. However, this leads to a major\nnetwork management problem. Any time a computer is moved or its network is assigned a new address,\nthe software on each individual computer must be updated. This is not difficult, but it is very time-\nconsuming because someone must go from office to office, editing files on each individual computer.", "source": "Page 164", "chapter_title": "Chapter 11"}
{"id": "7a1c176c5fc7-1", "text": "consuming because someone must go from office to office, editing files on each individual computer.\nThe easiest way around this is dynamic addressing. With this approach, a server is designated to\nsupply a network layer address to a computer each time the computer connects to the network. This is\ncommonly done for client computers but usually not for servers.\nTECHNICAL FOCUS 5-1\nSubnet Masks\nSubnet masks tell computers what part of an Internet Protocol (IP) address is to be used to\ndetermine whether a destination is on the same subnet or on a different subnet. A subnet mask is a\n4-byte binary number that has the same format as an IP address and is not routable on the network.\nA 1 in the subnet mask indicates that that position is used to indicate the subnet. A zero indicates\nthat it is not. Therefore, a mask can only contain a continuous stream of ones.\nA subnet mask of 255.255.255.0 means that the first 3 bytes indicate the subnet; all computers with\nthe same first 3 bytes in their IP addresses are on the same subnet. This is because 255 expressed in\nbinary is 11111111.\nIn contrast, a subnet mask of 255.255.0.0 indicates that the first 2 bytes refer to the same subnet.\nThings get more complicated when we use partial-byte subnet masks. For example, suppose that the\nsubnet mask was 255.255.255.128. In binary numbers, this is expressed as\n11111111.11111111.11111111.10000000\nThis means that the first 3 bytes plus the first bit in the fourth byte indicate the subnet address.\nSimilarly, a subnet mask of 255.255.254.0 would indicate the first 2 bytes plus the first 7 bits of the", "source": "Page 164", "chapter_title": "Chapter 11"}
{"id": "04c0c54afc59-2", "text": "third byte indicate the subnet address because, in binary numbers, this is\n11111111.11111111.11111110.00000000\nThe bits that are ones are called network bits because they indicate which part of an address is the\nnetwork or subnet part, whereas the bits that are zeros are called host bits because they indicate\nwhich part is unique to a specific computer or host.\nThe most common standard for dynamic addressing is the Dynamic Host Configuration Protocol\n(DHCP). DHCP does not provide a network layer address in a configuration file. Instead, there is a\nspecial software package installed on the client that instructs it to contact a DHCP server to obtain an", "source": "Page 164", "chapter_title": "Chapter 11"}
{"id": "9ca69383a6f0-0", "text": "address. In this case, when the computer is turned on and connects to the network, it first issues a\nbroadcast DHCP message that is directed to any DHCP server that can \u201chear\u201d the message. This message\nasks the server to assign the requesting computer a unique network layer address. The server runs a\ncorresponding DHCP software package that responds to these requests and sends a message back to the\nclient, giving it its network layer address (and its subnet mask).\nThe DHCP server can be configured to assign the same network layer address to the computer (based on\nits data link layer address) each time it requests an address, or it can lease the address to the computer by\npicking the \u201cnext available\u201d network layer address from a list of authorized addresses. Addresses can be\nleased for as long as the computer is connected to the network or for a specified time limit (e.g., 2 hours).\nWhen the lease expires, the client computer must contact the DHCP server to get a new address. Address\nleasing is commonly used by Internet Service Providers (ISPs) for dial-up users. ISPs have many more\nauthorized users than they have authorized network layer addresses because not all users can log in at the\nsame time. When a user logs in, his or her computer is assigned a temporary TCP/IP address that is\nreassigned to the next user when the first user hangs up.\nDynamic addressing greatly simplifies network management in non-dial-up networks as well. With\ndynamic addressing, address changes need to be made only to the DHCP server, not to each individual\ncomputer. The next time each computer connects to the network or whenever the address lease expires,\nthe computer automatically gets the new address.\n5.4.2 Address Resolution\nTo send a message, the sender must be able to translate the application layer address (or server name) of", "source": "Page 165", "chapter_title": "Chapter 11"}
{"id": "e1d29bc78aa7-1", "text": "the destination into a network layer address and in turn translate that into a data link layer address. This\nprocess is called address resolution. There are many different approaches to address resolution that\nranges from completely decentralized (each computer is responsible for knowing all addresses) to\ncompletely centralized (there is one computer that knows all addresses). TCP/IP uses two different\napproaches, one for resolving application layer addresses into IP addresses and a different one for\nresolving IP addresses into data link layer addresses.\nServer Name Resolution\nServer name resolution is the translation of application layer addresses into network layer addresses (e.g.,\ntranslating an Internet address such as www.yahoo.com into an IP address such as 204.71.200.74). This is\ndone using the Domain Name Service (DNS). Throughout the Internet, a series of computers called\nname servers provide DNS services. These name servers have address databases that store thousands of\nInternet addresses and their corresponding IP addresses. These name servers are, in effect, the \u201cdirectory\nassistance\u201d computers for the Internet. Anytime a computer does not know the IP number for a computer,\nit sends a message to the name server requesting the IP number.\nWhenever you register an Internet application layer address, you must inform the registrar of the IP\naddress of the name server that will provide DNS information for all addresses in that name range. For\nexample, because Indiana University owns the indiana.edu name, it can create any name it wants that\nends in that suffix (e.g., www.indiana.edu, www.kelley.indiana.edu, abc.indiana.edu). When it registers its\nname, it must also provide the IP address of the DNS server that it will use to provide the IP addresses for\nall the computers within this domain name range (i.e., everything ending in indiana.edu). Every\norganization that has many servers also has its own DNS server, but smaller organizations that have only", "source": "Page 165", "chapter_title": "Chapter 11"}
{"id": "1624b9a56476-2", "text": "organization that has many servers also has its own DNS server, but smaller organizations that have only\none or two servers often use a DNS server provided by their ISP. DNS servers are maintained by network\nmanagers, who update their address information as the network changes. DNS servers can also exchange\ninformation about new and changed addresses among themselves, a process called replication.\nWhen a computer needs to translate an application layer address into an IP address, it sends a special\nDNS request packet to its DNS server. This packet asks the DNS server to send to the requesting computer\nthe IP address that matches the Internet application layer address provided. If the DNS server has a\nmatching name in its database, it sends back a special DNS response packet with the correct IP address. If\nthat DNS server does not have that Internet address in its database, it will issue the same request to\nanother DNS server elsewhere on the Internet.\nFor example, if someone at the University of Toronto were to ask for a Web page on the server", "source": "Page 165", "chapter_title": "Chapter 11"}
{"id": "fcb93b8b2c27-0", "text": "(www.kelley.indiana.edu) at Indiana University, the software on the Toronto client computer would issue\na DNS request to the University of Toronto DNS server, called the resolving name server (Figure 5-12).\nThis DNS server probably would not know the IP address of our server, so it would send a DNS request to\none of the DNS root servers that it knows. The root server would respond to the resolving name server\nwith a DNS response that said \u201cI don\u2019t know the IP address you need, but ask this DNS server,\u201d and it\nwould include the IP address of the top-level domain (TLD) server for the requested website (in this\ncase, the .edu TLD server, because the destination website is in the .edu domain). The resolving name\nserver would then send a DNS request to the .edu TLD server. The .edu TLD domain server would\nrespond with a DNS response that tells the resolving name server to ask the authoritative name\nserver for indiana.edu and provides its IP address. The resolving name server would send a DNS request\nto the authoritative name server for indiana.edu. The authoritative name server would then respond to the\nresolving name server with the needed IP address, and the resolving name server would send a DNS\nresponse to the client computer with the IP address.\nFIGURE 5-12 How the DNS system works?\nThis is why it sometimes takes longer to access certain sites. Most DNS servers know only the names and\nIP addresses for the computers in their part of the network. Some store frequently used addresses (e.g.,\nwww.yahoo.com). If you try to access a computer that is far away, it may take a while before your\ncomputer receives a response from the resolving name server.", "source": "Page 166", "chapter_title": "Chapter 11"}
{"id": "9806b6361c85-0", "text": "Once your application layer software receives an IP address, it is stored on your computer in a DNS cache.\nThis way, if you ever need to access the same computer again, your computer does not need to contact its\nresolving name server. The DNS cache is routinely deleted whenever you turn off your computer.\nData Link Layer Address Resolution\nTo actually send a message on a multipoint circuit, the network layer software must know the data link\nlayer address of the receiving computer. The final destination may be far away (e.g., sending from Toronto\nto Indiana). In this case, the network layer would route the message by selecting a path through the\nnetwork that would ultimately lead to the destination. (Routing is discussed in the next section.) The first\nstep on this route would be to send the message to its router.\nTo send a message to another computer in its subnet, a computer must know the correct data link layer\naddress. In this case, the TCP/IP software sends a broadcast message to all computers in its subnet. A\nbroadcast message, as the name suggests, is received and processed by all computers in the same LAN\n(which is usually designed to match the IP subnet). The message is a specially formatted request using\nAddress Resolution Protocol (ARP) that says, \u201cWhoever is IP address xxx.xxx.xxx.xxx, please send\nme your data link layer address.\u201d The software in the computer with that IP address then sends an ARP\nresponse with its data link layer address. The sender transmits its message using that data link layer\naddress. The sending computer also stores the data link layer address in its address table for future use.\n5.5 ROUTING\nRouting is the process of determining the route or path through the network that a message will travel\nfrom the sending computer to the receiving computer. In some networks (e.g., the Internet), there are", "source": "Page 167", "chapter_title": "Chapter 11"}
{"id": "5ef227f07f63-1", "text": "many possible routes from one computer to another. In other networks (e.g., internal company networks),\nthere may only be one logical route from one computer to another. In either case, some device has to route\nmessages through the network.\nRouting is done by special devices called routers. Routers are usually found at the edge of subnets\nbecause they are the devices that connect subnets together and enable messages to flow from one subnet\nto another as the messages move through the network from sender to receiver. Figure 5-13 shows a small\nnetwork with two routers, R1 and R2. This network has five subnets, plus a connection to the Internet.\nEach subnet has its own range of addresses (e.g., 10.10.51.x), and each router has its IP address (e.g.,\n10.10.1.1). The first router (R1) has four connections, one to the Internet, one to router R2, and one to\neach of two subnets. Each connection, called an interface, is numbered from 0 to 3. The second router\n(R2) also has four interfaces, one that connects to R1 and three that connect to other subnets.\nEvery router has a routing table that specifies how messages will travel through the network. In its\nsimplest form, the routing table is a two-column table. The first column lists every network or computer\nthat the router knows about, and the second column lists the interface that connects to it. Figure 5-14\nshows the routing tables that might be used by routers in Figure 5-13. The first entry in R1\u2019s routing table\nsays that any message with an IP address in the range from 10.10.51.0 to 10.10.51.255 should be sent out\non interface 1.", "source": "Page 167", "chapter_title": "Chapter 11"}
{"id": "90e9f30c59de-2", "text": "on interface 1.\nA router uses its routing table to decide where to send the messages it receives. Suppose that a computer\nin the 10.10.43.x subnet sends an HTTP request for a Web page that is located on the company\u2019s Web\nserver, which is in the 10.10.20.x subnet (let\u2019s say the Web server has an IP address of 10.10.20.10). The\ncomputer would send the message to its router, R2. R2 would look at the IP address on the IP packet and\nsearch its routing table for a matching address. It would search through the table, from top to bottom,\nuntil it reached the third entry, which is a range of addresses that contains the Web server\u2019s address\n(10.10.20.10). The matching interface is number 2, so R2 would transmit the message on this interface.", "source": "Page 167", "chapter_title": "Chapter 11"}
{"id": "5714bb6dcfc5-0", "text": "FIGURE 5-13 A small corporate network\nFIGURE 5-14 Sample routing tables\nThe process would be similar if the same computer were to request a page somewhere on the Internet\n(e.g., www.yahoo.com). The computer would send the message to its router, R2. R2 would look at the IP\naddress on the IP packet (www.yahoo.com has an IP address of 69.147.125.65) and search its routing table\nfor a matching entry. It would look at the first four entries and not find a match. It would reach the final\nentry that says to send a message with any other address on interface 0, so R2 would transmit this\nmessage on interface 0 to router R1.", "source": "Page 168", "chapter_title": "Chapter 11"}
{"id": "0ff685ffcd72-0", "text": "The same process would be performed by R1. It would search through its routing table for an address that\nmatched 69.147.125.65 and not find it. When it reaches the final entry, R1 knows to send this message on\ninterface 0 into the Internet.\n5.5.1 Types of Routing\nThere are three fundamental approaches to routing: centralized routing, static routing, and dynamic\nrouting. As you will see in the TCP/IP Example section later in this chapter, the Internet uses all three\napproaches.\nCentralized Routing\nWith centralized routing, all routing decisions are made by one central computer or router. Centralized\nrouting is commonly used in host-based networks (see Chapter 2), and in this case, routing decisions are\nrather simple. All computers are connected to the central computer, so any message that needs to be\nrouted is simply sent to the central computer, which in turn retransmits the message on the appropriate\ncircuit to the destination.\nStatic Routing\nStatic routing is decentralized, which means that all computers or routers in the network make their\nown routing decisions following a formal routing protocol. In WANs, the routing table for each computer\nis developed by its individual network manager (although network managers often share information). In\nLANs or BNs, the routing tables used by all computers on the network are usually developed by one\nindividual or a committee. Most decentralized routing protocols are self-adjusting, meaning that they can\nautomatically adapt to changes in the network configuration (e.g., adding and deleting computers and\ncircuits).\nWith static routing, routing decisions are made in a fixed manner by individual computers or routers. The\nrouting table is developed by the network manager, and it changes only when computers are added to or\nremoved from the network. For example, if the computer recognizes that a circuit is broken or unusable", "source": "Page 169", "chapter_title": "Chapter 11"}
{"id": "7857923e8dc0-1", "text": "(e.g., after the data link layer retry limit has been exceeded without receiving an acknowledgment), the\ncomputer will update the routing table to indicate the failed circuit. If an alternate route is available, it will\nbe used for all subsequent messages. Otherwise, messages will be stored until the circuit is repaired. Static\nrouting is commonly used in networks that have few routing options that seldom change.\nDynamic Routing\nWith dynamic routing (or adaptive routing), routing decisions are made in a decentralized manner by\nindividual computers. This approach is used when there are multiple routes through a network, and it is\nimportant to select the best route. Dynamic routing attempts to improve network performance by routing\nmessages over the fastest possible route, away from busy circuits and busy computers. An initial routing\ntable is developed by the network manager but is continuously updated by the computers themselves to\nreflect changing network conditions.\nWith distance vector dynamic routing, routers count the number of hops along a route. A hop is one\ncircuit, so that router R1 in Figure 5-13 would know it could reach a computer in the 10.10.52.X subnet in\none hop, and a computer in the 10.10.43.X subnet in two hops, by going through R2. With this approach,\ncomputers periodically (usually every 1\u20132 minutes) exchange information on the hop count and\nsometimes on the relative speed of the circuits in route and how busy they are with their neighbors.\nWith link state dynamic routing, computers or routers track the number of hops in the route, the\nspeed of the circuits in each route, and how busy each route is. In other words, rather than knowing just a\nroute\u2019s distance, link state routing tries to determine how fast each possible route is. Each computer or\nrouter periodically (usually every 30 seconds or when a major change occurs) exchanges this information", "source": "Page 169", "chapter_title": "Chapter 11"}
{"id": "f893c03d272f-2", "text": "router periodically (usually every 30 seconds or when a major change occurs) exchanges this information\nwith other computers or routers in the network (not just their neighbors) so that each computer or router\nhas the most accurate information possible. Link state protocols are preferred to distance vector protocols\nin large networks because they spread more reliable routing information throughout the entire network\nwhen major changes occur in the network. They are said to converge more quickly.\nThere are two drawbacks to dynamic routing. First, it requires more processing by each computer or", "source": "Page 169", "chapter_title": "Chapter 11"}
{"id": "be2700408abf-0", "text": "router in the network than does centralized routing or static routing. Computing resources are devoted to\nadjusting routing tables rather than to sending messages, which can slow down the network. Second, the\ntransmission of routing information \u201cwastes\u201d network capacity. Some dynamic routing protocols transmit\nstatus information very frequently, which can significantly reduce performance.\n5.5.2 Routing Protocols\nA routing protocol is a protocol that is used to exchange information among computers to enable them to\nbuild and maintain their routing tables. You can think of a routing protocol as the language that is used to\nbuild the routing tables in Figure 5-14. When new paths are added or paths are broken and cannot be\nused, messages are sent among computers using the routing protocol.\nIt can be useful to know all the possible routes to a given destination. However, as a network gets quite\nlarge, knowing all possible routes becomes impractical; there are simply too many possible routes. Even at\nsome modest number of computers, dynamic routing protocols become impractical because of the amount\nof network traffic they generate. For this reason, networks are often subdivided into autonomous systems\nof networks.\nAn autonomous system is simply a network operated by one organization, such as IBM or Indiana\nUniversity, or an organization that runs one part of the Internet. Remember that we said that the Internet\nwas simply a network of networks. Each part of the Internet is run by a separate organization such as\nAT&T, MCI, and so on. Each part of the Internet or each large organizational network connected to the\nInternet can be a separate autonomous system.\nThe computers within each autonomous system know about the other computers in that system and\nusually exchange routing information because the number of computers is kept manageable. If an\nautonomous system grows too large, it can be split into smaller parts. The routing protocols used inside an\nautonomous system are called interior routing protocols.", "source": "Page 170", "chapter_title": "Chapter 11"}
{"id": "6894213acf38-1", "text": "autonomous system are called interior routing protocols.\nProtocols used between autonomous systems are called exterior routing protocols. Although interior\nrouting protocols are usually designed to provide detailed routing information about all or most\ncomputers inside the autonomous systems, exterior protocols are designed to be more careful in the\ninformation they provide. Usually, exterior protocols provide information about only the preferred or the\nbest routes rather than all possible routes.\nTECHNICAL FOCUS 5-2\nRouting on the Internet\nThe Internet is a network of autonomous system networks. Each autonomous system operates its\nown interior routing protocol while using Border Gateway Protocol (BGP) as the exterior routing\nprotocol to exchange information with the other autonomous systems on the Internet. Although\nthere are several interior routing protocols, Open Shortest Path First (OSPF) is the preferred\nprotocol and most organizations that run the autonomous systems forming large parts of the\nInternet use OSPF.\nFigure 5-15 shows how a small part of the Internet might operate. In this example, there are six\nautonomous systems (e.g., Sprint, AT&T), three of which we have shown in more detail. Each\nautonomous system has a border router that connects it to the adjacent autonomous systems and\nexchanges route information via BGP. In this example, autonomous system A is connected to\nautonomous system B, which in turn is connected to the autonomous system C. A is also connected\nto C via a route through systems D and E. If someone in A wants to send a message to someone in C,\nthe message should be routed through B because it is the fastest route. The autonomous systems\nmust share route information via BGP so that the border routers in each system know what routes\nare preferred. In this case, B would inform A that there is a route through it to C (and a route to E),", "source": "Page 170", "chapter_title": "Chapter 11"}
{"id": "bf1f6ad12912-2", "text": "and D would inform A that it has a route to E, but D would not inform A that there is a route through\nit to C. The border router in A would then have to decide which route to use to reach E.\nEach autonomous system can use a different interior routing protocol. In this example, B is a rather", "source": "Page 170", "chapter_title": "Chapter 11"}
{"id": "c5455b07f7c8-0", "text": "simple network with only a few devices and routes, and it uses RIP, a simpler protocol in which all\nrouters broadcast route information to their neighbors every minute or so. A and C are more\ncomplex networks and use OSPF. Most organizations that use OSPF create a special router called a\ndesignated router to manage the routing information. Every 15 minutes or so, each router sends\nits routing information to the designated router, which then broadcasts the revised routing table\ninformation to all other routers. If no designated router is used, then every router would have to\nbroadcast its routing information to all other routers, which would result in a very large number of\nmessages. In the case of autonomous system C, which has seven routers, this would require 42\nseparate messages (seven routers each sending to six others). By using a designated router, we now\nhave only 12 separate messages (the six other routers sending to the designated router, and the\ndesignated router sending the complete set of revised information back to the other six).", "source": "Page 171", "chapter_title": "Chapter 11"}
{"id": "1b03d8ff2daa-0", "text": "FIGURE 5-15 Routing on the Internet with Border Gateway Protocol (BGP), Open Shortest Path First\n(OSPF), and Routing Information Protocol (RIP)\nThere are many different protocols that are used to exchange routing information. Five are commonly\nused on the Internet: Border Gateway Protocol (BGP), Internet Control Message Protocol (ICMP),", "source": "Page 172", "chapter_title": "Chapter 11"}
{"id": "0a57b654d712-0", "text": "Routing Information Protocol (RIP), Intermediate System to Intermediate System (IS-IS), Open Shortest\nPath First (OSPF), and Enhanced Interior Gateway Routing Protocol (EIGRP).\nBorder Gateway Protocol (BGP) is a dynamic distance vector exterior routing protocol used on the\nInternet to exchange routing information between autonomous systems\u2014that is, large sections of the\nInternet. Although BGP is the preferred routing protocol between Internet sections, it is seldom used\ninside companies because it is large, complex, and often hard to administer.\nInternet Control Message Protocol (ICMP) is the simplest interior routing protocol on the Internet.\nICMP is simply an error-reporting protocol that enables computers to report routing errors to message\nsenders. ICMP also has a very limited ability to update routing tables.\nRouting Information Protocol (RIP) is a dynamic distance vector interior routing protocol that is\ncommonly used in smaller networks, such as those operated by one organization. The network manager\nuses RIP to develop the routing table. When new computers are added, RIP simply counts the number of\ncomputers in the possible routes to the destination and selects the route with the least number.\nComputers using RIP send broadcast messages every minute or so (the timing is set by the network\nmanager) announcing their routing status to all other computers. RIP is used by both TCP/IP and\nIPX/SPX.\nIntermediate System to Intermediate System (IS-IS) is a link state interior routing protocol that is\ncommonly used in large networks. IS-IS is an ISO protocol that has been added to many TCP/IP\nnetworks.\nOpen Shortest Path First (OSPF) is a dynamic hybrid interior routing protocol that is commonly used\non the Internet. It uses the number of computers in a route as well as network traffic and error rates to\nselect the best route. OSPF is more efficient than RIP because it normally doesn\u2019t use broadcast messages.", "source": "Page 173", "chapter_title": "Chapter 11"}
{"id": "98e9193020b0-1", "text": "Instead, it selectively sends status update messages directly to selected computers or routers. OSPF is the\npreferred interior routing protocol used by TCP/IP.\nEnhanced Interior Gateway Routing Protocol (EIGRP) is a dynamic hybrid interior routing\nprotocol developed by Cisco and is commonly used inside organizations. Hybrid means that it has some\nfeatures that act like distance vector protocols and some other features that act like link state protocols. As\nyou might expect, EIGRP is an improved version of the Interior Gateway Routing Protocol (IGRP).\nEIGRP records information about a route\u2019s transmission capacity, delay, reliability, and load. EIGRP is\nunique in that computers or routers store their own routing tables as well as the routing tables for all of\ntheir neighbors so they have a more accurate understanding of the network.\n5.5.3 Multicasting\nThe most common type of message in a network is the transmission between two computers. One\ncomputer sends a message to another computer (e.g., a client requesting a Web page). This is called a\nunicast message. Earlier in the chapter, we introduced the concept of a broadcast message that is sent\nto all computers on a specific LAN or subnet. The third type of message called a multicast message is\nused to send the same message to a group of computers.\nMANAGEMENT FOCUS 5-2\nCaptain D\u2019s Gets Cooking with Multicast\nCaptain D\u2019s has more than 500 company owned and franchised fast-food restaurants across North\nAmerica. Each restaurant has a small low-speed satellite link that can send and receive data.\nCaptain D\u2019s used to send its monthly software updates to each of its restaurants one at a time, which\nmeant transferring each file 500 times, once to each restaurant. You don\u2019t have to be a network\nwizard to realize that this is slow and redundant.", "source": "Page 173", "chapter_title": "Chapter 11"}
{"id": "6ad778264f35-2", "text": "wizard to realize that this is slow and redundant.\nCaptain D\u2019s now uses multicasting to send monthly software updates to all its restaurants at once.\nWhat once took hours is now accomplished in minutes.", "source": "Page 173", "chapter_title": "Chapter 11"}
{"id": "ec0f1fca0bb8-0", "text": "Multicasting also enables Captain D\u2019s to send large human resource file updates each week to all\nrestaurants and to transmit computer-based training videos to all restaurants each quarter. The\ntraining videos range in size from 500 to 1,000 megabytes, so without multicasting, it would be\nimpossible to use the satellite network to transmit the videos.\nSource: Adapted from \u201cCaptain D\u2019s Gets Cooking with Multicast from XcelleNet,\u201d\nwww.xcellenet.com.\nConsider a videoconferencing situation in which four people want to participate in the same conference.\nEach computer could send the same voice and video data from its camera to the computers of each of the\nother three participants using unicasts. In this case, each computer would send three identical messages,\neach addressed to the three different computers. This would work but would require a lot of network\ncapacity. Alternatively, each computer could send one broadcast message. This would reduce network\ntraffic (because each computer would send only one message), but every computer on the network would\nprocess it, distracting them from other tasks. Broadcast messages usually are transmitted only within the\nsame LAN or subnet, so this would not work if one of the computers were outside the subnet.\nThe solution is multicast messaging. Computers wishing to participate in a multicast send a message to\nthe sending computer or some other computer performing routing along the way using a special type of\npacket called Internet Group Management Protocol (IGMP). Each multicast group is assigned a\nspecial IP address to identify the group. Any computer performing routing knows to route all multicast\nmessages with this IP address onto the subnet that contains the requesting computer. The routing\ncomputer sets the data link layer address on multicast messages to a matching multicast data link layer\naddress. Each requesting computer must inform its data link layer software to process incoming messages", "source": "Page 174", "chapter_title": "Chapter 11"}
{"id": "1b0f384d7abc-1", "text": "address. Each requesting computer must inform its data link layer software to process incoming messages\nwith this multicast data link layer address. When the multicast session ends (e.g., the videoconference is\nover), the client computer sends another IGMP message to the organizing computer or the computer\nperforming routing to remove it from the multicast group.\n5.5.4 The Anatomy of a Router\nThere is a huge array of software and hardware that makes the Internet work, but the one indispensable\ndevice is the router. The router has three main functions: (1) it determines a path for a packet to travel\nover, (2) it transmits the packet across the path, and (3) it supports communication between a wide\nvariety of devices and protocols. Now we will look inside a router to see how these three functions are\nsupported by hardware and software.\nRouters are essentially special-purpose computers that consist of a CPU (central processing unit),\nmemory (both volatile and nonvolatile), and ports or interfaces that connect to them to the network\nand/or other devices so that a network administrator can communicate with them. What differentiates\nrouters from computers that we use in our everyday lives is that they are diskless and they don\u2019t come\nwith a monitor, keyboard, and mouse. They don\u2019t have these because they were designed to move data\nrather than display it.\nThere are three ways that a network manager can connect to a router and configure and maintain it: (1)\nconsole port, (2) network interface port, and (3) auxiliary port (see Figure 5-16). When the router is\nturned on for the very first time, it does not have an IP address assigned, so it cannot communicate on the\nnetwork. Because of this, the console port, also called the management port, is used to configure it. A", "source": "Page 174", "chapter_title": "Chapter 11"}
{"id": "03f96fecd526-2", "text": "network manager would use a blue rollover cable (not the Ethernet cable) to connect the router\u2019s console\nport to a computer that has terminal emulation software on it. The network manager would use this\nsoftware to communicate with the router and perform the basic setup (e.g., IP address assignment,\nrouting protocol selection). Once the basic setup is done, the network manager can log in to the router\nfrom any computer using the network interface using TCP/IP and Telnet with Secure Shell (SSH).\nAlthough routers come with an auxiliary port that allows an administrator to log via a direct,\nnonnetwork connection (e.g., using modems), this connection is rarely used today.\nA router, just like a computer, must have an operating system so that it can be configured. The operating\nsystem that is used in about 90% of routers is the Cisco Internetwork Operating Systems (IOS),\nalthough other operating systems exist as well. IOS uses a command line interface rather than a graphical\nuser interface. The network manager uses IOS commands to create a configuration file (also called a", "source": "Page 174", "chapter_title": "Chapter 11"}
{"id": "737674c8b1cb-0", "text": "config file) that defines how the router will operate. The config file can contain the type of routing protocol\nto be used, the interfaces that are active/enabled and those that are down, and what type of encryption is\nused. The config file is central to a router\u2019s operation, and the IOS refers to it hundreds of times per\nsecond to tell the router how to do its job.\nFIGURE 5-16 Anatomy of a router\nThe other important file is the Access Control List (ACL), which plays an important role in network\nsecurity. The ACL defines what types of packets should be routed and what types of packets should be\ndiscarded. The ACL is discussed in more detail in Chapter 10 on security.\n5.6 TCP/IP EXAMPLE", "source": "Page 175", "chapter_title": "Chapter 11"}
{"id": "1d7d20ba5001-0", "text": "This chapter has discussed the functions of the transport and network layers: linking to the application\nlayer, segmenting, session management, addressing, and routing. In this section, we tie all of these\nconcepts together to take a closer look at how these functions actually work using TCP/IP.\nWhen a computer is installed on a TCP/IP network (or dials into a TCP/IP network), it must be given four\npieces of the network layer addressing and routing information before it can operate. This information\ncan be provided by a configuration file or via a DHCP server. The information is\n1. Its IP address\n2. A subnet mask, so it can determine what addresses are part of its subnet\nFIGURE 5-17 Example Transmission Control Protocol/Internet Protocol (TCP/IP) network\n3. The IP address of a DNS server, so it can translate application layer addresses into IP addresses\n4. The IP address of an IP gateway (commonly called a router) leading outside of its subnet, so it can\nroute messages addressed to computers outside of its subnet (this presumes the computer is using\nstatic routing and there is only one connection from it to the outside world through which all\nmessages must flow; if it used dynamic routing, some routing software would be needed instead)\nThese four pieces of information are the minimum required. A server would also need to know its\napplication layer address.\nIn this section, we use the simple network shown in Figure 5-17 to illustrate how TCP/IP works. This\nfigure shows an organization that has three LANs connected by a BN. The BN also has a connection to the\nInternet. Each building is configured as a separate subnet. For example, Building A has the 128.192.98.x\nsubnet, whereas Building B has the 128.192.95.x subnet. The data center has the 128.192.50.x subnet. The", "source": "Page 176", "chapter_title": "Chapter 11"}
{"id": "e4831386c4cf-1", "text": "BN is its own subnet: 128.192.254.x. Each building is connected to the BN via a router that has two IP\naddresses and two data link layer addresses, one for the connection into the building and one for the\nconnection onto the BN. The organization has a couple Web servers, one DNS server, and one Mail server\nlocated in the data center. All networks use Ethernet as the data link layer and only focus on Web requests\nat the application layer.\nIn the next sections, we describe how messages are sent through the network. For the sake of simplicity,\nwe initially ignore the need to establish and close TCP connections. Once you understand the basic\nconcepts, we will then add these in to complete the example.", "source": "Page 176", "chapter_title": "Chapter 11"}
{"id": "a0b84e8ab84e-0", "text": "TECHNICAL FOCUS 5-3\nFinding Your Computer\u2019s TCP/IP Settings\nIf your computer can access the Internet, it must use TCP/IP. In Windows, you can find out your\nTCP/IP settings by looking at their properties. Click on the Start button and then select Control\nPanel and then select Network Connections. Double click on your Local Area Connection and then\nclick the Support tab.\nThis will show you your computer\u2019s IP address, subnet mask, and gateway, and whether the IP\naddress is assigned by a DHCP server. Figure 5-18 shows this information for one of our computers.\nIf you would like more information, you can click on the Details button. This second window shows\nthe same information, plus the computer\u2019s Ethernet address (called the physical address), as well as\ninformation about the DHCP lease and the DNS servers available.\nTry this on your computer. If you have your own home network with your own router, there is a\nchance that your computer has an IP address very similar to ours or someone else\u2019s in your class\u2014or\nthe same address, in fact. How can two computers have the same IP address? Well, they can\u2019t. This is\na security technique called network address translation in which one set of \u201cprivate\u201d IP addresses is\nused inside a network and a different set of \u201cpublic\u201d IP addresses is used by the router when it sends\nthe messages onto the Internet. Network address translation is described in detail in Chapter 11.\n5.6.1 Known Addresses\nSuppose that a client computer in Building A (e.g., 128.192.98.130) wanted to get a Web page from a Web\nserver A located in the data center (www2.anyorg.com). We will assume that this computer knows the\nnetwork layer and data link layer addresses of the Web server 1 (www1.anyorg.com) in the data center", "source": "Page 177", "chapter_title": "Chapter 11"}
{"id": "9ebd8dbcd09b-1", "text": "(e.g., it has previously requested pages from this server, so the addresses are stored in appropriate tables\nin the memory of the computer). Because the computer knows the IP address of the server, it uses its IP\naddress, not its application layer address.\nFIGURE 5-18 TCP/IP configuration information", "source": "Page 177", "chapter_title": "Chapter 11"}
{"id": "1bf6e0b5598e-0", "text": "FIGURE 5-19 Packet nesting. HTTP = Hypertext Transfer Protocol; IP = Internet Protocol; TCP =\nTransmission Control Protocol\nIn this case, the application layer software would pass an HTTP packet to the transport layer software\n(TCP) with the Internet address of the destination www1.anyorg.com: 128.192.50.2. The transport layer\nsoftware (TCP) would make sure that the request fits in one segment and hands it to the network layer.\nThe network layer software (IP) would then check the subnet mask and would recognize that the Web\nserver is located outside of its subnet. Any messages going outside the subnet must be sent to the router\n(128.192.98.1), whose job it is to process the message and send the message on its way into the outside\nnetwork. The network layer software would check its address table and find the Ethernet address for the\nrouter. It would, therefore, set the data link layer address to the router\u2019s Ethernet address on this subnet\n(00-0C-00-33-3A-0B) and pass the IP packet to the data link layer for transmission. The data link layer\nwould surround the frame with an Ethernet frame and transmit it over the physical layer to the Web\nserver (Figure 5-19).\nThe router would receive the message and its data link layer would perform error checking before passing\nthe packet to the network layer software (IP). The network layer software would read the IP address to\ndetermine the final destination. The router would recognize that this address (128.192.50.2) needed to be\nsent to the 128.192.50.x subnet. It knows that the router for this subnet is 128.192.254.98. It would pass", "source": "Page 178", "chapter_title": "Chapter 11"}
{"id": "e39d357ee15e-1", "text": "the packet back to its data link layer, giving the Ethernet address of the router (00-0C-00-33-3A-DA).\nThis router in the data center would receive the message (do error checking, etc.) and read the IP address\nto determine the final destination. The router would recognize that this address (128.192.50.2) was inside\nits 128.192.50.x subnet and would search its data link layer address table for this computer. It would then\npass the packet to the data link layer along with the Ethernet address (00-0C-00-33-3A-1C) for\ntransmission.\nThe www1.anyorg.com Web server would receive the message and process it. This would result in a series\nof TCP/IP packets addressed to the requesting client (128.192.98.130). These would make their way\nthrough the network in reverse order. The Web server would recognize that this IP address is outside its\nsubnet and would send the message to the 128.192.50.1 router using its Ethernet address (00-0C-00-33-\n3A-DC). This router would then send the message to the router for the 128.192.98.x subnet\n(128.192.254.98) using its Ethernet address (00-0C-00-33-3A-BB). This router would, in turn, send the\nmessage back to the client (128.192.98.130) using its Ethernet address (00-0C-00-33-3A-A3).\nThis process would work in the same way for Web servers located outside the organization on the\nInternet. In this case, the message would go from the client to the 128.192.98.1 router, which would send", "source": "Page 178", "chapter_title": "Chapter 11"}
{"id": "47ec69e330bb-2", "text": "it to the Internet router (128.192.254.99), which would send it to its Internet connection. The message\nwould be routed through the Internet, from router to router, until it reached its destination. Then the\nprocess would work in reverse to return the requested page.\n5.6.2 Unknown Addresses\nSuppose that the client computer in Building A (128.192.98.130) wants to retrieve a Web page from the\nwww1.anyorg.com Web server but does not know the IP address of the Web server. For simplicity, we will\nstart by assuming that the client knows the data link layer address of its subnet router, but after you read\nthrough this example, you will realize that obtaining a data link layer address is straightforward.\nThe Web browser realizes that it does not know the IP address after searching its IP address table and not\nfinding a matching entry. Therefore, it issues a DNS request to the name server (128.192.50.4). The DNS", "source": "Page 178", "chapter_title": "Chapter 11"}
{"id": "085da66cb51a-0", "text": "request is passed to the transport layer (TCP), which attaches a UDP datagram and hands the message to\nthe network layer.\nUsing its subnet mask, the network layer (IP) will recognize that the DNS server is outside of its subnet. It\nwill attach an IP packet and set the data link layer address to its router\u2019s address.\nThe router will process the message and recognize that to reach the 128.192.50.4 IP address, it must send\nthe packet to the data center router, 128.192.254.96 and does this by using this router\u2019s MAC address (00-\n0-00-33-3A-DA). When the data center router receives this packet, it will realize that it has a direct\nconnection to the network the DNS server is on and will transmit the packet using the DNS server\u2019s\nEthernet address (00-0C-00-CC-3A-B1).\nThe name server will process the DNS request and send the matching IP address back to the client via the\n128.198.98.x subnet router. The IP address for the desired computer makes its way back to the application\nlayer software, which stores it in its IP table.\nThe application layer then issues the HTTP request using the IP address for the Web server (128.192.50.2)\nand passes it to the transport layer, which in turn passes it to the network layer. The network layer uses its\nsubnet mask and recognizes that this computer is not on its subnet. Therefore, it will route the packet to\nits default gateway, 128.192.98.1, which will then send the HTTP request to the data center\u2019s router,\n128.192.254.96, which will deliver the HTTP request to the Web server 1.\nThis process works the same for a Web server outside the subnet, whether in the same organization or", "source": "Page 179", "chapter_title": "Chapter 11"}
{"id": "8234f7756f14-1", "text": "This process works the same for a Web server outside the subnet, whether in the same organization or\nanywhere on the Internet. If the Web server is far away (e.g., Australia), the process will likely involve\nsearching more than one name server, but it is still the same process.\nWhat would happen if the client in building A (128.192.98.130) did not know its router\u2019s Ethernet\naddress, which it needs to send the message to the router? It would broadcast an ARP request to all\ncomputers on its subnet, requesting that the computer whose IP address is 128.192.98.1 respond with its\nEthernet address.\nThis request is processed by all computers on the subnet, but only the router responds with an ARP packet\ngiving its Ethernet address. The network layer software on the client stores this address in its data link\nlayer address table (called ARP cache). Then the client computer could send the message.\nThis same ARP request/response process can occur at any point as a message moves through the network.\nFor example, suppose that the router in the data center (128.192.254.96) did not know the Ethernet\naddress of the DNS server (128.192.50.4). The DNS request would flow through the network in exactly the\nsame way as described earlier (because no computer knows whether the router knows or doesn\u2019t know the\nEthernet address) until the DNS request arrived at the data center router. This router would try to address\nthe message to the DNS server and would realize that it did not have the server\u2019s Ethernet address, so it\nwould issue an ARP request. The DNS server would respond with an ARP response containing its\nEthernet address, and the router would put that address on the message and send it to the server.\n5.6.3 TCP Connections", "source": "Page 179", "chapter_title": "Chapter 11"}
{"id": "5b5cb8560154-2", "text": "5.6.3 TCP Connections\nWhenever a computer transmits data to another computer, it must choose whether to use a connection-\noriented service via TCP or a connectionless service via UDP. Most application layer software such as Web\nbrowsers (HTTP), email (SMTP), FTP, and Telnet use connection-oriented services. This means that\nbefore the first packet is sent, the transport layer first sends a SYN segment to establish a session (also\nknown as the three-way handshake). Once the session is established, then the data packets begin to flow.\nOnce the data are finished, the session is closed with a FIN segment (also known as the four-way\nhandshake).\nIn the preceding examples, this means that the first packet sent is really an SYN segment, followed by a\nresponse from the receiver accepting the connection, and then the packets as described earlier. There is\nnothing magical about the SYN and FIN segments; they are addressed and routed in the same manner as\nany other packets. But they do add to the complexity and length of the example.\nA special word is needed about HTTP packets. When HTTP was first developed, Web browsers opened a\nseparate TCP session for each HTTP request. That is, when they requested a page, they would open a\nsession, send the single packet requesting the Web page, and close the session at their end. The Web", "source": "Page 179", "chapter_title": "Chapter 11"}
{"id": "f028330bccd5-0", "text": "server would open a session, send as many packets as needed to transmit the requested page, and then\nclose the session. If the page included graphic images, the Web browser would open and close a separate\nsession for each request. This requirement to open and close sessions for each request was time-\nconsuming and not really necessary. With the newest version of HTTP, Web browsers open one session\nwhen they first issue an HTTP request and leave that session open for all subsequent HTTP requests to\nthe same server.\n5.6.4 TCP/IP and Network Layers\nIn closing this chapter, we want to return to the layers in the network model and take another look at how\nmessages flow through the layers. Figure 5-20 shows how a Web request message from a client computer\nin Building A would flow through the network layers in the different computers and devices on its way to\nthe Web server (www1.anyorg.com, 128.192.50.2) in the Data Center.\nFIGURE 5-20 How messages move through the network layers.\nNote: The addresses in this example are destination addresses\nThe message starts at the application layer of the sending computer (the client in Building A,\n128.192.98.130), shown in the upper left corner of the figure, which generates an HTTP packet. This\npacket is passed to the transport layer, which surrounds the HTTP packet with a TCP segment. This is\nthen passed to the network layer, which surrounds it with an IP frame that includes the IP address of the\nfinal destination (128.192.50.2). This, in turn, is passed to the data link layer, which surrounds it within\nan Ethernet frame that also includes the Ethernet address of the next computer to which the message will", "source": "Page 180", "chapter_title": "Chapter 11"}
{"id": "717f0f51fc4e-1", "text": "an Ethernet frame that also includes the Ethernet address of the next computer to which the message will\nbe sent (00-0C-00-33-3A-0B). Finally, this is passed to the physical layer, which converts it into electrical\nimpulses for transmission through the cable to its next stop\u2014the router that serves as the gateway in\nBuilding A.\nWhen the message arrives at the router in Building A, its physical layer translates it from electrical\nimpulses into digital data and passes the Ethernet frame to the data link layer. The data link layer checks\nto make sure that the Ethernet frame is addressed to the router, performs error detection, strips off the", "source": "Page 180", "chapter_title": "Chapter 11"}
{"id": "6eaabf99db85-0", "text": "Ethernet frame, and passes its contents (the IP packet) to the network layer. The routing software running\nat the network layer looks at the destination IP address, determines the next computer to which the\npacket should be sent, and passes the outgoing packet down to the data link layer for transmission. The\ndata link layer surrounds the IP packet with a completely new Ethernet frame that contains the\ndestination address of the next computer to which the packet will be sent (00-0C-00-33-3A-DA). In\nFigure 5-20, this new frame is shown in a different color. This is then passed to the physical layer, which\ntransmits it through the network cable to its next stop\u2014the router that serves as the gateway in the Data\nCenter.\nWhen the message arrives at the router in the Data Center, it goes through the same process. The physical\nlayer passes the incoming packet to the data link layer, which checks the destination Ethernet address,\nperforms error detection, strips off the Ethernet frame, and passes the IP packet to the network layer\nsoftware. The software determines the next destination and passes the IP packet back to the data link\nlayer, which adds a completely new Ethernet frame with the destination address of its next stop (00-0C-\n00-33-3A-DC)\u2014its final destination.\nThe physical layer at the server receives the incoming packet and passes it to the data link layer, which\nchecks the Ethernet address, performs error detection, removes the Ethernet frame, and passes the IP\npacket to the network layer. The network layer examines the final destination IP address on the incoming\npacket and recognizes that the server is the final destination. It strips off the IP packet and passes the TCP\nsegment to the transport layer, which in turn strips off the TCP segment and passes the HTTP packet to\nthe application layer (the Web server software).", "source": "Page 181", "chapter_title": "Chapter 11"}
{"id": "9f5e8b5244c4-1", "text": "the application layer (the Web server software).\nThere are two important things to remember from this example. First, at all gateways (i.e., routers) along\nthe way, the packet moves through the physical layer and data link layer up to the network layer, but no\nhigher. The routing software operates at the network layer, where it selects the next computer to which\nthe packet should be sent, and passes the packet back down through the data link and physical layers.\nThese three layers are involved at all computers and devices along the way, but the transport and\napplication layers are only involved at the sending computer (to create the application layer packet and\nthe TCP segment) and at the receiving computer (to understand the TCP segment and process the\napplication layer packet). Inside the TCP/IP network itself, messages only reach layer 3\u2014no higher.\nSecond, at each stop along the way, the Ethernet frame is removed and a new one is created. The Ethernet\nframe lives only long enough to move the message from one computer to the next and then is destroyed.\nIn contrast, the IP packet and the packets above it (TCP and application layer) never change while the\nmessage is in transit. They are created and removed only by the original message sender and the final\ndestination.\n5.7 IMPLICATIONS FOR CYBER SECURITY\nThe original design of the Internet and TCP/IP was done with only two user groups in mind (researchers\nat universities and military personnel) so security was not a major design focus. Time has changed since\nthen, and today, more than 3.5 billion users are on the Internet (you can check out the live stats of\nInternet users here: http://www.internetlivestats.com/internet-users/). This \u201cdesign flaw\u201d has some\nunintended consequences when it comes to cyber security.", "source": "Page 181", "chapter_title": "Chapter 11"}
{"id": "836640158bd0-2", "text": "unintended consequences when it comes to cyber security.\nOne of the most exploited security flaws is the vulnerability created by the TCP three-way handshake that\ninitiates a connection between a client and a server (see Section 5.6.3). A hacker can use an army of\ncomputers (zombies) to start requesting TCP sessions from a server but never follow through with an\nactual Web page request. The server will keep a part of its memory reserved for these false connections\nand, as a consequence, may not be able to respond to legitimate requests and, eventually, may crash\nbecause it does not have enough memory. The largest attack of this kind was recorded in 2016 when it\nbrought down much of the Internet\u2019s domain name system (DNS) infrastructure.\nThere is another issue that you should keep in mind. The most basic way somebody can identify you on\nthe Internet is by your IP address. From your IP address, one can roughly determine your geographical\nlocation (city or area). In addition, most websites can track your operating system, browser version, time\nzone, and may other information in addition to your IP address. You may ask why would they do this?\nWell, there is big money in it. They can track you for advertising purposes or they would sell your", "source": "Page 181", "chapter_title": "Chapter 11"}
{"id": "75c0c951cc09-0", "text": "information to third entities.\nSUMMARY\nTransport and Network Layer Protocols TCP/IP are the standard transport and network\nprotocols used today. They perform addressing (finding destination addresses), routing (finding the\n\u201cbest\u201d route through the network), and segmenting (breaking large messages into smaller packets for\ntransmission and reassembling them at the destination).\nTransport Layer The transport layer (TCP) uses the source and destination port addresses to link\nthe application layer software to the network. TCP is also responsible for segmenting\u2014breaking large\nmessages into smaller segments for transmission and reassembling them at the receiver\u2019s end. When\nconnection-oriented routing is needed, TCP establishes a connection or session from the sender to\nthe receiver. When connectionless routing is needed, TCP is replaced with UDP. Quality of service\nprovides the ability to prioritize packets so that real-time voice packets are transmitted more quickly\nthan simple email messages.\nAddressing Computers can have three different addresses: application layer address, network layer\naddress, and data link layer address. Data link layer addresses are usually part of the hardware,\nwhereas network layer and application layer addresses are set by software. Network layer and\napplication layer addresses for the Internet are assigned by Internet registrars. Addresses within one\norganization are usually assigned so that computers in the same LAN or subnet have similar\naddresses, usually with the same first 3 bytes. Subnet masks are used to indicate whether the first 2 or\n3 bytes (or partial bytes) indicate the same subnet. Some networks assign network layer addresses in\na configuration file on the client computer, whereas others use dynamic addressing, in which a DHCP\nserver assigns addresses when a computer first joins the network.\nAddress Resolution Address resolution is the process of translating an application layer address\ninto a network layer address or translating a network layer address into a data link layer address. On", "source": "Page 182", "chapter_title": "Chapter 11"}
{"id": "67bf3ff78b19-1", "text": "into a network layer address or translating a network layer address into a data link layer address. On\nthe Internet, network layer resolution is done by sending a special message to a DNS server (also\ncalled a name server) that asks for the IP address (e.g., 128.192.98.5) for a given Internet address\n(e.g., www.kelley.indiana.edu). If a DNS server does not have an entry for the requested Internet\naddress, it will forward the request to another DNS server that it thinks is likely to have the address.\nThat server will either respond or forward the request to another DNS server, and so on until the\naddress is found or it becomes clear that the address is unknown. Resolving data link layer addresses\nis done by sending an ARP request in a broadcast message to all computers on the same subnet that\nasks the computer with the requested IP address to respond with its data link layer address.\nRouting Routing is the process of selecting the route or path through the network that a message\nwill travel from the sending computer to the receiving computer. With centralized routing, one\ncomputer performs all the routing decisions. With static routing, the routing table is developed by the\nnetwork manager and remains unchanged until the network manager updates it. With dynamic\nrouting, the goal is to improve network performance by routing messages over the fastest possible\nroute; an initial routing table is developed by the network manager but is continuously updated to\nreflect changing network conditions, such as message traffic. BGP, RIP, ICMP, EIGRP, and OSPF are\nexamples of dynamic routing protocols.\nTCP/IP Example In TCP/IP, it is important to remember that the TCP segments and IP packets are\ncreated by the sending computer and never change until the message reaches its final destination.\nThe IP packet contains the original source and ultimate destination address for the packet. The", "source": "Page 182", "chapter_title": "Chapter 11"}
{"id": "f39a863f605e-2", "text": "The IP packet contains the original source and ultimate destination address for the packet. The\nsending computer also creates a data link layer frame (e.g., Ethernet) for each message. This frame\ncontains the data link layer address of the current computer sending the packet and the data link\nlayer address of the next computer in the route through the network. The data link layer frame is\nremoved and replaced with a new frame at each computer at which the message stops as it works its\nway through the network. Thus, the source and destination data link layer addresses change at each\nstep along the route, whereas the IP source and destination addresses never change.\nKEY TERMS", "source": "Page 182", "chapter_title": "Chapter 11"}
{"id": "1a8819638c19-0", "text": "Access Control List (ACL)\nacknowledgment (ACK)\naddress resolution\nAddress Resolution Protocol (ARP)\napplication layer address\nauthoritative name server\nARP cache\nAutomatic Repeat reQuest (ARQ)\nautonomous systems\nauxiliary port\nBorder Gateway Protocol (BGP)\nborder router\nbroadcast message\ncentralized routing\nCisco Internetwork Operating Systems (IOS)\nclassless addressing\nConnectionless messaging\nconnection-oriented messaging\nconsole port\ncontinuous ARQ\ndata link layer address\ndesignated router\ndestination port address\ndistance vector dynamic routing\nDomain Name Service (DNS)\ndynamic addressing\nDynamic Host Configuration Protocol (DHCP)\ndynamic routing\nEnhanced Interior Gateway Routing Protocol (EIGRP)\nexterior routing protocol\nflow control\ngateway\nGo-Back-N ARQ\nhop\nhops\ninterface\nInterior Gateway Routing Protocol (IGRP)\ninterior routing protocol\nIntermediate System to Intermediate System (IS-IS)", "source": "Page 183", "chapter_title": "Chapter 11"}
{"id": "f372cda9c127-0", "text": "Internet address classes\nInternet Control Message Protocol (ICMP)\nInternet Corporation for Assigned Names and Numbers (ICANN)\nInternet Group Management Protocol (IGMP)\nLink Access Protocol for Modems [LAP-M]\nlink state dynamic routing\nloopback\nmulticasting\nmulticast message\nname server\nnegative acknowledgment (NAK)\nnetwork interface port\nnetwork layer address\nOpen Shortest Path First (OSPF)\nport address\nprivate IPv4 address space\nQuality of Service (QoS)\nReal-Time Streaming Protocol (RTSP)\nReal-Time Transport Protocol (RTP)\nreserved addresses\nresolving name server\nResource Reservation Protocol (RSVP)\nroot server\nrouter\nrouting\nRouting Information Protocol (RIP)\nsegment\nsegmenting\nSelective-Repeat ARQ\nsession\nsliding window\nsource port address\nstatic routing\nstop-and-wait ARQ\nsubnet\nsubnet mask\ntop-level domain (TLD)\nTransmission Control Protocol/Internet Protocol (TCP/IP)\nunicast message", "source": "Page 184", "chapter_title": "Chapter 11"}
{"id": "684167a76466-0", "text": "User Datagram Protocol (UDP)\nQUESTIONS\n1. What does the transport layer do?\n2. What does the network layer do?\n3. What are the parts of TCP/IP and what do they do? Who is the primary user of TCP/IP?\n4. Compare and contrast the three types of addresses used in a network.\n5. How is TCP different from UDP?\n6. How does TCP establish a session?\n7. What is a subnet and why do networks need them?\n8. What is a subnet mask?\n9. How does dynamic addressing work?\n10. What benefits and problems does dynamic addressing provide?\n11. What is address resolution?\n12. How does TCP/IP perform address resolution from URLs into network layer addresses?\n13. How does TCP/IP perform address resolution from IP addresses into data link layer addresses?\n14. What is routing?\n15. How does decentralized routing differ from centralized routing?\n16. What are the differences between connectionless and connection-oriented messaging?\n17. What is a session?\n18. What is QoS routing and why is it useful?\n19. Compare and contrast unicast, broadcast, and multicast messages.\n20. Explain how multicasting works.\n21. Explain how the client computer in Figure 5-16 (128.192.98.xx) would obtain the data link layer\naddress of its subnet router.\n22. Why does HTTP use TCP and DNS use UDP?\n23. How does static routing differ from dynamic routing? When would you use static routing? When\nwould you use dynamic routing?\n24. What type of routing does a TCP/IP client use? What type of routing does a TCP/IP gateway use?\nExplain.\n25. What is the transmission efficiency of a 10-byte Web request sent using HTTP, TCP/IP, and", "source": "Page 185", "chapter_title": "Chapter 11"}
{"id": "b79db957b27a-1", "text": "Ethernet? Assume that the HTTP packet has 100 bytes in addition to the 10-byte URL. Hint:\nRemember from Chapter 4 that efficiency = user data/total transmission size.\n26. What is the transmission efficiency of a 1,000-byte file sent in response to a Web request HTTP,\nTCP/IP, and Ethernet? Assume that the HTTP packet has 100 bytes in addition to the 1,000-byte file.\nHint: Remember from Chapter 4 that efficiency = user data/total transmission size.\n27. What is the transmission efficiency of a 5,000-byte file sent in response to a Web request HTTP,\nTCP/IP, and Ethernet? Assume that the HTTP packet has 100 bytes in addition to the 5,000-byte file.\nAssume that the maximum packet size is 1,200 bytes. Hint: Remember from Chapter 4 that efficiency\n= user data/total transmission size.\n28. Describe the anatomy of a router. How does a router differ from a computer?", "source": "Page 185", "chapter_title": "Chapter 11"}
{"id": "6a0430ed4314-0", "text": "EXERCISES\nA. Would you recommend dynamic addressing for your organization? Why?\nB. Look at your network layer software (either on a LAN or dial-in) and see what options are set\u2014but\ndon\u2019t change them! You can do this by using the RUN command to run winipcfg. How do these match\nthe fundamental addressing and routing concepts discussed in this chapter?\nC. Suppose that a client computer (128.192.98.130) in Building B in Figure 5-17 requests a large Web\npage from the Web server 2 in the Data Center (www2.anyorg.com). Assume that the client computer\nhas just been turned on and does not know any addresses other than those in its configuration tables.\nAssume that all gateways and Web servers know all network layer and data link layer addresses.\na. Explain what messages would be sent and how they would flow through the network to deliver\nthe Web page request to the server.\nb. Explain what messages would be sent and how they would flow through the network as the Web\nserver sent the requested page to the client.\nc. Describe, but do not explain in detail, what would happen if the Web page contained several\ngraphic images (e.g., GIF [Graphics Interchange Format] or JPEG [Joint Photographic Experts\nGroup] files).\nD. Network Solutions provides a service to find who owns domain names and IP addresses. Go to\nwww.networksolutions.com/whois. Find the owner of\na. books.com\nb. TV.com\nc. 74.128.18.22\nd. 129.79.78.188\nE. What is the subnet portion of the IP address and what is the subnet mask for the following:\na. 12.1.0.0/16\nb. 12.1.0.0/24", "source": "Page 186", "chapter_title": "Chapter 11"}
{"id": "78465766814d-1", "text": "b. 12.1.0.0/24\nc. 12.1.0.0/20\nd. 12.1.0.0/28\nF. You might be wondering how the first bytes for each address range were picked. Why do you think\nClass A\u2019s first byte is 1\u2013126, Class B\u2019s byte is 128\u2013191, and Class C\u2019s byte is 192\u2013223?\nMINICASES\nI. Central University Suppose that you are the network manager for Central University, a medium-\nsized university with 13,000 students. The university has 10 separate colleges (e.g., business, arts,\njournalism), 3 of which are relatively large (300 faculty and staff members, 2,000 students, and 3\nbuildings) and 7 of which are relatively small (200 faculty and staff, 1,000 students, and 1 building).\nIn addition, there are another 2,000 staff members who work in various administration departments\n(e.g., library, maintenance, finance) spread over another 10 buildings. There are 4 residence halls that\nhouse a total of 2,000 students. Suppose that the university has the 128.100.xxx.xxx address range on\nthe Internet. How would you assign the IP addresses to the various subnets? How would you control\nthe process by which IP addresses are assigned to individual computers? You will have to make some\nassumptions to answer both questions, so be sure to state your assumptions.\nII. Connectus Connectus is a medium-sized Internet Service Provider (ISP) that provides Internet\naccess and data communication services to several dozen companies across the United States and\nCanada. Connectus provides fixed data connections for clients\u2019 offices in about 50 cities and an\ninternal network that connects them. For reliability purposes, all centers are connected with at least", "source": "Page 186", "chapter_title": "Chapter 11"}
{"id": "bca6ab01d686-2", "text": "internal network that connects them. For reliability purposes, all centers are connected with at least\ntwo other centers so that if one connection goes down, the center can still communicate with the", "source": "Page 186", "chapter_title": "Chapter 11"}
{"id": "19e3bcbbc8ed-0", "text": "network. Predicting access volume is difficult because it depends on how many sales representatives\nare in which city. Connectus currently uses RIP as its routing protocol but is considering moving to\nOSPF. Should it stay with RIP or move to OSPF? Why?\nIII. Old Army Old Army is a large retail store chain operating about 1,000 stores across the United\nStates and Canada. Each store is connected to the Old Army data network, which is used primarily for\nbatch data transmissions. At the end of each day, each store transmits sales, inventory, and payroll\ninformation to the corporate head office in Atlanta. The network also supports email traffic, but its\nuse is restricted to department managers and above. Because most traffic is sent to and from the\nAtlanta headquarters, the network is organized in a hub and spoke design. The Atlanta office is\nconnected to 20 regional data centers, and each regional center is in turn connected to the 30\u201370\nstores in its region. Network volumes have been growing, but at a fairly predictable rate, as the\nnumber of stores and overall sales volume increase. The old Army currently uses RIP as its routing\nprotocol but is considering moving to OSPF. Should it stay with RIP or move to OSPF? Why?\nIV. General Stores General Stores is a large retail store chain operating about 1,300 stores across the\nUnited States and Canada. Each store is connected to the corporate data network. At the end of each\nday, each store transmits sales and payroll information to the corporate head office in Seattle.\nInventory data are transmitted in real time as products are sold to one of a dozen regional\ndistribution centers across North America. The network is also used for credit card validations as\ncustomers check out and pay for their purchases. The network supports email traffic, but its use is\nrestricted to department managers and above. The network is designed much like the Internet: One", "source": "Page 187", "chapter_title": "Chapter 11"}
{"id": "18d56975005b-1", "text": "restricted to department managers and above. The network is designed much like the Internet: One\nconnection from each store goes into a regional network that typically has a series of network\nconnections to other parts of the network. Network volumes have been growing, but at a fairly\npredictable rate, as the number of stores and overall sales volume increase. General Stores is\nconsidering implementing a digital telephone service that will allow it to transmit internal telephone\ncalls to other General Stores offices or stores through the data network. Telephone services outside of\nGeneral Stores will continue to be done normally. General Stores currently uses RIP as its routing\nprotocol but is considering moving to OSPF. Should it stay with RIP or move to OSPF? Why?\nTECH UPDATES\nIn every chapter, we will offer a couple of ideas to investigate.\nTopic A: The DNS Servers Hierarchy\nThe system of DNS Servers is essential for the Internet to work. Who came up with the idea of having this\ntype of directory? How did this hierarchy of servers evolved? What does it look like today? Provide a\ntimeline of the evolution of the DNS Servers hierarchy and its current state.\nTopic B: SQL Injection\nSQL Injection (SQLi) refers to an injection attack where an attacker can execute malicious SQL statements\n(also commonly referred to as a malicious payload) that control a web application\u2019s database server (also\ncommonly referred to as a Relational Database Management System\u2014RDBMS). Using the http://hack.me\nwebsite (a great environment to try out safely some hacking techniques) explore the SQL Injection and\nprovide a report about what you learned. Show how to perform and block an SQLi.\nDeliverables\nYour job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title Slide\n2. Short description of the topic", "source": "Page 187", "chapter_title": "Chapter 11"}
{"id": "663d91653715-2", "text": "1. Title Slide\n2. Short description of the topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use a lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along", "source": "Page 187", "chapter_title": "Chapter 11"}
{"id": "70cc9c27f201-0", "text": "5. How does it relate to material covered in class so far (and in the future)\n6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 5A\nUsing TCP/IP\nIn this chapter, we\u2019ve discussed the basic components of TCP/IP such as IP addresses, subnet masks, DNS\nrequests, and ARP requests. In this activity, we\u2019ll show you how to explore these items on your computer.\nAlthough this activity is designed for Windows computers, most of these commands will also work on\nApple computers.\nThis activity will use the command prompt, so start by clicking START, then RUN, and then type CMD\nand press enter. You should see the command window, which in Windows is a small window with a black\nbackground. Like all other windows, you can change its shape by grabbing the corner and stretching it.\nIPCONFIG: Reading Your Computer\u2019s Settings\nIn a focus box earlier in the chapter, we showed you how to find your computer\u2019s TRCP/IP settings using\nWindows. You can also do it by using the IPCONFIG command. In the command window, type\nIPCONFIG/ALL and press enter.\nYou should see a screen like that shown in Figure 5-19. The middle of the screen will show the TCP/IP\ninformation about your computer. You can see the IP address (192.168.1.102 in Figure 5-19); the subnet\nmask (255.255.255.0); the default gateway, which is the IP address of the router leading out of your\nsubnet (192.168.1.1); the DHCP server (192.168.1.1); and the available DNS servers (e.g., 63.240.76.4).", "source": "Page 188", "chapter_title": "Chapter 11"}
{"id": "6f52748576eb-1", "text": "Your computer will have similar, but different, information. As discussed in Technical Focus 5.3, your\ncomputer might be using \u201cprivate\u201d IP addresses the same as my computer shown in Figure 5-21, so your\naddresses may be identical to mine. We\u2019ll explain how network address translation (NAT) is done in\nChapter 11.\nC:\\Documents and Settings\\Administrator>ipconfig/all\nWindows IP Configuration\n  Host Name . . . . . . . . . . . . . : ALAN\n  Primary Dns Suffix . . . . . . . . .:\n  Node Type . . . . . . . . . . . . . : Unknown\n  IP Routing Enabled . . . . . . . . .: No\n  WINS Proxy Enabled . . . . . . . . .: No\n  DNS Suffix Search List . . . . . . .: insightbb.com\nEthernet adapter Local Area Connection:\n  Connection-specific DNS Suffix . . .: insightbb.com\n  Description . . . . . . . . . . . . : Intel(R) PRO/1000 MT Network Connection\n  Physical Address . . . . . . . . . .: 00-0D-56-D8-8D-96\n  Dhcp Enabled . . . . . . . . . . . .: Yes\n  Autoconfiguration Enabled . . . . . : Yes\n  IP Address . . . . . . . . . . . . .: 192.168.1.102\n  Subnet Mask . . . . . . . . . . . . : 255.255.255.0\n  Default Gateway . . . . . . . . . . : 192.168.1.1", "source": "Page 188", "chapter_title": "Chapter 11"}
{"id": "098d47812234-2", "text": "DHCP Server . . . . . . . . . . . . : 192.168.1.1\n  DNS Servers . . . . . . . . . . . . : 63.240.76.4\n \n \n \n \n \n204.127.198.4\n \n \n \n \n \n63.240.76.135\n  Lease Obtained . . . . . . . . . . .: Wednesday, February 20, 2008 8:09:37 AM\n  Lease Expires . . . . . . . . . . .: Tuesday, February 26, 2008 8:09:37 AM", "source": "Page 188", "chapter_title": "Chapter 11"}
{"id": "df03e878d243-0", "text": "C:\\Documents and Settings\\Administrator>\nFIGURE 5-21 IPCONFIG command\nDeliverables\n1. Use the ipconfig/all command on your computer. What is the IP address, subnet mask, IP address of\ndefault gateway, and MAC of your computer?\n2. Why does every computer on the Internet need to have these four numbers?\nPING: Finding Other Computers\nThe PING sends a small packet to any computer on the Internet to show you how long it takes the packet\nto travel from your computer to the target computer and back again. You can ping a computer using its IP\naddress or Web URL. Not all computers respond to ping commands, so not every computer you ping will\nanswer.\nStart by pinging your default gateway: just type PING followed by the IP address of your gateway. Figure\n5-22 shows that the PING command sends four packets to the target computer and then displays the\nmaximum, minimum, and average transit times. In Figure 5-22, you can see that pinging my gateway is\nfast: less than 1 millisecond for the packet to travel from my computer to my router and back again.\nNext, ping a well-known website in the United States to see the average times taken. Remember that not\nall websites will respond to the ping command. In Figure 5-22, you can see that it took an average of 52\nmilliseconds for a packet to go from my computer to Google and back again. Also, note that\nwww.google.com has an IP address of 216.239.37.99.\nNow, ping a website outside the United States. In Figure 5-20, you can see that it took an average of 239\nmilliseconds for a packet to go from my computer to the City University of Hong Kong and back again. If\nyou think about it, the Internet is amazingly fast.\nDeliverables", "source": "Page 189", "chapter_title": "Chapter 11"}
{"id": "936fd796ec23-1", "text": "you think about it, the Internet is amazingly fast.\nDeliverables\n1. Ping your own default gateway. How many packets were returned? How long did it take for your\ndefault gateway to respond?\n2. Ping google.com. How many packets were returned? How long did it take for you default gateway to\nrespond?\n3. Ping National Australian University www.anu.edu.au. How many packets were returned? How long\ndid it take for your default gateway to respond?\nARP: DISPLAYING PHYSICAL ADDRESSES\nRemember that to send a message to other computers on the Internet, you must know the physical\naddress (aka data link layer address) of the next computer to send the message to. Most computers on the\nInternet will be outside your subnet, so almost all messages your computer sends will be sent to your\ngateway (i.e., the router leaving your subnet). Remember that computers use ARP requests to find\nphysical addresses and store them in their ARP tables. To find out what data link layer addresses your\ncomputer knows, you can use the ARP command.\nAt the command prompt, type ARP-A and press enter. This will display the contents of your ARP table. In\nFigure 5-23, you can see that the ARP table in my computer has only one entry, which means that all the\nmessages from my computer since I turned it on have only gone to this one computer\u2014my router. You can\nalso see the physical address of my router: 00-04-5a-0b-d1-40.\nIf you have another computer on your subnet, ping it and then take a look at your ARP table again. In\nFigure 5-23, you can see the ping of another computer on my subnet (192.168.1.152) and then see the ARP", "source": "Page 189", "chapter_title": "Chapter 11"}
{"id": "9b8b1f59ab7e-2", "text": "table with this new entry. When I pinged 192.168.1.152, my computer had to find its physical address, so it\nissued an ARP request, and 192.168.1.152 responded with an ARP response, which my computer added", "source": "Page 189", "chapter_title": "Chapter 11"}
{"id": "d3f40ea5eb24-0", "text": "into the ARP table before sending the ping.\nDeliverables\n1. Type ARP-A at the command prompt. What are the entries in your ARP table?\n2. Suppose that there are no entries in your ARP table. Is this a problem? Why or why not?\nNSLOOKUP: Finding IP Addresses\nRemember that to send a message to other computers on the Internet, you must know their IP addresses.\nComputers use DNS servers to find IP addresses. You can issue a DNS request by using the NSLOOKUP\ncommand.\nType NSLOOKUP and the URL of a computer on the Internet and press enter. In Figure 5-24, you\u2019ll see\nthat www.cnn.com has several IP addresses and is also known as cnn.com\nDeliverable\nFind the IP address of google.com and another website of your choice.\nDNS Cache\nThe IPCONFIG/DISPLAYDNS command can be used to show the contents of the DNS cache. You can\nexperiment with this by displaying the cache, visiting a new website with your browser, and then\ndisplaying the cache again. Figure 5-25 shows part of the cache on my computer after visiting several sites.\nThe DNS cache contains information about all the websites I\u2019ve visited, either directly or indirectly (by\nhaving a Web page on one server pull a graphics file off of a different server).\nC:\\Documents and Settings\\Administrator>ping 192.168.1.1\nPinging 192.168.1.1 with 32 bytes of data:\nReply from 192.168.1.1: bytes = 32 time < 1ms TTL = 64\nReply from 192.168.1.1: bytes = 32 time < 1ms TTL = 64\nReply from 192.168.1.1: bytes = 32 time < 1ms TTL = 64", "source": "Page 190", "chapter_title": "Chapter 11"}
{"id": "c0f679ef112f-1", "text": "Reply from 192.168.1.1: bytes = 32 time < 1ms TTL = 64\nPing statistics for 192.168.1.1:\n Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),\nApproximate round trip times in milli-seconds:\n Minimum = 0ms, Maximum = 0ms, Average = 0ms\n_______________________________________________________________\nC:\\Documents and Settings\\Administrator>ping www.google.com\nPinging www.1.google.com [216.239.37.99] with 32 bytes of data:\nReply from 216.239.37.99: bytes = 32 time = 53ms TTL = 235\nReply from 216.239.37.99: bytes = 32 time = 52ms TTL = 236\nReply from 216.239.37.99: bytes = 32 time = 52ms TTL = 236\nReply from 216.239.37.99: bytes = 32 time = 53ms TTL = 235\nPing statistics for 216.239.37.99:\n Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),\nApproximate round trip times in milli-seconds:\n Minimum = 52ms, Maximum = 53ms, Average = 52ms\n_______________________________________________________________\nC:\\Documents and Settings\\Administrator>ping www.cityu.edu.hk\nPinging amber.cityu.edu.hk [144.214.5.218] with 32 bytes of data:\nReply from 144.214.5.218: bytes = 32 time = 240ms TTL = 236\nReply from 144.214.5.218: bytes = 32 time = 239ms TTL = 236", "source": "Page 190", "chapter_title": "Chapter 11"}
{"id": "b970ffcfdbf6-2", "text": "Reply from 144.214.5.218: bytes = 32 time = 239ms TTL = 236", "source": "Page 190", "chapter_title": "Chapter 11"}
{"id": "2adc0a7d789a-0", "text": "Reply from 144.214.5.218: bytes = 32 time = 240ms TTL = 236\nPing statistics for 144.214.5.218:\n Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),\nApproximate round trip times in milli-seconds:\n Minimum = 239ms, Maximum = 240ms, Average = 239ms \nFIGURE 5-22 PING command\nFor example, the second entry in this figure is ns1 .cisco.com, which has an IP address of 128.107.241.185\n(a 4-byte long address). The record type is one, which means this is a \u201chost\u201d\u2014that is, a computer on the\nInternet using IPv4. Because the DNS information might change, all entries have a maximum time to live\nset by the DNS that provides the information (usually 24 hours); the time to live value is the time in\nseconds that this entry will remain in the cache until it is removed.\nC:\\Documents and Settings\\Administrator>arp.-a.\nInterface: 192.168.1.102 --- 0x10003\n  Internet Address  Physical Address   Type\n  192.168.1.1     00-04-5a-0b-d1-40  dynamic\n__________________________________________________________\nC:\\Documents and Settings\\Administrator>ping 192.168.1.152\nPinging 192.168.1.152 with 32 bytes of data:\nReply from 192.168.1.152: bytes = 32 time < 1ms TTL = 64\nReply from 192.168.1.152: bytes = 32 time < 1ms TTL = 64", "source": "Page 191", "chapter_title": "Chapter 11"}
{"id": "b1f2a9280a18-1", "text": "Reply from 192.168.1.152: bytes = 32 time < 1ms TTL = 64\nReply from 192.168.1.152: bytes = 32 time < 1ms TTL = 64\nPing statistics for 192.168.1.152:\n  Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),\nApproximate round trip times in milli-seconds:\n  Minimum = 0ms, Maximum = 0ms, Average = 0ms\n__________________________________________________________\nC:\\Documents and Settings\\Administrator>arp -a\nInterface: 192.168.1.102 --- 0x10003\n Internet Address   Physical Address   Type\n 192.168.1.1 \n00-04-5a-0b-dl-40   dynamic\n 192.168.1.152     00-08-e1-00-21-f6   dynamic \nFIGURE 5-23 ARP command\nC:\\Documents and Settings\\Administrator>nslookup www.cnn.com\nServer: ns1.insightbb.com\nAddress: 63.240.76.135\nNon-authoritative answer:\nName: cnn.com\nAddresses: 64.236.16.116, 64.236.24.12, 64.236.24.20, 64.236.24.28\n \n \n64.236.29.120, 64.236.16.20, 64.236.16.52, 64.236.16.84\nAliases: www.cnn.com \nFIGURE 5-24 NSLOOKUP command\nThe very last entry in this figure is for ns1.v6.telekom.at. The record type of 28 means that this is a host", "source": "Page 191", "chapter_title": "Chapter 11"}
{"id": "edffd238bb2f-2", "text": "that uses IPv6, which you can see from the 16-byte long address in the record (2001:890:600:d1: :100).\nDeliverables\n1. Display your DNS cache using the command ipconfig/displaydns.", "source": "Page 191", "chapter_title": "Chapter 11"}
{"id": "fc69d53fe10d-0", "text": "2. How many entries are there in your cache?\n3. Open your browser and visit www.ietf.com. Once the page loads, display your DNS cache again. Copy\nthe DNS entry for this website.\nTRACERT: Finding Routes through the Internet\nThe TRACERT command will show you the IP addresses of computers in the route from your computer to\nanother computer on the Internet. Many networks have disabled TRACERT for security reasons, so it\ndoesn\u2019t always work. Type TRACERT and the URL of a computer on the Internet and press enter. In\nFigure 5-26, you\u2019ll see the route from my computer, through the Insight network, through the AT&T\nnetwork, through the Level 3 network, and then through the Google network until it reaches the server.\nTRACERT usually sends three packets, so beside each hop is the total time to reach that hop for each of\nthe three packets. You\u2019ll see that it took just over 50 milliseconds for a packet to go from my computer to\nGoogle. You\u2019ll also see that the times aren\u2019t always \u201cright,\u201d in that the first packet took 50 milliseconds to\nreach the bbrl Washington Level 3 router (step 9) but only 40 milliseconds to reach the next hop to the\ncar2 Washington Level 3 router (step 10). The time to each hop is measured separately, each with a\ndifferent packet, so sometimes a packet is delayed longer on one hop or another.", "source": "Page 192", "chapter_title": "Chapter 11"}
{"id": "0a7a1594bf77-0", "text": "FIGURE 5-25 DNS cache\nC:\\Documents and Settings\\Administrator>tracert www.google.com\nTracing route to www.1.google.com [216.239.37.104]\nover a maximum of 30 hops:\n  1 1 ms   1 ms   1 ms  192.168.1.1\n  2 7 ms  10 ms   8 ms  12-220-5-129.client.insightBB.com [12.220.5.129]\n  3 11 ms  12 ms  11 ms  12-220-1-78.client.insightBB.com [12.220.1.78]\n  4 17 ms  16 ms  16 ms  12-220-0-26.client.insightBB.com [12.220.0.26]\n  5 19 ms  18 ms  18 ms  tbr1-p011 901.cgcil.ip.att.net [12.123.4.226]\n  6 18 ms  16 ms  16 ms  ggr2-p310.cgcil.ip.att.net [12.123.6.65]\n  7 19 ms  18 ms  18 ms  so-9-1.car4.Chicagol.Level3.net [4.68.127.165]\n  8 19 ms  18 ms  19 ms  ae-2-52.bbr2.Chicago1.Level3.net [4.68.101.33]\n  9 50 ms  39 ms  39 ms  ae-2-0.bbr1.Washington1.Level3.net [4.68.128.201]", "source": "Page 194", "chapter_title": "Chapter 11"}
{"id": "a6ba61e1c6ee-1", "text": "10 40 ms  40 ms  39 ms  ae-12-53.car2.Washington1.Level3.net [4.68.121.83]\n 11 53 ms  78 ms  56 ms  unknown.Level3.net [166.90.148.174]\n 12 54 ms  52 ms  51 ms  72.14.232.106\n 13 55 ms  54 ms  53 ms  216.239.48.96\n 14 55 ms  55 ms  54 ms  216.239.48.110\n 15 52 ms  51 ms  52 ms  216.239.37.104\nTrace complete. \nFIGURE 5-26 TRACERT command\nDeliverables\n1. Type tracert google.com in your command window.\n2. How many computers/hops did it take the packet to reach Google?\n3. What was the shortest hop (in terms of time)? Why do you think this is the shortest hop?\nHANDS-ON ACTIVITY 5B\nExploring DNS Request and DNS Response\nIn this chapter, we talked about address resolution. This activity will help you see how your computer\nsends a DNS request for a website you never visited, before it can create a HTTP request packet to display\nthe website on your browser. We will use Wireshark for this activity. Use of Wireshark was explained in\nChapter 2.\n1. Use ipconfig/all command to find the IP address of your computer and your DNS server.\n2. So that we can explore the DNS request and response properly, the first step is to empty your DNS\ncache. Use ipconfig/flushdns command in the command prompt window to empty the DNS of your\ncomputer.", "source": "Page 194", "chapter_title": "Chapter 11"}
{"id": "2655a78484ec-2", "text": "computer.\n3. Open Wireshark and enter \u201cip.addr==your IP address\u201d into the filter to only capture packets that\neither originate or are destined for your computer.\n4. Start packet capture in Wireshark.\n5. With your browser, visit www.ietf.org.\n6. Stop packet capture after the Web page is loaded.", "source": "Page 194", "chapter_title": "Chapter 11"}
{"id": "7b3003df95e9-0", "text": "FIGURE 5-27 DNS capture\nDeliverables\n1. Locate the DNS query and response message for www.ietf.org. In Figure 5-27, they are packets 27 and\n28. Are these packets sent over UDP or TCP?\n2. What is the destination port for the DNS query message? What is the source port of the DNE\nresponse message?\n3. To what IP address is the DNS query message sent? Compare this IP address to your local DNS server\nIP address. Are these two IP addresses the same?\n4. The www.ietf.org contains several images. Before retrieving each image, does your host issue a new\nDNS query? Why or why not?\n5. Now locate the HTTP Get message. What is the source and destination IP address? Compare the\nsource to your IP address. Are these the same?\n6. Approximately how many HTTP GET request messages did your browser send? Why was there a\nneed to send additional HTTP GET messages?\nHANDS-ON ACTIVITY 5C", "source": "Page 195", "chapter_title": "Chapter 11"}
{"id": "58f7a39fc468-0", "text": "Converting Decimal Values into Binary, and Vice Versa.\nPART A\nBeing able to convert decimal values to binary (and vice versa) is very important in networking because\nthis is the basis for how subnetting is done. You may have done some of these exercises in high school and\nprobably didn\u2019t know why it was important to be able to convert decimal values into binary, and vice\nversa. This hands-on activity will help you recall how this is done or will teach how to do it in case you\nnever seen this before.\nAs you know, an IPv4 address consists of 32 bits that have been separated into 4 bytes (sometimes called\noctets), for example, 129.79.126.1. This is called the dotted decimal address. Each byte has 8 bits, and each\nof these bits can assume a value of 0 or 1. The following table shows how we convert each binary position\nto a decimal value:s\nBinary position 27\n26 25 24 23 22 21 20\nDecimal value\n128 64 32 16 8 4 2 1\nTo practice the conversion from binary to decimal, let\u2019s do a couple problems together:\n1. You have the following binary number: 10101010. Convert it into decimal.\n2. You have the following binary number: 01110111. Convert it into decimal.\nIt is important to notice what the range of possible decimal values for each byte is. The lower bound is\ngiven when each bit is 0 and the upper bound is when each bit is 1. So 00000000 will give us 0 and\n11111111 will give us 255. This is the reason why IPv4 addresses cannot go above the value of 255.\nDeliverable", "source": "Page 196", "chapter_title": "Chapter 11"}
{"id": "5a115a1dac84-1", "text": "Deliverable\nCalculate the decimal values of the following binary numbers: 11011011, 01111111, 10000000, 11000000,\n11001101.\nPart B\nNow let\u2019s practice the conversion of decimal value to binary. This is a bit trickier. Start by finding the\nhighest binary position that is equal to or smaller than the decimal number we are converting. All the\nother placeholders to the left of this number will be 0. Then subtract the placeholder value from the\nnumber. Then find the highest binary position that is equal to or smaller than the remainder. Keep\nrepeating these steps until the remainder is 0. Now, let\u2019s practice.\n3. Convert 60 into a binary number.\na. The placeholder that is equal to or lower than 60 is 32. Therefore, the first two bits for 60 are 0\nand the third one is 1 \u2212 001_ _ _ _ _ . The next step is to subtract 32 from 60, which equals 60 \u2212\n32 = 28.\nb. The placeholder that is equal to or lower than 32 is 16, which is the fourth bit from the left.\nTherefore, our binary number will look like this: 0011_ _ _ _. The next step is to subtract 16\nfrom 28, which equals 28 \u2212 16 = 12.\nc. The placeholder that is equal to or lower than 12 is 8, and this is the fifth bit from the left.\nTherefore, our binary number will look like this: 00111_ _ _. The next step is to subtract 8 from\n12, which equals 12 \u2212 8 = 4.\nd. The placeholder that is equal to or lower than 4 is 4, and this is the sixth bit from the left.", "source": "Page 196", "chapter_title": "Chapter 11"}
{"id": "83cc8e85b953-2", "text": "Therefore, our binary number will look like this: 001111_ _. The next step is to subtract 4 from 4,\nwhich equals 4 \u2212 4 = 0.\ne. Given that our remainder is 0, the additional bits are 0, and we find that our answer: 60 in\nbinary is 00111100.", "source": "Page 196", "chapter_title": "Chapter 11"}
{"id": "d76d57550db4-0", "text": "4. Convert 182 into a binary number.\n82= 10110110\n(Because 182 \u2212 128 = 54,54 \u2212 32 = 22,22 \u2212 16 = 6, and 6 \u2212 4 = 2)\nDeliverable\nCalculate the binary value for each of the following binary numbers: 126, 128, 191, 192, 223.\nHANDS-ON ACTIVITY 5D\nIntroduction to Subnetting\nIf you are not familiar with binary numbers, you may want to do Hands-On Activity 5C before you do this\nactivity.\nA subnet mask is a 32-bit binary number that tells us to which subnet a device belongs. A 1 indicates that\nthat bit is part of the subnet network address, and a 0 indicates that that bit is part of the unique host\naddress for the individual computer. The subnet mask is a continuous stream of ones followed by all\nzeros, so the subnet mask can assume only certain values. For example, a subnet mask could never have a\nvalue of 11111111.11111111.00000000.10000000.\nThe following table shows the subnet mask values in both binary and decimal notation for classes A, B,\nand C.\nFor example, a subnet mask of 255.255.255.0 for a computer with an address of 192.168.1.101 tells us that\nthe computer is in subnet 192.168.1.0 and has a unique address of 101 within that subnet.\nClass First\nByte\nRange\nByte Allocation\nSubnet Mask in Binary Notation\nSubnet Mask\nin Decimal\nNotation\nA\n1\u2013126 Network.Host.Host.Host\n11111111.00000000.00000000.00000000 255.0.0.0\nB\n128\u2013\n191", "source": "Page 197", "chapter_title": "Chapter 11"}
{"id": "a789fc1f7e1a-1", "text": "B\n128\u2013\n191\nNetwork.Network.Host.Host\n11111111.11111111.00000000.00000000\n255.255.0.0\nC\n192\u2013\n223\nNetwork.Network.Network.Host 11111111.11111111.11111111.00000000\n2555.255.255.0\nDeliverable\nFill in the following table and find the admissible values for a subnet mask.\nBinary Representation of a Byte Decimal Value\n10000000\n11000000\n11100000\n11110000\n11111000\n11111100\n11111110\n11111111\nSuppose that you were assigned the network 209.98.208.0, which is a Class C address. The usual subnet\nmask for a Class C address is 255.255.255.0, which provides one subnet with 253 host computers (there\nare 255 possible addresses, but the .255 address is reserved and cannot be assigned to a computer because\nthis is the broadcast address for this subnet, and the .0 address is reserved for the subnet itself). Suppose\nthat you need to create 10 subnets within this address space. This means that part of the address usually", "source": "Page 197", "chapter_title": "Chapter 11"}
{"id": "e1ec2d3368ec-0", "text": "used for host addresses must be used as part of the subnet address. How many bits do you need to use\nfrom the host space to create 10 subnets?\nSolution: If we use 1 bit, we will be able to create 2 subnets (they will have the following binary\nrepresentation: 11111111.11111111.11111111.00000000 and 111111111.11111111.11111111.10000000). If we use\n2 bits, we will be able to create 22 subnets, which is 4. Using 3 bits will give us 23 subnets, which is 8.\nTherefore, we need to use 4 bits (24 = 16), which will give us 16 subnets. This is more than we need, but if\nwe use 3 bits, it will not meet our needs. The subnet mask for this network will be\n1111111.11111111.11111111.11110000, or 255.255.255.240. This also means that we now only have 4 bits to\nuse for the host address on each network. So this means the maximum number of host addresses on each\nsubnet is 24 = 16.\nDeliverables\nNow that you understand how to make decisions regarding subnet masks, work on the following\nproblems:\n1. Given a Class C network and a number of subnets required, complete the table to identify the number\nof bits to borrow from the host field to use for the subnet field and the maximum number of host\naddresses available per subnet.\nNumber of\nSubnets\nRequired\nNumber of Bits to\nBorrow for the Subnet\nField\nMaximum Number\nof Hosts per Subnet\nSubnet Mask in Binary\nand Decimal\nRepresentation\n2\n5\n12\n24\n40", "source": "Page 198", "chapter_title": "Chapter 11"}
{"id": "cec6b6883f41-1", "text": "and Decimal\nRepresentation\n2\n5\n12\n24\n40\n2. Given a Class B network and a number of subnets required, complete the table to identify the number\nof bits to borrow from the host field for the subnet field and the maximum number of host addresses\navailable per subnet.\nNumber of\nSubnets\nRequired\nNumber of Bits to\nBorrow for the Subnet\nField\nMaximum Number\nof Hosts per Subnet\nSubnet Mask in Binary\nand Decimal\nRepresentation\n5\n8\n35\n200\n400\n3. Given a Class A network and a number of subnets required, complete the table to identify the number\nof bits to borrow from the host field for the subnet field and the maximum number of host addresses\navailable per subnet.\nNumber of\nSubnets\nRequired\nNumber of Bits to\nBorrow for the Subnet\nField\nMaximum Number\nof Hosts per Subnet\nSubnet Mask in Binary\nand Decimal\nRepresentation\n10\n20\n80\n400\n2000", "source": "Page 198", "chapter_title": "Chapter 11"}
{"id": "25e7100a7381-0", "text": "HANDS-ON ACTIVITY 5E\nSubnetting Class C Addresses\nTo do this activity, you need to do Hands-On Activity 5D. First, we explain how to find the subnet address\nfor each subnet, the range of host addresses, and the direct broadcast address. Then you will be asked to\ndo a similar exercise by yourself.\nAssume that you have been assigned the 192.168.1.0/24 network. You need to create 6 subnets.\na. How many bits do you need to borrow from the host field for the subnet field?\nWe need to borrow 3 bits: 1 bit would give us 2 subnets, 2 would give us 4, and 3 would give us 8.\nb. What is the maximum number of subnets that can be created with this number of bits?\nWe can create 23 = 8 subnets.\nc. How many bits can be used to create the host space?\nEach byte has 8 bits\u2014we are using 3 bits to define the subnets, and this leaves us with 5 bits for the\nhost space.\nd. What is the maximum number of host addresses available per subnet?\n25 \u2212 2 = 32 \u2212 2 = 30. We have 5 bits for the host space, and each bit can assume a value of 1 or 0 (25).\nHowever, two addresses on each subnet are reserved\u2014the first one (all zeros) for the subnet address\nand last address (all ones) for the broadcast address.\ne. What prefix would you use? What is the subnet mask, in binary and decimal format?\nRecall that the prefix indicates the number of bits used to identify the network. Given that this is a", "source": "Page 199", "chapter_title": "Chapter 11"}
{"id": "34b2c49023a9-1", "text": "Class C address and we use 3 bytes plus 3 additional bits for subnets (8 + 8 + 8 + 3 = 27), our prefix\nwill be /27. Recall that the subnet mask is a continuous stream of 1s\u2014in our case, 27 of them.\nTherefore, the subnet mask in binary is 11111111.11111111.11111111.11100000.\nSubnet\nNumber\nSubnet Address (first\naddress on the subnet)\nRange of Host\nAddresses\nDirect Broadcast Address (last\naddress on the subnet)\n0\n192.168.1.0\n192.168.1.1\u2013\n192.168.1.30\n192.168.1.31\n1\n192.168.1.32\n192.168.1.33\u2013\n192.168.1.62\n192.168.1.63\n2\n192.168.1.64\n192.168.1.65\u2013\n192.168.1.94\n192.168.1.95\n3\n192.168.1.96\n192.168.1.97\u2013\n192.168.1.126\n192.168.1.127\n4\n192.168.1.128\n192.168.1.129\u2013\n192.168.1.158\n192.168.1.159\n5\n192.168.1.160\n192.168.1.161\u2013\n192.168.1.190\n192.168.1.191\n6\n192.168.1.192\n192.168.1.193\u2013\n192.168.1.222\n192.168.1.223\n7\n192.168.1.224\n192.168.1.225\u2013\n192.168.1.254", "source": "Page 199", "chapter_title": "Chapter 11"}
{"id": "d25768b666fa-2", "text": "192.168.1.225\u2013\n192.168.1.254\n192.168.1.255\nWe need to convert this binary number into a decimal to get the subnet mask. Hands-On Activity 5C\nmight come in handy here. The subnet mask in decimal is 255.255.255.224.\nf. What is the increment value?\nThe increment value is the amount by which the subnet address increases from one subnet to the next", "source": "Page 199", "chapter_title": "Chapter 11"}
{"id": "3fd5e3c8be3f-0", "text": "and is given by the placeholder value of the last 1 in the subnet mask. Because the last byte in the\nsubnet mask has three 1s, the third number 1 represents 32 (see Hands-On Activity 5C). So, the\nincrement value is 32.\ng. Complete the following table; define each of the subnets, the range of host addresses on the subnet,\nand the directed broadcast address on the subnet. Explanation of this table:\nIn part b, we indicated that there were eight subnets. The best way to fill out the table is to identify\nthe subnet addresses for all subnets. The very first subnet\u2019s IP address is when all the bits in the last\nbyte are 0, giving us the following decimal value: 192.168.1.0. Recall from part f that the incremental\nvalue is 32, which means that the second subnet\u2019s IP address will have the third placeholder equal to\n1, giving us the following address: 192.168.1.32. To find the third subnet\u2019s IP address, we need to\nmultiply the increment value (32) by 2, resulting in 192.168.1.64. You would continue until the eighth\nsubnet, in which all the first 3 bits in the last byte equal 1, giving us 192.168.1.224. The direct\nbroadcast address\u2019s value is one less than the next subnet\u2019s IP address. Also, this address will have all\nthe host bits in the last byte equal to 1. For simplicity, I will only convert the last byte of several\nbroadcast addresses to binary to illustrate this:\nBroadcast Address Last Byte Converted to Binary (network bits | host bits)\n192.168.1.31\n0 0 0 | 1 1 1 1 1\n192.168.1.63", "source": "Page 200", "chapter_title": "Chapter 11"}
{"id": "ced80a54e69c-1", "text": "192.168.1.63\n0 0 1 | 1 1 1 1 1\n192.168.1.95\n0 1 0 | 1 1 1 1 1\n192.168.1.127\n0 1 1 | 1 1 1 1 1\nThe addresses between the subnet address and the broadcast address can be assigned to any hosts on\nthe network.\nDeliverables\nAssume that you have been assigned 192.168.111.129/28.\n1. How many bits are borrowed to create the subnet field? ________________\n2. What is the maximum number of subnets that can be created with this number of bits?\n________________\n3. How many bits can be used to create the host space? ________________\n4. What is the maximum number of host addresses available per subnet? ________________\n5. What is the subnet mask, in binary and decimal format? ________________\n6. Complete the following table and calculate the subnet that this address is on, and define all the other\nsubnets (the range of host addresses on the subnet and the directed broadcast address on the subnet).\nSubnet Number\nSubnet Address Range of Host Addresses Direct Broadcast Address\n0\n1\n2\n3\n4\n5\n6\n7\n\u2026\nLast subnet number\n7. Answer the following:", "source": "Page 200", "chapter_title": "Chapter 11"}
{"id": "a47be6f055d7-0", "text": "a. What subnet is 192.168.111.129 on?\nb. A junior network administrator is trying to assign 192.168.111.127 as a static IP address for a\ncomputer on the network but is getting an error message. Why?\nc. Can 192.168.111.39 be assigned as an IP address?\nHANDS-ON ACTIVITY 5F\nIPv6 Addresses\nThe IPv4 address space provides approximately 4.3 billion addresses, but only 3.7 billion addresses are\nassignable because the IPv4 addressing system separates the addresses into classes and reserves some\naddresses for multicasting, testing, and other specific uses. The IPv4 address space has almost been\nexhausted, which is why it is vital to understand the IPv6 protocol.\nThe 32-bit IPv4 address is a series of four 8-bit fields separated by dots, such as 129.79.126.1. However,\nlarger 128-bit IPv6 addresses need a different representation because of their size. IPv6 addresses use\ncolons to separate entries in a series of 16-bit hexadecimal.\nA sample IPv6 address is 2031:0000:130F:0000:0000: 09C0:876A:130B. IPv6 does not require\nexplicit address string notation. Because the IPv6 addresses are much longer than their IPv4 counterparts,\nseveral rules to shorten the addresses were developed:\nLeading zeros in a field are optional. For example, the field 09C0 equals 9C0, and the field 0000\nequals 0. So 2031:0000:130F:0000:0000:09C0:876A:130B can be written as\n2031:0:130F:0:0:9C0:876A:130B.\nPreferred Representation", "source": "Page 201", "chapter_title": "Chapter 11"}
{"id": "410de94ec1ff-1", "text": "Preferred Representation\nCompressed Representation\nA0B0:10F0:A110:1001:5000:0000:0000:0001\n0000:0000:0000:0000:0000:0000:0000:0001\n2001:0000:0000:1234:0000:0000:0000:45FF\n3ffe:0000:0010:0000:1010:2a2a:0000:1001\n3FFE:0B00:0C18:0001:0000:1234:AB34:0002\nFEC0:0000:0000:1000:1000:0000:0000:0009\nFF80:0000:0000:0000:0250:FFFF:FFFF:FFFF\nSuccessive fields of zeros can be represented as two colons \u201c::\u201d. However, this shorthand method can\nonly be used once in an address, for example, 2031:0:130F:0000:0000:9C0:876A:130B can be\nwritten as 2031:0:130F::9C0:876A:130B.\nAn unspecified address is written as \u201c::\u201d because it contains only zeros.\nDeliverables\n1. Use the preceding guidelines to compress the following IPv6 addresses into the shortest forms\npossible.\n2. Research on the Internet which IPv6 addresses are routable on the Internet.", "source": "Page 201", "chapter_title": "Chapter 11"}
{"id": "1a4037f72b23-0", "text": "PART THREE NETWORK TECHNOLOGIES", "source": "Page 202", "chapter_title": "Chapter 11"}
{"id": "b324c42449ca-0", "text": "CHAPTER 6\nNETWORK DESIGN\nThe chapters in the first section of the book provided a fundamental understanding of how networks work\nusing the five-layer model. This chapter starts the next section of the book, which focuses on how we\ndesign networks. We usually design networks in seven network architecture components: local area\nnetworks (LANs), building backbone networks, campus backbones that connect buildings, wide area\nnetworks (WANs) that connect campuses, Internet access, e-commerce edge, and data centers. Network\ndesign is an iterative process in which the designer examines users\u2019 needs, develops an initial set of\ntechnology designs, assesses their cost, and then revisits the needs analysis until the final network design\nemerges.\nOBJECTIVES\nUnderstand the seven network architecture components\nDescribe the overall process of designing and implementing a network\nDescribe techniques for developing a logical network design\nDescribe techniques for developing a physical network design\nUnderstand network design principles\nOUTLINE\n6.1 Introduction\n6.1.1 Network Architecture Components\n6.1.2 The Traditional Network Design Process\n6.1.3 The Building-Block Network Design Process\n6.2 Needs Analysis\n6.2.1 Network Architecture Component\n6.2.2 Application Systems\n6.2.3 Network Users\n6.2.4 Categorizing Network Needs\n6.2.5 Deliverables\n6.3 Technology Design\n6.3.1 Designing Clients and Servers\n6.3.2 Designing Circuits\n6.3.3 Network Design Tools\n6.3.4 Deliverables\n6.4 Cost Assessment\n6.4.1 Request for Proposal\n6.4.2 Selling the Proposal to Management\n6.4.3 Deliverables\n6.5 Implications for Cyber Security", "source": "Page 203", "chapter_title": "Chapter 11"}
{"id": "d8f361c0a034-0", "text": "Summary\n6.1 INTRODUCTION\nAll but the smallest organizations have networks, which means that most network design projects are the\ndesign of upgrades or extensions to existing networks, rather than the construction of entirely new\nnetworks. Even the network for an entirely new building is likely to be integrated with the organization\u2019s\nexisting backbone network or wide area network (WAN), so even new projects can be seen as extensions\nof existing networks. Nonetheless, network design is very challenging.\n6.1.1 Network Architecture Components\nNetwork designers usually think about networks as seven distinct network architecture components when\nthey design networks. Figure 6-1 shows a typical network for a large enterprise. This organization has\nthree enterprise campuses in different cities that are connected by a WAN provided by a common\ncarrier such as AT&T. Each campus has several buildings that are connected by a backbone network.\nThe first network architecture component is the local area network (LAN), which enables users to\naccess the network. Some vendors call this component the access layer because it provides access to the\nnetwork. Chapter 7 describes LANs, both wired and wireless, because when we build LANs today, we\nusually provide both wired and wireless access. The technologies we use in the LAN are probably familiar\nto you because you have used them, and perhaps you have even installed them in your home or\napartment: They are network hubs, switches, and wireless access points.\nThe second network architecture component is the building backbone network, which some vendors\ncall the distribution layer, because it distributes network traffic to and from the LANs. The building\nbackbone typically uses the same basic technology that we use in the LAN (a network switch), but usually\nwe buy faster switches because the building backbone carries more network traffic than a LAN. Chapter 8\ndescribes building backbones.\nThe third network architecture component is the campus backbone (sometimes called the core layer),", "source": "Page 204", "chapter_title": "Chapter 11"}
{"id": "569898e70e36-1", "text": "The third network architecture component is the campus backbone (sometimes called the core layer),\nwhich connects all the buildings on one campus. The campus backbone is usually faster than the\nbackbones we use inside buildings because it typically carries more traffic than they do. We use routers or\nlayer 3 switches that do routing when we design the campus backbone. Chapter 8 also describes campus\nbackbones.\nThe fourth network architecture component is the data center, which contains the organization\u2019s servers\n(e.g., database servers, email servers). The data center is essentially a LAN, but because so much traffic\ngoes to and from the data center, it is typically designed and managed very differently than the LANs\nintended for user access. The data center is usually located centrally on the enterprise campus, with a\nvery, very-high-speed connection into the campus backbone. There is usually one primary data center for\nthe organization, typically found on its main headquarters campus. It is common for large organizations\nto have several data centers spread around the world. Many enterprise campuses have their own smaller\ndata centers that store data just for that campus. We briefly discuss data center LAN design in Chapter 7.", "source": "Page 204", "chapter_title": "Chapter 11"}
{"id": "22308d1d797d-0", "text": "FIGURE 6-1 Network architecture components\nThe last three components of the network architecture make up the enterprise edge, the parts of the\nnetwork that are at the edge of an enterprise campus and connect that campus to the rest of the world.\nOne of these is the wide area network (WAN), which is discussed in Chapter 9. A WAN is a private\nnetwork that connects its different campus locations, usually leased from a common carrier such as\nAT&T. The WAN is for the private use of the organization and only carries its network traffic from one\ncampus to another, unlike the Internet, which carries traffic from many different organizations. The\ncircuits used in the WAN are traditionally very different than the Ethernet we use in the LAN, but this is\nchanging.\nAnother network architecture component is the Internet access component, which enables the\norganization to connect to the Internet. The Internet and the technologies we use to connect to it are\ndiscussed in Chapter 10. Large organizations use the same technologies to connect to the Internet as they\nuse in the WAN. Small companies and individuals like us typically use cable modem from your cable\ncompany (e.g., Comcast or Time Warner) or DSL from AT&T.\nThe final network architecture component is the e-commerce edge. The e-commerce edge is a special\nLAN with a group of servers that enables electronic data exchange between the organization and the\nexternal entities with which it does business (such as its customers or suppliers). For example, the\norganization\u2019s primary Web server is located in the e-commerce edge. Like the data center, the design of\nthe LAN for the e-commerce edge is specialized; we briefly discuss it in Chapter 7 and again in Chapter 11\non security, because the e-commerce edge often requires different security.\nNetwork design usually begins at the access layer, not the core layer. The needs of the users drive the", "source": "Page 205", "chapter_title": "Chapter 11"}
{"id": "93109c8f5da9-1", "text": "network design (as well as the applications in the data center). This is the reason that we discuss LANs\nfirst (Chapter 7) and then move into the distribution and core layers (Chapter 8), with the enterprise edge\ncoming last (WANs in Chapter 9 and the Internet in Chapter 10).\nMost organizations put the last five components in the same building. The switches and routers that", "source": "Page 205", "chapter_title": "Chapter 11"}
{"id": "667a40c799d3-0", "text": "compose the campus backbone, the data center, and the enterprise edge are usually placed in one central\nbuilding on campus so that data move very quickly between the enterprise edge, the campus backbone,\nand the data center.\n6.1.2 The Traditional Network Design Process\nThe traditional network design process follows a very structured systems analysis and design\nprocess similar to that used to build application systems. First, the network analyst meets with users to\nidentify user needs and the application systems planned for the network. Second, the analyst develops a\nprecise estimate of the amount of data that each user will send and receive and uses this to estimate the\ntotal amount of traffic on each part of the network. Third, the circuits needed to support this traffic plus a\nmodest increase in traffic are designed, and cost estimates are obtained from vendors. Finally, 1 or 2 years\nlater, the network is built and implemented.\nThis traditional process, although expensive and time consuming, works well for static or slowly evolving\nnetworks. Unfortunately, networking today is significantly different from what it was when the traditional\nprocess was developed. Three forces are making the traditional design process less appropriate for many\nof today\u2019s networks.\nFirst, the underlying technology of the client and server computers, networking devices, and the circuits\nthemselves is changing very rapidly. In the early 1990s, mainframes dominated networks, the typical\nclient computer was an 8-MHz 386 with 1 megabyte (MB) of random access memory (RAM) and 40 MB of\nhard disk space, and a typical circuit was a 9,600-bps mainframe connection or a 1-Mbps LAN. Today,\nclient computers and servers are significantly more powerful, and circuit speeds of 1 Gbps (one billion bits\nper second) are common. We now have more processing capability and network capacity than ever before;", "source": "Page 206", "chapter_title": "Chapter 11"}
{"id": "9de9d53f11e8-1", "text": "per second) are common. We now have more processing capability and network capacity than ever before;\nboth are no longer scarce commodities that we need to manage carefully.\nSecond, the growth in network traffic is immense. The challenge is not in estimating today\u2019s user demand\nbut in estimating its growth rate. In the early 1990s, email and the Web were novelties primarily used by\nuniversity professors and scientists. In the past, network demand was essentially driven by predictable\nbusiness systems such as order processing. Today, much network demand is driven by less predictable\nuser behavior, such as email and the Web. Many experts expect the rapid increase in network demand to\ncontinue, especially as video, voice, and multimedia applications become commonplace on networks. At a\n10% growth rate, user demand on a given network will increase by one-third in 3 years. At 20%, it will\nincrease by about 75% in 3 years. At 30%, it will double in less than 3 years. A minor mistake in estimating\nthe growth rate can lead to major problems. With such rapid growth, it is no longer possible to accurately\npredict network needs for most networks. In the past, it was not uncommon for networks to be designed\nto last for 5\u201310 years. Today, most network designers use a 3- to 5-year planning horizon.\nFinally, the balance of costs has changed dramatically over the years. In the early 1990s, the most\nexpensive item in any network was the hardware (circuits, devices, and servers). Today, the most\nexpensive part of the network is the staff members who design, operate, and maintain it. As the costs have\nshifted, the emphasis in network design is no longer on minimizing hardware cost (although it is\nimportant); the emphasis today is on designing networks to reduce the staff time needed to operate them.", "source": "Page 206", "chapter_title": "Chapter 11"}
{"id": "d91cfe2a4fb1-2", "text": "important); the emphasis today is on designing networks to reduce the staff time needed to operate them.\nThe traditional process minimizes the equipment cost by tailoring the equipment to a careful assessment\nof needs but often results in a mishmash of different devices with different capabilities. Two resulting\nproblems are that staff members need to learn to operate and maintain many different devices and that it\noften takes longer to perform network management activities because each device may use slightly\ndifferent software.\nToday, the cost of staff time is far more expensive than the cost of equipment. Thus, the traditional\nprocess can lead to a false economy\u2014save money now in equipment costs but pay much more over the\nlong term in staff costs.\nMANAGEMENT FOCUS 6-1\nAverage Life-Spans", "source": "Page 206", "chapter_title": "Chapter 11"}
{"id": "127cd239fbf9-0", "text": "A recent survey of network managers found that most expect their network hardware to last 3\u20135\nyears\u2014not because the equipment wears out, but because rapid changes in capabilities make\notherwise good equipment obsolete. As Joel Snyder, a senior partner at OpusOne (a network\nconsulting firm), puts it: \u201cYou might go buy a firewall for a 1.5 Mbps circuit at a remote office and\nthen 2 weeks later have your cable provider offer you 50 Mbps.\u201d\nLife expectancy for selected network equipment:\nRack-mounted switch 4.5 years Wi-Fi access point 3 years\nChassis switch\n4.5 years Desktop PC\n3.5 years\nBackbone router\n5 years\nLaptop PC\n2.5 years\nBranch office router\n4 years\nMainframe\n8.5 years\n6.1.3 The Building-Block Network Design Process\nSome organizations still use the traditional process of network design, particularly for those applications\nfor which hardware or network circuits are unusually expensive (e.g., WANs that cover long distances\nthrough many different countries). However, many other organizations now use a simpler approach to\nnetwork design that we call the building-block process. The key concept in the building-block process\nis that networks that use a few standard components throughout the network are cheaper in the long run\nthan networks that use a variety of different components on different parts of the network.\nRather than attempting to accurately predict user traffic on the network and build networks to meet those\ndemands, the building-block process instead starts with a few standard components and uses them over\nand over again, even if they provide more capacity than is needed. The goal is simplicity of design. This\nstrategy is sometimes called \u201cnarrow and deep\u201d because a very narrow range of technologies and devices\nis used over and over again (very deeply throughout the organization). The results are a simpler design", "source": "Page 207", "chapter_title": "Chapter 11"}
{"id": "a350b3dba063-1", "text": "is used over and over again (very deeply throughout the organization). The results are a simpler design\nprocess and a more easily managed network built with a smaller range of components.\nIn this chapter, we focus on the building-block process to network design. The basic design process\ninvolves three steps that are performed repeatedly: needs analysis, technology design, and cost\nassessment (Figure 6-2). This process begins with needs analysis, during which the designer attempts\nto understand the fundamental current and future network needs of the various users, departments, and\napplications. This is likely to be an educated guess at best. Users\u2019 access needs and the needs of\napplications drive the network design process from the top into the center of the network. These needs are\nclassified as typical or high volume. Specific technology needs are identified (e.g., the ability to dial in with\ncurrent modem technologies).\nThe next step, technology design, examines the available technologies and assesses which options will\nmeet users\u2019 needs. The designer makes some estimates about the network needs of each category of user\nand circuit in terms of current technology (e.g., 1 Gbps Ethernet) and matches needs to technologies.\nBecause the basic network design is general, it can easily be changed as needs and technologies change.\nThe difficulty, of course, lies in predicting user demand so one can define the technologies needed. Most\norganizations solve this by building more capacity than they expect to need and by designing networks\nthat can easily grow and then closely monitoring growth so they expand the network ahead of the growth\npattern.\nIn the third step, cost assessment, the relative costs of the technologies are considered. The process\nthen cycles back to the needs analysis, which is refined using the technology and cost information to\nproduce a new assessment of users\u2019 needs. This, in turn, triggers changes in the technology design and", "source": "Page 207", "chapter_title": "Chapter 11"}
{"id": "837d33dabb8e-2", "text": "cost assessment, and so on. By cycling through these three processes, the final network design is\nestablished (Figure 6-3).\n6.2 NEEDS ANALYSIS\nThe goal of needs analysis is to understand why the network is being built and what users and applications\nit will support. In many cases, the network is being designed to improve poor performance or enable new", "source": "Page 207", "chapter_title": "Chapter 11"}
{"id": "ffc0f3a66858-0", "text": "applications to be used. In other cases, the network is upgraded to replace unreliable or aging equipment\nor to standardize equipment so that only one type of equipment, one protocol (e.g., TCP/IP, Ethernet), or\none vendor\u2019s equipment is used everywhere in the network.\nOften, the goals in network design are slightly different between LANs and backbone networks (BNs) on\nthe one hand and WANs on the other. In the LAN and BN environments, the organization owns and\noperates the equipment and the circuits. Once they are paid for, there are no additional charges for usage.\nHowever, if major changes must be made, the organization will need to spend additional funds. In this\ncase, most network designers tend to err on the side of building too big a network\u2014that is, building more\ncapacity than they expect to need.\nFIGURE 6-2 Network design", "source": "Page 208", "chapter_title": "Chapter 11"}
{"id": "97b065456367-0", "text": "FIGURE 6-3 The cyclical nature of network design\nIn contrast, in most WANs, the organization leases circuits from a common carrier and pays for them on a\nmonthly or per-use basis. Understanding capacity becomes more important in this situation because\nadditional capacity comes at a noticeable cost. In this case, most network designers tend to err on the side\nof building too small a network, because they can lease additional capacity if they need it\u2014but it is much\nmore difficult to cancel a long-term contract for capacity they are not using.\nMuch of the needs analysis may already have been done because most network design projects today are\nnetwork upgrades rather than the design of entirely new networks. In this case, there is already a fairly\ngood understanding of the existing traffic in the network and, most important, of the rate of growth of\nnetwork traffic. It is important to gain an understanding of the current operations (application systems\nand messages). This step provides a baseline against which future design requirements can be gauged. It\nshould provide a clear picture of the present sequence of operations, processing times, work volumes, the\ncurrent communication network (if one exists), existing costs, and user/management needs. Whether the\nnetwork is a new network or a network upgrade, the primary objective of this stage is to define (1) the", "source": "Page 209", "chapter_title": "Chapter 11"}
{"id": "c48632af03e9-0", "text": "geographic scope of the network and (2) the users and applications that will use it.\nThe goal of the needs analysis step is to produce a logical network design, which is a statement of the\nnetwork elements needed to meet the needs of the organization. The logical design does not specify\ntechnologies or products to be used (although any specific requirements are noted). Instead, it focuses on\nthe fundamental functionality needed, such as a high-speed access network, which in the technology\ndesign stage will be translated into specific technologies (e.g., switched 100Base-T).\n6.2.1 Network Architecture Component\nThe first step in needs analysis is to break the network into the seven network architecture\ncomponents in Figure 6-1: LANs, building backbones, campus backbones, WANs, Internet access, e-\ncommerce edge, and data centers. Not all layers are present in all networks. Small networks, for example,\nmay not have a core backbone because there is only one building. Likewise, the data center is typically\ndesigned and managed separately.\nSometimes, the current network infrastructure imposes constraints. For example, if we are adding a new\nbuilding to an existing office complex that used 1 Gbps Ethernet in the LANs, then we will probably\nchoose to use the same in the new building. All such constraints are noted.\nIt is easiest to start with the highest level, so most designers begin by drawing a network diagram for any\nWANs with enterprise campuses that must be connected. A diagram that shows the logical network going\nbetween the locations is sufficient. Details such as the type of circuit and other considerations will be\nadded later. Next, the individual enterprise campus diagrams are drawn, usually in a series of separate\ndiagrams, but for a simple network, one diagram may be sufficient.\nMANAGEMENT FOCUS 6-2\nA New Hospital Network", "source": "Page 210", "chapter_title": "Chapter 11"}
{"id": "5d18237cb363-1", "text": "MANAGEMENT FOCUS 6-2\nA New Hospital Network\nKingston Hospital is part of the National Health Service in the United Kingdom. The hospital is one\nof the largest in London, with more than 3,500 employees. As the health-care industry moves into a\ndigital environment, the network becomes critical. Mobile computing on tablets at the patient\nbedside enables doctors, nurses, and other staff to provide care without relying on paper notes,\nwhich can be easily lost or misunderstood because of illegible handwriting.\nThe access layer is primarily wireless LAN, with 650 wireless access points spread throughout the\nhospital. The hospital provides more than 200 tablets to staff to review patient records, update\nobservations, and order tests and medications. Pharmacists use laptops and workstations on wheels\nto manage and deliver prescriptions.\nThese access points and wired LANs are connected into building backbones that run at 1 Gbps. These\nin turn are connected into two large campus backbone switches that provide 10 Gbps.\nAdapted from: \u201cLaying Foundations for Digital Hospital Vision,\u201d Cisco Systems Inc.\nAt this point, the designers gather general information and characteristics of the environment in which\nthe network must operate. For example, they determine whether there are any legal requirements, such as\nlocal, state/provincial, federal, or international laws, regulations, or building codes, that might affect the\nnetwork.\n6.2.2 Application Systems\nNext, the designers must review the list of applications that will use the network and identify the location\nof each. This information should be added to the emerging network documentation. This process is called\nbaselining. Next, those applications that are expected to use the network in the future are added.\nIn many cases, the applications will be relatively well defined. Specific internal applications (e.g., payroll)", "source": "Page 210", "chapter_title": "Chapter 11"}
{"id": "101d3bd0f921-2", "text": "and external applications (e.g., Web servers) may already be part of the \u201cold\u201d network. However, it is\nimportant to review the organization\u2019s long- and short-range plans concerning changes in company goals,", "source": "Page 210", "chapter_title": "Chapter 11"}
{"id": "d5a50b8f33a9-0", "text": "strategic plans, development plans for new products or services, projections of sales, research and\ndevelopment projects, major capital expenditures, possible changes in product mix, new offices that must\nbe served by the communications network, security issues, and future commitments to technology. For\nexample, a major expansion in the number of offices or a major electronic commerce initiative will have a\nsignificant impact on network requirements.\nIt is also helpful to identify the hardware and software requirements of each application that will use the\nnetwork and, if possible, the protocol each application uses (e.g., HTTP over TCP/IP, Windows file\naccess). This knowledge helps now and will be particularly useful later when designers develop\ntechnological solutions.\n6.2.3 Network Users\nIn the past, application systems accounted for the majority of network traffic. Today, much network traffic\nis produced by the discretionary use of the Internet. Applications such as email and the Web are\ngenerating significant traffic, so the network manager is no longer in total control of the network traffic\ngenerated on his or her networks. This is likely to continue in the future as network-hungry applications\nsuch as desktop videoconferencing become more common. Therefore, in addition to understanding the\napplications, you must also assess the number and type of users that will generate and receive network\ntraffic and identify their location on the emerging network diagram. We usually assume that most users\nwill want both wired and wireless access to the network, although there are exceptions. Hotels may only\nprovide wireless access for guests, and some offices may only provide wired access.\n6.2.4 Categorizing Network Needs\nAt this point, the network has been designed in terms of geographic scope, application systems, and users.\nThe next step is to assess the relative amount of traffic generated in each part of the network. With the\ntraditional design approach, this involves considerable detailed analysis. With the building-block", "source": "Page 211", "chapter_title": "Chapter 11"}
{"id": "9a239d0529d8-1", "text": "traditional design approach, this involves considerable detailed analysis. With the building-block\napproach, the goal is to provide some rough assessment of the relative magnitude of network needs. Each\napplication system is assessed in general terms to determine the amount of network traffic that can be\nexpected to generate today and in the future, compared with other applications. Likewise, each user is\ncategorized as either a typical user or a high-traffic user. These assessments will be refined in the next\nstage of the design process.\nThis assessment can be problematic, but the goal is some relative understanding of the network needs.\nSome simple rules of thumb can help. For example, applications that require large amounts of multimedia\ndata or those that load executables over the network are likely to be high-traffic applications. Applications\nthat are time sensitive or need constant updates (e.g., financial information systems, order processing) are\nlikely to be high-traffic applications.\nOnce the network requirements have been identified, they also should be organized into mandatory\nrequirements, desirable requirements, and wish-list requirements. This information enables\nthe development of a minimum level of mandatory requirements and a negotiable list of desirable\nrequirements that are dependent on cost and availability. For example, desktop video-conferencing may\nbe a wish-list item, but it will be omitted if it increases the cost of the network beyond what is desired.\nAt this point, the local facility network diagrams are prepared. For a really large network, there may be\nseveral levels. The choice is up to the designer, provided the diagrams and supporting text clearly explain\nthe network\u2019s needs.", "source": "Page 211", "chapter_title": "Chapter 11"}
{"id": "c3c145f0710f-0", "text": "FIGURE 6-4 Sample needs assessment logical network design for a single building. LAN = local area\nnetwork\n6.2.5 Deliverables\nThe key deliverable for the needs assessments stage is a set of logical network diagrams, showing the\napplications, circuits, clients, and servers in the proposed network, each categorized as either typical or\nhigh traffic. The logical diagram is the conceptual plan for the network and does not consider the specific\nphysical elements (e.g., routers, switches, circuits) that will be used to implement the network.\nFigure 6-4 shows the results of a needs assessment for a building that includes the access layer (LANs),\nthe distribution layer (building backbone), and the core layer (campus backbone). This figure shows the\ndistribution and access components in the building with the series of six access LANs connected by one\nbuilding backbone, which is in turn connected to a campus core back-bone. One of the six LANs is\nhighlighted as a high-traffic LAN, whereas the others are typical ones. We normally would assume that the\nLANs need both wired and wireless access unless the requirements stated differently. Three mandatory\napplications are identified that will be used by all network users: email, Web, and file sharing. One wish-\nlist requirement (desktop videoconferencing) is also identified for a portion of the network.", "source": "Page 212", "chapter_title": "Chapter 11"}
{"id": "b15fd714b296-0", "text": "6.3 TECHNOLOGY DESIGN\nOnce the needs have been defined in the logical network design, the next step is to develop a physical\nnetwork design (or a set of possible designs). The physical network design starts with the client and\nserver computers needed to support the users and applications. If the network is a new network, new\ncomputers will need to be purchased. If the network is an existing network, the servers may need to be\nupgraded to the newest technology. Once these are designed, then the circuits and devices connecting\nthem are designed.\n6.3.1 Designing Clients and Servers\nThe idea behind the building-block approach is to specify needs in terms of some standard units. Typical\nusers are allocated the base-level client computers, as are servers supporting typical applications. Users\nand servers for applications needing more powerful computers are assigned some advanced computer. As\nthe specifications for computers rapidly improve and costs drop (usually every 6 months), today\u2019s typical\nuser may receive the type of computer originally intended for the advanced user when the network is\nactually implemented, and the advanced users may end up with a computer not available when the\nnetwork was designed.\n6.3.2 Designing Circuits\nThe same is true for network circuits and devices (e.g., hubs, routers, switches). There are two interrelated\ndecisions in designing network circuits and devices: the fundamental technology and protocols (e.g.,\nEthernet) and the capacity of each circuit (e.g., 100 Mbps, 1,000 Mbps). These are interrelated because\neach technology offers different circuit capacities.\nDesigning the circuit capacity means capacity planning, estimating the size and type of the standard\nand advanced network circuits for each type of network (LAN, backbone, WAN). As you will learn in\nChapter 7 on LANs, wired and wireless circuits come in standard sizes. Most users with a desktop or", "source": "Page 213", "chapter_title": "Chapter 11"}
{"id": "03f5dd5bb806-1", "text": "laptop computer don\u2019t need to send files that are over a gigabyte in size at a time (i.e., 1,000 Meg). And if\nthey do, they understand there may be a slight delay. Therefore, circuits for wired LANs are typically 100\nMbps or 1 Gbps. Wireless circuits are a little different, so we\u2019ll avoid them until Chapter 7.\nDesigning circuit capacities for backbone networks is more challenging because backbones move traffic\nfrom many computers at one time and there are more choices in standard sizes. This requires some\nassessment of the current and future circuit loading (the amount of data transmitted on a circuit). This\nanalysis can focus on either the average circuit traffic or the peak circuit traffic. For example, in an online\nbanking network, traffic volume peaks usually are in the midmorning (bank opening) and just prior to\nclosing. Airline and rental car reservations network designers look for peak volumes before and during\nholidays or other vacation periods, whereas telephone companies normally have their highest peak\nvolumes on Mother\u2019s Day. Designing for peak circuit traffic is the ideal.\nThe designer usually starts with the total characters transmitted per day on each circuit or, if possible, the\nmaximum number of characters transmitted per 2-second interval if peaks must be met. You can calculate\nmessage volumes by counting messages in a current network and applying some estimated growth rate. If\nan existing network is in place, network monitors/analyzers (see Chapter 12) may be able to provide an\nactual circuit character count of the volume transmitted per minute or per day.\nA good rule of thumb is that 80% of this circuit loading information is easy to gather. The last 20% needed\nfor very precise estimates is extremely difficult and expensive to find. However, precision usually is not a\nmajor concern because of the stairstep nature of communication circuits and the need to project future", "source": "Page 213", "chapter_title": "Chapter 11"}
{"id": "2388ff059800-2", "text": "major concern because of the stairstep nature of communication circuits and the need to project future\nneeds. For example, the difference between 100 Mbps and 1 Gbps is quite large, and assessing which level\nis needed for typical traffic does not require a lot of precision. Forecasts are inherently less precise than\nunderstanding current network traffic. The turnpike effect is an expression that means that traffic\nincreases much faster than originally forecast. It comes from the traffic forecasting that was done for the\nconstruction of the early interstate highways. When a new, faster highway (or network) is built, people are\nmore likely to use it than the old slow one because it is available, is very efficient, and provides new\ncapabilities. The annual growth factor for network use may vary from 5% to 50% and, in some cases, may\nexceed 100% for high-growth organizations.", "source": "Page 213", "chapter_title": "Chapter 11"}
{"id": "6de23185d032-0", "text": "Although no organization wants to overbuild its network and pay for more capacity than it needs, in most\ncases, upgrading a network costs 50% to 80% more than building it right the first time. Few organizations\ncomplain about having too much network capacity, but being under capacity can cause significant\nproblems. Given the rapid growth in network demand and the difficulty in accurately predicting it, most\norganizations intentionally overbuild (build more capacity into their network than they plan to use), and\nmost end up using this supposedly unneeded capacity within 3 years.\nIn any network, there may be a bottleneck, a circuit that is filled almost to its capacity and thus is the\ncritical point that determines whether users get good or bad response times. When users complain about a\nslow network, it is usually because there is a bottleneck circuit somewhere in the network. Of course, the\nbottleneck could also be a slow Web server that is simply receiving more traffic than it can handle, but\nusually the problem is a circuit.\nTake another look at Figure 6-4. Suppose we specified 1 Gbps circuits as the standard for the LANs. If\neach LAN has 20 computers, then this is in theory a total capacity of 120 Gbps in the building (6 LANs \u00d7\n20 computers each \u00d7 1 Gbps = 120 Gbps). Not all the computers will be sending or receiving at the same\ntime, so this is artificially high, but it is a theoretical maximum.\nIf this is the case, what speed should we specify for the building backbone? We have a few standard\nspeeds, as you will learn in Chapter 8: 1 Gbps, 10 Gbps, 40 Gbps, 100 Gbps. A 1-Gbps backbone is\nprobably too slow and would end up being a bottleneck. Is 10 Gbps enough? It\u2019s hard to say without", "source": "Page 214", "chapter_title": "Chapter 11"}
{"id": "a34965ad1699-1", "text": "knowing the circuit loading. Without the circuit loading, most network designers would set the building\nbackbone speed at one level above the standard LAN speed, which in this case would be 10 Gbps.", "source": "Page 214", "chapter_title": "Chapter 11"}
{"id": "17140955c478-0", "text": "FIGURE 6-5 Physical network design for a single building\nThis problem continues at the next architecture component\u2014the campus core backbone. If each building\nhas a 10-Gbps backbone, what speed should the campus backbone that connects all the buildings be?\nWithout a circuit loading, it\u2019s hard to say. Once again, most network designers would set the building\nbackbone speed at one level above the building backbone speed, which in this case would be 40 Gbps. And\nthis is where reality sets in. Today, the technology for 40 Gbps is very expensive\u2014so expensive, in fact,\nthat most organizations don\u2019t buy it unless they really need it. Chances are, the campus backbone would\nbe designed at 10 Gbps, which means it might be the bottleneck\u2014at least for traffic on campus.\nFigure 6-5 shows the physical design for the network in Figure 6-4. Take a moment to look at it and\ncompare Figures 6-4 and 6-5.\nAs we move beyond the campus to the enterprise edge, network design becomes a bit more difficult. As\nyou will learn in Chapter 9, on WANs, and Chapter 10, on the Internet, the technologies we use for WANs\nand Internet access are quite different from what we use for LANs and backbones. Their speeds are much,\nmuch slower and much more expensive. A typical WAN circuit speed is between 1 Mbps and 50 Mbps.\nYes, that was Mbps; in other words, more than 100 times slower than the speed of our backbone\nnetworks. Thus, the bottleneck in most enterprise networks is the WAN and the Internet, not the\nenterprise campus network.", "source": "Page 215", "chapter_title": "Chapter 11"}
{"id": "563b5c6c7f9d-0", "text": "This is also true for the network in your house or apartment. Most wireless LAN access points you buy\ntoday provide speeds of 100\u2013400 Mbps, yet your Internet connection is usually less than 25 Mbps. This\nmeans the response times you experience when you\u2019re on the Internet will be the same whether you buy a\nreally fast, state-of-the-art wireless access point or an old one that provides only 50 Mbps, because the\nbottleneck is the Internet access, not the wireless LAN. Unless you\u2019re spending a lot of money on a really\nfast Internet connection, don\u2019t waste your money on a really fast wireless access point.\n6.3.3 Network Design Tools\nNetwork modeling and design tools can perform a number of functions to help in the technology design\nprocess. With most tools, the first step is to enter a diagram or model of the existing network or proposed\nnetwork design. Some modeling tools require the user to create the network diagram from scratch. That\nis, the user must enter all of the network components by hand, placing each server, client computer, and\ncircuit on the diagram and defining what each is.\nOther tools can \u201cdiscover\u201d the existing network; that is, once installed on the network, they will explore\nthe network to draw a network diagram. In this case, the user provides some starting point, and the\nmodeling software explores the network and automatically draws the diagram itself. Once the diagram is\ncomplete, the user can then change it to reflect the new network design. Obviously, a tool that can perform\nnetwork discovery by itself is most helpful when the network being designed is an upgrade to an existing\nnetwork and when the network is very complex.\nOnce the diagram is complete, the next step is to add information about the expected network traffic and\nsee if the network can support the level of traffic that is expected. Simulation, a mathematical technique", "source": "Page 216", "chapter_title": "Chapter 11"}
{"id": "6ce97491719b-1", "text": "see if the network can support the level of traffic that is expected. Simulation, a mathematical technique\nin which the network comes to life and behaves as it would under real conditions, is used to model the\nbehavior of the communication network. Applications and users generate and respond to messages while\nthe simulator tracks the number of packets in the network and the delays encountered at each point in the\nnetwork.\nSimulation models may be tailored to the users\u2019 needs by entering parameter values specific to the\nnetwork at hand (e.g., this computer will send an average of three 100-byte packets per minute and\nreceive one hundred 1,500-byte packets per minute). Alternatively, the user may prefer to rely primarily\non the set of average values provided by the network.\nOnce the simulation is complete, the user can examine the results to see the estimated response times\nthroughout. It is important to note that these network design tools provide only estimates, which may\nvary from the actual results. At this point, the user can change the network design in an attempt to\neliminate bottlenecks and rerun the simulation. Good modeling tools not only produce simulation results\nbut also highlight potential trouble spots (e.g., servers, circuits, or devices that experienced long response\ntimes). The very best tools offer suggestions on how to overcome the problems that the simulation\nidentified.\n6.3.4 Deliverables\nThe key deliverable is a set of one or more physical network designs like that in Figure 6-5, which is the\ndesign for a single building. Most designers like to prepare several physical designs so they can trade-off\ntechnical benefits (e.g., performance) against cost. In most cases, the critical part is the design of the\nnetwork circuits and devices. In the case of a new network designed from scratch, it is also important to\ndefine the client computers with care because these will form a large portion of the total cost of the", "source": "Page 216", "chapter_title": "Chapter 11"}
{"id": "1bf4bb7b7037-2", "text": "define the client computers with care because these will form a large portion of the total cost of the\nnetwork. Usually, however, the network will replace an existing network and only a few of the client\ncomputers in the existing network will be upgraded.\n6.4 COST ASSESSMENT\nThe purpose of this step is to assess the costs of various physical network design alternatives produced in\nthe previous step. The main items are the costs of software, hardware, and circuits. These three factors are\nall interconnected and must be considered along with the performance and reliability required. All factors\nare interrelated with regard to cost.", "source": "Page 216", "chapter_title": "Chapter 11"}
{"id": "80012547dc17-0", "text": "Estimating the cost of a network is quite complex because many factors are not immediately obvious.\nSome of the costs that must be considered are as follows:\nCircuit costs, including costs of circuits provided by common carriers or the cost of purchasing and\ninstalling your own cable\nNetwork devices such as switches and routers\nHardware costs, including servers, printers, uninterruptible power supplies, and backup tape drives\nSoftware costs for network operating system, application software, and middleware\nNetwork management costs, including special hardware, software, and training needed to develop a\nnetwork management system for ongoing redesign, monitoring, and diagnosis of problems\nTest and maintenance costs for special monitoring equipment and software, plus the cost of onsite\nspare parts\nCosts for WAN and Internet circuits leased from common carriers\n6.4.1 Request for Proposal\nAlthough some network components can be purchased off the shelf, most organizations develop a\nrequest for proposal (RFP) before making large network purchases. RFPs specify what equipment,\nsoftware, and services are desired and ask vendors to provide their best prices. Some RFPs are very\nspecific about what items are to be provided in what time frame. In other cases, items are defined as\nmandatory, important, or desirable, or several scenarios are provided and the vendor is asked to propose\nthe best solution. In a few cases, RFPs specify generally what is required and the vendors are asked to\npropose their own network designs. Figure 6-6 provides a summary of the key parts of an RFP.\nOnce the vendors have submitted their proposals, the organization evaluates them against specified\ncriteria and selects the winner(s). Depending on the scope and complexity of the network, it is sometimes\nnecessary to redesign the network on the basis of the information in the vendors\u2019 proposals.\nOne of the key decisions in the RFP process is the scope of the RFP. Will you use one vendor or several", "source": "Page 217", "chapter_title": "Chapter 11"}
{"id": "45ba2f32c431-1", "text": "vendors for all hardware, software, and services? Multivendor environments tend to provide better\nperformance because it is unlikely that one vendor provides the best hardware, software, and services in\nall categories. Multivendor networks also tend to be less expensive because it is unlikely that one vendor\nwill always have the cheapest hardware, software, and services in all product categories.\nMultivendor environments can be more difficult to manage, however. If equipment is not working\nproperly and it is provided by two different vendors, each can blame the other for the problem.\n6.4.2 Selling the Proposal to Management\nOne of the main problems in network design is obtaining the support of senior management. To\nmanagement, the network is simply a cost center, something on which the organization is spending a lot\nof money with little apparent change. The network keeps on running just as it did the year before.\nThe key to gaining the acceptance of senior management lies in speaking management\u2019s language. It is\npointless to talk about upgrades from 100 Mbps to 1 Gbps on the backbone because this terminology is\nmeaningless from a business perspective. A more compelling argument is to discuss the growth in\nnetwork use. For example, a simple graph that shows network usage growing at 25% per year, compared\nwith the network budget growing at 10% per year, presents a powerful illustration that the network costs\nare well managed, not out of control.\nLikewise, a focus on network reliability is an easily understandable issue. For example, if the network\nsupports a mission-critical system such as order processing or moving point-of-sale data from retail stores\nto corporate offices, it is clear from a business perspective that the network must be available and\nperforming properly, or the organization will lose revenue.\nInformation in a Typical Request for Proposal\nBackground information", "source": "Page 217", "chapter_title": "Chapter 11"}
{"id": "1f6c6debe05a-0", "text": "Organizational profile\nOverview of current network\nOverview of new network\nGoals of new network\nNetwork requirements\nChoice sets of possible network designs (hardware, software, circuits)\nMandatory, desirable, and wish-list items\nSecurity and control requirements\nResponse-time requirements\nGuidelines for proposing new network designs\nService requirements\nImplementation time plan\nTraining courses and materials\nSupport services (e.g., spare parts on site)\nReliability and performance guarantees\nBidding process\nTime schedule for the bidding process\nGround rules\nBid evaluation criteria\nAvailability of additional information\nInformation required from vendor\nVendor corporate profile\nExperience with similar networks\nHardware and software benchmarks\nReference list\nFIGURE 6-6 Request for proposal\n6.4.3 Deliverables\nThere are three key deliverables for this step. The first is an RFP that goes to potential vendors. The\nsecond deliverable, after the vendor has been selected, is the revised physical network diagram (e.g.,\nFigure 6-5) with the technology design complete. Exact products and costs are specified at this point (e.g.,\na 24-port 1000Base-T Cisco Ethernet switch). The third deliverable is the business case that provides\nsupport for the network design, expressed in business objectives.\n6.5 IMPLICATIONS FOR CYBER SECURITY\nThinking of networks as seven separate architectural components also helps with network security. Each\ncomponent is a distinct module that can be managed separately in terms of security. The components with\nthe tightest security are usually the core layer and the data center. Servers in the data center are usually\nheavily protected so that no traffic from outside the network can reach them. Data on these servers are\nusually encrypted, so that if an attacker manages to break-in and steal data, the encryption must be\nbroken before the data are useful.", "source": "Page 218", "chapter_title": "Chapter 11"}
{"id": "70749037a340-1", "text": "broken before the data are useful.\nSecurity for the enterprise edge is typically managed differently than security for the rest of the network.\nSince many external attacks are launched over the Internet, security for the Internet Access component", "source": "Page 218", "chapter_title": "Chapter 11"}
{"id": "948cc0e7ae5d-0", "text": "has to be managed carefully\u2014and constantly. Interestingly, the e-commerce edge often has the lightest\nsecurity because it needs to permit access to anyone in the world. After all, if your customers can\u2019t reach\nyour Web server or your email server, what use are they? Nonetheless, the e-commerce edge is carefully\nmonitored because it is a prime target.\nEach building has its own access and distribution layers, and although there may be some similarities\namong buildings, each building can be managed separately. Think about your university. Would you have\nsimilar security for a typical classroom building versus the university administration building?\nSUMMARY\nNetwork Architecture Components Network designers usually think about networks as seven\nnetwork architecture components. LANs (wired and wireless) provide users access to the network\n(access layer). Building backbones (distribution layer) connect the LANs inside one building. Campus\nbackbones (core layer) connect the different buildings. The data center houses the organization\u2019s\nmain servers. At the enterprise edge, we have WAN access that connects to other campuses operated\nby the organization, Internet access, and the e-commerce edge, which enables a business to support\nits customers and/or suppliers.\nTraditional Network Design The traditional network design approach follows a very structured\nsystems analysis and design process similar to that used to build application systems. It attempts to\ndevelop precise estimates of network traffic for each network user and network segment. Although\nthis is expensive and time consuming, it works well for static or slowly evolving networks.\nUnfortunately, computer and networking technology is changing very rapidly, the growth in network\ntraffic is immense, and hardware and circuit costs are relatively less expensive than they used to be.\nTherefore, use of the traditional network design approach is decreasing.\nBuilding-Block Approach to Network Design The building-block approach attempts to build\nthe network using a series of simple predefined building components, resulting in a simpler design", "source": "Page 219", "chapter_title": "Chapter 11"}
{"id": "4042938d3e77-1", "text": "the network using a series of simple predefined building components, resulting in a simpler design\nprocess and a more easily managed network built with a smaller range of components. The basic\nprocess involves three steps that are performed repeatedly. Needs analysis involves developing a\nlogical network design that includes the geographic scope of the network and a categorization of\ncurrent and future network needs of the various network segments, users, and applications as either\ntypical or high traffic. The next step, technology design, results in a set of one or more physical\nnetwork designs. Network design and simulation tools can play an important role in selecting the\ntechnology that typical and high-volume users, applications, and network segments will use. The final\nstep, cost assessment, gathers cost information for the network, usually through an RFP that specifies\nwhat equipment, software, and services are desired and asks vendors to provide their best prices. One\nof the keys to gaining acceptance by senior management of the network design lies in speaking\nmanagement\u2019s language (cost, network growth, and reliability), not the language of the technology\n(Ethernet, ATM, and DSL).\nKEY TERMS\naccess layer\nbaseline\nbottleneck\nbuilding backbone network\nbuilding-block process\ncampus backbone\ncapacity planning\ncircuit loading\ncommon carrier", "source": "Page 219", "chapter_title": "Chapter 11"}
{"id": "c02ade57227d-0", "text": "core layer\ncost assessment\ndata center\ndistribution layer\ne-commerce edge\nenterprise campuses\nenterprise edge\ngeographic scope\nInternet access\nlogical network design\nlocal area network (LAN)\nmandatory requirements\nneeds analysis\nnetwork architecture component\nphysical network design\nrequest for proposal (RFP)\nsimulation\ntechnology design\ntraditional network design process\nturnpike effect\nwide area network (WAN)\nwish-list requirements\nQUESTIONS\n1. What are the keys to designing a successful data communications network?\n2. How does the traditional approach to network design differ from the building-block approach?\n3. Describe the three major steps in the current network design.\n4. What is the most important principle in designing networks?\n5. Why is it important to analyze needs in terms of both application systems and users?\n6. Describe the key parts of the technology design step.\n7. How can a network design tool help in network design?\n8. On what should the design plan be based?\n9. What is an RFP, and why do companies use them?\n10. What are the key parts of an RFP?\n11. What are some major problems that can cause network designs to fail?\n12. What is a network baseline, and when is it established?\n13. What issues are important to consider in explaining a network design to senior management?\n14. What is the turnpike effect, and why is it important in network design?\n15. What are the seven network architecture components?", "source": "Page 220", "chapter_title": "Chapter 11"}
{"id": "f7af1b740aab-0", "text": "16. What is the difference between a building backbone and a campus backbone, and what are the\nimplications for the design of each?\n17. What are typical speeds for the LAN, building back-bone, and campus backbone? Why?\n18. What is a bottleneck, and why do network managers care about them?\n19. Is it important to have the fastest wireless LAN technology in your apartment? What about in the\nlibrary of your school? Explain.\n20. Why do you think some organizations were slow to adopt a building-block approach to network\ndesign?\n21. For what types of networks are network design tools most important? Why?\nEXERCISES\nA. What factors might cause peak loads in a network? How can a network designer determine if they are\nimportant, and how are they taken into account when designing a data communications network?\nB. Collect information about two network design tools and compare and contrast what they can and\ncannot do.\nMINICASES\nI. Computer Dynamics Computer Dynamics is a microcomputer software development company\nthat has a 300-computer network. The company is located in three adjacent five-story buildings in an\noffice park, with about 100 computers in each building. The LANs in each building are similar, but\none building has the data center on the second floor. There are no other office locations. The current\nnetwork is poorly designed for its current needs and must be completely replaced. Develop a logical\ndesign for this enterprise campus that considers the seven network architecture components. There\nare no other campuses, so you can omit WAN access. You will need to make some assumptions, so be\nsure to document your assumptions and explain why you have designed the network in this way.\nII. Drop and Forge Drop and Forge is a manufacturing firm with a 60-computer network on its", "source": "Page 221", "chapter_title": "Chapter 11"}
{"id": "3a154bbedb2b-1", "text": "Toledo, Ohio, campus. The company has one very large manufacturing plant with an adjacent office\nbuilding. The office building houses 50 computers, with an additional 10 computers in the plant. The\ncurrent network is old and needs to be completely replaced. Develop a logical design for this\nenterprise campus that considers the seven network architecture components. There are no other\ncampuses, so you can omit WAN access. You will need to make some assumptions, so be sure to\ndocument your assumptions and explain why you have designed the network in this way.\nIII. AdviceNet AdviceNet is a consulting firm with offices in Toronto, New York, Los Angeles, Dallas,\nand Atlanta. The firm currently uses the Internet to transmit data, but its needs are growing and it is\nconcerned over the security of the Internet. The New York office is the primary headquarters with\n200 computers spread across four floors and has the enterprise data center. Develop a logical design\nfor the New York enterprise campus that considers the seven network architecture components.\nDescribe the assumptions you have made.\nIV. Accurate Accounting Accurate Accounting is a regional accounting firm that has 15 local offices\nthroughout Georgia, Florida, and the Carolinas. The company is constructing a new office building for\nuse as its main headquarters. The building will have two floors with a total of 40 offices, each with a\ndesktop computer. Develop a logical design for the Atlanta headquarters enterprise campus that\nconsiders the seven network architecture components. You will need to make some assumptions, so\nbe sure to document your assumptions and explain why you have designed the network in this way.\nV. Donald\u2019s Distributing Donald\u2019s Distributing is a regional trucking firm that is constructing a new\noffice building (its only office). The network has 80 desktop computers and 2 servers. Develop a\nlogical design for the enterprise campus that considers the seven network architecture components.", "source": "Page 221", "chapter_title": "Chapter 11"}
{"id": "304cd2fea2b5-2", "text": "logical design for the enterprise campus that considers the seven network architecture components.\nYou will need to make some assumptions, so be sure to document your assumptions and explain why\nyou have designed the network in this way.", "source": "Page 221", "chapter_title": "Chapter 11"}
{"id": "6f429b242f68-0", "text": "TECH UPDATES\nIn every chapter, we will offer a couple of ideas to investigate.\nTopic A: Securing Code\nSecuring coding is the practice of developing computer software in a way that guards against the\naccidental introduction of security vulnerabilities. Defects, bugs, and logic flaws are consistently the\nprimary cause of commonly exploited software vulnerabilities. Several vulnerabilities that must be\nprevented through secure coding are as follows: buffer overflow, format string attack prevention, and\ninteger overflow prevention. Investigate these vulnerabilities (and others) and provide examples of how to\nprotect against them.\nTopic B: Emergency of Python as a must Know Language for Cybersecurity\nProgramming has become essential to cybersecurity. IT security professionals must efficiently write\napplications and scripts; often on short notice. The Python language provides unmatched ease, flexibility,\nand functionality for both new and experienced coders. It has emerged as a top choice for cybersecurity\nprofessionals because it lessens development effort and the coder\u2019s learning curve. What are some\n\u201cbasics\u201d that a cybersecurity professional must know when it comes to python. Provide examples.\nDeliverables\nYour job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title Slide\n2. Short description of the topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use a lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along\n5. How does it relate to material covered in class so far (and in the future)\n6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 6A", "source": "Page 222", "chapter_title": "Chapter 11"}
{"id": "3de95fdc9d52-1", "text": "HANDS-ON ACTIVITY 6A\nNetwork Design Software\nThere are many different network design software tools. Some are simple drawing tools; others offer\npowerful network simulation modeling capabilities. One powerful tool that provides a free demo version\nthat can be downloaded is SmartDraw.", "source": "Page 222", "chapter_title": "Chapter 11"}
{"id": "b7edeee51c21-0", "text": "FIGURE 6-7 SmartDraw software\nThe first step is to download and install the SmartDraw software. The software is available at\nwww.smartdraw.com.\nSmartDraw comes with a variety of network icons and templates that can be used to quickly build network\ndiagrams. Figure 6-7 shows the main drawing screen in SmartDraw and a network diagram.\nDeliverable\nSelect a network and draw it.", "source": "Page 223", "chapter_title": "Chapter 11"}
{"id": "c68eed590c64-0", "text": "CHAPTER 7\nWIRED AND WIRELESS LOCAL AREA NETWORKS\nThis chapter examines the three major network architecture components that use local area networks\n(LANs): the LANs that provide network access to users, the data center, and the e-commerce edge. We\nfocus on the LANs that provide network access to users as these are more common. This chapter draws\ntogether the concepts from the first section of the book on fundamental concepts to describe how wired\nand wireless LANs work. We first summarize the major components of LANs and then describe the two\nmost commonly used LAN technologies: wired and wireless Ethernet. The chapter ends with a discussion\nof how to design LANs and how to improve LAN performance.\nOBJECTIVES\nUnderstand the major components of LANs\nUnderstand the best practice recommendations for LAN design\nBe able to design wired Ethernet LANs\nBe able to design wireless Ethernet LANs\nBe able to improve LAN performance\nOUTLINE\n7.1 Introduction\n7.2 LAN Components\n7.2.1 Network Interface Cards\n7.2.2 Network Circuits\n7.2.3 Network Hubs, Switches, and Access Points\n7.2.4 Network Operating Systems\n7.3 Wired Ethernet\n7.3.1 Topology\n7.3.2 Media Access Control\n7.3.3 Types of Ethernet\n7.4 Wireless Ethernet\n7.4.1 Topology\n7.4.2 Media Access Control\n7.4.3 Wireless Ethernet Frame Layout\n7.4.4 Types of Wireless Ethernet\n7.4.5 Security\n7.5 The Best Practice LAN Design\n7.5.1 Designing User Access with Wired Ethernet\n7.5.2 Designing User Access with Wireless Ethernet\n7.5.3 Designing the Data Center\n7.5.4 Designing the e-Commerce Edge", "source": "Page 224", "chapter_title": "Chapter 11"}
{"id": "bf044daf7b9d-0", "text": "7.5.5 Designing the SOHO Environment\n7.6 Improving LAN Performance\n7.6.1 Improving Server Performance\n7.6.2 Improving Circuit Capacity\n7.6.3 Reducing Network Demand\n7.7 Implications for Cyber Security\nSummary\n7.1 INTRODUCTION\nThis chapter focuses on the first major network architecture component: the local area networks (LANs)\nthat provide users access to the network. Most large organizations have numerous wired and wireless\nLANs connected by backbone networks. In this chapter, we discuss the fundamental components of a\nLAN, along with two technologies commonly used in LANs\u2014traditional wired Ethernet (IEEE 802.3),\nwhich is commonly used to connect desktop computers, and wireless Ethernet (IEEE 802.11, commonly\ncalled Wi-Fi), which often is used to connect laptop computers and mobile devices. There used to be many\ndifferent types of LAN technologies, but gradually the world has changed so that Ethernet dominates. The\nmajority of LAN design is done for the LANs that enable users to access the network, whether wired or\nwireless, because there are more of these LANs than any other type. Therefore, this chapter focuses on the\ndesign of these access LANs. However, the data center and e-commerce edge also use LANs, so we include\nsections on the unique design needs of these two network architecture components.\nA Day in the Life: LAN Administrator\nMost days start the same way. The LAN administrator arrives early in the morning before most\npeople who use the LAN. The first hour is spent checking for problems. All the network hardware\nand servers in the server room receive routine diagnostics. All the logs for the previous day are\nexamined to find problems. If problems are found (e.g., a crashed hard disk), the next few hours are", "source": "Page 225", "chapter_title": "Chapter 11"}
{"id": "010df0829527-1", "text": "spent fixing them. Next, the daily backups are done. This usually takes only a few minutes, but\nsometimes a problem occurs and it takes an hour.\nThe next step is to see if there are any other activities that need to be performed to maintain the\nnetwork. This involves checking email for security alerts (e.g., Windows updates and antivirus\nupdates). If critical updates are needed, they are done immediately. There are usually emails from\nseveral users that need to be contacted, concerning either problems with the LAN or requests for\nnew hardware or software to be installed. These new activities are prioritized into the work queue.\nAnd then the real work begins. Work activities include tasks such as planning for the next roll out of\nsoftware upgrades. This involves investigating the new software offerings, identifying what hardware\nplatforms are required to run them, and determining which users should receive the upgrades. It\nalso means planning for and installing new servers or network hardware such as firewalls.\nOf course, some days can be more exciting than others. When a new virus hits, everyone is involved\nin cleaning up the compromised computers and installing security patches on the other computers.\nSometimes, virus attacks can be fun when you see that your security settings work and beat the virus.\nSource: With thanks to Steve Bushert.\n7.2 LAN COMPONENTS\nThere are several components in a traditional LAN (Figure 7-1). The first two are the client computer and\nthe server. Clients and servers have been discussed in Chapter 2, so they are not discussed further here.\nThe other components are network interface cards (NICs), network circuits, hubs/switches/access points,", "source": "Page 225", "chapter_title": "Chapter 11"}
{"id": "624995d3d89d-0", "text": "and the network operating system.\n7.2.1 Network Interface Cards\nThe network interface card (NIC) is used to connect the computer to the network cable in a wired\nnetwork and is one part of the physical layer connection among the computers in the network. In a\nwireless network, the NIC is a radio transmitter that sends and receives messages on a specific radio\nfrequency. All desktop computers have a wired NIC built in, while virtually all laptops have both a wired\nNIC and a wireless NIC. You can purchase a wireless NIC for a desktop computer (often as a USB device).\nFIGURE 7-1 Local area network components\n7.2.2 Network Circuits\nEach computer must be physically connected by network circuits to the other computers in the network.\nWired LANs\nMost LANs are built with unshielded twisted-pair (UTP) cable, shielded twisted-pair (STP)\ncable, or fiber-optic cable. (Common cable standards are discussed in the following box. We should\nadd that these cable standards specify the minimum quality cable required; it is possible, for example, to\nuse category 5e UTP cable that is rated for 1,000 Mbps in a LAN that runs at 100 Mbps.)\nMany LANs use UTP cable. Its low cost makes it very useful. STP is only used in special areas that produce\nelectrical interference, such as factories near heavy machinery or hospitals near MRI scanners.\nFiber-optic cable is even thinner than UTP wire and therefore takes far less space when cabled throughout\na building. It is also much lighter, weighing less than 10 pounds per 1,000 feet. Because of its high\ncapacity, fiber-optic cabling is perfect for BNs, although it is beginning to be used in LANs.\nWireless LANs", "source": "Page 226", "chapter_title": "Chapter 11"}
{"id": "b6e4c4d2b826-1", "text": "Wireless LANs\nWireless LANs (WLANs) use radio transmissions to send data between the NIC and the access point\n(AP). Most countries (but not all) permit WLANs to operate in two frequency ranges: the 2.4 and 5 GHz\nrange. These same frequency ranges can be used by cordless phones and baby monitors, which means that\nyour WLAN and your cordless phone may interfere with each other. Under ideal conditions, the radio\ntransmitters in the NICs and APs can transmit 100\u2013150 meters (300\u2013450 feet). In practice, the range is\nmuch shorter as walls absorb the radio waves. The other problem is that as the distance from the AP\nincreases, the maximum speed drops, often very dramatically.\nWhen we design a WLAN, it is important to ensure that the APs don\u2019t interfere with each other. If all APs\ntransmitted on the same frequency, the transmissions of one AP would interfere with another AP.\nTherefore, each AP is set to transmit on a different channel, very much like the different channels on\nyour TV. Each channel uses a different part of the 2.4 or 5 GHz frequency range so that there is no", "source": "Page 226", "chapter_title": "Chapter 11"}
{"id": "8dbeb05e5a7c-0", "text": "interference among the different channels. When a computer first starts using the WLAN, its NIC\nsearches all available channels within the appropriate frequency range and then picks the channel that has\nthe strongest signal.\nTECHNICAL FOCUS 7-1\nCommonly Used Network Cable Standards\nName\nType Maximum Data Rate Often Used By\nCost1 ($/foot)\nCategory 12\nUTP\n1 Mbps\nTelephone\n0.04\nCategory 33\nUTP\n10 Mbps\n10Base-T Ethernet\n0.06\nCategory 5\nUTP\n100 Mbps\n100Base-T Ethernet\n0.07\nCategory 5\nSTP\n100 Mbps\n100Base-T Ethernet\n0.18\nCategory 5e4\nUTP\n1 Gbps\n1000Base-T Ethernet\n0.10\nCategory 65\nUTP\n10 Gbps\n10GBase-T\n0.20\nCategory 76\nSTP\n100 Gbps\n100GBase-T\n0.35\nOM1 (62.5/125) Fiber\n10 Gbps\n10 GbE Ethernet\n0.45\nOM5 (50/125)\nFiber\n100 Gbps\n100 GbE Ethernet\n0.65\nNotes\n1These costs are approximate costs for cable only (no connectors). They often change but will give you a sense of the relative\ndifferences in costs among the different options.\n2Category 1 is standard voice-grade twisted-pair wires, but it can also be used to support low-speed analog data transmission.\n3Categories 2 and 4 cables are old standards and no longer in use today.\n4Category 5e is an improved version of category 5 that has better insulation and a center plastic pipe inside the cable to keep the", "source": "Page 227", "chapter_title": "Chapter 11"}
{"id": "f681a7279f2c-1", "text": "individual wires in place and reduce noise from cross-talk, so that it is better suited to 1000Base-T.\n5Category 6 cable has less ranges than the other types of cable (maximum 55 meters) but they are still long enough for many LAN\ninstallations.\n6Category 7 cables have a maximum range of 15 meters, which means they are typically used between networking devices that are near\neach other (e.g., in a rack or data center).\n7.2.3 Network Hubs, Switches, and Access Points\nNetwork hubs and switches serve two purposes. First, they provide an easy way to connect network\ncables. A hub or a switch can be thought of as a junction box, permitting new computers to be connected\nto the network as easily as plugging a power cord into an electrical socket. Each connection point where a\ncable can be plugged in is called a port. Each port has a unique number. Switches can be designed for use\nin small-office, home-office (SOHO) environments (see Figure 7-2a) or for large enterprise\nenvironments (see Figure 7-2b).\nSimple hubs and switches are commonly available in 4-, 8-, 16-, and 24-port sizes, meaning that they\nprovide anywhere between 4 and 24 ports into which network cables can be plugged. When no cables are\nplugged in, the signal bypasses the unused port. When a cable is plugged into a port, the signal travels\ndown the cable as though it were directly connected to the hub or switch. Some switches also enable\ndifferent types of cables to be connected and perform the necessary conversions (e.g., twisted-pair cable to\ncoaxial cable and twisted-pair cable to fiber-optic cable).", "source": "Page 227", "chapter_title": "Chapter 11"}
{"id": "fa9fb2c13e50-0", "text": "FIGURE 7-2 LAN switches\nMANAGEMENT FOCUS 7-1\nCable Problems at the University of Georgia\nLike many organizations, the Terry College of Business at the University of Georgia is headquartered\nin a building built before the computer age. When local area network cabling was first installed in the\nearly 1980s, no one foresaw the rapid expansion that was to come. Cables and hubs were installed\npiecemeal to support the needs of the handful of early users.\nThe network eventually grew far beyond the number of users it was designed to support. The\nnetwork cabling gradually became a complex, confusing, and inefficient mess. There was no logical\npattern for the cables, and there was no network cable plan. Worse still, no one knew where all the\ncables and hubs were physically located. Before a new user was added, a network technician had to\nopen up a ceiling and crawl around to find a hub. Hopefully, the hub had an unused port to connect\nthe new user, or else the technician would have to find another hub with an empty port.\nTo complicate matters even more, asbestos was discovered. Now network technicians could not open\nthe ceiling and work on the cable unless asbestos precautions were taken. This meant calling in the\nuniversity\u2019s asbestos team and sealing off nearby offices. Installing a new user to the network (or\nfixing a network cable problem) now took 2 days and cost $2,000.\nThe solution was obvious. The university spent $400,000 to install new category 5 twisted-pair cable\nin every office and to install a new high-speed fiber-optic backbone network between network\nsegments.\nSecond, hubs and switches act as repeaters. Signals can travel only so far in a network cable before they\nattenuate and can no longer be recognized. (Attenuation was discussed in Chapter 4.) All LAN cables are", "source": "Page 228", "chapter_title": "Chapter 11"}
{"id": "b7f236aaa2e7-1", "text": "rated for the maximum distance they can be used (typically 100 meters for twisted-pair cable and 400\nmeters to several kilometers for fiber-optic cable).\nA wireless access point (AP) is a radio transceiver that plays the same role as a hub or switch in wired\nEthernet LANs. It enables the computers near it to communicate with each other, and it also connects\nthem into wired LANs, typically using 100Base-T or 1000Base-T. All NICs in the WLAN transmit their", "source": "Page 228", "chapter_title": "Chapter 11"}
{"id": "5415f8cf9643-0", "text": "frames to the AP, and then the AP retransmits the frames over the wireless network or over the wired\nnetwork to their destination. Therefore, if a frame has to be transmitted from one wireless computer to\nanother, it is transmitted twice, once from the sender to the AP and then from the AP to the destination.\nAt first glance, this may seem a bit strange because it doubles the number of transmissions in the WLAN.\nHowever, very few frames are ever sent from client computer to client computer in a WLAN. Most frames\nare exchanged between client computers and a server of some kind. Therefore, a server should never be\nplaced on a WLAN because client computers cannot reach it directly but have to communicate with it via\nthe AP. Even if they are intended to serve clients on a WLAN, they should always be placed on the wired\nportion of the LAN.\nFigure 7-3a shows an AP for use in SOHO environments. This AP is wired into the regular Ethernet LAN\nand has a separate power supply that is plugged into a normal electrical outlet. Figure 7-3b shows an AP\nfor use in large enterprises. It is also wired into the regular Ethernet LAN, but it uses power over\nEthernet (POE) so it needs no external power; the power is provided from a POE switch over the\nunused wires in a category 5/5e cable. POE APs are more expensive, but can be located anywhere you can\nrun Cat 5/5e cable, even if there are no power outlets nearby.\nMost WLANs are installed using APs that have omnidirectional antennas, which means that the\nantenna transmits in all directions simultaneously. Some antennas are built into the AP itself, while\nothers stick up above it. One common omnidirectional antenna is the dipole antenna shown in Figure 7-", "source": "Page 229", "chapter_title": "Chapter 11"}
{"id": "57d9a8093bca-1", "text": "3a; others are built into the AP box, as is Figure 7-3b.\nThe other type of antenna that can be used on APs is the directional antenna, which, as the name\nsuggests, projects a signal only in one direction. Because the signal is concentrated in a narrower, focused\narea, the signal is stronger and therefore will carry farther than the signal from an AP using an\nomnidirectional antenna. Directional antennas are most often used on the inside of an exterior wall of a\nbuilding, pointing to the inside of the building. This keeps the signal inside the building (to reduce\nsecurity issues) and also has the benefit of increasing the range of the AP.\nMany wireless routers are sold for use in SOHO environments. The wireless routers are both a wireless AP\nand a router, and many also contain a 1000Base-T switch. It is important not to use the term wireless\nrouter when you mean a wireless AP.\nFIGURE 7-3 Wireless access points\nMANAGEMENT FOCUS 7-2\nManaging Network Cabling\nYou must consider a number of items when installing cables or when performing cable maintenance.\nYou should do the following:\nPerform a physical inventory of any existing cabling systems and document those findings in the\nnetwork cable plan.", "source": "Page 229", "chapter_title": "Chapter 11"}
{"id": "d443cb062e41-0", "text": "Properly maintain the network cable plan. Always update cable documentation immediately on\ninstalling or removing a cable or hub. Insist that any cabling contractor provide \u201cas-built\u201d plans\nthat document where the cabling was actually placed, in case of minor differences from the\nconstruction plan.\nEstablish a long-term plan for the evolution of the current cabling system to whatever cabling\nsystem will be in place in the future.\nObtain a copy of the local city fire codes and follow them. For example, cables used in airways\nwithout conduit need to be plenum-certified (i.e., covered with a fire-retardant jacket).\nConceal all cables as much as possible to protect them from damage and for security reasons.\nProperly number and mark both ends of all cable installations as you install them. If a\ncontractor installs cabling, always make a complete inspection to ensure that all cables are\nlabeled.\n7.2.4 Network Operating Systems\nThe network operating system (NOS) is the software that controls the network. Every NOS provides\ntwo sets of software: one that runs on the network server(s) and one that runs on the network client(s).\nThe server version of the NOS provides the software that performs the functions associated with the data\nlink, network, and application layers and usually the computer\u2019s own operating system. The client version\nof the NOS provides the software that performs the functions associated with the data link and the\nnetwork layers and must interact with the application software and the computer\u2019s own operating system.\nMost NOSs provide different versions of their client software that run on different types of computers, so\nthat Windows computers, for example, can function on the same network as Apple computers. In most\ncases (e.g., Windows and Linux), the client NOS software is included with the operating system itself.\nNOS Server Software", "source": "Page 230", "chapter_title": "Chapter 11"}
{"id": "cb9a94c45044-1", "text": "NOS Server Software\nThe NOS server software enables the file server, print server, or database server to operate. In addition to\nhandling all the required network functions, it acts as the application software by executing the requests\nsent to it by the clients (e.g., copying a file from its hard disk and transferring it to the client, printing a file\non the printer, executing a database request, and sending the result to the client). NOS server software\nreplaces the normal operating system on the server. By replacing the existing operating system, it provides\nbetter performance and faster response time because a NOS is optimized for its limited range of\noperations. The most commonly used NOS are Windows Server and Linux.\nNOS Client Software\nThe NOS software running at the client computers provides the data link layer and network layer. Most\noperating systems today are designed with networking in mind. For example, Windows provides built-in\nsoftware that will enable it to act as a client computer with a Windows Server.\nOne of the most important functions of a NOS is a directory service. Directory services provide\ninformation about resources on the network that are available to the users, such as shared printers,\nshared file servers, and application software. A common example of directory services is Microsoft\u2019s\nActive Directory Service (ADS).\nActive Directory Service works in much the same manner as TCP/IP\u2019s DNS service, and in fact ADS\nservers, called domain controllers, can also act as DNS servers. Network resources are typically\norganized into a hierarchical tree. Each branch on the tree contains a domain, a group of related\nresources. For example, at a university, one domain might be the resources available within the business\nschool, and another domain might be the resources in the computer science school, while another might\nbe in the medical school. Domains can contain other domains, and in fact the hierarchical tree of domains", "source": "Page 230", "chapter_title": "Chapter 11"}
{"id": "b8ad4ae02606-2", "text": "within one organization can be linked to trees in other organizations to create a forest of shared network\nresources.\nWithin each domain, there is a server (the domain controller) that is responsible for resolving address\ninformation (much like a DNS server resolves address information on the Internet). The domain", "source": "Page 230", "chapter_title": "Chapter 11"}
{"id": "75a90883a95f-0", "text": "controller is also responsible for managing authorization information (e.g., who is permitted to use each\nresource) and making sure that resources are available only to authorized users. Domain controllers in the\nsame tree (or forest) can share information among themselves, so that a domain controller in one part of\nthe tree (or forest) can be configured to permit access to resources to any user that has been approved by\nanother domain controller in a different part of the tree (or forest).\nIf you login to a Microsoft server or domain controller that provides ADS, you can see all network\nresources that you are authorized to use. When a client computer wishes to view available resources or\naccess them, it sends a message using an industry standard directory protocol called lightweight\ndirectory access protocol (LDAP) to the ADS domain controller. The ADS domain controller resolves\nthe textual name in the LDAP request to a network address and\u2014if the user is authorized to access the\nresource\u2014provides contact information for the resource.\nNetwork Profiles\nA network profile specifies what resources on each server are available on the network for use by other\ncomputers and which devices or people are allowed what access to the network. The network profile is\nnormally configured when the network is established and remains in place until someone makes a change.\nIn a LAN, the server hard disk may have various resources that can or cannot be accessed by a specific\nnetwork user (e.g., data files and printers). Furthermore, a password may be required to grant network\naccess to the resources.\nIf a device such as a hard disk on one of the network\u2019s computers is not included on the network profile, it\ncannot be used by another computer on the network. For example, if you have a hard disk (C) on your\ncomputer and your computer is connected to this LAN but the hard disk is not included on the network\nprofile assignment list, then no other computer can access that hard disk.", "source": "Page 231", "chapter_title": "Chapter 11"}
{"id": "84a4b1512275-1", "text": "profile assignment list, then no other computer can access that hard disk.\nIn addition to profiling disks and printers, there must be a user profile for each person who uses the LAN,\nto add some security. Each device and each user is assigned various access codes, and only those users\nwho log in with the correct code can use a specific device. Most LANs keep audit files to track who uses\nwhich resource. Security is discussed in Chapter 9.\n7.3 WIRED ETHERNET\nAlmost all LANs installed today use some form of Ethernet. Ethernet was originally developed by DEC,\nXerox, and Intel but has since become a standard formalized by the IEEE as IEEE 802.3. The IEEE\n802.3 version of Ethernet is slightly different from the original version but the differences are minor.\nLikewise, another version of Ethernet has also been developed that differs slightly from the 802.3\nstandard.\nEthernet is a layer 2 protocol, which means it operates at the data link layer. Every Ethernet LAN needs\nhardware at layer 1, the physical layer, that matches the requirements of the Ethernet software at layer 2.\n7.3.1 Topology\nTopology is the basic geometric layout of the network\u2014the way in which the computers on the network\nare interconnected. It is important to distinguish between a logical topology and a physical topology. A\nlogical topology is how the network works conceptually, much like a logical data flow diagram (DFD) or\nlogical entity relation diagram (ERD) in systems analysis and design or database design. A physical\ntopology is how the network is physically installed, much like a physical DFD or physical ERD.\nHub-Based Ethernet\nHub-based Ethernet is seldom used by companies today, but cheap consumer-grade hubs are still\navailable. Knowledge about hub-based Ethernet will be useful when we discuss wireless Ethernet. When", "source": "Page 231", "chapter_title": "Chapter 11"}
{"id": "2a5a30477d34-2", "text": "available. Knowledge about hub-based Ethernet will be useful when we discuss wireless Ethernet. When\nwe use hubs, Ethernet\u2019s logical topology is a bus topology. All computers are connected to one half-\nduplex circuit running the length of the network that is called the bus. The top part of Figure 7-4 shows\nEthernet\u2019s logical topology. All frames from any computer flow onto the central cable (or bus) and\nthrough it to all computers on the LAN. Every computer on the bus receives all frames sent on the bus,\neven those intended for other computers. Before processing incoming frames, the Ethernet software on", "source": "Page 231", "chapter_title": "Chapter 11"}
{"id": "3dca98b2790d-0", "text": "each computer checks the data link layer address and processes only those frames addressed to that\ncomputer.\nThe bottom part of Figure 7-4 shows the physical topology of an Ethernet LAN when a hub is used. From\nthe outside, an Ethernet LAN appears to be a star topology, because all cables connect to the central hub.\nNonetheless, it is logically a bus.\nWith hubs, all computers share the same multipoint circuit and must take turns using it. This shared\nmultipoint circuit is often called a collision domain, because if two computers ever did accidentally\ntransmit at the same time, there would be a collision. When one computer transmits, all the other\ncomputers must wait, which is very inefficient. Because all frames are sent to all computers in the same\ncollision domain, security is a problem because any frame can be read by any computer. Most companies\ndon\u2019t use hub-based Ethernet today, but products are still available and are very cheap. Wireless Ethernet,\nwhich we discuss in a later section, works much the same as hub-based Ethernet.\nFIGURE 7-4 Ethernet topology using hubs\nSwitch-Based Ethernet\nAlmost all corporate installations of Ethernet today use switches, not hubs. When we use switches,\nEthernet\u2019s topology is a logical star and a physical star (Figure 7-5). From the outside, the switch looks\nalmost identical to a hub, but inside, it is very different. A switch is an intelligent device with a small\ncomputer built in that is designed to manage a set of separate point-to-point circuits. That means that\neach circuit connected to a switch is not shared with any other devices; only the switch and the attached\ncomputer use it. The physical topology looks essentially the same as Ethernet\u2019s physical topology: a star.\nOn the inside, the logical topology is a set of separate point-to-point circuits, also a star. Many switches", "source": "Page 232", "chapter_title": "Chapter 11"}
{"id": "6d61a95c0a6a-1", "text": "support full duplex circuits, meaning that each circuit can simultaneously send and receive.\nWhen a switch receives a frame from a computer, it looks at the address on the frame and retransmits the\nframe only on the circuit connected to that computer, not to all circuits as a hub would. Therefore, no\ncomputer needs to wait because another computer is transmitting; every computer can transmit at the\nsame time, resulting in much faster performance. As a result, each port on the switch is in a separate", "source": "Page 232", "chapter_title": "Chapter 11"}
{"id": "a2ac62ef3bb5-0", "text": "collision domain, and there are only two devices on it: the switch and the computer/device on the other\nend of the cable. Today, no one buys a hub unless she or he can\u2019t afford a switch.\nSo how does a switch know which circuit is connected to what computer? The switch uses a forwarding\ntable that is very similar to the routing tables discussed in Chapter 5. The table lists the Ethernet address\nof the computer connected to each port on the switch. When the switch receives a frame, it compares the\ndestination address on the frame to the addresses in its forwarding table to find the port number on which\nit needs to transmit the frame. Because the switch uses the Ethernet address to decide which port to use\nand because Ethernet is a data link layer or layer 2 protocol, this type of switch is called a layer 2 switch.\nFIGURE 7-5 Ethernet topology using switches\nWhen switches are first turned on, their forwarding tables are empty; they do not know what Ethernet\naddress is attached to what port. Switches learn addresses to build the forwarding table. When a switch\nreceives a frame, it reads the frame\u2019s data link layer source address and compares this address to its\nforwarding table. If the address is not in the forwarding table, the switch adds it, along with the port on\nwhich the frame was received.\nIf a switch receives a frame with a destination address that is not in the forwarding table, the switch must\nstill send the frame to the correct destination. In this case, it must retransmit the frame to all ports, except\nthe one on which the frame was received. The attached computers, being Ethernet and assuming they are\nattached to a hub, will simply ignore all frames not addressed to them. The one computer for whom the\nframe is addressed will recognize its address and will process the frame, which includes sending an", "source": "Page 233", "chapter_title": "Chapter 11"}
{"id": "7bd001d9e66a-1", "text": "frame is addressed will recognize its address and will process the frame, which includes sending an\nacknowledgement (ACK) or a negative acknowledgement (NAK) back to the sender. When the switch\nreceives the ACK or NAK, it will add this computer\u2019s address and the port number on which the ACK or\nNAK was received to its forwarding table and then send the ACK or NAK on its way.\nSo, for the first few minutes until the forwarding table is complete, the switch acts like a hub. But as its\nforwarding table becomes more complete, it begins to act more and more like a switch. In a busy network,\nit takes only a few minutes for the switch to learn most addresses and match them to port numbers. To", "source": "Page 233", "chapter_title": "Chapter 11"}
{"id": "e8d9dac428d2-0", "text": "make a switch work faster, the most active connections are placed on the top of the forwarding table. If a\ncomputer is not communicating for more than 300 seconds, its entry is usually removed from the\nforwarding table.\nThere are three modes in which switches can operate. The first is cut-through switching. With cut-\nthrough switching, the switch begins to transmit the incoming packet on the proper outgoing circuit as\nsoon as it has read the destination address in the frame. In other words, the switch begins transmitting\nbefore it has received the entire frame. The advantage of this is low latency (the time it takes a device\nfrom receiving a frame to transmitting it) and results in a very fast network. The disadvantage is that the\nswitch begins transmitting before it has read and processed the frame check sequence at the end of the\nframe; the frame may contain an error, but the switch will not notice until after almost all of the frame has\nbeen transmitted. Cut-through switching can only be used when the incoming data circuit has the same\ndata rate as the outgoing circuit.\nWith the second switching mode, called store-and-forward switching, the switch does not begin\ntransmitting the outgoing frame until it has received the entire incoming frame and has checked to make\nsure it contains no errors. Only after the switch is sure there are no errors does the switch begin\ntransmitting the frame on the outgoing circuit. If errors are found, the switch simply discards the frame.\nThis mode prevents an invalid frame from consuming network capacity, but provides higher latency and\nthus results in a slower network (unless many frames contain errors). Store-and-forward switching can be\nused regardless of whether the incoming data circuit has the same data rate as the outgoing circuit\nbecause the entire frame must be stored in the switch before it is forwarded on its way.\nThe final mode, called fragment-free switching, lies between the extremes of cut-through switching", "source": "Page 234", "chapter_title": "Chapter 11"}
{"id": "d76f3ceac362-1", "text": "The final mode, called fragment-free switching, lies between the extremes of cut-through switching\nand store-and-forward switching. With fragment-free switching, the first 64 bytes of the frame are read\nand stored. The switch examines the first 64 bytes (which contain all the header information for the\nframe), and if all the header data appear correct, the switch presumes that the rest of the frame is error\nfree and begins transmitting. Fragment-free switching is a compromise between cut-through and store-\nand-forward switching because it has higher latency and better error control than cut-through switching,\nbut lower latency and worse error control than store-and-forward switching. Most switches today use cut-\nthrough or fragment-free switching.\n7.3.2 Media Access Control\nWhen several computers share the same collision domain (i.e., multipoint circuit), it is important to\ncontrol their access to the media. If two computers on the same circuit transmit at the same time, their\ntransmissions will become garbled. These collisions must be prevented, or if they do occur, there must be\na way to recover from them. This is called media access control.\nEthernet uses a contention-based media access control technique called Carrier Sense Multiple\nAccess with Collision Detection (CSMA/CD). CSMA/CD, like all contention-based techniques, is\nvery simple in concept: wait until the circuit is free and then transmit. Computers wait until no other\ndevices are transmitting, then transmit their frames. As an analogy, suppose you are talking with a small\ngroup of friends (four or five people). As the discussion progresses, each person tries to grab the floor\nwhen the previous speaker finishes. Usually, the other members of the group yield to the first person who\njumps in right after the previous speaker.\nEthernet\u2019s CSMA/CD protocol can be termed \u201cordered chaos.\u201d As long as no other computer attempts to", "source": "Page 234", "chapter_title": "Chapter 11"}
{"id": "2eac0cb4ee20-2", "text": "transmit at the same time, everything is fine. However, it is possible that two computers located some\ndistance from each other can both listen to the circuit, find it empty, and begin simultaneously. This\nsimultaneous transmission is called a collision. The two frames collide and destroy each other.\nThe solution to this is to listen while transmitting, better known as collision detection (CD). If the NIC\ndetects any signal other than its own, it presumes that a collision has occurred and sends a jamming\nsignal. All computers stop transmitting and wait for the circuit to become free before trying to retransmit.\nThe problem is that the computers that caused the collision could attempt to retransmit at the same time.\nTo prevent this, each computer waits a random amount of time after the colliding frame disappears before\nattempting to retransmit. Chances are both computers will choose a different random amount of time and\none will begin to transmit before the other, thus preventing a second collision. However, if another\ncollision occurs, the computers wait a random amount of time before trying again. This does not eliminate", "source": "Page 234", "chapter_title": "Chapter 11"}
{"id": "4624dd0dbd70-0", "text": "collisions completely, but it reduces them to manageable proportions.\n7.3.3 Types of Ethernet\nFigure 7-6 summarizes the many different types of Ethernet in use today. The 10Base-T standard\nrevolutionized Ethernet and made it the most popular type of LANin the world. Today, 100Base-T and\n1000Base-T are the most common forms of Ethernet.\nOther types of Ethernet include 1000Base-F (which runs at 1 Gbps and is sometimes called 1 GbE), 10\nGbE (10 Gbps), 40 GbE (40 Gbps), and 100 GbE (100 Gbps). They can use Ethernet\u2019s traditional half-\nduplex approach, but most are configured to use full duplex. Each is also designed to run over fiber-optic\ncables, but some may also use traditional twisted-pair cables (e.g., Cat 5e). For example, two common\nversions of 1000Base-F are 1000Base-LX and 1000Base-SX, both of which use fiber-optic cable, running\nup to 440 and 260 meters, respectively; 1000Base-T, which runs on four pairs of category 5 twisted-pair\ncable, but only up to 100 meters; and 1000Base-CX, which runs up to 24 meters on one category 5 cable.\nSimilar versions of 10 and 40 GbE that use different media are also available.\nFIGURE 7-6 Types of Ethernet\nMANAGEMENT FOCUS 7-3\nMoving to Gigabit Ethernet\nKotak Mahindra Group, one of India\u2019s leading financial services provider, offers comprehensive\nfinancial solutions such as commercial banking, stock brokering, mutual funds, life insurance, and", "source": "Page 235", "chapter_title": "Chapter 11"}
{"id": "602ac7886dd4-1", "text": "financial solutions such as commercial banking, stock brokering, mutual funds, life insurance, and\ninvestment banking. They employ 20,000 people at more than 1,300 branches in India and around\nthe world.\nBecause of the high network traffic in their main data center location, Kotak installed gigabit", "source": "Page 235", "chapter_title": "Chapter 11"}
{"id": "179f09647b38-0", "text": "Ethernet switches in their core network. The switches provide 512 ports of 10 GbE, with the ability to\nupgrade to 40 and 100 Gbps. The switches have an internal switching capacity of 15 Tbps (15 trillion\nbits per second), so there is room for growth.\nSource: Adapted from \u201cKotak Group Builds State-of-the-Art Data Center on Cisco Nexus 7000 Switch,\u201d Cisco Customer Case\nStudy, Cisco Systems.\nSome organizations use 10/100/1000 Ethernet, which is a hybrid that can run at any of these three\nspeeds; 10/100/1000 NICs and switches detect the signal transmitted by the computer or device on the\nother end of the cable and will use 10 Mbps, 100 Mbps, or 1 Gbps, depending on which the other device\nuses.\n7.4 WIRELESS ETHERNET\nWireless Ethernet (commonly called Wi-Fi) is the commercial name for a set of standards developed\nby the IEEE 802.11 standards group. A group of vendors selling 802.11 equipment trademarked the\nname Wi-Fi to refer to 802.11 because they believe that consumers are more likely to buy equipment with\na catchier name than 802.11. Wi-Fi is intended to evoke memories of Hi-Fi, as the original stereo music\nsystems in the 1960s were called.\nThe 802.11 family of technologies is much like the Ethernet family. They reuse many of the Ethernet 802.3\ncomponents and are designed to connect easily into Ethernet LANs. For these reasons, IEEE 802.11 is\noften called wireless Ethernet. Just as there are several different types of Ethernet (e.g., 10Base-T,\n100Base-T, and 1000Base-T), there are several different types of 802.11.", "source": "Page 236", "chapter_title": "Chapter 11"}
{"id": "be658225ddca-1", "text": "7.4.1 Topology\nThe logical and physical topologies of Wi-Fi are the same as those of hub-based Ethernet: a physical star\nand a logical bus. There is a central AP to which all computers direct their transmissions (star), and the\nradio frequencies are shared (bus) so that all computers must take turns transmitting.\n7.4.2 Media Access Control\nMedia access control in Wi-Fi is Carrier Sense Multiple Access with Collision Avoidance\n(CSMA/CA), which is similar to the contention-based CSMA/CD approach used by Ethernet. With\nCSMA/CA, computers listen before they transmit, and if no one else is transmitting, they proceed with\ntransmission. Detecting collisions is more difficult in radio transmission than in transmission over wired\nnetworks, so Wi-Fi attempts to avoid collisions to a greater extent than traditional Ethernet. CSMA/CA\nhas two media access control approaches. However, before a computer can transmit in a WLAN, it must\nfirst establish an association with a specific AP, so that the AP will accept its transmissions.\nAssociating with an AP\nSearching for an available AP is called scanning, and a NIC can engage in either active or passive\nscanning. During active scanning, a NIC transmits a special frame called probe frame on all active\nchannels on its frequency range. When an AP receives a probe frame, it responds with a probe response\nthat contains all the necessary information for a NIC to associate with it. A NIC can receive several probe\nresponses from different APs. It is up to the NIC to choose with which AP to associate. This usually\ndepends on the speed rather than distance from an AP. Once a NIC associates with an AP, they start\nexchanging packets over the channel that is specified by the AP.\nDuring passive scanning, the NIC listens on all channels for a special frame called a beacon frame that", "source": "Page 236", "chapter_title": "Chapter 11"}
{"id": "ccc5d5a668f9-2", "text": "During passive scanning, the NIC listens on all channels for a special frame called a beacon frame that\nis sent out by an AP. The beacon frame contains all the necessary information for a NIC to associate with\nit. Once a NIC detects this beacon frame, it can decide to associate with it and start communication on the\nfrequency channel set by the AP.\nDistributed Coordination Function\nThe first media access control method is the distributed coordination function (DCF) (also called\nphysical carrier sense method because it relies on the ability of computers to physically listen before", "source": "Page 236", "chapter_title": "Chapter 11"}
{"id": "52777d385fd4-0", "text": "they transmit). With DCF, each frame in CSMA/CA is sent using stop-and-wait ARQ. After the sender\ntransmits one frame, it immediately stops and waits for an ACK from the receiver before attempting to\nsend another frame. When the receiver of a frame detects the end of the frame in a transmission, it waits a\nfraction of a second to make sure the sender has really stopped transmitting, and then immediately\ntransmits an ACK (or a NAK). The original sender can then send another frame, stop and wait for an ACK,\nand so on. While the sender and receiver are exchanging frames and ACKs, other computers may also\nwant to transmit. So when the sender ends its transmission, you might ask, why doesn\u2019t some other\ncomputer begin transmitting before the receiver can transmit an ACK? The answer is that the physical\ncarrier sense method is designed so that the time the receiver waits after the frame transmission ends\nbefore sending an ACK is significantly less time than the time a computer must listen to determine that no\none else is transmitting before initiating a new transmission. Thus, the time interval between a frame and\nthe matching ACK is so short that no other computer has the opportunity to begin transmitting.\nPoint Coordination Function\nThe second media access control technique is called the point coordination function (PCF) (also\ncalled the virtual carrier sense method). Not all manufacturers have implemented PCF in their APs.\nDCF works well in traditional Ethernet because every computer on the shared circuit receives every\ntransmission on the shared circuit. However, in a wireless environment, this is not always true. A\ncomputer at the extreme edge of the range limit from the AP on one side may not receive transmissions\nfrom a computer on the extreme opposite edge of the AP\u2019s range limit. In Figure 7-1, all computers may be", "source": "Page 237", "chapter_title": "Chapter 11"}
{"id": "6e068e8b7a5d-1", "text": "within the range of the AP, but may not be within the range of each other. In this case, if one computer\ntransmits, the other computer on the opposite edge may not sense the other transmission and transmit at\nthe same time causing a collision at the AP. This is called the hidden node problem because the computers\nat the opposite edges of the WLAN are hidden from each other.\nWhen the hidden node problem exists, the AP is the only device guaranteed to be able to communicate\nwith all computers on the WLAN. Therefore, the AP must manage the shared circuit using a controlled-\naccess technique, not the contention-based approach of traditional Ethernet. With this approach, any\ncomputer wishing to transmit first sends a request to send (RTS) to the AP, which may or may not be\nheard by all computers. The RTS requests permission to transmit and to reserve the circuit for the sole use\nof the requesting computer for a specified time period. If no other computer is transmitting, the AP\nresponds with a clear to send (CTS), specifying the amount of time for which the circuit is reserved for\nthe requesting computer. All computers hear the CTS and remain silent for the specified time period. The\nvirtual carrier sense method is optional. It can always be used, never used, or used just for frames\nexceeding a certain size, as set by the WLAN manager.\nControlled-access methods provide poorer performance in low-traffic networks because computers must\nwait for permission before transmitting rather than just waiting for an unused time period. However,\ncontrolled-access techniques work better in high-traffic WLANs, because without controlled access, there\nare many collisions. Think of a large class discussion in which the instructor selects who will speak\n(controlled access) versus one in which any student can shout out a comment at any time.\n7.4.3 Wireless Ethernet Frame Layout", "source": "Page 237", "chapter_title": "Chapter 11"}
{"id": "d7d2e5aff5eb-2", "text": "7.4.3 Wireless Ethernet Frame Layout\nAn 801.11 data frame is illustrated in Figure 7-7. We notice two major differences when we compare the\n802.11 frame to the 802.3 frame used in wired Ethernet (see Chapter 4). First, the wireless Ethernet frame\nhas four address fields rather than two like the wired Ethernet. These four address fields are source\naddress, transmitter address, receiver address, and destination address. The source and destination\naddress have the same meaning as in wired Ethernet. However, because every NIC has to communicate\nvia an AP (it cannot directly communication with another NIC), there is a need to add the address of the\nAP and also any other device that might be needed to transmit the frame. To do this, the transmitter and\nreceived address fields are used.\nSecond, there is new field called sequence control that indicates how a large frame is fragmented\u2014split\ninto smaller pieces. Recall that in wired networks this is done by the transport layer, not the data link\nlayer. Moving the segmentation to the data link layer for wireless makes the transmission transparent to\nthe higher layers. The price, however, is less efficiency because of the size of the frame and thus also a\nhigher error rate.", "source": "Page 237", "chapter_title": "Chapter 11"}
{"id": "fa189801b559-0", "text": "7.4.4 Types of Wireless Ethernet\nWi-Fi is one of the fastest changing areas in networking. There are many different versions of Wi-Fi; all\nbut the last two or three versions are obsolete but may still be in use in some companies. All the different\ntypes are backward compatible, which means that laptops and APs that use new versions can\ncommunicate with laptops and APs that use older versions. However, this backward compatibility comes\nwith a price. These old laptops become confused when other laptops operate at high speeds near them, so\nwhen an AP detects the presence of a laptop using an old version, it prohibits laptops that use the newer\nversions from operating at high speeds. Thus, one old laptop will slow down all the other new laptops\naround it.\nWe focus on the three latest versions of 802.11.\nFIGURE 7-7 A wireless Ethernet frame\n802.11n\nIEEE 802.11n is an obsolete version, but many organizations continue to use it because it is cheap. Under\nperfect conditions, it provides three channels of 450 Mbps each with a maximum range of 100 meters or\n300 feet, although in practice both the speed and range are lower. Older versions of 802.11n provide a\nmaximum speed of 300 Mbps. You would probably think the three channels are numbered 1, 2, and 3, but\nthey aren\u2019t. The three channels are numbered 1, 6, and 11, because the underlying technology provides 11\nchannels, with channels 1, 6, and 11 designed so they do not overlap and cause interference with each\nother. It is also possible to configure a dual-band AP so it combines all the channels into one \u201cdual-\nband\u201d channel that provides 600 Mbps.\n802.11ac", "source": "Page 238", "chapter_title": "Chapter 11"}
{"id": "1bfa7b07a878-1", "text": "band\u201d channel that provides 600 Mbps.\n802.11ac\nIEEE 802.11ac is the current version, and it has a number of differences from the earlier version. This\nversion runs in two different frequency spectrums simultaneously (2.4 and 5 GHz) to provide high speed\ndata rates. To make things more confusing, there are several different versions of the standard, and\nvendors can choose what aspects to implement. Some vendors have introduced products that conform to\nthe standard but operate only in the 2.4 GHz spectrum. These products offer fewer channels and/or\nslower data rates, so we now need to read product labels very carefully before buying equipment. One\nimportant innovation is that the RTS/CTS media access control is sent on a separate frequency range, so\nthat it does not interfere with data transmission. The default modulation technique is 256-QAM (8 bits\nper symbol), increased from 64-QAM (6 bits per symbol) in 802.11n, so the increase in data transmission\nspeed is greater than the increase in frequency range would suggest (see Chapter 3).\nOne version of the standard, the one most vendors have implemented as we write this, provides eight\nchannels each running at 433 Mbps with a maximum effective range of 50 meters (150 feet) under perfect\nconditions. The actual throughput after you consider the efficiency of the data link protocol (see Chapter\n4) is about 300 Mbps. As you get farther from the AP, the speed drops, so users will only see the\nmaximum speed within 20\u201330 meters of the AP, depending on the interference in the environment. At\nmaximum range, data rates are likely to be about 90 Mbps per channel (60 Mbps throughput).\nAnother version of the standard enables the user to configure the number of channels and the capacity", "source": "Page 238", "chapter_title": "Chapter 11"}
{"id": "7436d32421d7-2", "text": "Another version of the standard enables the user to configure the number of channels and the capacity\neach will have. This is made more complex by enabling each AP to have a different number of antennas,\nwith each additional antenna enabling faster speeds\u2014but only if the devices attached to the AP also have\nmore antennas, which is usually not the case; most laptops have only two antennas. It also enables special\nantennas that shape the radio beam, so that the signal is focused only in certain directions, to further\nimprove speed and quality. So technically, 802.11ac could provide one channel of 6.9 Gbps (or a\nthroughput of 4.9 Gbps), but only under perfect conditions, when talking to a nonstandard laptop.\n802.11ax\nIEEE 802.11ax (sometimes called Wi-FI 6) is newest version of wireless Ethernet that is being rolled out", "source": "Page 238", "chapter_title": "Chapter 11"}
{"id": "b36d273855c9-0", "text": "in commercial products. This version runs in three different frequency spectrums (2.4, 5, and 6 GHz) to\nprovide very high speed data rates. It provides 9.6 Gbps across 8 channels or about 1.2 Gbps per channel\nunder prefect conditions. The entire data stream can be combined into one large channel. The default\nmodulation technique was improved so it now uses 1024-QAM (10 bits per symbol), which is one reason\nfor this increase (see Chapter 3). Range is limited to 35 meters, but the effective range is much less, likely\n7\u201310 meters (20\u201330 feet). This range sounds very short, but is likely to be sufficient in large office\nbuildings where APs are installed close together because there are many users in the same area. For\nexample, at many universities, each classroom has its own AP, meaning an effective range of 10 meters is\nfine.\nOne new innovation in 802.11ax is the ability for the AP to combine packets destined for different devices\ninto the same physical layer transmission. With prior versions of 802.11, each Ethernet packet was sent as\na separate transmission. Now the same physical layer transmission can contain Ethernet packets destined\nto different computers. A second new innovation is the ability to \u201ccolor\u201d packets so an AP can tell that an\nincoming packet is actually from another AP whose transmission range overlaps with its range, not one of\nthe client computers in its WLAN. This means the AP can ignore the incoming packet and thus save a little\nbit of processing time. APs will also have the ability to detect overlapping APs and weaken their\ntransmission signal to shorten the range so there is less overlap.\n7.4.5 Security\nSecurity is important to all networks and types of technology, but it is especially important for wireless", "source": "Page 239", "chapter_title": "Chapter 11"}
{"id": "7fbfe5662a4a-1", "text": "Security is important to all networks and types of technology, but it is especially important for wireless\nnetworks. With a WLAN, anyone walking or driving within the range of an AP (even outside the offices)\ncan begin to use the network.\nFinding WLANs is quite simple. You just walk or drive around different office buildings with your WLAN-\nequipped client computer and see if it picks up a signal. There are also many special-purpose software\ntools available on the Internet that will enable you to learn more about the WLANs you discover, with the\nintent of helping you to break into them. This type of wireless reconnaissance is often called wardriving\n(see www.wardriving.com).\nWEP\nOne older wireless security technique is Wired Equivalent Privacy (WEP). With WEP, the AP\nrequires the user to have a key to communicate with it. All data sent to and from the AP are encrypted so\nthat they can only be understood by computers or devices that have the key (encryption is discussed in\nmore detail in Chapter 11). If a computer does not have the correct WEP key, it cannot understand any\nmessages transmitted by the AP, and the AP will not accept any data that are not encrypted with the\ncorrect key.\nThe WEP keys are produced dynamically, much like the way in which a DHCP server is used to\ndynamically produce IP addresses. When an AP first discovers a new client computer, it requires the user\nto log in before it will communicate with the client computer. The user ID and password supplied by the\nuser are transmitted to a login server, and if the server determines that they are valid, the server generates\na WEP key that will be used by the AP and client computer to communicate for this session. Once the\nclient logs out or leaves the WLAN, the WEP key is discarded, and the client must log in again and receive", "source": "Page 239", "chapter_title": "Chapter 11"}
{"id": "d7238747afbb-2", "text": "a new WEP key.\nWEP has a number of serious weaknesses, and most experts agree that a determined hacker can break\ninto a WLAN that uses only WEP security. A good way to think about WEP is that it is like locking your\ndoors when you leave: It won\u2019t keep out a professional criminal, but it will protect against a casual thief.\nWPA\nWi-Fi Protected Access (WPA) is a newer, more secure type of security. WPA works in ways similar to\nWEP: Every frame is encrypted using a key, and the key can be fixed in the AP or can be assigned\ndynamically as users login. The difference is that the WPA key is longer than the WEP key and thus is\nharder to break. More importantly, the key is changed for every frame that is transmitted to the client.\nEach time a frame is transmitted, the key is changed.", "source": "Page 239", "chapter_title": "Chapter 11"}
{"id": "970932687e0f-0", "text": "802.11i\n802.11i (also called WPA2) is the newest, most secure type of WLAN security. The user logs in to a login\nserver to obtain the master key. Armed with this master key, the user\u2019s computer and the AP negotiate a\nnew key that will be used for this session until the user leaves the WLAN. 802.11i uses the Advanced\nEncryption Standard (AES) discussed in Chapter 11 as its encryption method.\nMAC Address Filtering\nWith MAC address filtering, the AP permits the owner to provide a list of MAC addresses (i.e., layer 2\naddresses). The AP only processes frames sent by computers whose MAC address is in the address list; if a\ncomputer with a MAC address not in the list sends a frame, the AP ignores it. Unfortunately, this provides\nno security against a determined hacker. There is software available that will change the MAC address on\na wireless NIC, so a determined hacker could use a packet sniffer (e.g., Wireshark) to discover a valid\nMAC address and then use the software to change his MAC address to one the AP would accept. MAC\naddress filtering is like WEP; it will protect against a casual thief, but not against a professional.\nMANAGEMENT FOCUS 7-4\nWi-Fi Access Points in Light Bulbs\nOne product that has the potential to revolutionize SOHO networking is the Wi-Fi light bulb. For\nyears, we\u2019ve had LED bulbs that can be controlled over Wi-Fi. The new bulbs take this one step\nfurther: each bulb becomes a Wi-Fi AP.\nThese light bulbs contain a Wi-Fi extender chip. They receive the Wi-Fi signal from your existing AP,\nand then retransmit it. The current range is about 100 feet (30 meters). This means you put the first", "source": "Page 240", "chapter_title": "Chapter 11"}
{"id": "65dee6f2cb9a-1", "text": "Wi-Fi bulb in a light socket that is within range of your AP. Then you put the next bulb within 100\nfeet of the first bulb, and so on, until your entire house, patio, backyard, etc. is covered in Wi-Fi.\nAnywhere you can plug in a light bulb, you can have Wi-Fi.\n7.5 THE BEST PRACTICE LAN DESIGN\nThis section focuses on the design of wired and wireless LANs that provide network access to users. The\ndata center and e-commerce edge also use LANs, so we include sections on the unique needs of these two\nnetwork architecture components. The past few years have seen major changes in LAN technologies (e.g.,\ngigabit Ethernet and high-speed wireless Ethernet). As technologies have changed and costs have\ndropped, so too has our understanding of the best practice design for LANs.\nOne of the key questions facing network designers is the relationship between Wi-Fi and wired Ethernet.\nThe data rates for Wi-Fi have increased substantially with the introduction of each new version of 802.11,\nso they are similar to the data rates offered by 100Base-T wired Ethernet. The key difference is that\n100Base-T wired Ethernet using switches provides 100 Mbps to each user, whereas Wi-Fi shares its\navailable capacity among every user on the same AP, so as more users connect to the APs, the network\ngets slower and slower.\nWi-Fi is considerably cheaper than wired Ethernet because the largest cost of LANs is not the equipment,\nbut in paying someone to install the cables. The cost to install a cable in an existing building is typically\nbetween $150 and $400 per cable, depending on whether the cable will have to be run through drywall,\nbrick, ceilings, and so on. Installing cable in a new building during construction is cheaper, typically $50\u2013\n$100 per cable.", "source": "Page 240", "chapter_title": "Chapter 11"}
{"id": "4165f37ce693-2", "text": "$100 per cable.\nMost organizations today install wired Ethernet to provide access for desktop users and install Wi-Fi as\noverlay networks. They build the usual switched Ethernet networks as the primary LAN, but they\nalso install Wi-Fi for laptops and mobile devices. Some organizations have begun experimenting with Wi-\nFi by moving groups of users off the wired networks onto Wi-Fi as their primary network to see whether\nWi-Fi is suitable as a primary network.", "source": "Page 240", "chapter_title": "Chapter 11"}
{"id": "c333d4580eb2-0", "text": "Today, we still believe the best practice is to use wired Ethernet for the primary LAN, with Wi-Fi as an\noverlay network. However, this may change. Stay tuned.\nMANAGEMENT FOCUS 7-5\nWill Wi-Fi Replace Wired LANS?\nAs KPMG, one of the largest consulting firms in the world, began to build a new 2,800-person\nheadquarters near Amsterdam, KPMG\u2019s IT group realized that their traditional wired network\napproach would have required 18,000 cable runs, 55 chassis switches, and 260 LAN switches. The\nup-front cost was expected to exceed $6 million, and the recurring operating costs would run into\nthe millions annually as well.\nKPMG began to wonder if there was a better way. Could they build an entirely wireless network that\nwould meet their needs?\nAfter careful analysis, KPMG decided they were not ready to go completely wireless. However, they\ndecided to shift a substantial portion of their traditionally wired users to wireless. They cut their\nwired network by half and installed more than 500 802.11n APs throughout the new facility to\nprovide complete coverage for data and voice. The new network design cut the initial cost by $2\nmillion and reduced annual operating costs by $750,000 per year.\nThe new design also delivered substantial green benefits. APs use about 5% of the electricity that 48-\nport switches require for power and cooling. By eliminating half the switches, the new design\neliminated more than 350 metric tons of carbon dioxide emissions each year.\n7.5.1 Designing User Access with Wired Ethernet\nMany organizations today install switched 100Base-T or 1000Base-T over category 5e wiring for their\nwired LANs. It is relatively low cost and fast.", "source": "Page 241", "chapter_title": "Chapter 11"}
{"id": "e14da2abe1c0-1", "text": "wired LANs. It is relatively low cost and fast.\nIn the early days of LANs, it was common practice to install network cable wherever it was convenient.\nLittle long-term planning was done. The exact placement of the cables was often not documented, making\nfuture expansion more difficult\u2014you had to find the cable before you could add a new user.\nWith today\u2019s explosion in LAN use, it is critical to plan for the effective installation and use of LAN\ncabling. The cheapest point at which to install network cable is during the construction of the building;\nadding cable to an existing building can cost significantly more. Indeed, the costs to install cable (i.e.,\npaying those doing the installation and additional construction) are usually substantially more than the\ncost of the hubs and switches, making it expensive to reinstall the cable if the cable plan does not meet the\norganization\u2019s needs.\nMost buildings under construction today have a separate LAN cable plan, as they have plans for\nelectrical cables. Each floor has a data wiring closet that contains one or more network hubs or switches.\nCables are run from each room on the floor to this wiring closet.\n7.5.2 Designing User Access with Wireless Ethernet\nSelecting the best practice wireless technology is usually simple. You pick the newest one, cost permitting.\nToday, 802.11ax is the newest standard, but in time, there will be a new one.\nDesigning the physical WLAN is more challenging than designing a wired LAN because the potential for\nradio interference means that extra care must be taken in the placement of APs to ensure that their signals\ndo not overlap. With the design of LANs, there is considerable freedom in the placement of switches,\nsubject to the maximum limits to the length of network cables. In WLANs, however, the placement of the", "source": "Page 241", "chapter_title": "Chapter 11"}
{"id": "090b6dd8f94c-2", "text": "APs needs to consider both the placement of other APs and the sources of interference in the building.\nThe physical WLAN design begins with a site survey. The site survey determines the feasibility of the\ndesired coverage, the potential sources of interference, the current locations of the wired network into", "source": "Page 241", "chapter_title": "Chapter 11"}
{"id": "de2fccab436d-0", "text": "which the WLAN will connect, and an estimate of the number of APs required to provide coverage.\nWLANs work very well when there is a clear line of sight between the AP and the wireless computer. The\nmore walls there are between the AP and the computer, the weaker the wireless signal becomes. The type\nand thickness of the wall also has an impact; traditional drywall construction provides less interference\nthan does concrete block construction.\nAn AP with an omnidirectional antenna broadcasts in all directions. Its coverage area is a circle with a\ncertain radius. Wi-Fi has a long range, but real-world tests of Wi-Fi in typical office environments have\nshown that data rates slow down dramatically when the distance from a laptop to the AP exceeds 50 feet.\nTherefore, many wireless designers use a radius of 50 feet when planning traditional office environments,\nwhich ensures access high-quality coverage.\nOne may design wireless LANs using this 50-foot-radius circle, but because most buildings are square, it\nis usually easier to design using squares. Figure 7-8 shows that a 50-foot radius translates into a square\nthat is approximately 70 feet on each edge. For this reason, most designers plan wireless LANs using 50-\nto 75-foot squares, depending on the construction of the building: smaller squares in areas where there\nare more walls that can cause more interference and larger squares in areas with fewer walls. Each new\ngeneration of wireless LAN technology has reduced the effective range of APs to increase their speed. So\nsome designers prefer to use 50-foot squares everywhere.\nFigure 7-9 shows a sample building that has two parts. The lower-left corner is a 150 foot \u00d7 150 foot\nsquare, while the rest of the building is a 150 foot \u00d7 450 foot rectangle. Let\u2019s assume that the large", "source": "Page 242", "chapter_title": "Chapter 11"}
{"id": "32e51a2a6eb0-1", "text": "rectangle part is an open office environment, while the smaller part uses drywall. If we put two rows of\nAPs in the large rectangle part, we could probably space them so that each AP covered a 75-foot square.\nThis would take a total of 12 APs for this area (see Figure 7-9). This same spacing probably won\u2019t work for\nthe small area with drywall, so we would probably design using 50-foot squares, meaning we need nine\nAPs in this area (see Figure 7-9).\nWhen designing a wireless LAN, it is important to ensure that the APs don\u2019t interfere with each other. If\nall APs transmitted on the same frequency, the transmissions of one AP would interfere with another AP\nwhere their signals overlapped\u2014just like what happens on your car radio when two stations are in the\nsame frequency. Therefore, each AP is set to transmit on a different channel, very much like the different\nchannels on your TV. Figure 7-9 shows how we could set the APs to the three commonly used channels (1,\n6, and 11) so that there is minimal overlap between APs using the same channel.", "source": "Page 242", "chapter_title": "Chapter 11"}
{"id": "94b630959f32-0", "text": "FIGURE 7-8 Design parameters for Wi-Fi access point range\nFIGURE 7-9 A Wi-Fi design (the numbers indicate the channel numbers)", "source": "Page 243", "chapter_title": "Chapter 11"}
{"id": "581dc1600bff-0", "text": "Suppose you had a conference room or classroom that needed several APs to provide adequate Wi-Fi for\neveryone who will use it. You could put several APs in the same room and set them on different channels\nso their signals did not interfere with each other. One challenge is managing the number of users on each\nAP. Laptops and mobile phones connect to the AP with the strongest signal, which means most will\nconnect to the same AP. If too many users connect to one AP, it will get very busy and Wi-Fi speeds will be\nslow, while the other APs in the room will be only lightly used. This occurs because standard APs are\nautonomous and do not talk to each other. Each AP only responds to the devices that request access to it.\nMost large companies install managed APs that are different than the SOHO APs we install in our\nhomes and apartments. Managed APs are wired into a Wi-Fi Controller (rather than a normal hub or\nswitch). They report what devices are attached to them and how busy they are to the controller, which\nbalances traffic across the APs it manages. If a laptop connects to a very busy AP when there are less busy\nAPs nearby, the controller will instruct the AP to deny access to the laptop and the laptop will\nautomatically try to connect to the next AP it sees. As a result, the number of devices connected to each AP\nand the amount of traffic each receives is balanced across the set of APs managed by the controller, and\noverall network performance improves.\nAfter the initial design is complete, a site survey is done using a temporary AP and a computer or device\nthat can actually measure the strength of the wireless signal. The temporary AP is installed in the area as\ncalled for in the initial design, and the computer or device is carried throughout the building measuring", "source": "Page 244", "chapter_title": "Chapter 11"}
{"id": "735ed689d19a-1", "text": "called for in the initial design, and the computer or device is carried throughout the building measuring\nthe strength of the signal. Actually measuring the strength of the signal in the environment is far more\naccurate than relying on estimated ranges.\nDesign becomes more difficult in a multistory building because the signals from the APs travel up and\ndown as well as in all horizontal directions. The design must include the usual horizontal mapping but\nalso an added vertical mapping to ensure that APs on different floors do not interfere with one another\n(Figure 7-10). Because floors are usually thicker than walls, signals travel further horizontally than\nvertically, making design a bit more difficult. It becomes even more difficult if your set of floors in a large\noffice tower is surrounded by APs of other companies. You have to design your network not to interfere\nwith theirs.\nMost wireless LAN APs offer the ability to provide two separate wireless networks. The primary network is\nsecured by a password that is entered when you first connect to the network. This password is\nremembered by the device so that you never have to enter the password a second time. This password\nsecures the access to the network, and all connections use some form of encryption, such as WPA2, so that\nno one can read your messages (even if someone accesses the same AP using the same password). This\nnetwork is typically used by regular users of the network such as employees of an organization or the\nhomeowner in a SOHO network.", "source": "Page 244", "chapter_title": "Chapter 11"}
{"id": "d93619b83a4f-0", "text": "FIGURE 7-10 A Wi-Fi design in the three dimensions (the numbers indicate the channel numbers)\nThe second network is a guest network that is secured by a separate password that is entered on a Web\npage when you first connect to the network. This network is not secure, meaning that other users with the\nright hacking software can read the messages you send and receive. However, because the network will\nnot allow users on the network without the password, it means that access can be controlled so that only\nauthorized users have access. This network is typically used by guests who need temporary access. The\nguest network is often configured so it provides slower speeds than the primary network, so if the AP gets\nbusy, it prioritizes traffic for regular users over traffic for guest users.\n7.5.3 Designing the Data Center\nThe data center is where the organization houses its primary servers. In most large organizations, the data\ncenter is huge because it contains the data center as well as the campus backbone switches and the\nenterprise edge. Figure 7-11 shows the data center building at Indiana University. This building, which is\nbuilt partially underground to withstand an F5 tornado, is 87,000 square feet, of which 33,000 square\nfeet is used for servers. The servers can store about 50 petabytes of data (about 50 million gigabytes).\nDesigning the data center requires considerable expertise, because most data on a network flow from or to\nthe data center. In all large-scale networks today, servers are placed together in server farms or clusters,\nwhich sometimes have hundreds of servers that perform the same task. Yahoo.com, for example, has more\nthan a thousand Web servers that do nothing but respond to Web search requests. In this case, it is\nimportant to ensure that when a request arrives at the server farm, it is immediately forwarded to a server", "source": "Page 245", "chapter_title": "Chapter 11"}
{"id": "69ba3135874e-1", "text": "that is not busy\u2014or that is the least busy.", "source": "Page 245", "chapter_title": "Chapter 11"}
{"id": "0c9a5dd0d7dd-0", "text": "A special device called a load balancer or load balancing switch acts as a router at the front of the\nserver farm (Figure 7-12). All requests are directed to the load balancer at its IP address. When a request\nhits the load balancer, it forwards it to one specific server using its IP address. Sometimes a simple round-\nrobin formula is used (requests go to each server one after the other in turn); in other cases, more\ncomplex formulas track how busy each server actually is. If a server crashes, the load balancer stops\nsending requests to it, and the network continues to operate without the failed server. Load balancing\nmakes it simple to add servers (or remove servers) without affecting users. You simply add or remove the\nserver(s) and change the software configuration in the load balancing switch; no one is aware of the\nchange.\nFIGURE 7-11 The data center at Indiana University", "source": "Page 246", "chapter_title": "Chapter 11"}
{"id": "2a962881e7a4-0", "text": "FIGURE 7-12 Network with load balancer\nServer virtualization is somewhat the opposite of server farms and load balancing. Server\nvirtualization is the process of creating several logically separate servers (e.g., a Web server, an email\nserver, and a file server) on the same physical computer. The virtual servers run on the same physical\ncomputer but appear completely separate to the network (and if one crashes, it does not affect the others\nrunning on the same computer).\nOver time, many firms have installed new servers to support new projects, only to find that the new server\nwas not fully used; the server might only be running at 10% of its capacity and sitting idle for the rest of\nthe time. One underutilized server is not a problem, but imagine if 20\u201330% of a company\u2019s servers are\nunderutilized. The company has spent too much money to acquire the servers, and more importantly, it is\ncontinuing to spend money to monitor, manage, and update the underused servers. Even the space and\npower used by having many separate computers can noticeably increase operating costs. Server\nvirtualization enables firms to save money by reducing the number of physical servers they buy and\noperate, while still providing all the benefits of having logically separate devices and operating systems.", "source": "Page 247", "chapter_title": "Chapter 11"}
{"id": "1244b83dbc02-0", "text": "FIGURE 7-13 The storage area network (SAN) at the Kelley School of Business at Indiana University\nSome operating systems enable virtualization natively, which means that it is easy to configure and run\nseparate virtual servers. In other cases, special-purpose virtualization software (e.g., VMware) is installed\non the server and sits between the hardware and the operating systems; this software means that several\ndifferent operating systems can be installed on the same physical computer.", "source": "Page 248", "chapter_title": "Chapter 11"}
{"id": "6acb7b969118-0", "text": "A storage area network (SAN) is a LAN devoted solely to data storage. When the amount of data to be\nstored exceeds the practical limits of servers, the SAN plays a critical role. The SAN has a set of high-speed\nstorage devices and servers that are networked together using a very high speed network. When data are\nneeded, clients send the request to a server on the LAN, which obtains the information from the devices\non the SAN and then returns it to the client.\nThe devices on the SAN may be a large set of database servers or a set of network-attached disk arrays. In\nother cases, the devices may be network-attached storage (NAS) devices. A NAS is not a general-\npurpose computer, such as a server that runs a server operating system (e.g., Windows and Linux);\ninstead, it has a small processor and a large amount of disk storage and is designed solely to respond to\nrequests for files and data. NAS can also be attached to LANs, where they function as fast file servers.\nFigure 7-13 shows the SAN for the Kelley School of Business at Indiana University. This SAN stores 125\nterabytes of data.\n7.5.4 Designing the e-Commerce Edge\nThe e-commerce edge contains the servers that are designed to serve data to customers and suppliers,\nsuch as the corporate Web server. The e-commerce edge is essentially a smaller, specialized version of the\ndata center. It contains all the same equipment as the data center (e.g., load balancer, SAN, and UPS), but\nthis equipment supports access by users external to the organization. It is often connected directly to the\nInternet access part of the network via a very-high-speed circuit as well as the campus backbone.\nThe e-commerce edge often has different security requirements than the servers in the data center", "source": "Page 249", "chapter_title": "Chapter 11"}
{"id": "20748b7d4248-1", "text": "The e-commerce edge often has different security requirements than the servers in the data center\nintended for use by employees inside the organization because the e-commerce edge is primarily intended\nto serve those external to the organization. We discuss the special security needs of the e-commerce edge\nin Chapter 11.\n7.5.5 Designing the SOHO Environment\nMost of what we have discussed so far has focused on network design in large enterprises. What about\nLAN design for SOHO environments? SOHO environments can be small versions of enterprise designs, or\ncan take a very different approach.\nFigure 7-14a shows a SOHO LAN designed similar to a small enterprise design that provides both wired\nand wireless Ethernet (it\u2019s in Alan\u2019s house). Virtually all of the rooms in the house are wired with\n1000Base-T Ethernet over Cat 5e cable, which terminates in a 24-port patch panel. You can see from the\nfigure that only five of the rooms are actually wired from the patch panel into the 16-port switch; one of\nthose wires connects the AP mounted in an upstairs hallway (not shown) that provides wireless access\nthroughout the house and onto the back deck and gazebo. There is a separate router and cable modem.\nThe AP, switch, and router are all Cisco or Linksys equipment and are the original 2001 equipment, and\nstill work well. The cable modem is an off-brand provided by the ISP and has broken and been replaced\nevery 3 years.\nFigure 7-14b shows a more modern\u2014and probably more common\u2014SOHO LAN that provides only\nwireless access (it\u2019s in Alexandra\u2019s house). This has a cable modem that connects into a wireless router;\nthe wireless router is a wireless AP, a router, and a switch for wired Ethernet all in one box. This network", "source": "Page 249", "chapter_title": "Chapter 11"}
{"id": "0f484c0eff47-2", "text": "is simpler and cheaper because it contains fewer devices and is used only for wireless access. Alexandra\ndoesn\u2019t have a desktop computer at home, but she could easily connect one if she wanted by adding a\nwireless NIC into a desktop; the 802.11n WLAN provides ample capacity for a small SOHO network.", "source": "Page 249", "chapter_title": "Chapter 11"}
{"id": "0382d3e6395d-0", "text": "FIGURE 7-14 SOHO LAN designs", "source": "Page 250", "chapter_title": "Chapter 11"}
{"id": "7f8d12088b4e-0", "text": "FIGURE 7-15 Powerline adapter\nInstalling cables for wired Ethernet is expensive, so most SOHO designs use wireless Ethernet. Sometimes\na house is big enough that one WAP won\u2019t cover the entire building and the outdoor area. Powerline\nnetworking is an old technology that is making a comeback for exactly this situation. Powerline\nnetworking provides Ethernet over the existing electrical power wires in your house at rates up to 1 Gbps.\nThe powerline adapters convert the traditional wired Ethernet signal that runs over Cat 5e cables into a", "source": "Page 251", "chapter_title": "Chapter 11"}
{"id": "a15d4f62dd30-0", "text": "signal that can travel over the electrical powerwires.\nYou buy a kit that has two powerline adapters. You plug one adapter into a power outlet in one room and\nthe other into an outlet in a different room. Then you connect an Ethernet cable into each adapter and you\ncan begin transmitting between the two powerline adapters. Figure 7-15 shows the powerline adapter that\none of our friends has at his house in Hawaii. He has one WAP near his back door to provide wireless\ncoverage for the rear of his house and the backyard, which is plugged into this powerline adapter. He has a\nsecond WAP connected to the second powerline adapter upstairs near the front of his house to provide\ncoverage for the rest of his house and his front yard.\n7.6 IMPROVING LAN PERFORMANCE\nWhen LANs had only a few users, performance was usually very good. Today, however, when most\ncomputers in an organization are on LANs, performance can be a problem. Performance is usually\nexpressed in terms of throughput (the total amount of user data transmitted in a given time period) or in\nresponse time (how long it takes to get a response from the destination). In this section, we discuss how to\nimprove throughput. We focus on dedicated-server networks because they are the most commonly used\ntype of LANs, but many of these concepts also apply to peer-to-peer networks.\nTECHNICAL FOCUS 7-2\nError Control in Wired Ethernet\nEthernet provides a strong error control method using stop-and-wait ARQ with a CRC-32 error\ndetection field (see Chapter 4). However, the normal way of installing wired Ethernet doesn\u2019t use\nstop-and-wait ARQ.\nIn the early days of Ethernet, LAN environments were not very reliable, so error control was", "source": "Page 252", "chapter_title": "Chapter 11"}
{"id": "74dc3f14bfe9-1", "text": "In the early days of Ethernet, LAN environments were not very reliable, so error control was\nimportant. However, today\u2019s wired Ethernet LANs are very reliable; errors seldom occur. Stop-and-\nwait ARQ uses considerable network capacity because every time a frame is transmitted, the sender\nmust stop and wait for the receiver to send an ACK. By eliminating the need to stop and wait and the\nneed to send acknowledgments, Ethernet can significantly improve network performance\u2014almost\ndoubling the number of messages that can be transmitted in the same time period. Ethernet does\nstill add the CRC and does still check it for errors, but any frame with an error is simply discarded.\nIf Ethernet doesn\u2019t provide error control, then higher layers in the network model must. In general,\nTCP is configured to provide error control by using continuous ARQ (see Chapter 5) to ensure that\nall frames that have been sent are actually received at the final destination. If a frame with an error is\ndiscarded by Ethernet, TCP will recognize that a frame has been lost and ask the sender to\nretransmit. This moves responsibility for error control to the edges of the network (i.e., the sender\nand receiver) rather than making every computer along the way responsible for ensuring reliable\nmessage delivery.\nTo improve performance, you must locate the bottleneck, the part of the network that is restricting the\ndata flow. Generally speaking, the bottleneck will lie in one of two places. The first is the network server.\nIn this case, the client computers have no difficulty sending requests to the network server, but the server\nlacks sufficient capacity to process all the requests it receives in a timely manner. The second location is a\nnetwork circuit, either the access LAN, the building backbone, the campus backbone, or the circuit into", "source": "Page 252", "chapter_title": "Chapter 11"}
{"id": "390cabdb85c0-2", "text": "the data center. In this case, the server (or more likely, a server farm) can easily process all the client\nrequests it receives, but a circuit lacks enough capacity to transmit all the requests to the server.\nThe first step in improving performance, therefore, is to identify whether the bottleneck lies in a circuit or\nthe server. To do so, you simply watch the utilization of the server during periods of poor performance. If\nthe server utilization is high (e.g., 80\u2013100%), then the bottleneck is the server; it cannot process all the\nrequests it receives in a timely manner. If the server utilization is low during periods of poor performance,\nthen the problem lies with a network circuit; some circuits cannot transmit messages as quickly as", "source": "Page 252", "chapter_title": "Chapter 11"}
{"id": "3d7f2548de63-0", "text": "necessary.\nMost organizations focus on ways to improve the server and the circuits to remove bottle-necks. These\nactions address only the supply side of the equation\u2014that is, increasing the capacity of the LAN as a\nwhole. The other way to reduce performance problems is to attack the demand side: reduce the amount of\nnetwork use by the clients, which we also discuss. Figure 7-16 provides a performance checklist.\n7.6.1 Improving Server Performance\nImproving server performance can be approached from two directions simultaneously: software and\nhardware.\nSoftware\nThe NOS is the primary software-based approach to improving network performance. Some NOSs are\nfaster than others, so replacing the NOS with a faster one will improve performance.\nEach NOS provides a number of software settings to fine-tune network performance. Depending on the\nnumber, size, and type of messages and requests in your LAN, different settings can have a significant\neffect on performance. The specific settings differ by NOS but often include things such as the amount of\nmemory used for disk caches, the number of simultaneously open files, and the amount of buffer space.\nPerformance Checklist\nIncrease Server Performance\nSoftware\nFine-tune the network operating system settings\nHardware\nAdd more servers and spread the network applications across the servers to balance\nthe load\nUpgrade to a faster computer\nIncrease the server\u2019s memory\nIncrease the number and speed of the server\u2019s hard disk(s)\nIncrease Circuit Capacity\nUpgrade to a faster circuit\nIncrease the number of circuits\nReduce Network Demand\nMove files from the server to the client computers\nIncrease the use of disk caching on client computers\nChange user behavior\nFIGURE 7-16 Improving local area network performance\nHardware\nOne obvious solution if your network server is overloaded is to buy a second server (or more). Each server", "source": "Page 253", "chapter_title": "Chapter 11"}
{"id": "6fb499d5256c-1", "text": "is then dedicated to supporting one set of application software (e.g., one handles email, another handles\nthe financial database, and another stores customer records). The bottleneck can be broken by carefully\nidentifying the demands each major application software package places on the server and allocating them\nto different servers.\nSometimes, however, most of the demand on the server is produced by one application that cannot be\nsplit across several servers. In this case, the server itself must be upgraded. The first place to start is with\nthe server\u2019s CPU. Faster CPUs mean better performance. If you are still using an old computer as a LAN", "source": "Page 253", "chapter_title": "Chapter 11"}
{"id": "4f5563e39fdb-0", "text": "server, this may be the answer; you probably need to upgrade to the latest and greatest. Clock speed also\nmatters: the faster, the better. Most computers today also come with CPU-cache (a very fast memory\nmodule directly connected to the CPU). Increasing the cache will increase CPU performance.\nA second bottleneck is the amount of memory in the server. Increasing the amount of memory increases\nthe probability that disk caching will work, thus increasing performance.\nA third bottleneck is the number and speed of the hard disks in the server. The primary function of the\nLAN server is to process requests for information on its disks. Slow hard disks give slow network\nperformance. The obvious solution is to buy the fastest disk drive possible. Even more important,\nhowever, is the number of hard disks. Each computer hard disk has only one read/write head, meaning\nthat all requests must go through this one device. By using several smaller disks rather than one larger\ndisk (e.g., five 200 gigabyte disks rather than one 1 terabyte disk), you now have more read/write heads,\neach of which can be used simultaneously, dramatically improving throughput. A special type of disk drive\ncalled RAID (redundant array of inexpensive disks) builds on this concept and is typically used in\napplications requiring very fast processing of large volumes of data, such as multimedia. Of course, RAID\nis more expensive than traditional disk drives, but costs have been shrinking. RAID can also provide fault\ntolerance, which is discussed in Chapter 11.\nSeveral vendors sell special-purpose network servers that are optimized to provide extremely fast\nperformance. Many of these provide RAID and use symmetric multiprocessing (SMP) that enables\none server to use up to 16 CPUs. Such servers provide excellent performance but cost more (often\n$5,000\u2013$15,000).\n7.6.2 Improving Circuit Capacity", "source": "Page 254", "chapter_title": "Chapter 11"}
{"id": "8b670b18d5a8-1", "text": "7.6.2 Improving Circuit Capacity\nImproving the capacity of a circuit means increasing the volume of simultaneous messages the circuit can\ntransmit from network clients to the server(s). One obvious approach is simply to buy a bigger circuit. For\nexample, if you are now using a 100Base-T LAN, upgrading to 1000Base-T LAN will improve capacity. Or\nif you have 802.11n, then upgrade to 802.11ac or 802.11ax. You can also add more circuits so that there\nare two or even three separate high-speed circuits between busy parts of the network, such as the core\nbackbone and the data center. Most Ethernet circuits can be configured to use full duplex (see Chapter 4),\nwhich is often done for backbones and servers.\nAnother approach is to segment the network. If there is more traffic on a LAN than it can handle, you can\ndivide the LAN into several smaller segments. Breaking a network into smaller parts is called network\nsegmentation. In a wired LAN, this means adding one of more new switches and spreading the\ncomputers across these new switches. In a wireless LAN, this means adding more APs that operate on\ndifferent channels. If wireless performance is significantly worse than expected, then it is important to\ncheck for sources of interference near the AP and the computers such as Bluetooth devices and cordless\nphones.\n7.6.3 Reducing Network Demand\nOne way to reduce network demand is to move files to client computers. Heavily used software packages\nthat continually access and load modules from the network can place unusually heavy demands on the\nnetwork. Although user data and messages are often only a few kilobytes in size, today\u2019s software packages\ncan be many megabytes in size. Placing even one or two such applications on client computers can greatly", "source": "Page 254", "chapter_title": "Chapter 11"}
{"id": "b64ffad538d7-2", "text": "improve network performance (although this can create other problems, such as increasing the difficulty\nin upgrading to new versions of the software).\nMost organizations now provide both wired and wireless networks, so another way to reduce demand is to\nshift it from wired networks to wireless networks, or vice versa, depending on which has the problem. For\nexample, you can encourage wired users to go wireless or install wired Ethernet jacks in places where\nwireless users often sit.\nBecause the demand on most LANs is uneven, network performance can be improved by attempting to\nmove user demands from peak times to off-peak times. For example, early morning and after lunch are\noften busy times when people check their email. Telling network users about the peak times and\nencouraging them to change their habits may help; however, in practice, it is often difficult to get users to", "source": "Page 254", "chapter_title": "Chapter 11"}
{"id": "a35f5f1cdec2-0", "text": "change. Nonetheless, finding one application that places a large demand on the network and moving it\ncan have a significant impact (e.g., printing several thousand customer records after midnight).\n7.7 IMPLICATIONS FOR CYBER SECURITY\nMost attacks from external hackers come over the Internet. However, it is still important to secure the\nLAN from unauthorized users. For wired LANs, this means securing network devices, such as switches\nand APs. All devices should be placed in locked closets, with access tightly controlled. For WLANs, this\nmeans using encryption and secured access that requires users to login before they can use the Wi-Fi. This\nis particularly important for Wi-Fi APs whose signal extends outside of buildings onto public streets, or to\nother floors in an office building that are occupied by other firms.\nA very useful way to protect both the LAN and WLAN is to do MAC address filtering. Your users would\nregister all devices that could send and receive packets on a network. Then, when a device wants to\ncommunicate (e.g., is plugged into a port in the wall or tries to associate with an AP), its MAC address is\nchecked against the list of registered devices. All devices that are not registered are denied access to the\nnetwork.\nFinally, organizations protect their internal network through network segmentation. On the WLAN, this\ncan be done through different SSIDs (SSID stands for Service Set Identifier, but nobody ever says this).\nSSID is simply the name of the network that you connect to. We are sure you faced this situation when you\nwent to a coffee shop and wanted to connect to the Internet and your laptop offered you multiple different\nnetworks to connect to. In business networks, one SSID would be used for the registered devices that can\naccess all services offered by the network, and another guest SSID would only offer Internet access and at\nlower capacity (to deter people from staying on it too long).", "source": "Page 255", "chapter_title": "Chapter 11"}
{"id": "bd638d487da7-1", "text": "lower capacity (to deter people from staying on it too long).\nSUMMARY\nLAN Components The NIC enables the computer to be physically connected to the network and\nprovides the physical layer connection among the computers. Wired LANs use UTP wires, STP wires,\nand/or fiber-optic cable. Network hubs and switches provide an easy way to connect network cables\nand act as repeaters. Wireless NICs provide radio connections to APs that link wireless computers\ninto the wired network. The NOS is the software that performs the functions associated with the data\nlink and the network layers and interacts with the application software and the computer\u2019s own\noperating system. Every NOS provides two sets of software: one that runs on the network server(s)\nand one that runs on the network client(s). A network profile specifies what resources on each server\nare available for network use by other computers and which devices or people are allowed what\naccess to the network.\nEthernet (IEEE 802.3) Ethernet, the most commonly used LAN protocol in the world, uses a\ncontention-based media access technique called CSMA/CD. There are many different types of\nEthernet that use different network cabling (e.g., 10Base-T, 100Base-T, 1000Base-T, and 10 GbE).\nSwitches are preferred to hubs because they are significantly faster.\nWireless Ethernet Wireless Ethernet (often called Wi-Fi) is the most common type of wireless\nLAN. It uses physical star/logical bus topology with both controlled and contention-based media\naccess control. 802.11ac, the newest version, provides 433Mbps over three channels or faster speeds\nover fewer channels.\nBest Practice LAN Design Most organizations install 100Base-T or 10/100/1000 Ethernet as their\nprimary LAN and also provide wireless LANs as an overlay network. For SOHO networks, the best", "source": "Page 255", "chapter_title": "Chapter 11"}
{"id": "b472b986d4af-2", "text": "LAN choice may be wireless. Designing the data center and e-commerce edge often uses specialized\nequipment such as server farms, load balancers, virtual servers, SANs, and UPS.\nImproving LAN Performance Every LAN has a bottleneck, a narrow point in the network that\nlimits the number of messages that can be processed. Generally speaking, the bottleneck will lie in\neither the network server or a network circuit. Server performance can be improved with a faster NOS\nthat provides better disk caching, by buying more servers and spreading applications among them or\nby upgrading the server\u2019s CPU, memory, NIC, and the speed and number of its hard disks. Circuit", "source": "Page 255", "chapter_title": "Chapter 11"}
{"id": "f37dd9c97f7b-0", "text": "capacity can be improved by using faster technologies (e.g., 1000Base-T), by adding more circuits,\nand by segmenting the network into several separate LANs by adding more switches or APs. Overall\nLAN performance also can be improved by reducing the demand for the LAN by moving files off the\nLAN, moving users from wired Ethernet to wireless or vice versa, and by shifting users\u2019 routines.\nKEY TERMS\naccess point (AP)\nActive Directory Service (ADS)\nassociation\nbeacon frame\nbottleneck\nbus topology\ncable plan\ncabling\nCarrier Sense Multiple Access with Collision Avoidance (CSMA/CA)\nCarrier Sense Multiple Access with Collision Detection (CSMA/CD)\nchannel\nclear to send (CTS)\ncollision\ncollision detection (CD)\ncollision domain\ncut-through switching\ndirectional antenna\ndistributed coordination function (DCF)\ndomain controller\ndual-band AP\nEthernet\nfiber-optic cable\nforwarding table\nfragment-free switching\nframe\nhub\nIEEE 802.3\nIEEE 802.11\nlatency\nlayer 2 switch\nlightweight directory access protocol (LDAP)\nload balancer\nload balancing switch\nlogical topology", "source": "Page 256", "chapter_title": "Chapter 11"}
{"id": "499e9940ae6f-0", "text": "MAC address filtering\nmanaged APs\nnetwork-attached storage (NAS)\nnetwork interface card (NIC)\nnetwork operating system (NOS)\nnetwork profile\nnetwork segmentation\nnetwork server\nomnidirectional antenna\noverlay network\nphysical carrier sense method\nphysical topology\npoint coordination function (PCF)\nport\npower over Ethernet (POE)\npowerline networking\nprobe frame\nredundant array of inexpensive disks (RAID)\nrequest to send (RTS)\nserver virtualization\nshielded twisted-pair (STP)\nsite survey\nsmall-office, home-office (SOHO)\nstorage area network (SAN)\nstore-and-forward switching\nswitch\nswitched Ethernet\nsymmetric multiprocessing (SMP)\ntopology\ntwisted-pair cable\nunshielded twisted-pair (UTP) cable\nvirtual carrier sense\nwardriving\nWireless Ethernet (Wi-Fi)\nWi-Fi Controller\nWi-Fi Protected Access (WPA)\nWired Equivalent Privacy (WEP)\nWireless LAN (WLAN)\n10Base-T", "source": "Page 257", "chapter_title": "Chapter 11"}
{"id": "6fe2809ff2bf-0", "text": "100Base-T\n1000Base-T\n10/100/1000 Ethernet\n1 GbE\n10 GbE\n40 GbE\n100 GbE\n802.11ac\n802.11ax\n802.11n\nQUESTIONS\n1. Define local area network.\n2. Describe at least three types of servers.\n3. Describe the basic components of a wired LAN.\n4. Describe the basic components of a wireless LAN.\n5. What types of cables are commonly used in wired LANs?\n6. Compare and contrast category 5 UTP, category 5e UTP, and category 5 STP.\n7. What is a cable plan and why would you want one?\n8. What does a NOS do? What are the major software parts of a NOS?\n9. How does wired Ethernet work?\n10. How does a logical topology differ from a physical topology?\n11. Briefly describe how CSMA/CD works.\n12. Explain the terms 100Base-T, 100Base-F, 1000Base-T, 10 GbE, and 10/100/1000 Ethernet.\n13. How do Ethernet switches know where to send the frames they receive? Describe how switches gather\nand use this knowledge.\n14. Compare and contrast cut-through, store-and-forward, and fragment-free switching.\n15. Compare and contrast the two types of antennas.\n16. How does Wi-Fi perform media access control?\n17. How does Wi-Fi differ from shared Ethernet in terms of topology, media access control, and error\ncontrol, Ethernet frame?\n18. Explain how CSMA/CA DCF works.\n19. Explain how CSMA/CA PCF works.\n20. Explain how association works in WLAN.\n21. What are the best practice recommendations for wired LAN design?", "source": "Page 258", "chapter_title": "Chapter 11"}
{"id": "0f5c974bd4a7-1", "text": "21. What are the best practice recommendations for wired LAN design?\n22. What are the best practice recommendations for WLAN design?\n23. What is a site survey, and why is it important?\n24. How do you decide how many APs are needed and where they should be placed for best performance?\n25. How does the design of the data center differ from the design of the LANs intended to provide user\naccess to the network?", "source": "Page 258", "chapter_title": "Chapter 11"}
{"id": "e9f998a9467f-0", "text": "26. What are three special-purpose devices you might find in a data center and what do they do?\n27. What is a bottleneck and how can you locate one?\n28. Describe three ways to improve network performance on the server.\n29. Describe three ways to improve network performance on circuits.\n30. Many of the wired and wireless LANs share the same or similar components (e.g., error control).\nWhy?\n31. As WLANs become more powerful, what are the implications for networks of the future? Will wired\nLANS still be common or will we eliminate wired offices?\nEXERCISES\nA. Survey the LANs used in your organization. Are they wireless or wired? Why?\nB. Document one LAN (or LAN segment) in detail. What devices are attached, what cabling is used, and\nwhat is the topology? What does the cable plan look like?\nC. You have been hired by a small company to install a simple LAN for its 18 Windows computers.\nDevelop a simple LAN and determine the total cost; that is, select the cables, hubs/switches, and so\non, and price them. Assume that the company has no network today and that the office is small\nenough that you don\u2019t need to worry about cable length.\nMINICASES\nI. Designing a New Ethernet One important issue in designing Ethernet lies in making sure that if a\ncomputer transmits a frame, any other computer that attempts to transmit at the same time will be\nable to hear the incoming frame before it stops transmitting, or else a collision might go unnoticed.\nFor example, assume that we are on the earth and send an Ethernet frame over a very long piece of\ncategory 5 wire to the moon. If a computer on the moon starts transmitting at the same time as we do", "source": "Page 259", "chapter_title": "Chapter 11"}
{"id": "39c081af0f15-1", "text": "on the earth and finishes transmitting before our frame arrives at the moon, there will be a collision,\nbut neither computer will detect it; the frame will be garbled, but no one will know why. So, in\ndesigning Ethernet, we must make sure that the length of cable in the LAN is shorter than the length\nof the shortest possible frame that can be sent. Otherwise, a collision could go undetected.\na. Let\u2019s assume that the smallest possible message is 64 bytes (including the 33-byte overhead). If\nwe use 100Base-T, how long (in meters) is a 64-byte message? While electricity in the cable\ntravels a bit slower than the speed of light, once you include delays in the electrical equipment in\ntransmitting and receiving the signal, the effective speed is only about 40 million meters per\nsecond. (Hint: First calculate the number of seconds it would take to transmit the frame then\ncalculate the number of meters the signal would travel in that time, and you have the total length\nof the frame.)\nb. If we use 10 GbE, how long (in meters) is a 64-byte frame?\nc. The answer in part b is the maximum distance any single cable could run from a switch to a\ncomputer in an Ethernet LAN. How would you overcome the problem implied by this?\nII. Pat\u2019s Petunias You have been called in as a network consultant by your cousin Pat, who operates a\nsuccessful mail-order flower business. She is moving to a new office and wants to install a network for\nher telephone operators, who take phone calls and enter orders into the system. The number of\noperators working varies depending on the time of day and day of the week. On slow shifts, there are\nusually only 10 operators, whereas at peak times, there are 50. She has bids from different companies", "source": "Page 259", "chapter_title": "Chapter 11"}
{"id": "fbdd37a9625e-2", "text": "to install (1) Wi-Fi or (2) a switched Ethernet 100Base-T network. She wants you to give her some\nsense of the relative performance of the alternatives so she can compare that with their different\ncosts. What would you recommend?\nIII. Eureka! Eureka! is a telephone- and Internet-based concierge service that specializes in obtaining\nthings that are hard to find (e.g., Super Bowl tickets, first-edition books from the 1500s, and Faberg\u00e9", "source": "Page 259", "chapter_title": "Chapter 11"}
{"id": "0f45c22684c1-0", "text": "eggs). It currently employs staff members who work 24 hours per day (over three shifts), with usually\nfive to seven staff members working at any given time. Staff members answer the phone and respond\nto requests entered on the Eureka! website. Much of their work is spent on the phone and on\ncomputers searching on the Internet. They have just leased a new office and are about to wire it. They\nhave bids from different companies to install (a) a 100Base-T network or (b) a Wi-Fi network. What\nwould you recommend? Why?\nIV. Tom\u2019s Home Automation Your cousin Tom runs a small construction company that builds\ncustom houses. He has just started a new specialty service that he is offering to other builders on a\nsubcontracting basis: home automation. He provides a complete service of installing cable in all the\nrooms in which the homeowner wants data access and installs the necessary networking devices to\nprovide a LAN that will connect all the computers in the house to the Internet. Most homeowners\nchoose to install a DSL or cable modem Internet connection that provides a 12\u201325 Mbps from the\nhouse to the Internet. Tom has come to you for advice about whether he should continue to offer\nwiring services (which often cost $50 per room) or whether wireless is a better direction. What type\nof LAN would you recommend?\nV. Sally\u2019s Shoes Sally Smith runs a shoe store in the mall that is about 30 feet by 50 feet in size,\nincluding a small office and a storage area in the rear. The store has one inventory computer in the\nstorage area and one computer in the office. She is replacing the two cash registers with computers\nthat will act as cash registers but will also be able to communicate with the inventory computer. Sally\nwants to network the computers with a LAN. What sort of LAN design would you recommend? Draw\na picture.", "source": "Page 260", "chapter_title": "Chapter 11"}
{"id": "eeb2d169f113-1", "text": "a picture.\nVI. South West State University South West State University installed a series of four Wi-Fi\nomnidirectional APs spread across the ceiling of the main floor of its library. The main floor has\nseveral large, open areas plus two dozen or so small offices spread around the outside walls. The\nWLAN worked well for one semester, but now more students are using the network, and performance\nhas deteriorated significantly. What would you recommend that they do? Be sure to support your\nrecommendations.\nVII. Household Wireless Your sister is building a new two-story house (which measures 50 feet long\nby 30 feet wide) and wants to make sure that it is capable of networking her family\u2019s three computers\ntogether. She and her husband are both consultants and work out of their home in the evenings and a\nfew days a month (each has a separate office with a computer, plus a laptop from the office that is\noccasionally used). The kids also have a computer in their playroom. They have several options for\nnetworking their home:\na. Wire the two offices and playroom with Ethernet Cat 5e cable and put in a 1000Base-T switch for\n$40.\nb. Install one Wi-Fi AP ($85) and put Wi-Fi cards in the three computers for $50 each (their\nlaptops already have Wi-Fi).\nc. Any combination of these options.What would you recommend? Justify your recommendation.\nVIII. Ubiquitous Offices Ubiquitous Offices provides temporary office space in cities around the\ncountry. They have a standard office layout that is a single floor with outside dimensions of 150 feet\nwide by 150 feet long. The interior is drywall offices. They have 1000Base-T but want to add wireless", "source": "Page 260", "chapter_title": "Chapter 11"}
{"id": "86d24b0b6c3b-2", "text": "access as well. How many APs would you buy, and where would you put them? Draw the office and\nshow where the APs would go.\nIX. ABC Warehouse ABC Warehouse is a single-floor facility with outside dimensions of 100 feet wide\nby 350 feet long. The interior is open, but there are large metal shelving units throughout the building\nto hold all the goods in the warehouse. How many APs would you buy, and where would you put\nthem? Draw the warehouse and show where the APs would go.\nX. Metro Motel Metro Motel is a four-story motel on the outskirts of town. The outside dimensions of\nthe motel are 60 feet wide by 200 feet long, and each story is about 10 feet high. Each floor (except\nthe ground floor) has 20 rooms (drywall construction). There is a central corridor with rooms on both\nsides. How many APs would you buy, and where would you put them? Draw the motel and show\nwhere the APs would go.", "source": "Page 260", "chapter_title": "Chapter 11"}
{"id": "9ca1438aa562-0", "text": "TECH UPDATES\nPick one of these topics to investigate.\nTopic A: Port Scanning\nPort scanning is the process of sending a series of messages to a target computer in the hopes of finding a\nway to break in. Port scanning software generates standard query messages that target \u201cwell-known\u201d port\nnumbers (e.g., port 25 for email; see Chapter 5) to see if the computer responds, thus giving the assailant\nan idea where to probe for weaknesses. What devices are out there that one can use for port scanning?\nWhy is this activity considered to be so serious? How can a network be protected against port scanning?\nTopic B: Common Security Violations\nYou may try to secure your network as much as you can, but when your users don\u2019t follow your security\npolicy guidance, all is lost. Investigate what are the five most common cyber security policy violations and\ndiscuss how they open the doors for hackers. For example, you could do a scavenger hunt (and provide\nphotos) that show that people can be very reckless and leave their laptops open while unattended or post\nor have sticky notes with passwords attached to monitors. Have fun! But don\u2019t break the law.\nDeliverables\nYour job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title Slide\n2. Short description of topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along\n5. How does it relate to material covered in class so far (and in the future)\n6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References", "source": "Page 261", "chapter_title": "Chapter 11"}
{"id": "84462f66e846-1", "text": "7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 7A\nTracing Ethernet\nTracePlus Ethernet is a network monitoring tool that enables you to see how much network capacity you\nare using. If you\u2019re working from home with a broadband Internet connection, you\u2019ll be surprised how\nlittle of the Ethernet capacity you\u2019re actually using. Your LAN connection is probably 1,000 Mbps (or 300\nMbps if you\u2019re using wireless), while the broadband connection into your home or apartment is only 20\u2013\n30 Mbps. The bottleneck is the broadband connection, so you use only a small percentage of your LAN\ncapacity.\n1. Download and install TracePlus. A free trial version of TracePlus is available at Cnet\n(download.cnet.com/TracePlus-Ethernet/3000-2085_4-29031.html). The URL might move, so if\nthis link doesn\u2019t work, search on the Internet. Just be careful what you download and where you get\nit. We like Cnet as safe download sites, but you can also check Norton SafeWeb for their ratings of\nsites (safeweb.norton.com).\n2. Start TracePlus and monitor your network. Leave it open in one part of your screen as you surf the", "source": "Page 261", "chapter_title": "Chapter 11"}
{"id": "e19c5d9afadd-0", "text": "Internet, check email, or watch a video.\nFigure 7-17 shows a sample TracePlus screen while I was surfing the Internet and checking email with\nMicrosoft Outlook. The dashboard at the bottom of the screen shows the real-time usage. You can see that\nwhen I took this screen shot, my computer was sending and receiving about 100 packets per second (or if\nyou prefer, 100 frames per second), for a total of just under 1 Mbps of data. This is less than 1% of the total\nEthernet bandwidth (i.e., network capacity), because I have switched to 100Base-T on my computer. The\ndashboard also shows that I\u2019m sending and receiving almost no broadcast or multicast data.\nImmediately above the dashboard is the summary for my computer (192.1681.104 (Alan 2)). In the 2\nminutes and 30 seconds of monitoring, my computer received 1,875 inbound packets with a total of 2.236\nmegabytes of data for a utilization of 0.118%. The average bits per second was about 118 Kbps. During the\nsame time, my computer sent slightly fewer outbound packets (1,232), but the average packet was about\n10 times smaller because the total amount of data sent was only 218,569 bytes. Most packets were 128\u2013\n511 bytes in length, but some were smaller and some were larger.\nFIGURE 7-17 TracePlus\nThe Nodes tab in the upper right of the screen shows the nodes on my network that TracePlus can\nmonitor. These include my computer (Alan 2), a second computer (Orcelia), my router (192.168.1.1), a\nwireless AP (Aironet) with two connections (into the LAN and out to the wireless LAN), and the Indiana", "source": "Page 262", "chapter_title": "Chapter 11"}
{"id": "912bd92cba4b-1", "text": "University VPN server (because I had my VPN connected; Chapter 11 discusses VPNs). You can see that all\nof these devices have little utilization (under 1%), as well as the total number of packets these devices have\nsent and received. You can click through the other tabs in this area to see the packet distribution.\nThe panel on the left of the screen shows additional information about the types of packets, errors, and\npacket sizes.", "source": "Page 262", "chapter_title": "Chapter 11"}
{"id": "e8db451bc590-0", "text": "Deliverables\n1. How many packets can your computer send and receive?\n2. What is the total data rate on your network?\n3. What is your network utilization?\nHANDS-ON ACTIVITY 7B\nWardriving\nWireless LANS are often not secure. It is simple to bring your laptop computer into a public area and\nlisten for wireless networks. This is called wardriving (because it is often done from a car). As long as you\ndo not attempt to use any networks without authorization, wardriving is quite legal. There are many good\nsoftware tools available for wardriving. Our favorites are Net Surveyor (available from\nnutsaboutnets.com/netsurveyor-wifi-scanner) or Wireless NetView (available from download.cnet.com).\nBoth are simple to use, yet powerful.\nThe first step is to download and install the software on a laptop computer that has wireless capability.\nJust be careful what you download as these sites sometimes have other software on the same page. Once\nyou have installed the software, simply walk or drive to a public area and start it up. Figure 7-18 shows an\nexample of the 13 networks I discovered in my home town of Bloomington, Indiana, when I parked my car\nin a neighborhood near the university that has a lot of rental houses and turned on Wireless Netview. I\nrearranged the order of the columns in Netview, so your screen might look a little different than mine\nwhen you first start up Netview.\nNetView displays information about each wireless LAN it discovers. The first column shows the name of\nthe WLAN (the SSID). The second column shows the last signal strength it detected, whereas the third\ncolumn shows the average signal strength. I used NetView from my parked car on the street, so the signal", "source": "Page 263", "chapter_title": "Chapter 11"}
{"id": "ffd888df5ef8-1", "text": "strengths are not strong, and because I wasn\u2019t moving, the average signal strength and the last signal\nstrength are the same.\nYou can examine the \u201cPHY Types\u201d column and see that most APs are 802.11n, although there are three\nolder 802.11g APs. Values in the \u201cMaximum Speed\u201d column are quite variable. There are some newer\n8011.n APs that are running at the top speed of 450 Mbps. Some 802.11n APs provide 144 Mbps, which\nsuggests that these WLANs are likely to be older APs that are not capable of the higher speeds of newer\n802.11n APs. You can also see that there are three 802.11g APs that provide only 54 Mbps. The \u201cChannel\u201d\ncolumn shows a fairly even distribution of channels 1, 6, and 11, indicating that most users have\nconfigured them to use the three standard channels. However, the owner of the FatJesse WLAN has\nconfigured it to run on channel 2.\nAll the APs in this neighborhood were secure. They had implemented encryption. However, the very first\nAP (2WIRE935) was using WEP, which is a very old standard. It\u2019s better than nothing, but its owner\nshould switch to WPA or WPA2.\nFigure 7-19 shows a similar screen capture in the Kelley School of Business at Indiana University. If you\nlook closely, you\u2019ll see that this only shows a small subset of the APs that were visible to NetView. There\nwere more than 50 APs in total. In this case, you\u2019ll see a more standard configuration, with virtually all the\nAPs being 802.11n running at 216 Mbps in channels 1, 6, and 12 (although you can\u2019t see the ones in", "source": "Page 263", "chapter_title": "Chapter 11"}
{"id": "79c884c1e36a-2", "text": "channel 12). All the APs on the IU Secure or eduaroam are secured, whereas attwifi and IU Guest are not\nsecured. You can also see two rogue APs (both have names starting with \u201cPD\u201d) that are 802.11g, WEP-\nsecured, running at 54 Mbps.", "source": "Page 263", "chapter_title": "Chapter 11"}
{"id": "f0af26ec4843-0", "text": "FIGURE 7-18 WLANs in a neighborhood in Bloomington, Indiana\nFIGURE 7-19 WLANs at Indiana University\nDeliverables\n1. Capture a snapshot for the screen having all the information related to the various network\nconnections that you collected during your warwalking.\n2. What different versions of 802.11 did you see, what were their maximum speeds, and what channels\nwere used?\n3. How many networks were secure?\n4. What is your overall assessment of the WLAN usage with respect to security?", "source": "Page 264", "chapter_title": "Chapter 11"}
{"id": "8d5ac8a240ce-0", "text": "HANDS-ON ACTIVITY 7C\nApollo Residence LAN Design\nApollo is a luxury residence hall that will serve honor students at your university. The residence will be\neight floors, with a total of 162 two-bedroom, one-bathroom apartments. The building is steel-frame\nconstruction with concrete on the outside and drywall on the inside that measures 240 feet by 150 feet.\nThe first floor has an open lobby with a seating area and separate office area, whereas the second floor has\nmeeting rooms. Floors 3\u20138 each contain apartments and a large open lounge with a seating area (see\nFigure 7-20). Visio files for the residence are available on this book\u2019s website.\nYour team was hired to design a network for this residence hall. To improve its quality of service, the\nuniversity has decided to install wired network connections in each apartment so that every room can\nhave one IP phone as well as network access. For security reasons, the university wants two separate\nnetworks: a LAN that will provide secure wired and wireless access to all registered students and a public\nwireless LAN that will provide Internet access to visitors.\nThis activity focuses only on the design of the LAN that will be provided on each floor of six floors with\napartments (floors 3\u20138). Do not consider floors 1 and 2 at this point; we will add those in the Hands-On\nActivity at the end of the next chapter. We have not yet discussed how to design a building backbone or\ncampus backbone, so just assume that the backbone will connect into a LAN switch using one 100Base-T\nor 1000Base-T.\nDeliverables\n1. Design the network for this residence hall and draw where the network equipment would be placed\n(use the floor plans provided).\n2. Specify the products in your design and provide their cost and the total cost of the network. There are", "source": "Page 265", "chapter_title": "Chapter 11"}
{"id": "040cfa89f775-1", "text": "two options for specifying product. Option 1 is to use the generic LAN equipment list in Figure 7-21.\nOption 2 is to use CDW (www.cdw.com) to find LAN equipment. If you use CDW, you must use only\nCisco devices (to ensure quality).\nFIGURE 7-20 Plans for Floors 3\u20138 of Apollo Residence", "source": "Page 265", "chapter_title": "Chapter 11"}
{"id": "30abe8c393e9-0", "text": "FIGURE 7-21 LAN equipment price list", "source": "Page 266", "chapter_title": "Chapter 11"}
{"id": "2de21500049c-0", "text": "CHAPTER 8\nBACKBONE NETWORKS\nThis chapter examines backbone networks (BNs) that are used in the distribution layer (within building\nbackbones) and the core layer (campus backbones). We discuss the three primary backbone architectures\nand the recommended best practice design guidelines on when to use them. The chapter ends with a\ndiscussion of how to improve BN performance and of the future of BNs.\nOBJECTIVES\nUnderstand the Internetworking devices used in BNs\nUnderstand the switched backbone architecture\nUnderstand the routed backbone architecture\nUnderstand virtual LAN architecture\nUnderstand the best practice recommendations for backbone design\nBe aware of ways to improve BN performance\nOUTLINE\n8.1 Introduction\n8.2 Switched Backbones\n8.3 Routed Backbones\n8.4 Virtual LANs\n8.4.1 Benefits of VLANs\n8.4.2 How VLANs Work\n8.5 The Best Practice Backbone Design\n8.6 Improving Backbone Performance\n8.6.1 Improving Device Performance\n8.6.2 Improving Circuit Capacity\n8.6.3 Reducing Network Demand\n8.7 Implications for Cyber Security\nSummary\n8.1 INTRODUCTION\nChapter 6 outlined the seven major components in a network (see Figure 6-1). Chapter 7, on LANs,\ndescribed how to design the LANs that provide user access to the network as well as the LANs in the data\ncenter and e-commerce edge. This chapter focuses on the next two major network architecture\ncomponents: the BNs that connect the access LANs with a building (called the distribution layer) and the\nbackbone networks that connect the different buildings on one enterprise campus (called the core layer).\nBackbones used to be built with special technologies, but today most BNs use high-speed Ethernet. There", "source": "Page 267", "chapter_title": "Chapter 11"}
{"id": "55a6746e9708-1", "text": "are two basic components to a BN: the network cable and the hardware devices that connect other\nnetworks to the BN. The cable is essentially the same as that used in LANs, except that it is often fiber\noptic to provide higher data rates. Fiber optic is also used when the distances between the buildings on an", "source": "Page 267", "chapter_title": "Chapter 11"}
{"id": "72cb7dbaf106-0", "text": "enterprise campus are farther apart than the 100 meters that standard twisted-pair cable can reach. The\nhardware devices can be computers or special-purpose devices that just transfer messages from one\nnetwork to another. These include switches, routers, and VLAN switches.\nSwitches operate at the data link layer. These are the same layer 2 switches discussed in Chapter 7 in\nthat they use the data link layer address to forward packets between network segments. They learn\naddresses by reading the source and destination addresses.\nRouters operate at the network layer. They connect two different TCP/IP subnets. Routers are the\n\u201cTCP/IP gateways\u201d that we first introduced in Chapter 5. Routers strip off the data link layer packet,\nprocess the network layer packet, and forward only those messages that need to go to other networks on\nthe basis of their network layer address. Routers may be special-purpose devices or special network\nmodules in other devices (e.g., wireless access points for home use often include a built-in router). In\ngeneral, they perform more processing on each message than switches and therefore operate more slowly.\nVLAN switches are a special combination of layer 2 switches and routers. They are complex devices\nintended for use in large networks that have special requirements. We discuss these in Section 8.4.\nIn the sections that follow, we describe the three basic BN architectures and discuss at which layer they\nare often used. We assume that you are comfortable with the material on TCP/IP in Chapter 5; if you are\nnot, you may want to go back and review Section 5.6 \u201cTCP/IP Example,\u201d before you continue reading. We\nthen explain the best practice design guidelines for the distribution layer and the core layer and discuss\nhow to improve performance.\n8.2 SWITCHED BACKBONES", "source": "Page 268", "chapter_title": "Chapter 11"}
{"id": "5056054fe174-1", "text": "how to improve performance.\n8.2 SWITCHED BACKBONES\nSwitched backbones are probably the most common type of BN used in the distribution layer (i.e.,\nwithin a building); most new building BNs designed today use switched backbones.\nSwitched BNs use a star topology with one switch at its center. Figure 8-1 shows a switched backbone\nconnecting a series of LANs. There is a switch serving each LAN (access layer) that is connected to the\nbackbone switch at the bottom of the figure (distribution layer). Most organizations now use switched\nbackbones in which all network devices for one part of the building are physically located in the same\nroom, often in a rack of equipment. This has the advantage of placing all network equipment in one place\nfor easy maintenance and upgrade, but it does require more cable. In most cases, the cost of the cable is\nonly a small part of the overall cost to install the network, so the cost is greatly outweighed by the\nsimplicity of maintenance and the flexibility it provides for future upgrades.\nThe room containing the rack of equipment is sometimes called the main distribution facility (MDF)\nor central distribution facility (CDF). Figure 8-2 shows a photo of an MDF room at Indiana University.\nFigure 8-3 shows the equipment diagram of this same room. The cables from all computers and devices in\nthe area served by the MDF (often hundreds of cables) are run into the MDF room. Once in the room, they\nare connected into the various devices. The devices in the rack are connected among themselves using\nvery short cables called patch cables.\nWith rack-mounted equipment, it becomes simple to move computers from one LAN to another. Usually,\nall the computers in the same general physical location are connected to the same switch and thus share", "source": "Page 268", "chapter_title": "Chapter 11"}
{"id": "f3d5f3a990c4-2", "text": "all the computers in the same general physical location are connected to the same switch and thus share\nthe capacity of the switch. Although this often works well, it can cause problems if many of the computers\non the switch are high-traffic computers. For example, if all the busy computers on the network are\nlocated in the upper-left area of the figure, the switch in this area may become a bottleneck.\nWith an MDF, all cables run into the MDF. If one switch becomes overloaded, it is straight-forward to\nunplug the cables from several high-demand computers from the overloaded switch and plug them into\none or more less-busy switches. This effectively spreads the traffic around the network more efficiently\nand means that network capacity is no longer tied to the physical location of the computers; computers in\nthe same physical area can be connected into different network segments.\nSometimes a chassis switch is used instead of a rack. A chassis switch enables users to plug modules\ndirectly into the switch. Each module is a certain type of network device. One module might be a 16-port\n100Base-T switch, another might be a router, whereas another might be a 4-port 1000Base-F switch, and\nso on. The switch is designed to hold a certain number of modules and has a certain internal capacity, so", "source": "Page 268", "chapter_title": "Chapter 11"}
{"id": "23d375e91bf3-0", "text": "that all the modules can be active at one time. For example, a switch with four 1000Base-T switches (with\n24 ports each) and one 1000Base-F port would have to have an internal switching capacity of at least 97\nGbps ((4 \u00d7 24 \u00d7 1 Gbps) + (1 \u00d7 1 Gbps)).\nFIGURE 8-1 Rack-mounted switched backbone network architecture\nThe key advantage of chassis switches is their flexibility. It becomes simple to add new modules with\nadditional ports as the LAN grows and to upgrade the switch to use new technologies. For example, if you\nwant to add gigabit Ethernet, you simply lay the cable and insert the appropriate module into the chassis\nswitch.", "source": "Page 269", "chapter_title": "Chapter 11"}
{"id": "5fc87a3f31ea-0", "text": "FIGURE 8-2 An MDF with rack-mounted equipment. A layer 2 chassis switch with five 100Base-T\nmodules (center of photo) connects to four 24-port 100Base-T switches. The chassis switch is connected\nto the campus backbone using 1000Base-F over fiber-optic cable. The cables from each room are wired\ninto the rear of the patch panel (shown at the top of the photo), with the ports on the front of the patch\npanel labeled to show which room is which. Patch cables connect the patch panel ports to the ports on the\nswitches. MDF = main distribution facility", "source": "Page 270", "chapter_title": "Chapter 11"}
{"id": "117835ba278e-0", "text": "Source: Photo courtesy of the author, Alan Dennis.\nFIGURE 8-3 MDF network diagram. MDF = main distribution facility\nMANAGEMENT FOCUS 8-1\nSwitched Backbones at Indiana University\nAt Indiana University we commonly use switched backbones in our buildings. Figure 8-4 shows a\ntypical design. Each floor in the building has a set of switches and access points that serve the LANs\non that floor. Each of these LANs and WLANs are connected into a switch for that floor, thus\nforming a switched backbone on each floor. Typically, we use switched 100Base-T within each floor.\nThe switch forming the switched backbone on each floor is then connected into another switch in the\nbasement, which provides a switched backbone for the entire building. The building backbone is\nusually a higher-speed network running over fiber-optic cable (e.g., 100Base-F or 1 GbE). This\nswitch, in turn, is connected into a high-speed router that leads to the campus backbone (a routed\nbackbone design).", "source": "Page 271", "chapter_title": "Chapter 11"}
{"id": "0e55866ff6f8-0", "text": "FIGURE 8-4 Switched backbones at Indiana University\n8.3 ROUTED BACKBONES\nRouted backbones move packets along the backbone on the basis of their network layer address (i.e.,\nlayer 3 address). Routed backbones are sometimes called subnetted backbones or hierarchical backbones\nand are most commonly used to connect different buildings on the same enterprise campus backbone\nnetwork (i.e., at the core layer).\nFigure 8-5 illustrates a routed backbone used at the core layer. A routed backbone is the basic backbone\narchitecture we used to illustrate how TCP/IP worked in Chapter 5. There are a series of LANs (access\nlayer) connected to a switched backbone (distribution layer). Each backbone switch is connected to a\nrouter. Each router is connected to a core router (core layer). These routers break the network into\nseparate subnets. The LANs in one building are a separate subnet from the LANs in a different building.\nMessage traffic stays within each subnet unless it specifically needs to leave the subnet to travel elsewhere\non the network, in which case the network layer address (e.g., TCP/IP) is used to move the packet. For\nexample, in a switched backbone, a broadcast message (such as an ARP) would be sent to every single\ncomputer in the network. A routed backbone ensures that broadcast messages stay in the one network\nsegment (i.e., subnet) where they belong and are not sent to all computers. This leads to a more efficient\nnetwork.", "source": "Page 272", "chapter_title": "Chapter 11"}
{"id": "98a2506c161a-0", "text": "FIGURE 8-5 Routed backbone architecture\nEach set of LANs is usually a separate entity, relatively isolated from the rest of the network. There is no\nrequirement that all LANs share the same technologies. Each set of LANs can contain its own server\ndesigned to support the users on that LAN, but users can still easily access servers on other LANs over the\nbackbone, as needed.\nA Day in the Life: Network Operations Manager\nThe job of the network operations manager is to ensure that the network operates effectively. The\noperations manager typically has several network administrators and network managers that report\nto him or her and is responsible for both day-to-day operations and long-term planning for the\nnetwork. The challenge is to balance daily firefighting with longer-term planning; they're always", "source": "Page 273", "chapter_title": "Chapter 11"}
{"id": "33fe6ee07a5c-0", "text": "looking for a better way to do things. Network operations managers also meet with users to ensure\ntheir needs are met. While network technicians deal primarily with networking technology, a\nnetwork operations manager deals extensively with both technology and the users.\nAtypical day starts with administrative work that includes checks on all servers and backup\nprocesses to ensure that they are working properly and that there are no security issues. Then it's on\nto planning. One typical planning item includes planning for the acquisition of new desktop or\nlaptop computers, including meeting with vendors to discuss pricing, testing new hardware and\nsoftware, and validating new standard configurations for computers. Other planning is done around\nnetwork upgrades, such as tracking historical data to monitor network usage, projecting future user\nneeds, surveying user requirements, testing new hardware and software, and actually planning the\nimplementation of new network resources.\nOne recent example of long-term planning was the migration from a Novell file server to Microsoft\nADS file services. The first step was problem definition; what were the goals and the alternatives?\nThe key driving force behind the decision to migrate was to make it simpler for the users (e.g., now\nthe users do not need to have different accounts with different passwords) and to make it simpler for\nthe network staff to provide technical support (e.g., now there is one less type of network software to\nsupport). The next step was to determine the migration strategy: a Big Bang (i.e., the entire network\nat once) or a phased implementation (several groups of users at a time). The migration required a\ntechnician to access each individual user's computer, so it was impossible to do a Big Bang. The next\nstep was to design a migration procedure and schedule whereby groups of users could be moved at a\ntime (e.g., department by department). A detailed set of procedures and a checklist for network", "source": "Page 274", "chapter_title": "Chapter 11"}
{"id": "a7692ba5ed2a-1", "text": "time (e.g., department by department). A detailed set of procedures and a checklist for network\ntechnicians were developed and extensively tested. Then each department was migrated on a 1-week\nschedule. One key issue was revising the procedures and checklist to account for unexpected\noccurrences during the migration to ensure that no data were lost. Another key issue was managing\nuser relationships and dealing with user resistance.\nSource: With thanks to Mark Ross.\nThe primary advantage of the routed backbone is that it clearly segments each part of the network\nconnected to the backbone. Each segment (usually a set of LANs or switched backbone) has its own\nsubnet addresses that can be managed by a different network manager. Broadcast messages stay within\neach subnet and do not move to other parts of the network.\nThere are two primary disadvantages to routed backbones. First, the routers in the network impose time\ndelays. Routing takes more time than switching, so routed networks can sometimes be slower. Second,\nrouters are more expensive and require more management than switches.\nFigure 8-5 shows one core router. Many organizations actually use two core routers to provide better\nsecurity, as we discuss in Chapter 11.\n8.4 VIRTUAL LANS\nFor many years, the design of LANs remained relatively constant. However, in recent years, the\nintroduction of high-speed switches has begun to change the way we think about LANs. Switches offer the\nopportunity to design radically new types of LANs. Most large organizations today have implemented the\nvirtual LAN (VLAN), a new type of LAN\u2013BN architecture made possible by intelligent, high-speed\nswitches.\nVirtual LANs are networks in which computers are assigned to LAN segments by software rather than by\nhardware. In the first section, we described how in rack-mounted collapsed BNs a computer could be", "source": "Page 274", "chapter_title": "Chapter 11"}
{"id": "12b2222bef05-2", "text": "moved from one hub to another by unplugging its cable and plugging it into a different hub. VLANs\nprovide the same capability via software so that the network manager does not have to unplug and replug\nphysical cables to move computers from one segment to another.\nOften, VLANs are faster and provide greater opportunities to manage the flow of traffic on the LAN and\nBN than do the traditional LAN and routed BN architectures. However, VLANs are significantly more\ncomplex, so they usually are used only for large networks.", "source": "Page 274", "chapter_title": "Chapter 11"}
{"id": "f0fe1472188c-0", "text": "The simplest example is a single-switch VLAN, which means that the VLAN operates only inside one\nswitch. The computers on the VLAN are connected into the one switch and assigned by software into\ndifferent VLANs (Figure 8-6). The network manager uses special software to assign the dozens or even\nhundreds of computers attached to the switch to different VLAN segments. The VLAN segments function\nin the same way as physical LAN segments or subnets; the computers in the same VLAN act as though\nthey are connected to the same physical switch or hub in a certain subnet. Because VLAN switches can\ncreate multiple subnets, they act like routers, except the subnets are inside the switch, not between\nswitches. Therefore, broadcast messages sent by computers in one VLAN segment are sent only to the\ncomputers on the same VLAN.\nVirtual LANs can be designed so that they act as though computers are connected via hubs (i.e., several\ncomputers share a given capacity and must take turns using it) or via switches (i.e., all computers in the\nVLAN can transmit simultaneously). Although switched circuits are preferred to the shared circuits of\nhubs, VLAN switches with the capacity to provide a complete set of switched circuits for hundreds of\ncomputers are more expensive than those that permit shared circuits.\nWe should also note that it is possible to have just one computer in a given VLAN. In this case, that\ncomputer has a dedicated connection and does not need to share the network capacity with any other\ncomputer. This is commonly done for servers.\n8.4.1 Benefits of VLANs\nHistorically, we have assigned computers to subnets based on geographic location; all computers in one\npart of a building have been placed in the same subnet. With VLANs, we can put computers in different\ngeographic locations in the same subnet. For example, in Figure 8-6, a computer in the lower left could be", "source": "Page 275", "chapter_title": "Chapter 11"}
{"id": "3767726b84ac-1", "text": "put on the same subnet as one in the upper right\u2014a separate subnet from all the other computers.\nA more common implementation is a multiswitch VLAN, in which several switches are used to build\nthe VLANs (Figure 8-7). VLANs are most commonly found in building backbone networks (i.e., access and\ndistribution layers) but are starting to move into core backbones between buildings. In this case, we can\nnow create subnets that span buildings. For example, we could put one of the computers in the upper left\nof Figure 8-7 in the same subnet as the computers in the lower right, which could be in a completely\ndifferent building. This enables us to create subnets based on who you are, rather than on where you are;\nwe have an accounting subnet and a marketing subnet, not a Building A and a Building B subnet. We now\nmanage security and network capacity by who you are, not by where your computer is. Because we have\nseveral subnets, we need to have a router\u2014but more on that shortly.", "source": "Page 275", "chapter_title": "Chapter 11"}
{"id": "224687b5f0cc-0", "text": "FIGURE 8-6 VLAN-based backbone network architecture\nVirtual LANs offer two other major advantages compared to the other network architectures. The first lies\nin their ability to manage the flow of traffic on the LAN and backbone very precisely. VLANs make it much\nsimpler to manage the broadcast traffic, which has the potential to reduce performance and to allocate\nresources to different types of traffic more precisely. The bottom line is that VLANs often provide faster\nperformance than the other backbone architectures.", "source": "Page 276", "chapter_title": "Chapter 11"}
{"id": "763d0ee5a9a5-0", "text": "FIGURE 8-7 Multiswitch VLAN-based backbone network design\nThe second advantage is the ability to prioritize traffic. The VLAN tag information included in the\nEthernet packet defines the VLAN to which the packet belongs and also specifies a priority code based on\nthe IEEE 802.1q standard (see Chapter 4). As you will recall from Chapter 5, the network and transport\nlayers can use Resource Reservation Protocol (RSVP) quality of service (QoS), which enables them to\nprioritize traffic using different classes of service. RSVP is most effective when combined with QoS\ncapabilities at the data link layer. (Without QoS at the hardware layers, the devices that operate at the\nhardware layers [e.g., layer 2 switches] would ignore QoS information.) With the Ethernet packet's ability\nto carry VLAN information that includes priorities, we now have QoS capabilities in the data link layer.\nThis means we can connect VOIP telephones directly into a VLAN switch and configure the switch to\nreserve sufficient network capacity so that they will always be able to send and receive voice messages.\nThe biggest drawbacks to VLANs are their cost and management complexity. VLAN switches also are\nmuch newer technologies that have only recently been standardized. Such \u201cleading-edge\u201d technologies\nsometimes introduce other problems that disappear only after the specific products have matured.\n8.4.2 How VLANs Work\nVLANs work somewhat differently than the traditional Ethernet/IP approach described in the previous\nchapters. Each computer is assigned into a specific VLAN that has a VLAN ID number (which ranges\nfrom 1 to 1005 or to 4094, depending on whether the extended range standard is used). Each VLAN ID is\nmatched to a traditional IP subnet, so each computer connected to a VLAN switch also receives a\ntraditional IP address assigned by the VLAN switch (the switch acts as a DHCP server; see Chapter 5).", "source": "Page 277", "chapter_title": "Chapter 11"}
{"id": "78ad8b9315de-1", "text": "Most VLAN switches can support only 255 separate VLANs simultaneously, which means each switch can\nsupport up to 255 separate IP subnets, which is far larger than most organizations want in any single\ndevice.\nMANAGEMENT FOCUS 8-2\nVLANs in Shangri-La", "source": "Page 277", "chapter_title": "Chapter 11"}
{"id": "9a1b6ea7dd26-0", "text": "Shangri-La's Rasa Sayang Resort and Spa is a five-star luxury resort hotel located on the scenic Batu\nFeringgi Beach in Penang, Malaysia. The resort has two main buildings, the 189-room Garden Wing\nand the 115-room Rasa Wing, with an additional 11 private spa villas.\nOver the years, the resort had installed three separate networks: one for the resort's operations, one\nfor its POS (point-of-sales) system, and one for Internet access for guests (which was wired, not\nwireless). The networks were separate to ensure security, so that users of one network could not gain\naccess to another.\nAs part of a multi-million-dollar renovation, the resort decided to upgrade its network to gigabit\nspeeds and to offer wireless Internet access to its guests. Rather than build three separate networks\nagain, it decided to build one network using VLANs. The resort installed 12 wireless access points\nand 24 VLAN switches, plus two larger core VLAN switches. The VLAN architecture provides\nseamless management of the wired and wireless components as one integrated network and ensures\nrobust performance and security.\nSource: Adapted from \u201cWireless Access amidst Lush Greenery of Penang Shangri-La's Resort,\u201d HP ProCurve Customer Case\nStudy, Hewlett-Packard.\nComputers are assigned into the VLAN (and the matching IP subnet) based on the physical port on the\nswitch into which they are connected. Don't confuse the physical port on the switch (which is the jack the\ncable plugs into) with the TCP port number from Chapter 5; they are different\u2014it's another example of\nnetworking using the same word (\u201cport\u201d) to mean two different things. The network manager uses\nsoftware to assign the computers to specific VLANs using their physical port numbers, so it is simple to\nmove a computer from one VLAN to another.", "source": "Page 278", "chapter_title": "Chapter 11"}
{"id": "8beed8f367fe-1", "text": "move a computer from one VLAN to another.\nWhen a computer transmits an Ethernet frame, it uses the traditional Ethernet and IP addresses we\ndiscussed in previous chapters (e.g., Chapters 4 and 5) to move the frame through the network because it\ndoesn't know that it is attached to a VLAN switch. Recall that as a message moves through the network,\nthe IP address is used to specify the final destination and the Ethernet address is used to move the\nmessage from one computer to the next along the route to the final destination. Some devices, such as\nlayer 2 switches, are transparent; the Ethernet frame passes through them unchanged. Other devices,\nsuch as routers, remove the Ethernet frame and create a new Ethernet frame to send the message to the\nnext computer. VLANs are transparent\u2014although they do change the frame at times.\nLet's use Figure 8-7 to explain how VLAN switches work. We'll assume this network uses the first 3 bytes\nto specify the IP subnet. In this example, we have three VLAN switches with three IP subnets (179.58.10.x,\n179.58.3.x, and 179.58.11.x) and three VLANs (10, 20, and 30). A router is used to enable communication\namong the different IP subnets.\nSuppose a computer connected to switch 2 (IP 179.58.10.102) sends a message to a computer on the same\nIP subnet that is also connected to switch 2 (IP 179.58.10.103). The sending computer will recognize that\nthe destination computer is in the same IP subnet, create an Ethernet frame with the destination\ncomputer's Ethernet address (using ARP if needed to find the Ethernet address), and transmit the frame\nto VLANswitch 2. When a VLANswitch receives a frame that is destined for another computer in the same", "source": "Page 278", "chapter_title": "Chapter 11"}
{"id": "333e876a45ec-2", "text": "subnet on the same VLAN switch, the switch acts as a traditional layer 2 switch: it forwards the frame\nunchanged to the correct computer. Remember from Chapter 7 that switches build a forwarding table that\nlists the Ethernet address of every computer connected to the switch. When a frame arrives at the switch,\nthe switch looks up the Ethernet address in the forwarding table, and if it finds the address, then it\nforwards the frame to the correct computer. We discuss what happens if the Ethernet address is not in the\nforwarding table in a moment.\nSuppose that a computer wants to send a message to a computer in the same subnet, but that the\ndestination computer is actually on a different VLAN switch. For example, in Figure 8-7, suppose this\nsame computer (IP 179.58.10.102) sends a message to a computer on switch 3 (179.58.10.50). The sending\ncomputer will act exactly the same because to it, the situation is the same. It doesn't know where the\ndestination computer is; it just knows that the destination is on its own subnet. The sending computer will\ncreate an Ethernet frame with the destination computer's Ethernet address (using ARP if needed to find\nthe Ethernet address) and transmit the frame to VLAN switch 2. Switch 2 receives the frame, looks up the\ndestination Ethernet address in its forwarding table, and recognizes that the frame needs to go to switch 3.", "source": "Page 278", "chapter_title": "Chapter 11"}
{"id": "5da53e9e81cc-0", "text": "Virtual LAN switches use Ethernet 802.1q tagging to move frames from one switch to another. Chapter 4\nshowed that the layout of an Ethernet frame contains a VLAN tag field which VLAN switches use to move\nframes among switches. When a VLAN switch receives an Ethernet frame that needs to go to a computer\non another VLANswitch, it changes the Ethernet frame by inserting the VLAN ID number and a priority\ncode into the VLAN tag field. When a switch is configured, the network administrator defines which\nVLANs span which switches and also defines VLAN trunks\u2014circuits that connect two VLAN switches\nand enable traffic to flow from one switch to another. As a switch builds its forwarding table, it receives\ninformation from other switches and inserts the Ethernet addresses of computers attached to them into\nits forwarding table along with the correct trunk to use to send frames to them.\nIn this case, switch 2 receives the frame and uses the forwarding table to identify that it needs to send the\nframe over the trunk to switch 3. It changes the frame by inserting the VLAN ID and priority code into the\ntag field and transmits the frame over the trunk to switch 3. Switch 3 receives the frame, looks the\nEthernet address up in its forwarding table, and identifies the specific computer to which the frame needs\nto be sent. The switch removes the VLAN tag information and transmits the revised frame to the\ndestination computer. In this way, neither the sending computer nor the destination computer is aware\nthat the VLAN exists. The VLAN is transparent.\nSuppose the same sending computer (179.58.10.102) wants to send a message to a computer on a different\nsubnet in the same VLAN (e.g., 179.58.7.30 on the same switch or 179.58.11.20 on switch 3). The sending", "source": "Page 279", "chapter_title": "Chapter 11"}
{"id": "9ff53da05bbf-1", "text": "computer recognizes that the destination is on a different subnet and therefore creates an Ethernet frame\nwith a destination Ethernet address of its router (179.58.10.1) and sends the frame to switch 2.\nAt this point, everything works the same as in the previous example. Switch 2 looks up the destination\nEthernet address in its forwarding table and recognizes that the frame needs to go to switch 1 because the\nrouter's Ethernet address is listed in the forwarding table as being reachable through switch 1. Switch 2\nsets the VLAN tag information and sends the frame over the trunk to switch 1. Switch 1 looks up the\ndestination Ethernet address in its forwarding table and sees that the router is attached to it. Switch 2\nremoves the VLAN tag field and sends the frame to the router.\nThe router is a layer 3 device, so when it receives the message, it strips off the Ethernet frame and reads\nthe IP packet. It looks in its routing table and sees that the destination IP address is within a subnet it\ncontrols (either 179.58.7.x or 179.58.11.x, depending on to which destination computer the packet was\nsent). The router creates a new Ethernet frame and sets the destination Ethernet address to the\ndestination computer (using an ARP if needed) and sends the frame to switch 1.\nSwitch 1 reads the Ethernet address and looks it up in its forwarding table. It discovers the frame needs to\ngo to switch 2 (for 179.58.7.30) or switch 3 (for 179.58.11.20), sets the VLAN tag field, and forwards the\nframe over the trunk to the correct switch. This switch in turn removes the VLAN tag information and\nsends the frame to the correct computer.\nUntil now, we've been talking about unicast messages\u2014messages from one computer to another\u2014that are", "source": "Page 279", "chapter_title": "Chapter 11"}
{"id": "774450173417-2", "text": "the majority of network traffic. However, what about broadcast messages, such as ARPs, that are sent to\nall computers in the same subnet? Each computer on a VLAN switch is assigned into a subnet with a\nmatching VLAN ID. When a computer issues a broadcast message, the switch identifies the VLAN ID of\nthe sending computer and then sends the frame to all other computers that have the same VLAN ID.\nThese computers may be on the same switch or on different switches. For example, suppose computer\n179.58.10.102 issues an ARP to find an Ethernet address (e.g., the router's address). Switch 2 would send\nthe broadcast frame to all attached computers with the same VLAN ID (e.g., 179.58.10.103). Switch 2's\ntrunking information also tells it that VLAN 10 spans switch 1 and switch 3, so it sends the frame to them.\nThey, in turn, use their tables to send it to their attached computers that are in the same VLAN (which\nincludes the router). Note that the router has multiple IP addresses and VLAN IDs because it is connected\nto several different VLANs and subnets (three, in our example here).\nWe have also assumed that the VLAN switch has a complete forwarding table\u2014a table that lists all the\nEthernet addresses of all the computers in the network. Just like a layer 2 switch, the VLAN switch learns\nEthernet addresses as it sends and receives messages. Where the VLAN switch is first turned on, the\nforwarding table is empty, just like the forwarding table of a layer 2 switch; however, its VLAN ID and\ntrunk tables are complete because these are defined by the network administrator. Suppose the switch has\njust been turned on and has an empty forwarding table. It receives an Ethernet frame, looks up the", "source": "Page 279", "chapter_title": "Chapter 11"}
{"id": "8c00cb2c0041-0", "text": "destination address in the forwarding table, and does not find where to send it. What happens?\nIf the VLAN switch were a layer 2 switch, it would send the frame to all ports. However, a VLAN switch\ncan be a bit smarter than this. If you think about how IP works, you will see that an Ethernet frame is\nalways sent to a computer in the same IP subnet as the sending computer. Any time a frame needs to\nmove to a different subnet, it goes through a router that sits on both subnets. Think about it for a minute\nbefore you continue reading. Therefore, any time the VLAN switch can't find a destination Ethernet\naddress in the forwarding table, it treats the frame as a broadcast frame and sends it to all the computers\nin the same subnet, which in VLAN terms means all the computers with the same VLAN ID.\nThis means that a VLAN architecture can improve performance by reducing traffic in the network\ncompared with a switched backbone architecture. Because a switched backbone uses layer 2 switches, all\nthe computers are in the same subnet, and all broadcast traffic goes to all computers. By using a VLAN we\ncan limit where broadcast traffic flows by dividing the network into separate subnets, so that broadcast\nmessages only go to computers in the same subnet.\n8.5 THE BEST PRACTICE BACKBONE DESIGN\nThe past few years have witnessed radical changes in the backbone, both in terms of new technologies\n(e.g., gigabit Ethernet) and in architectures (e.g., VLANs). Fifteen years ago, the most common backbone\narchitecture was the routed backbone, connected to a series of shared 10Base-T hubs in the LAN.\nToday, the most effective architecture for the distribution layer in terms of cost and performance is a\nswitched backbone (either rack-mounted or using a chassis switch) because it provides the best", "source": "Page 280", "chapter_title": "Chapter 11"}
{"id": "782a326574a8-1", "text": "switched backbone (either rack-mounted or using a chassis switch) because it provides the best\nperformance at the least cost. For the core layer, most organizations use a routed backbone. Many large\norganizations are now implementing VLANs, especially those that have departments spread over multiple\nbuildings, but VLANs add considerable cost and complexity to the network.\nGiven the trade-offs in costs, there are several best practice recommendations. First, the best practice\narchitecture is a switched backbone or VLAN for the distribution layer and a routed backbone for the core\nlayer. Second, the best practice recommendation for backbone technology is gigabit Ethernet. Considering\nthe LAN and backbone environments together, the ideal network design is likely to be a mix of layer 2 and\nVLAN Ethernet switches. Figure 8-8 shows one likely design. The access layer (i.e., the LANs) uses\n1000Base-T layer 2 Ethernet switches running on Cat 5e or Cat 6 twisted-pair cables to provide flexibility\nfor 100Base-T or 1000Base-T. The distribution layer uses layer 2 or VLAN switches that use 100Base-T or\nmore commonly 1000Base-T/F (over fiber or Cat 6) to connect to the access layer. To provide good\nreliability, some organizations may provide redundant switches, so if one fails, the backbone continues to\noperate. The core layer uses routers or VLAN Ethernet switches running 10 GbE or 40 GbE over fiber.\nFIGURE 8-8 The best practice network design\n8.6 IMPROVING BACKBONE PERFORMANCE", "source": "Page 280", "chapter_title": "Chapter 11"}
{"id": "8b36501aee78-0", "text": "The method for improving the performance of BNs is similar to that for improving LAN performance.\nFirst, find the bottleneck and then remove it (or, more accurately, move the bottleneck somewhere else).\nYou can improve the performance of the network by improving the performance of the devices in the\nnetwork, by upgrading the circuits between them, and by changing the demand placed on the network\n(Figure 8-9).\n8.6.1 Improving Device Performance\nThe primary functions of computers and devices in BNs are forwarding/routing messages and serving up\ncontent. If the devices and computers are the bottleneck, routing can be improved with faster devices or a\nfaster routing protocol. Distance vector routing is faster than dynamic routing (see Chapter 5) but\nobviously can impair circuit performance in high-traffic situations. Link state routing is usually used in\nWANs because there are many possible routes through the network. BNs often have only a few routes\nthrough the network, so link state routing may not be too helpful because it will delay processing and\nincrease the network traffic because of the status reports sent through the network. Distance vector\nrouting will often simplify processing and improve performance.\nPerformance Checklist\nIncrease Device Performance\nChange to a more appropriate routing protocol (either distance vector or link\nstate)\nIncrease the devices' memory\nIncrease Circuit Capacity\nUpgrade to a faster circuit\nAdd circuits\nReduce Network Demand\nChange user behavior\nReduce broadcast messages\nFIGURE 8-9 Facility map of the Western Trucking headquarters\nMost backbone devices are store-and-forward devices. One simple way to improve performance is to\nensure that they have sufficient memory. If they don't, the devices will lose packets, requiring them to be\nretransmitted.\n8.6.2 Improving Circuit Capacity\nIf network circuits are the bottlenecks, there are several options. One is to increase circuit capacity (e.g.,", "source": "Page 281", "chapter_title": "Chapter 11"}
{"id": "771394a1a720-1", "text": "by going from 100Base-T Ethernet to gigabit Ethernet). Another option is to add additional circuits\nalongside heavily used ones so that there are several circuits between some devices.\nIn many cases, the bottleneck on the circuit is only in one place\u2014the circuit to the server. A switched\nnetwork that provides 100 Mbps to the client computers but a faster circuit to the server (e.g., 1000Base-\nT) can improve performance at very little cost.\n8.6.3 Reducing Network Demand\nOne way to reduce network demand is to restrict applications that use a lot of network capacity, such as\ndesktop videoconferencing, medical imaging, or multimedia. In practice, it is often difficult to restrict\nusers. Nonetheless, finding one application that places a large demand on the network and moving it can\nhave a significant impact.\nMuch network demand is caused by broadcast messages, such as those used to find data link layer\naddresses (see Chapter 5). Some network operating system and application software packages written for\nuse on LANs also use broadcast messages to send status information to all computers on the LAN. For", "source": "Page 281", "chapter_title": "Chapter 11"}
{"id": "5da5b749a133-0", "text": "example, broadcast messages inform users when printers are out of paper or when the server is running\nlow on disk space. When used in a LAN, such messages place little extra demand on the network because\nevery computer on the LAN gets every message.\nThis is not the case for routed backbones because messages do not normally flow to all computers, but\nbroadcast messages can consume a fair amount of network capacity in switched back-bones. In many\ncases, broadcast messages have little value outside their individual LAN. Therefore, some switches and\nrouters can be set to filter broadcast messages so that they do not go to other networks. This reduces\nnetwork traffic and improves performance.\n8.7 IMPLICATIONS FOR CYBER SECURITY\nAs security becomes more important, most routers now have software that enables the network manager\nto create an access control list (ACL) that specifies what traffic the router should allow through and\nwhat traffic the router should block. Each packet that arrives at the router is checked against the rules in\nthe ACL. At a minimum the ACL specifies the source IP address, the destination IP address, and the action\nthe router should take, either to permit or deny entry. Routers can be configured to block all traffic that is\nnot explicitly permitted entry by rules in the ACL.\nMany routers have more sophisticated ACL software that enables the ACL to have different rules for\ndifferent interfaces, so that packets coming from outside the organization have different rules than\npackets moving between different parts of the organization. Some ACL software can also specify rules for\nthe application layer packet type (e.g., HTTP, SMTP, FTP) so that only HTTP packets are sent to Web\nservers, only SMTP are sent to email servers, and so on, to prevent attackers from trying to upload\nunauthorized files.\nVLANs are the most secure type of backbone because they enable ACL and other security measures to be", "source": "Page 282", "chapter_title": "Chapter 11"}
{"id": "52d041e9047f-1", "text": "applied at the switch level. This means that every packet from every device is subjected to security, not\njust those that pass through a routed backbone. It is in theory possible to have the same type of security\non a switched backbone, but very few, if any, manufacturers make switches with the same level of ACL\nsoftware as that available on routers or VLAN switches.\nSUMMARY\nSwitched Backbones These use the same layer 2 switches as LANs to connect the different LANs\ntogether. The switches are usually placed in a rack in the same room (called an MDF or an\nIntermediate Distribution Facility (IDF)) to make them easy to maintain.\nRouted Backbones These use routers to connect the different LANs or subnets. Routed backbones\nare slower than switched backbones, but they prevent broadcast traffic from moving between the\ndifferent parts of the network.\nVLAN Backbones These combine the best features of switched and routed backbones. They are\nvery complex and expensive, so they are mostly used by large companies.\nBest Practice Backbone Design The best practice backbone architecture for most organizations is\na switched backbone (using a rack or a chassis switch) or VLAN in the distribution layer and a routed\nbackbone in the core layer. The recommended technology is gigabit Ethernet.\nImproving Backbone Performance Backbone performance can be improved by choosing the\nbest network layer routing protocols. Upgrading to faster circuits and adding additional circuits on\nvery busy backbones can also improve performance. Finally, one could move servers closer to the end\nusers or reduce broadcast traffic to reduce backbone traffic.\nKEY TERMS\naccess control list (ACL)\nchassis switch", "source": "Page 282", "chapter_title": "Chapter 11"}
{"id": "5eaa425cbb64-0", "text": "IEEE 802.1q\nlayer 2 switches\nmain distribution facility (MDF)\nmodules\nmultiswitch VLAN\npatch cables\nrack\nrouted backbones\nrouter\nsingle-switch VLAN\nswitched backbones\nswitches\nvirtual LAN (VLAN)\nVLAN ID\nVLAN switches\nVLAN tag\nVLAN trunks\nQUESTIONS\n1. How does a layer 2 switch differ from a router?\n2. How does a layer 2 switch differ from a VLAN?\n3. How does a router differ from a VLAN?\n4. Under what circumstances would you use a switched backbone?\n5. Under what circumstances would you use a routed backbone?\n6. Under what circumstances would you use a VLAN backbone?\n7. Explain how routed backbones work.\n8. In Figure 8-5, would the network still work if we removed the routers in each building and just had\none core router? What would be the advantages and disadvantages of doing this?\n9. Explain how switched backbones work.\n10. What are the key advantages and disadvantages of routed and switched backbones?\n11. Compare and contrast rack-based and chassis-based switched backbones.\n12. What is a module and why are modules important?\n13. Explain how single-switch VLANs work.\n14. Explain how multiswitch VLANs work.\n15. What is IEEE 802.1q?\n16. What are the advantages and disadvantages of VLANs?\n17. How can you improve the performance of a BN?\n18. Why are broadcast messages important?\n19. What are the preferred architectures used in each part of the backbone?", "source": "Page 283", "chapter_title": "Chapter 11"}
{"id": "2387a99eaab3-0", "text": "20. Some experts are predicting that Ethernet will move into the WAN. What do you think?\nEXERCISES\nA. Survey the BNs used in your organization. Is the campus core backbone different from the\ndistribution backbones used in the buildings? Why?\nB. Document one BN in detail. What devices are attached, what cabling is used, and what is the\ntopology? What networks does the backbone connect?\nC. You have been hired by a small company to install a backbone to connect four 100base-T Ethernet\nLANs (each using one 24-port hub) and to provide a connection to the Internet. Develop a simple\nbackbone and determine the total cost (i.e., select the backbone technology and price it, select the\ncabling and price it, select the devices and price them, and so on). Prices are available at\nwww.datacommwarehouse.com, but use any source that is convenient. For simplicity, assume that\ncategory 5, category 5e, category 6, and fiber-optic cable have a fixed cost per circuit to buy and\ninstall, regardless of distance, $50, $60, $120, and $300, respectively.\nMINICASES\nI. Pat's Engineering Works Pat's Engineering Works is a small company that specializes in complex\nengineering consulting projects. The projects typically involve one or two engineers who do data-\nintensive analyses for companies. Because so much data are needed, the projects are stored on the\ncompany's high-capacity server but moved to the engineers' workstations for analysis. The company\nis moving into new offices and wants you to design its network. It has a staff of eight engineers (which\nis expected to grow to 12 over the next 5 years), plus another eight management and clerical\nemployees who also need network connections but whose needs are less intense. Design the network.", "source": "Page 284", "chapter_title": "Chapter 11"}
{"id": "1c1b7d715280-1", "text": "employees who also need network connections but whose needs are less intense. Design the network.\nBe sure to include a diagram.\nII. Hospitality Hotel Hospitality Hotel is a luxury hotel whose guests are mostly business travelers. To\nimprove its quality of service, it has decided to install network connections in each of its 600 guest\nrooms and 12 conference meeting rooms. Last year, the hotel upgraded its own internal networks to\nswitched 100Base-T, but it wants to keep the public network (i.e., the guest and meeting rooms)\nseparate from its private network (i.e., its own computer systems). Your task is to design the public\nnetwork and decide how to connect the two networks together. Be sure to include a diagram.\nIII. Indiana University Reread Management Focus 8-1. What other alternatives do you think Indiana\nUniversity considered? Why do you think they did what they did?\nIV. Shangri-La Reread Management Focus 8-2. What other alternatives do you think the Shangri-La\nResort considered? Why do you think they did what they did?\nV. Chicago Consulting You are the network manager for a consulting firm that needs to install a\nbackbone to connect four 100Base-T Ethernet LANs (each using a 24-port switch). Develop a simple\nbackbone and determine the total cost (i.e., select the device and price it). Prices are available at\nwww.cdw.com, but you can use any source that is convenient.\nVI. Western Trucking Western Trucking operates a large fleet of trucks that deliver shipments for\ncommercial shippers such as food stores, retailers, and wholesalers. Their main headquarters\nbuilding and secondary building are shown in Figure 8-10. They want to upgrade to a faster network.\nDesign a new network for them, including the specific backbone and LAN technologies to be used.", "source": "Page 284", "chapter_title": "Chapter 11"}
{"id": "d876b2e0bc49-2", "text": "Design a new network for them, including the specific backbone and LAN technologies to be used.\nAssume that the main office building is 170 feet by 100 feet in size and that the secondary building is\n100 feet by 50 feet. The two buildings are 100 feet apart.", "source": "Page 284", "chapter_title": "Chapter 11"}
{"id": "8f8dc43445d4-0", "text": "FIGURE 8-10 Facility map of the Western Trucking headquarters\nTECH UPDATES\nPick one of these topics to investigate.\nTopic A: Data Privacy\nEvery organization and individual cares about data privacy. Data breaches (such as credit card theft, social\nsecurity number theft, payroll information theft, health records theft) are one of the biggest cybersecurity\nconcerns for the next decade. Why? Well, because personal data is a valuable black market commodity. If\nsomeone has your financial information they can obviously use it to buy things; if they have non-financial\npersonal information, they can use it to impersonate you to get a credit card or a loan, and leave you stuck\nto pay the bill. While there is legislation, such as the GDPR (General Data Protection Regulation) passed\nby the European Union, organizations are also aware of the negative consequences of a breach. What are\nthe current regulations (laws) regarding data privacy where you live? What are the penalties for a data\nbreach? How much is your personal data worth on the black market?\nTopic B: Phishing Techniques and Malware", "source": "Page 285", "chapter_title": "Chapter 11"}
{"id": "046b24f9df8d-0", "text": "The two biggest cybersecurity threats for the next decade phishing and malware. I'm sure that you know a\nperson (perhaps a friend \n) who says\u2014\u201cPhishing? I would NEVER fall for it!\u201d How does phishing\nwork? What techniques do phishers use to lure users to click on a link, download a file, or provide\nusername/password? Once you click on a link or download a file, you may download malware. What is\nmalware? What are the most recent malware attacks and what industries suffered from them the most?\nWhat is the economic cost of these attacks? Search the academic and popular press literature to identify\ntrends.\nDeliverables\nYour job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title Slide\n2. Short description of the topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use a lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along\n5. How does it relate to material covered in class so far (and in the future)\n6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 8A\nNetwork Mapping\nNetwork mapping software enables you to generate a map of the computers on all the LANs connected to\na backbone. There are many good network mapping packages. Two of my favorites are LANState and\nNetwork Topology Mapper (www.solarwinds.com/network-topology-mapper.aspx). LANState is simpler\nto use but works best for small networks. Network Topology Mapper is more complex but can map large", "source": "Page 286", "chapter_title": "Chapter 11"}
{"id": "14a21d5e0f6b-1", "text": "networks. This activity will focus on LANState.\nMapping a Small Network\nThe first step is to download and install LANState. A demo version of the software is available free of\ncharge from 10-Strike Software (www.10-strike.com/lanstate).\nYou begin by creating a new network map; choose File and then select the Map Creation Wizard. Then\nchoose Scan IP address range and click Next. You will be asked to enter an address range. Choose some\nrange, ideally the address range of a small network. I choose to use my home network range (192.168.1.1\nthrough 192.168.2.254), which has two wireless routers (192.168.1.1 and 192.168.2.1). After you have\nadded the address range to scan, click Next. Step 2 is to select how you will detect the devices on your\nnetwork. The most common approach is to use an ICMP ping, which was discussed in Chapter 5. This\napproach sends an ICMP to each possible address in the range you specified. Not all computers are\nconfigured to respond to pings for security reasons, so this approach may not reveal all the computers and\ndevices in your network. Make sure that the box in front of ICMP Ping is checked.\nThe second approach is to send an ARP request for every computer in the address range you specified (see\nChapter 5). The advantage of this approach is that every device will respond to an ARP request. The\ndisadvantage is that you can only use ARPs for devices and computers in your same subnet. Make sure\nthat the box in front of ARP ping is checked.", "source": "Page 286", "chapter_title": "Chapter 11"}
{"id": "99172f9f13d8-0", "text": "To speed up your network, make sure the box in front of Search SNMP hosts is not checked. SNMP is a\nnetwork management protocol that we will discuss in Chapter 12. If you're using a small network, it\nprobably does not have SNMP. If you're using a large network that uses SNMP, you probably don't have\nthe password required (unless you're the network manager). Click Next, and after 10\u201320 seconds, you\nshould see a list of devices and computers that were discovered.\nFigure 8-11 shows the small network in Alan's house. I have a router (192.168.1.1) that connects a number\nof computers to the Internet. I also have a second wireless access router (192.168.2.1) and a printer\n(192.168.1.186). When I did this map, four computers and my networked TV were turned on and\nresponded to LANState's pings (192.168.1.104, 192.168.1.129, 192.168.1.130, 192.168.131, and\n192.168.1.188). You will also see that the broadcast address of 192.168.1.255 showed up, although there is\nno device on this address. Computers and devices that are not turned on do not respond to the pings and\ntherefore are not mapped. Because I use dynamic addressing, the addresses of my computers will change\nevery time I turn them on.\nClick Next and the network map will be shown. See Figure 8-12. You can also left-click on any device and\nchoose System Information and General to learn more about that device. Figure 8-13 also shows the\ninformation about one computer (192.168.1.188). It shows the MAC address (i.e., the Ethernet address),", "source": "Page 287", "chapter_title": "Chapter 11"}
{"id": "7de1596ae285-1", "text": "the card manufacturer, and the DNS name (i.e., application layer address) for this computer.\nFIGURE 8-11 Computers and devices at Alan's house", "source": "Page 287", "chapter_title": "Chapter 11"}
{"id": "a6eae53bd75d-0", "text": "FIGURE 8-12 Network map for Alan's house", "source": "Page 288", "chapter_title": "Chapter 11"}
{"id": "125c4d3fd700-0", "text": "FIGURE 8-13 System information for 192.168.1.188\nDeliverables\n1. Use the 10-Strike Software to draw a map of your home network or some other network. Describe two\nto five components on your map just like the example in the textbook shows.\n2. Use the System Information and provide additional information (e.g., MAC address and card\nmanufacturer) about at least two devices on your network.\nHANDS-ON ACTIVITY 8B\nApollo Residence Network Design\nApollo is a luxury residence hall that will serve honor students at your university. The residence will be\neight floors, with a total of 162 two-bedroom, one-bathroom apartments on floors 3\u20138. Read Hands-On\nActivity 7D, which provides the description of the building and a figure showing floors 3\u20138.\nThe first floor has an open lobby with a seating area and separate office area (see Figure 8-14), whereas\nthe second floor has meeting rooms (see Figure 8-15). Floors 1 and 2 are smaller than the upper floors\n(100 feet by 70 feet) because a parking garage is built around the outside of these floors. Visio files for the\nresidence are available on this book's website. The offices and server room on the first floor is for the\nuniversity's residence hall administration, which manages all the university's residences. One design goal\nis to keep this network as separate as possible from the network in the rest of the building to provide\ngreater security.", "source": "Page 289", "chapter_title": "Chapter 11"}
{"id": "b14a0ccfcd81-0", "text": "FIGURE 8-14 Apollo Residence first floor\nFIGURE 8-15 Apollo Residence second floor\nDeliverables\n1. Your team was hired to design the network for this residence hall. Design the LANs for each floor, the", "source": "Page 290", "chapter_title": "Chapter 11"}
{"id": "d40d72722488-0", "text": "distribution layer backbone that will connect the different floors in the building, and the part of the\nnetwork that will connect into the campus core backbone. Draw where the network equipment would\nbe placed (use the floor plans provided).", "source": "Page 291", "chapter_title": "Chapter 11"}
{"id": "41a4e0e3c6fc-0", "text": "FIGURE 8-16 Equipment price list\n2. Specify the products in your design and provide their cost and the total cost of the network. There are\ntwo options for specifying product. Option 1 is to use the generic LAN equipment list in Figure 8-16.\nOption 2 is to use CDW (www.cdw.com) to find LAN equipment. If you use CDW, you must use only\nCisco devices (to ensure quality).", "source": "Page 293", "chapter_title": "Chapter 11"}
{"id": "325caf32a624-0", "text": "CHAPTER 9\nWIDE AREA NETWORKS\nThe wide area network (WAN) is a key part of the enterprise edge. Most organizations do not build their\nown WAN communication circuits, preferring instead to lease them from common carriers or to use the\nInternet. This chapter focuses on the WAN architectures and telecommunications services offered by\ncommon carriers for use in enterprise WANs, not the underlying technology that the carriers use to\nprovide them. We discuss the three principal types of WAN services that are available: dedicated-circuit\nservices, packet-switched services, and virtual private network (VPN) services. We conclude by discussing\nhow to improve WAN performance and how to select services to build WANs.\nOBJECTIVES\nUnderstand dedicated-circuit services and architectures\nUnderstand packet-switched services and architectures\nUnderstand Internet-based VPN services and architectures\nUnderstand the best practice recommendations for WAN design\nBe familiar with how to improve WAN performance\nOUTLINE\n9.1 Introduction\n9.2 Dedicated-Circuit Networks\n9.2.1 Basic Architecture\n9.2.2 T-Carrier Services\n9.2.3 SONET Services\n9.3 Packet-Switched Networks\n9.3.1 Basic Architecture\n9.3.2 Frame Relay Services\n9.3.3 MPLS Services\n9.3.4 Ethernet Services\n9.4 Virtual Private Networks\n9.4.1 Basic Architecture\n9.4.2 VPN Types\n9.4.3 How VPNs Work\n9.5 The Best Practice WAN Design\n9.5.1 Software Defined WAN\n9.5.2 Choosing WAN Circuits\n9.6 Improving WAN Performance\n9.6.1 Improving Device Performance\n9.6.2 Improving Circuit Capacity\n9.6.3 Reducing Network Demand", "source": "Page 294", "chapter_title": "Chapter 11"}
{"id": "c19927687292-0", "text": "9.7 Implications for Cyber Security\nSummary\n9.1 INTRODUCTION\nWide area networks (WANs) typically run long distances, connecting different offices in different\ncities or countries. Some WANs run much shorter distances, connecting different buildings in the same\ncity. Most organizations do not own the land across which WANs are built, so instead they rent or lease\ncircuits from common carriers\u2014private companies such as AT&T, Bell Canada, Verizon, and BellSouth\nthat provide communication services to the public. For example, Indiana University has eight campuses\n(e.g., Indianapolis, Bloomington, South Bend, Fort Wayne, etc.). We use WAN circuits to connect the\ndifferent campuses so students on any campus can access resources on any campus. Our Bloomington\ncampus has two separate locations in the city of Bloomington, that are not physically connected, so we use\na WAN circuit from a common carrier to connect them.\nAs a customer, you do not lease physical cables per se; you lease circuits that provide certain transmission\ncharacteristics. The carrier decides whether it will use twisted-pair cable, coaxial cable, fiber optics, or\nother medium for its circuits. You have to sign a contract with a common carrier who will install and\noperate the circuit and any change requires going back to the common carrier.\nCommon carriers are profit oriented, and their primary products are services for voice and data\ntransmissions, both over traditional wired circuits and cellular services. A common carrier that provides\nlocal telephone services (e.g., BellSouth) is commonly called a local exchange carrier (LEC), whereas\none that provides long-distance services (e.g., AT&T) is commonly called an interexchange carrier\n(IXC). As the LECs move into the long-distance market and IXCs move into the local telephone market,\nthis distinction may disappear.", "source": "Page 295", "chapter_title": "Chapter 11"}
{"id": "cdd4ffc4c470-1", "text": "this distinction may disappear.\nIn this chapter, we examine the WAN architectures and technologies from the viewpoint of a network\nmanager rather than that of a common carrier. We focus less on internal operations and how the specific\ntechnologies work and more on how these services are offered to network managers and how they can be\nused to build networks because network managers are less concerned with how the services work and\nmore concerned with how they can use them effectively.\nLikewise, we focus on WAN services in North America because the majority of our readers are in North\nAmerica. Although there are many similarities in the way data communications networks and services\nhave evolved in different countries, there also are many differences. Most countries have a federal\ngovernment agency that regulates data and voice communications. In the United States, the agency is the\nFederal Communications Commission (FCC); in Canada, it is the Canadian Radio-Television\nand Telecommunications Commission (CRTC). Each state or province also has its own public\nutilities commission (PUC) to regulate communications within its borders.\nThe market for WAN services has rapidly changed over the past few years for two reasons. The first is that\nthe underlying technologies have changed. WAN technology development had stagnated, and the\ntechnologies were mature and stable. Then several start-ups disrupted the market by developing WAN\ncircuits based on Ethernet over fiber, and offering them at significantly lower prices with more flexible\ndata rates. Once it became clear that the technology worked, the old common carriers were forced to offer\nthe same new services at similarly low prices.\nThe second reason is that more companies are using cloud-based services (both SAAS applications (e.g.,\nSalesforce, Dropbox) as well as PAAS and IAAS (e.g., Amazon Web Services)) (see Chapter 2) rather than\ndeploying applications on servers on their own internal networks. Cloud-based services live on the", "source": "Page 295", "chapter_title": "Chapter 11"}
{"id": "720eae9ba564-2", "text": "deploying applications on servers on their own internal networks. Cloud-based services live on the\nInternet, so companies need a reliable, fast, and secure way for employees to access critical business\napplications over the Internet from their offices. This means that the old approach of using common\ncarrier circuits to connect company offices must be extended to include circuits that provide reliable\nservice over the Internet.\nIn this chapter, we discuss three types of WAN services that are used to connect company offices to each\nother or to cloud providers. The first two use common carrier networks: dedicated-circuit services\n(e.g., T1) and packet-switched services (e.g., Ethernet). The third uses the public Internet to provide a", "source": "Page 295", "chapter_title": "Chapter 11"}
{"id": "554b56dd0dcb-0", "text": "virtual private network (VPN). You may be familiar with using VPN software to provide privacy as you\nsurf the Internet. This is a just one of the benefits that VPN provide.\n9.2 DEDICATED-CIRCUIT NETWORKS\nWith a dedicated-circuit network, the user leases circuits from the common carrier for his or her exclusive\nuse 24 hours per day, 7 days per week. It is like having your own private network, but it is managed by the\ncommon carrier. Dedicated-circuit networks are sometimes called private line services. Dedicated-circuit\nnetworks became popular in the early 1990s, so the fundamental technology is decades old. Dedicated\nservices have evolved and improved over the years, but their basic design is old. Some experts believe that\nthey will slowly disappear over the next 10 years, as packet-switched services become more popular.\n9.2.1 Basic Architecture\nWith a dedicated-circuit network, you lease circuits from common carriers. All connections are point to\npoint, from one building in one city to another building in the same or a different city. The carrier installs\nthe circuit connections at the two end points of the circuit and makes the connection between them. The\ncircuits run through the common carrier\u2019s cloud, but the network behaves as if you have your own\nphysical circuits running from one point to another (Figure 9-1).\nThe user leases the desired circuit from the common carrier (specifying the physical end points of the\ncircuit) and installs the equipment needed to connect computers and devices (e.g., routers or switches) to\nthe circuit. This equipment may include multiplexers or a channel service unit (CSU) and/or a data\nservice unit (DSU); a CSU/DSU is the WAN equivalent of a network interface card (NIC) in a LAN. The", "source": "Page 296", "chapter_title": "Chapter 11"}
{"id": "c8847fd27f7a-1", "text": "device takes the outgoing packet (usually an Ethernet packet at the data link layer and an IP packet at the\nnetwork layer) and translates it to use the data link layer and network protocols used in the WAN.\nDedicated circuits are billed at a flat fee per month, and the user has unlimited use of the circuit. Once you\nsign a contract, making changes can be expensive because it means rewiring the buildings and signing a\nnew contract with the carrier. Therefore, dedicated circuits require careful planning, both in terms of\nlocations and the amount of capacity you purchase.\nThere are three basic architectures used in dedicated-circuit networks: ring, star, and mesh. In practice,\nmost networks use a combination of architectures.", "source": "Page 296", "chapter_title": "Chapter 11"}
{"id": "8e914e1e66b2-0", "text": "FIGURE 9-1 Dedicated-circuit services. CSU = channel service unit; DSU = data service unit; MUX =\nmultiplexer", "source": "Page 297", "chapter_title": "Chapter 11"}
{"id": "a1ae5c74c796-0", "text": "FIGURE 9-2 Ring-based design\nRing Architecture\nA ring architecture connects all computers in a closed loop with each computer linked to the next\n(Figure 9-2). The circuits are full-duplex or half-duplex circuits, meaning that messages flow in both\ndirections around the ring. Computers in the ring may send data in one direction or the other, depending\non which direction is the shortest to the destination.\nOne disadvantage of the ring topology is that messages can take a long time to travel from the sender to\nthe receiver. Messages usually travel through several computers and circuits before they reach their\ndestination, so traffic delays can build up very quickly if one circuit or computer becomes overloaded. A\nlong delay in any one circuit or computer can have significant impacts on the entire network.\nIn general, the failure of any one circuit or computer in a ring network means that the network can\ncontinue to function. Messages are simply routed away from the failed circuit or computer in the opposite\ndirection around the ring. However, if the network is operating close to its capacity, this will dramatically\nincrease transmission times because the traffic on the remaining part of the network may come close to\ndoubling (because all traffic originally routed in the direction of the failed link will now be routed in the\nopposite direction through the longest way around the ring).\nStar Architecture\nA star architecture connects all computers to one central computer that routes messages to the\nappropriate computer (Figure 9-3). The star topology is easy to manage because the central computer\nreceives and routes all messages in the network. It can also be faster than the ring network because any\nmessage needs to travel through at most two circuits to reach its destination, whereas messages may have", "source": "Page 298", "chapter_title": "Chapter 11"}
{"id": "f5093ab32cc5-0", "text": "to travel through far more circuits in the ring network. However, the star topology is the most susceptible\nto traffic problems because the central computer must process all messages on the network. The central\ncomputer must have sufficient capacity to handle traffic peaks, or it may become overloaded and network\nperformance will suffer.\nFIGURE 9-3 Star-based design\nIn general, the failure of any one circuit or computer affects only the one computer on that circuit.\nHowever, if the central computer fails, the entire network fails because all traffic must flow through it. It is\ncritical that the central computer be extremely reliable.\nMesh Architecture\nIn a full-mesh architecture, every computer is connected to every other computer (Figure 9-4a). Full-\nmesh networks are seldom used because of the extremely high cost. Partial-mesh architecture\n(usually called just mesh architecture), in which many, but not all, computers are connected, is far\nmore common (Figure 9-4b). Most WANs use partial-mesh topologies.\nThe effects of the loss of computers or circuits in a mesh network depend entirely on the circuits available\nin the network. If there are many possible routes through the network, the loss of one or even several\ncircuits or computers may have few effects beyond the specific computers involved. However, if there are\nonly a few circuits in the network, the loss of even one circuit or computer may seriously impair the\nnetwork.\nIn general, mesh networks combine the performance benefits of both ring networks and star networks.\nMesh networks usually provide relatively short routes through the network (compared with ring\nnetworks) and provide many possible routes through the network to prevent any one circuit or computer", "source": "Page 299", "chapter_title": "Chapter 11"}
{"id": "32e29d72146b-0", "text": "from becoming overloaded when there is a lot of traffic (compared with star networks, in which all traffic\ngoes through one computer).\nThe drawback is that mesh networks use decentralized routing so that each computer in the network\nperforms its own routing. This requires more processing by each computer in the network than in star or\nring networks. Also, the transmission of network status information (e.g., how busy each computer is)\n\u201cwastes\u201d network capacity.", "source": "Page 300", "chapter_title": "Chapter 11"}
{"id": "3f6ba38da26e-0", "text": "FIGURE 9-4 Mesh design\nThere are two types of dedicated-circuit services in common use today: T-carrier services and\nsynchronous optical network (SONET) services. Both T-carrier and SONET have their own data link\nprotocols, which are beyond the scope of this chapter.\n9.2.2 T-Carrier Services\nT-carrier circuits are the most commonly used form of dedicated-circuit services in North America\ntoday. As with all dedicated-circuit services, you lease a dedicated circuit from one building in one city to\nanother building in the same or different city. Costs are a fixed amount per month, regardless of how\nmuch or how little traffic flows through the circuit. There are several types of T-carrier circuits as shown\nin Figure 9-5, but only T1 and T3 are in common use today.\nFIGURE 9-5 T-carrier services\nA T1 circuit (also called a DS1 circuit) provides a data rate of 1.544 Mbps. T1 circuits can be used to\ntransmit data but often are used to transmit both data and voice. In this case, inverse TDM provides\ntwenty-four 64-Kbps circuits. Digitized voice using pulse code modulation (PCM) requires a 64-Kbps\ncircuit (see Chapter 3), so a T1 circuit enables 24 simultaneous voice channels. Most common carriers\nmake extensive use of PCM internally and transmit most of their voice telephone calls in digital format\nusing PCM, so you will see many digital services offering combinations of the standard PCM 64-Kbps\ncircuit.\nA T3 circuit allows transmission at a rate of 44.736 Mbps, although most articles refer to this rate as 45\nmegabits per second. This is equal to the capacity of 28 T1 circuits. T3 circuits are becoming popular as", "source": "Page 302", "chapter_title": "Chapter 11"}
{"id": "4e0a38d5be72-1", "text": "the transmission medium for corporate MANs and WANs because of their higher data rates. Although T2\ncircuits and T4 circuits are defined standards, they are not commercially available, and, therefore, we\ndon\u2019t discuss them here.\nFractional T1, sometimes called FT1, offers portions of a 1.544-Mbps T1 circuit for a fraction of its full\ncost. Many (but not all) common carriers offer sets of 64 Kbps DS-0 channels as FT1 circuits. The most\ncommon FT1 services provide 128 Kbps, 256 Kbps, 384 Kbps, 512 Kbps, and 768 Kbps.\n9.2.3 SONET Services\nThe synchronous optical network (SONET) is the American standard (ANSI) for high-speed\ndedicated-circuit services. The ITU-T recently standardized an almost identical service that easily\ninterconnects with SONET under the name synchronous digital hierarchy (SDH).\nSONET transmission speeds begin at the OC-1 level (optical carrier level 1) of 51.84 Mbps. Each\nsucceeding rate in the SONET fiber hierarchy is defined as a multiple of OC-1, with SONET data rates\ndefined as high as 160 Gbps. Figure 9-6 presents the commonly used SONET and SDH services. Each level", "source": "Page 302", "chapter_title": "Chapter 11"}
{"id": "2efd678ba3c4-0", "text": "above OC-1 is created by an inverse multiplexer. Notice that the slowest SONET transmission rate (OC-1)\nof 51.84 Mbps is slightly faster than the T3 rate of 44.376 Mbps.\nFIGURE 9-6 SONET and SDH services. OC = optical carrier (level); SDH = synchronous digital hierarchy;\nSONET = synchronous optical network\n9.3 PACKET-SWITCHED NETWORKS\nPacket-switched networks operate more like Ethernet and IP networks used in the LANs and BNs\nthan like dedicated-circuit networks. With dedicated-circuit networks, a circuit is established between the\ntwo communicating routers that provides a guaranteed data transmission capability that is available for\nuse by only those two devices. In contrast, packet-switched services enable multiple connections to exist\nsimultaneously between computers over the same physical circuit, just like LANs and BNs.\n9.3.1 Basic Architecture\nWith packet-switched services, the user buys a connection into the common carrier cloud (Figure 9-7).\nThe user pays a fixed fee for the connection into the network (depending on the type and capacity of the\nservice) and is charged for the number of packets transmitted. Many common carriers now offer fixed\nprice plans, so they do not charge per packet, which has dramatically affected the market for packet-\nswitched services. Many companies were dubious about packet-switched services because it was hard to\nknow how much they would actually cost. After all, which would you prefer for your mobile phone\u2014a fixed\nprice per month or price that varied depending upon how much data you used? When the first few\ncommon carriers moved to fixed price plans, the rest soon followed, and more companies are now\nchoosing packet-switched services.\nThe user\u2019s connection into the network is a packet assembly/disassembly device (PAD), which can", "source": "Page 303", "chapter_title": "Chapter 11"}
{"id": "604441803c20-1", "text": "The user\u2019s connection into the network is a packet assembly/disassembly device (PAD), which can\nbe owned and operated by the customer or by the common carrier. The PAD converts the sender\u2019s data\ninto the network layer and data link layer packets used by the packet network and sends them through the\npacket-switched network. At the other end, another PAD reassembles the packets back into the network\nlayer and data link layer protocols expected by the destination (usually Ethernet and IP) and delivers\nthem to the appropriate computer router.", "source": "Page 303", "chapter_title": "Chapter 11"}
{"id": "f73524814bd1-0", "text": "FIGURE 9-7 Packet-switched services. PAD = packet assembly/disassembly device\nMANAGEMENT FOCUS 9-1\nCleveland Transit\nThe Greater Cleveland Regional Transit Authority (GCRTA) has about 2,400 employees and\nprovides bus, trolley, and rail services to about 1.3 million people in the Cleveland area. It has many\noffice locations throughout the region, and more than half of its employees are on the move as they\nwork.\nA recent blackout highlighted how vulnerable GCRTA was to network outages. Communications\nwere knocked out, including systems supporting the transit police.\nGCRTA redesigned its WAN to use a SONET ring. SONET provides high-speed data services, and the\nring topology ensures maximum reliability. Even if one part of the ring is knocked out, whether by\npower failures or someone accidentally cutting a line, the network will continue to operate.\nSource: Adapted from \u201cStaying on Track,\u201d Case Study, AT&T.\nOne of the key advantages of packet-switched services is that different locations can have different\nconnection speeds into the common carrier cloud. The PAD compensates for differences in transmission\nspeed between sender and receiver; for example, the circuit at the sender might be 50 Mbps, whereas the\nreceiver only has a 1.5 Mbps circuit. In contrast, a dedicated circuit must have the same speed at both the\nsender and receiver.\nPacket-switched networks enable packets from separate messages with different destinations to be", "source": "Page 304", "chapter_title": "Chapter 11"}
{"id": "d933c124f35b-0", "text": "interleaved for transmission, unlike dedicated circuits, which have one sender and one receiver.\nThe connections between the different locations in the packet network are called permanent virtual\ncircuits (PVCs), which means that they are defined for frequent and consistent use by the network. They\ndo not change unless the network manager changes the network. Some common carriers also permit the\nuse of switched virtual circuits (SVCs), which change dynamically based on traffic, although this is\nnot common. Changing PVCs is done using software, but common carriers usually charge each time a PVC\nis established or removed.\nPacket-switched services are often provided by different common carriers than the one from which\norganizations get their usual telephone and data services. Therefore, organizations often lease a dedicated\ncircuit (e.g., T1) from their offices to the packet-switched network point of presence (POP). The POP is\nthe location at which the packet-switched network (or any common carrier network, for that matter)\nconnects into the local telephone exchange.\nThere are three types of packet-switched services: frame relay, MPLS, and Ethernet.\n9.3.2 Frame Relay Services\nFrame relay is one of the oldest used packet services in the United States. It is still available, but at\nthis point, most companies are no longer installing it. It is a legacy technology. We include it because you\nare still likely to see it for several years.\nFrame relay uses T carrier and SONET as its circuits, so its speeds are identical to them (e.g., 1.5 Mbps,\n45 Mbps, 155 Mbps, and 622 Mbps). It is an unreliable packet service because it does not perform error\ncontrol. Frame relay checks for errors but simply discards packets with errors. It is up to the software at\nthe source and destination to control for lost messages.", "source": "Page 305", "chapter_title": "Chapter 11"}
{"id": "fd34477813c9-1", "text": "the source and destination to control for lost messages.\nSome common carriers permit users to specify two different types of data rates that are negotiated per\nconnection and for each PVC as it is established. The committed information rate (CIR) is the data\nrate the PVC guarantees to transmit. If the network accepts the connection, it guarantees to provide that\nlevel of service. Most connections also specify a maximum allowable rate (MAR), which is the\nmaximum rate that the network will attempt to provide, over and above the CIR. The circuit will attempt\nto transmit all packets up to the MAR, but all packets that exceed the CIR are marked as discard eligible\n(DE). If the network becomes overloaded, DE packets are discarded. So although users can transmit more\ndata than the CIR, they do so at a risk of lost packets and the need to retransmit them.\nA Day in the Life: Networking and Telecommunications Vice\nPresident\nA vice president is a person in an executive-level position whose focus is to set the strategic direction\nfor the organization. A vice president has very little to do with the day-to-day operations; much like\nan admiral in a navy fleet, he or she defines the direction, but the individual captains running each\nship actually make sure that everything that needs to happen gets done.\nThe vice president works with the chief information officer (CIO) and other executive leadership of\nthe organization to identify the key organizational goals that have implications for the network. The\nvice president works with his or her staff to revise the strategic networking plan to ensure that the\nnetwork is capable of supporting the organization\u2019s goals. The key elements of the strategic plan are\nthe networking architectures, key technologies, and vendors. Once the strategy has been set, the vice\npresident\u2019s job is to instruct the senior managers to execute the strategy and then let them do their\njobs.", "source": "Page 305", "chapter_title": "Chapter 11"}
{"id": "1c645f5c2180-2", "text": "jobs.\nIn most cases, the changes to the networking strategic plan are relatively minor, but sometimes there\nare dramatic changes that require a major shift in strategic direction. For example, in recent years,\nwe\u2019ve seen a major change in the fundamental capabilities of network tools and applications. Our\narchitecture strategy during the 1990s was driven by the fact that network management tools were\npoor and maintenance costs per server were high; the fundamental architecture strategy was to\nminimize the number of servers. Today, network management tools are much better, maintenance", "source": "Page 305", "chapter_title": "Chapter 11"}
{"id": "287baf632d03-0", "text": "costs per server are significantly lower, and network traffic has changed both in volume and in the\nnumber and complexity of services supported (e.g., Web, email, H.323, and IPv6); the strategy today\nis to provide a greater number of servers, each of which is dedicated to supporting one specific type\nof traffic.\nSource: With thanks to Brian Voss.\n9.3.3 MPLS Services\nMultiprotocol label switching (MPLS) is a technology that is hard to classify because it is so old that\nit doesn\u2019t fit the 5-layer network model (yet it is still widely used). We classify it as a layer 2 service (i.e., a\ndata link layer protocol like Ethernet) because it is commonly used with IP for routing at layer 3. Some\ncommon carriers starting called their MPLS services IP services, but today most have reverted to the\noriginal MPLS name.\nWith MPLS, the PAD at the sending site takes the message (which usually is an Ethernet frame containing\nan IP packet), strips off the Ethernet frame, and uses the IP address in the IP packet to route the packet\nthrough the carrier\u2019s packet-switched network to its final destination. MPLS uses either T carrier or\nSONET as its wiring, so its speeds are identical to them (e.g., 1.5 Mbps, 45 Mbps, 155 Mbps, and 622\nMbps).\n9.3.4 Ethernet Services\nAlthough we have seen rapid increases in capacities and sharp decreases in costs in LAN and BN\ntechnologies, changes in WAN services offered by common carriers saw only modest changes for many\nyears. That changed about 10 years ago with the introduction of several Internet start-ups (e.g., Yipes)\noffering Ethernet services.\nMost organizations today use Ethernet and IP in the LAN and BN environments, yet the WAN packet", "source": "Page 306", "chapter_title": "Chapter 11"}
{"id": "ad05277a74e9-1", "text": "Most organizations today use Ethernet and IP in the LAN and BN environments, yet the WAN packet\nnetwork services discussed earlier (T carrier, SONET, and frame relay) use different layer 2 protocols. Any\nLAN or BN traffic, therefore, must be translated or encapsulated into a new protocol and destination\naddresses generated for the new protocol. This takes time, slowing network throughput. It also adds\ncomplexity, meaning that companies must add staff knowledgeable in the different WAN protocols,\nsoftware, and hardware these technologies require. This is one reason why many common carriers are\nstarting to call these technologies \u201clegacy technologies,\u201d signaling their demise.\nMANAGEMENT FOCUS 9-2\nA Georgia Ethernet WAN\nMarietta City Schools (MCS) is a school district northwest of Atlanta, Georgia, that has 8,000\nstudents and 1,200 employees at 13 schools plus an administrative office. Its WAN was a traditional\nSONET network using OC-1 circuits in a star design connecting each school to the MCS\nadministrative office.\nThe network was expensive and did not offer sufficient room for growth as MCS contemplated\nmoving to more digital education. MCS implemented an Ethernet WAN and then gradually phased\nout the old SONET WAN.\nMCS contracted with Zayo, a large common carrier that provides services to businesses and\ngovernments but not the consumer market (which is why you\u2019ve probably never heard of them).\nEach school and the administrative office now has its own 1 Gbps Ethernet over fiber connection into\nthe Zayo network and can easily send data to any of MCS\u2019s 14 sites. Because it is a packet-switched\nnetwork, each location can have a different speed, and MCS is already considering upgrading the\nbusier sites to 10 Gbps.\nSource: Adapted from Education/E-Rate: Multi-Campus Network Upgrade; Ethernet Augmentation for Georgia School District,", "source": "Page 306", "chapter_title": "Chapter 11"}
{"id": "dcb8ee59a047-2", "text": "Zayo Group, LLC.", "source": "Page 306", "chapter_title": "Chapter 11"}
{"id": "e36d01b2a004-0", "text": "Frame relay and MPLS services use the traditional telephone company WAN networks (i.e., T carrier and\nSONET) provided by common carriers such as AT&T and BellSouth. In contrast, Ethernet services bypass\nthis network; companies offering Ethernet services have laid their own gigabit Ethernet fiber-optic\nnetworks in large cities. When an organization signs up for service, the packet network company installs\nnew fiber-optic cables from their citywide backbone into the organization\u2019s office complex and connects it\nto an Ethernet switch. The organization simply plugs its network into its Ethernet switch and begins using\nthe service. All traffic entering the packet network must be Ethernet, using IP.\nThe Ethernet circuit is usually a standard 1 Gbps cable, although the company can order and pay for a\nlarger cable to be installed (e.g., a 10-Gbps cable). The data rate is set by software at the common carrier\u2019s\nend of the circuit. Currently, most common carriers offer Ethernet services with data rates of 1 Mbps\u201310\nGbps, in 1-Mbps increments. Changing the desired data rate is simple, because it is done in software. This\nis in sharp contrast to MPLS (or T-carrier services) which require a new cable to be installed. Thus,\nEthernet services are much more flexible than the old WAN technologies, and because they are usually\nmuch lower cost than traditional packet-switched networks, they have significantly changed the nature of\nWANs over the past few years. Because this is an emerging technology, we should see many changes in the\nnext few years. Many experts predict Ethernet is the future of WANs, and we will see MPLS services\ndisappear.\n9.4 VIRTUAL PRIVATE NETWORKS\nA virtual private network (VPN) provides the equivalent of a private packet-switched network over", "source": "Page 307", "chapter_title": "Chapter 11"}
{"id": "a7707877ef34-1", "text": "A virtual private network (VPN) provides the equivalent of a private packet-switched network over\nthe public Internet. It involves establishing a series of PVCs that run over the Internet so that the network\nacts like a set of dedicated circuits even though the data flows over the Internet. VPN services are much,\nmuch cheaper than the dedicated circuit or packet-switched services discussed above because they use the\nInternet, not a common carrier network to carry the data. The common carrier is only responsible to\nensure a good quality service between you and the nearest Internet POP, and after your packets reach the\nInternet POP, anything can happen and no one is responsible. Thus, VPN services are very cheap, but only\nas reliable as the Internet. Sometimes it is fast, and sometimes it is not. Nonetheless, because of the low\ncost of VPN services, many companies are including them in their WAN.\n9.4.1 Basic Architecture\nWith a VPN, you first lease an Internet connection at whatever access rate and access technology you\nchoose for each location you want to connect. For example, you might lease a T1 circuit from a common\ncarrier that runs from your office to your Internet service provider (ISP). Or you might use a DSL or\ncable modem, which are discussed in the next chapter. You pay the common carrier for the circuit and the\nISP for Internet access. Then you connect a VPN gateway (a specially designed router) to each Internet\naccess circuit to provide access from your networks to the VPN. See Figure 9-8.\nThe VPN gateways enable you to create PVCs through the Internet that are called tunnels (Figure 9-9).\nThe VPN gateway at the sender takes the outgoing packet and encapsulates it with a protocol that is used\nto move it through the tunnel to the VPN gateway on the other side. The VPN gateway at the receiver", "source": "Page 307", "chapter_title": "Chapter 11"}
{"id": "fdd5e193a2aa-2", "text": "strips off the VPN packet and delivers the packet to the destination network. The VPN is transparent to\nthe users; it appears as though a traditional packet-switched network PVC is in use. The VPN is also\ntransparent to the ISP and the Internet as a whole; there is simply a stream of Internet packets moving\nacross the Internet. VPN software is commonly used on home computers or laptops to provide the same\nsecure tunnels to people working from offsite.\nVPNs operate either at layer 2 or layer 3. A layer 2 VPN uses the layer 2 packet (e.g., Ethernet) to select\nthe VPN tunnel and encapsulates the entire packet, starting with the layer 2 packet. Layer 2 tunneling\nprotocol (L2TP) is an example of a layer 2 VPN. A layer 3 VPN uses the layer 3 packet (e.g., IP) to select\nthe VPN tunnel and encapsulates the entire packet, starting with the layer 3 packet; it discards the\nincoming layer 2 packet and generates an entirely new layer 2 packet at the destination. IPSec is an\nexample of a layer 3 VPN.", "source": "Page 307", "chapter_title": "Chapter 11"}
{"id": "3ca6d7f8128e-0", "text": "FIGURE 9-8 Virtual private network (VPN) services\nFIGURE 9-9 A virtual private network (VPN)\nThe primary advantages of VPNs are low cost and flexibility. Because they use the Internet to carry\nmessages, the major cost is Internet access, which is inexpensive compared with the cost of dedicated-\ncircuit services and packet-switched services from a common carrier. Likewise, anywhere you can", "source": "Page 308", "chapter_title": "Chapter 11"}
{"id": "0177f853067b-0", "text": "establish Internet service, you can quickly put in a VPN.\nThere are two important disadvantages. First, traffic on the Internet is unpredictable. Sometimes packets\ntravel quickly, but at other times, they take a long while to reach their destination. Although some VPN\nvendors advertise quality of service (QoS) capabilities, these apply only in the VPN devices themselves; on\nthe Internet, a packet is a packet. Second, because the data travel on the Internet, security is always a\nconcern. Most VPNs encrypt the packet at the source VPN device before it enters the Internet and decrypt\nthe packet at the destination VPN device. (See Chapter 11 for more on encryption.)\n9.4.2 VPN Types\nThree types of VPNs are in common use: intranet VPN, extranet VPN, and access VPN. An intranet VPN\nprovides virtual circuits between organization offices over the Internet. Figure 9-9 illustrates an intranet\nVPN. Each location has a VPN gateway that connects the location to another location through the\nInternet.\nAn extranet VPN is the same as an intranet VPN, except that the VPN connects several different\norganizations, often customers and suppliers, over the Internet.\nAn access VPN enables employees to access an organization\u2019s networks from a remote location.\nEmployees have access to the network and all the resources on it in the same way as employees physically\nlocated on the network. The user uses VPN software on his or her computer to connect to the VPN device\nat the office. The VPN gateway accepts the user\u2019s log-in, establishes the tunnel, and the software begins\nforwarding packets over the Internet. Compared with a typical ISP-based remote connection, the access\nVPN is a more secure connection than simply sending packets over the Internet. Figure 9-9 shows an\naccess VPN.\n9.4.3 How VPNs Work", "source": "Page 309", "chapter_title": "Chapter 11"}
{"id": "d000107c26e6-1", "text": "access VPN.\n9.4.3 How VPNs Work\nWhen packets move across the Internet, they are much like postcards in the paper mail. Anyone can read\nwhat they contain. VPNs provide security by encapsulating (i.e., surrounding) packets in a separate,\nsecure packet that is encrypted. No one can read the encapsulated data without knowing the password\nthat is used to decrypt the packet. Layer 2 and layer 3 VPNs work very similarly, except that layer 2 VPNs\nencapsulate the user\u2019s data starting with the layer 2 packet (the Ethernet frame), while layer 3 VPNs\nencapsulate the user\u2019s data starting with the layer 3 packet (the IP packet).\nFigure 9-10 shows how a layer 3 access VPN using IPSec works. Suppose that an employee is working at\nhome with a LAN that uses a router to connect to the Internet via an ISP using DSL (we explain how DSL\nworks in the next chapter). When the employee wants to use the VPN, he or she starts the VPN software\non his or her computer and uses it to log into the VPN gateway at the office. The VPN software creates a\nnew \u201cinterface\u201d on the employee\u2019s computer that acts exactly like a separate connection into the Internet.\nInterfaces are usually hardware connections, but the VPN is a software interface, although the employee\u2019s\ncomputer doesn\u2019t know this\u2014it\u2019s just another interface. Computers can have multiple interfaces; a laptop\ncomputer often has two interfaces, one for wire Ethernet and one for wireless Wi-Fi.\nThe VPN gateway at the office is also a router and a DHCP server. The VPN gateway assigns an IP address\nto the VPN interface on the employee\u2019s computer that is an IP address in a subnet managed by the VPN\ngateway. For example, if the VPN gateway has an IP address of 156.56.198.1 and managed the", "source": "Page 309", "chapter_title": "Chapter 11"}
{"id": "8aaf3ed9c1c2-2", "text": "156.56.198.x subnet, it would assign an IP address in this subnet domain (e.g., 156.56.198.55).", "source": "Page 309", "chapter_title": "Chapter 11"}
{"id": "ba4dcc5df868-0", "text": "FIGURE 9-10 Using VPN software. Shaded area depicts encrypted packets\nThe employee\u2019s computer now thinks it has two connections to the Internet: the traditional interface that\nhas the computer\u2019s usual IP address and the VPN interface that has an IP address assigned by the VPN\ngateway. The VPN software on the employee\u2019s computer makes the VPN interface the default interface for\nall network traffic to and from the Internet, which ensures that all messages leaving the employee\u2019s\ncomputer flow through the VPN interface to the VPN gateway at the office.\nSuppose the employee sends an HTTP request to a Web server at the office (or somewhere else on the\nInternet). The Web browser software will create an HTTP packet that is passed to the TCP software (which\nadds a TCP segment), and this, in turn, is passed to the IP software managing the VPN interface. The IP\nsoftware creates the IP packet using the source IP address assigned by the VPN gateway. Normally, the IP\nsoftware would then pass the IP packet to the Ethernet software that manages the Ethernet interface into\nthe employee\u2019s LAN, but because the IP packet is being sent out the VPN interface, the IP packet is passed\nto the VPN software managing the VPN interface. Figure 9-10 shows the message as it leaves the network\nsoftware and is passed to the VPN for transmission: an HTTP packet, surrounded by a TCP segment,\nsurrounded by an IP packet.\nThe VPN software receives the IP packet, encrypts it, and encapsulates it (and its contents: the TCP\nsegment and the HTTP packet) with an Encapsulating Security Payload (ESP) packet using IPSec\nencryption. The contents of the ESP packet (the IP packet, the TCP segment, and the HTTP packet) are\nencrypted so that no one except the VPN gateway at the office can read them. You can think of the IPSec", "source": "Page 310", "chapter_title": "Chapter 11"}
{"id": "7fd8b3c30a1c-1", "text": "packet as an application layer packet whose destination is the office VPN gateway. How do we send an\napplication layer packet over the Internet? Well, we pass it to the TCP software, which is exactly what the\nVPN software does.\nThe VPN software passes the ESP packet (and its encrypted contents) to the employee\u2019s computer normal\nInternet interface for transmission. This interface has been sitting around waiting for transmissions, but\nbecause the VPN interface is defined as the primary interface to use, it has received no messages to", "source": "Page 310", "chapter_title": "Chapter 11"}
{"id": "e50e1a4ad0d3-0", "text": "transfer except those from the VPN software.\nThis interface treats the ESP packet as an application layer packet that needs to be sent to the VPN\ngateway at the office. It attaches a transport layer packet (a UDP datagram in this case, not a TCP\nsegment). It then passes the ESP packet to the IP software, which creates an IP packet with an IP\ndestination address of the VPN gateway at the office and a source IP of the employee\u2019s computer\u2019s normal\nInternet interface. It passes this IP packet to the Ethernet software, which adds an Ethernet frame and\ntransmits it to the employee\u2019s router.\nThe employee\u2019s router receives the Ethernet frame, strips off the frame, and reads the IP packet. It sees\nthat the packet needs to be sent to the VPN gateway at the office, which means sending the packet to the\nemployee\u2019s ISP over the DSL circuit. Because DSL uses PPP as its layer 2 protocol, it adds a PPP frame\nand sends the packet over the DSL circuit to the ISP.\nThe router at the ISP strips off the PPP frame and reads the IP packet, which it uses to route the packet\nthrough the Internet. As the packet moves over the Internet, the layer 2 frame changes at each hop,\ndepending on the circuit in use. For example, if the ISP uses a T3 circuit, then the ISP creates an\nappropriate layer 2 frame to move the packet over the T3 circuit (which is usually a PPP frame).\nThe packet travels from the Internet to the ISP that connects the office to the Internet and arrives at the\noffice\u2019s router. This router will strip off the incoming layer 2 frame (suppose the office uses a T-3\nconnection with PPP as shown in the figure), read the IP packet, and create an Ethernet frame that will\nsend the packet to the office VPN gateway. The VPN gateway will strip off the Ethernet frame, read the IP", "source": "Page 311", "chapter_title": "Chapter 11"}
{"id": "86182917902e-1", "text": "packet, strip it off, read the UDP datagram, strip it off, and hand the ESP packet to its VPN software. The\nVPN gateway\u2019s software will decrypt the ESP packet and deencapsulate the IP packet (and the TCP\nsegment and HTTP packet it contains) from the ESP packet. The VPN gateway now has the IP packet (and\nthe TCP segment and HTTP packet) that was originally created by the software on the employee\u2019s\ncomputer. The VPN gateway reads this IP packet and creates an Ethernet frame to send it on the next hop\nto its destination and transmits it into the office network, where it ultimately reaches the Web server. On\nthis last leg of the journey after it leaves the VPN gateway, the packet is not encrypted and can be read like\na normal packet on the Internet.\nThe return path from the Web server back to the employee\u2019s computer is very similar. The Web server will\nprocess the HTTP request packet and create an HTTP response packet that it sends back to the employee\u2019s\ncomputer. The source address on the IP packet that the Web server received was the IP address associated\nwith the VPN interface on the employee\u2019s computer, so the Web server uses this address as the destination\nIP address. This packet is therefore routed back to the VPN gateway, because the subnet for this IP\naddress is defined as being in the subnet that the VPN gateway manages. Once again, the return packet is\nnot encrypted on this part of the journey.\nWhen the packet arrives at the VPN gateway, it looks up the VPN IP address in its table and sees the usual\nIP address of the computer associated with that VPN address. The VPN gateway creates an ESP packet\nand encrypts the IP packet from the Web server (and the TCP segment and HTTP packet it contains). It\nthen treats the ESP packet as an application layer packet that needs to be sent to the VPN software on the", "source": "Page 311", "chapter_title": "Chapter 11"}
{"id": "08eabb89edb7-2", "text": "employee\u2019s computer; it passes it to its TCP software for a UDP datagram, then to its IP software for an IP\npacket, and then to its Ethernet software for an Ethernet frame and transmission back through the VPN\ntunnel.\nWhen the packet eventually reaches the employee\u2019s computer, it comes in the normal Internet interface\nand eventually reaches the TCP software that strips off the UDP datagram. The TCP software sees that the\nESP packet inside the UDP datagram is destined for the VPN software (remember that TCP port numbers\nare used to identify to which application layer software a packet should go). The VPN software removes\nthe ESP packet and passes the IP packet it contains to the IP software, which, in turn, strips off the IP\npacket, and passes the TCP segment it contains to the TCP software, which strips off the TCP segments\nand passes the HTTP packet it contains to the Web browser.\n9.5 THE BEST PRACTICE WAN DESIGN\nDeveloping best practice recommendations for WAN design is more difficult than for LANs and backbone\nnetworks because the network designer is buying services from different companies rather than buying", "source": "Page 311", "chapter_title": "Chapter 11"}
{"id": "e81b43c2f9ae-0", "text": "products. The relatively stable environment of the past is now rapidly changing with the introduction of\nEthernet and Internet VPN services, and changing organizational needs as more organizations use cloud-\nbased services. We will continue to see major changes in the industry and in the available services and\ntheir costs.\nWe also need to point out that the technologies in this chapter are primarily used to connect different\ncorporate locations. Technologies primarily used for Internet access (e.g., DSL and cable modem) are\ndiscussed in the next chapter.\n9.5.1 Software Defined WAN\nThe increased complexity in WANs means that many organizations are implementing a Software\nDefined WAN (SDWAN). A SDWAN uses software to control and manage the routers used in the WAN.\nThis enables the network manager to balance the use of the different network services, so that the network\nmakes decisions about cost and reliability in real time as network conditions change. That is, the SDWAN\nsoftware makes trade-offs between the greater reliability of common carrier services that come at a higher\ncost (e.g., packet switched services) versus the less reliable Internet-based VPN services that are cheaper.\nAn SDWAN provides four benefits. First, it provides centralized management\u2013one software system to see\nthe network status and manage all the devices and circuits in the WAN. Second, it reduces costs by\nbalancing network traffic over circuits that have different costs and capacities (this also means that\ncompanies can buy cheaper circuits that will only be used as the network gets busy). Third, it provides\nmore visibility over network traffic so network managers can see end-to-end traffic flows to better predict\nfuture growth and know what new circuits are needed before traffic slowdowns become a problem.\nFinally, SDWANs provide good security because most routers that are compatible with SDWAN software\nalso have built-in VPN capabilities, so they routinely encrypt traffic from router to router in the SDWAN.", "source": "Page 312", "chapter_title": "Chapter 11"}
{"id": "baa4dc915e14-1", "text": "The architecture of an SDWAN has three parts, which are also called planes. The top level is the\nManagement Plane, which some vendors call an Orchestration Plane. This is the software that is\nused to control the network. This software provides a dashboard that enables the network managers to see\nthe status of the network and change the network settings. For example, you can define the rules by which\nthe network will make decisions. Some network management software (which we will discuss in Chapter\n12) includes SDWAN capabilities.\nThe second plane is the Control Plane. This is the software that controls the network and makes the\ndecisions. It is the brains of the SDWAN. The control plane decides how to revise the WAN using the rules\nset by the network manager using the management plane, and regularly sends revised routing tables and\ncontrol information to the routers.\nThe third plane is the Data Plane. This plane includes the routers that implement the network. The\nrouters must be compatible with the SDWAN control plane. Remember from Chapter 5 that most routers\nspeak a variety of different routing protocols that are used to manage the routing tables, so some older\nrouters will also work in an SDWAN. However, for the SDWAN to work properly, the routers need to be\n\u201cmanaged\u201d routers (which we will also discuss in Chapter 12).\n9.5.2 Choosing WAN Circuits\nWe use the same two factors for choosing WAN services as we have previously for LANs and backbones\n(effective data rates and cost), plus add one additional factor: reliability.\nFigure 9-11 summarizes the major services available today for the WAN, grouped by the type of service. A\nfew patterns should emerge from the table. For WANs with low-to-typical data transmission needs, VPN", "source": "Page 312", "chapter_title": "Chapter 11"}
{"id": "8f5ad095ede2-2", "text": "services are a good alternative, provided the lack of reliability is not a major issue. Otherwise, Ethernet\nand MPLS are good choices because they offer good flexibility. See Figure 9-12.\nFor networks with high data transmission needs (10\u201350 Mbps) there are several distinct choices. If cost is\nmore important than reliability, then a VPN is a possible choice. If you need flexibility in the location of\nyour network connections and you are not completely sure of the volume of traffic you will have between\nlocations, Ethernet, or MPLS are good choices. If you have a mature network with predictable demands,\nthen T3 is probably a good choice.", "source": "Page 312", "chapter_title": "Chapter 11"}
{"id": "7afc441e6c81-0", "text": "FIGURE 9-11 WAN services\nNetwork Needs\nRecommendation\nLow to Typical Traffic\n(10 Mbps or Less)\nVPN if reliability is less important\nEthernet or MPLS otherwise\nHigh Traffic\n(10\u201350 Mbps)\nEthernet or MPLS\nT3 if traffic is stable and predictable\nVery High Traffic\n(more than 50 Mbps)\nEthernet or MPLS\nSONET if traffic is stable and predictable\nFIGURE 9-12 Best practice WAN recommendations\nFor very-high-traffic networks (50 Mbps\u2013100 Gbps), Ethernet is a dominant choice, with MPLS as an\nalternative. Some organizations may prefer the more mature SONET services, depending on whether the\ngreater flexibility of packet services provides value or a dedicated circuit makes more sense.\nUnless their data needs are stable, network managers often start with more flexible packet-switched\nservices and move to the usually cheaper dedicated-circuit services once their needs have become clear\nand an investment in dedicated services is safer. Some packet-switched services even permit organizations\nto establish circuits with a zero-CIR (and rely entirely on the availability of the MAR) so network\nmanagers can track their needs and lease only what they need.\nNetwork managers often add a packet network service as an overlay network on top of a network built\nwith dedicated circuits to handle peak data needs; data usually travel over the dedicated-circuit network,\nbut when it becomes overloaded with traffic, the extra traffic is routed to the packet network.\nMANAGEMENT FOCUS 9-3\nUnited Federal Credit Union Implements an SDWAN\nThe United Federal Credit Union (UFCU) has two dozen branches across the U.S. Midwest that\nsupports its 120,000 customers. Each branch is connected to the UFCU data center using an MPLS\npacket network. Most branches have a 3-Mbps connection (i.e., the common carrier has two T1", "source": "Page 313", "chapter_title": "Chapter 11"}
{"id": "c2c2decc050c-1", "text": "circuits running at 1.5 Mbps each into the PAD at each branch).\nThis WAN design had two problems. First, most branches were nearing capacity on the MPLS\nnetwork, which meant that UFCU needed to change its MPLS contract to increase capacity to 4.5\nMbps (i.e., the carrier would install a third T1 circuit into each branch). Second, the MPLS network\nwas a single point of failure, meaning that if the MPLS network went down, all ATMs stopped\nworking, the phones stopped working, and staff were forced to conduct business on paper.", "source": "Page 313", "chapter_title": "Chapter 11"}
{"id": "e95875ec500a-0", "text": "Instead of increasing the capacity of its MPLS network, UFCU implemented a new SDWAN design\nthat added a VPN circuit to each branch (using a standard highspeed public Internet circuit). Soon\nafter implementing the SDWAN, the MPLS connection at one of the branches failed, and the\nnetwork immediately rerouted over the VPN, so there was no impact on branch operations. Likewise,\nwhen network demand surged past the capacity of the MPLS network at several branches, the\nSDWAN rerouted traffic onto the VPN, and staff did not experience any delays. The SDWAN enabled\nUFCU to improve the capacity and reliability of its WAN by adding a low cost, high-speed, but less\nreliable Internet circuit to each branch that was only used when needed\nSource: Adapted from \u201cUnited Federal Credit Union Delivers Superior Member Service with a Talari SD-WAN,\u201d Case Study,\nOracle.\n9.6 IMPROVING WAN PERFORMANCE\nImproving the performance of WANs is handled in the same way as improving LAN performance. You\nbegin by checking the devices in the network, by upgrading the circuits between the locations, and by\nchanging the demand placed on the network (Figure 9-13).\n9.6.1 Improving Device Performance\nIn some cases, the key bottleneck in the network is not the circuits; it is the devices that provide access to\nthe circuits (e.g., routers). One way to improve network performance is to upgrade the devices and\ncomputers that connect backbones to the WAN. Most devices are rated for their speed in converting input\npackets to output packets (called latency). Not all devices are created equal; some vendors produce\ndevices with lower latencies than others.\nAnother strategy is examining the routing protocol, either static or dynamic. Dynamic routing will\nincrease performance in networks that have many possible routes from one computer to another and in", "source": "Page 314", "chapter_title": "Chapter 11"}
{"id": "d36e8fb97418-1", "text": "increase performance in networks that have many possible routes from one computer to another and in\nwhich message traffic is \u201cbursty\u201d\u2014that is, in which traffic occurs in spurts, with many messages at one\ntime, and few at others. But dynamic routing imposes an overhead cost by increasing network traffic. In\nsome cases, the traffic and status information sent between computers accounts for more than 50% of all\nWAN message traffic. This is clearly a problem because it drastically reduces the amount of network\ncapacity available for users\u2019 messages. Dynamic routing should use no more than 10\u201320% of the\nnetwork\u2019s total capacity.\n9.6.2 Improving Circuit Capacity\nThe first step is to analyze the message traffic in the network to find which circuits are approaching\ncapacity. These circuits then can be upgraded to provide more capacity. Less-used circuits can be\ndowngraded to save costs. A more sophisticated analysis involves examining why circuits are heavily\nused. For example, in Figure 9-2, the circuit from San Francisco to Vancouver may be heavily used, but\nmuch traffic on this circuit may not originate in San Francisco or be destined for Vancouver. It may, for\nexample, be going from Los Angeles to Toronto, suggesting that adding a circuit here would improve\nperformance to a greater extent than upgrading the San Francisco-to-Vancouver circuit.\nThe capacity may be adequate for most traffic but not for meeting peak demand. One solution may be to\nadd a packet-switched service that is used only when demand exceeds the capacity of the dedicated-circuit\nnetwork. The use of a service as a backup for heavy traffic provides the best of both worlds. The lower-cost\ndedicated circuit is used constantly, and the backup service is used only when necessary to avoid poor\nresponse times.\nPerformance Checklist\nIncrease Computer and Device Performance\nUpgrade devices\nChange to a more appropriate routing protocol (either static or dynamic)\nIncrease Circuit Capacity", "source": "Page 314", "chapter_title": "Chapter 11"}
{"id": "8bc9ce1e3476-0", "text": "Analyze message traffic and upgrade to faster circuits where needed\nCheck error rates\nReduce Network Demand\nChange user behavior\nAnalyze network needs of all new systems\nMove data closer to users\nFIGURE 9-13 Improving performance of metropolitan and local area networks\nSometimes a shortage of capacity may be caused by a faulty circuit. As circuits deteriorate, the number of\nerrors increases. As the error rate increases, throughput falls because more messages have to be\nretransmitted. Before installing new circuits, monitor the existing ones to ensure that they are operating\nproperly or ask the common carrier to do it.\n9.6.3 Reducing Network Demand\nThere are many ways to reduce network demand. One step is to require a network impact statement for all\nnew application software developed or purchased by the organization. This focuses attention on the\nnetwork impacts at an early stage in application development. Another simple approach is to use data\ncompression techniques for all data in the network.\nAnother more difficult approach is to shift network usage from peak or high-cost times to lower-demand\nor lower-cost times. For example, the transmission of detailed sales and inventory reports from a retail\nstore to headquarters could be done after the store closes. This takes advantage of off-peak rate charges\nand avoids interfering with transmissions requiring higher priority such as customer credit card\nauthorizations.\nThe network also can be redesigned to move data closer to the applications and people who use them. This\nalso will reduce the amount of traffic in the network. Distributed database applications enable databases\nto be spread across several different computers. For example, instead of storing customer records in one\ncentral location, you could store them according to region.\n9.7 IMPLICATIONS FOR CYBER SECURITY\nA WAN is usually one of the most secure parts of the network, unless, of course, you\u2019re using a VPN over", "source": "Page 315", "chapter_title": "Chapter 11"}
{"id": "a2b3eb17a60b-1", "text": "the Internet. WAN services are provided by common carriers who serve thousands of customers, so it is\ndifficult to identify one company\u2019s WAN traffic in a sea of traffic from thousands of companies.\nHowever, the possibility remains that an attacker could break into the common carrier\u2019s network. The cost\nof encryption is low, so most large organizations routinely use VPNs to encrypt their data on their WAN,\nregardless of whether they use the Internet or services provided by common carriers.\nSUMMARY\nDedicated-Circuit Networks A dedicated circuit is leased from the common carrier for exclusive\nuse 24 hours per day, 7 days per week. You must carefully plan the circuits you need because changes\ncan be expensive. The three common architectures are ring, star, and mesh. T-carrier circuits have a\nset of digital services ranging from FT1 (64 Kbps) to T1 (1.5 Mbps) to T3 (45 Mbps). A SONET service\nuses fiber optics to provide services ranging from OC-1 (51 Mbps) to OC-192 (10 Gbps).\nPacket-Switched Networks Packet switching is a technique in which messages are split into small\nsegments. The user buys a connection into the common carrier cloud and pays a fixed fee for the\nconnection into the network and for the number of packets transmitted. Frame relay is a legacy\nservice that provides data rates of 64 Kbps\u201345 Mbps. MPLS services provide speeds from 64 Kbps to\nas much as 40 Gbps. Ethernet services use Ethernet and IP to transmit packets at speeds between 1\nMbps and 10 Gbps, with the data rates set by software (with no need to install a new cable) so they\nare more flexible.", "source": "Page 315", "chapter_title": "Chapter 11"}
{"id": "060e4af5f428-0", "text": "VPNs A VPN provides a packet service network over the Internet. The sender and receiver have VPN\ndevices that enable them to send data over the Internet in encrypted form through a VPN tunnel.\nAlthough VPNs are inexpensive, traffic delays on the Internet can be unpredictable.\nThe Best Practice WAN Design For small WANs with low-to-typical data transmission needs,\nVPN or MPLS services are reasonable alternatives. For high-traffic networks (10\u201350 Mbps), Ethernet\nor MPLS services are a good choice, but some organizations may prefer the more mature\u2014and\ntherefore proven\u2014T3 services. For very-high-traffic networks (50 Mbps\u2013 100 Gbps), Ethernet or\nMPLS services are a dominant choice, but again some organizations may prefer the more mature\nSONET services. Unless their data needs are stable, network managers often start with more flexible\npacket-switched services or Internet VPN services and move to the usually cheaper dedicated-circuit\nservices once their needs have become clear and an investment in dedicated services is safer.\nImproving WAN Performance One can improve network performance by improving the speed of\nthe devices themselves and by using a better routing protocol. Analysis of network usage can show\nwhat circuits need to be increased or decreased in capacity, what new circuits need to be leased, and\nwhen additional switched circuits may be needed to meet peak demand. Reducing network demand\nmay also improve performance. Including a network usage analysis for all new application software,\nusing data compression, shifting usage to off-peak times, establishing priorities for some\napplications, or redesigning the network to move data closer to those who use it are all ways to reduce\nnetwork demand.\nKEY TERMS\naccess VPN\nCanadian Radio-Television and Telecommunications Commission (CRTC)\nchannel service unit/data service unit (CSU/DSU)\ncommitted information rate (CIR)\ncommon carrier\ncontrol plane\ndata plane", "source": "Page 316", "chapter_title": "Chapter 11"}
{"id": "36fe5d18cbf7-1", "text": "committed information rate (CIR)\ncommon carrier\ncontrol plane\ndata plane\ndedicated-circuit services\ndiscard eligible (DE)\nEthernet services\nEncapsulating Security Payload (ESP)\nextranet VPN\nFederal Communications Commission (FCC)\nfractional T1 (FT1)\nframe relay\nfull-mesh architecture\ninterexchange carrier (IXC)\nInternet service provider (ISP)\nintranet VPN\nIPSec\nL2TP\nlatency\nlayer 2 VPN", "source": "Page 316", "chapter_title": "Chapter 11"}
{"id": "7579d21bfcc4-0", "text": "layer 3 VPN\nlocal exchange carrier (LEC)\nmanagement plane\nmaximum allowable rate (MAR)\nmesh architecture\nmultiprotocol label switching (MPLS)\norchestration plane\npacket assembly/disassembly device (PAD)\npacket services\npacket-switched services\npartial-mesh architecture\npermanent virtual circuits (PVC)\npoint of presence (POP)\npublic utilities commission (PUC)\nring architecture\nSoftware Defined WAN (SDWAN)\nstar architecture\nswitched virtual circuits (SVCs)\nsynchronous digital hierarchy (SDH)\nsynchronous optical network (SONET)\nT-carrier circuit\nT1 and T2 circuits\nT3 and T4 circuits\nvirtual private network (VPN)\nVPN gateway\nVPN software\nwide area networks (WANs)\nQUESTIONS\n1. What are common carriers, local exchange carriers, and interexchange carriers?\n2. Who regulates common carriers and how is it done?\n3. How do Ethernet services work in the WNA?\n4. Compare and contrast dedicated-circuit services and packet-switched services.\n5. Is a WAN that uses dedicated circuits easier or harder to design than one that uses packet-switched\ncircuits? Explain.\n6. Compare and contrast ring architecture, star architecture, and mesh architecture.\n7. What are the most commonly used T-carrier services? What data rates do they provide?\n8. Distinguish among T1, T2, T3, and T4 circuits.\n9. Describe SONET. How does it differ from SDH?", "source": "Page 317", "chapter_title": "Chapter 11"}
{"id": "409495e95846-0", "text": "10. How do packet-switching services differ from other WAN services?\n11. Where does packetizing take place?\n12. Compare and contrast frame relay and Ethernet services.\n13. Which is likely to be the longer-term winner: MPLS or Ethernet services?\n14. Explain the differences between CIR and MAR.\n15. How do VPN services differ from common carrier services?\n16. Explain how VPN services work.\n17. Compare the three types of VPN.\n18. How can you improve WAN performance?\n19. Describe three important factors in selecting WAN services.\n20. Are Ethernet services a major change in the future of networking or a technology blip?\n21. What is SDWAN and what benefits does it provide?\n22. What is the architecture of an SDWAN?\n23. Are there any WAN technologies that you would avoid if you were building a network today? Explain.\n24. Suppose you joined a company that had a WAN composed of SONET, T carrier, and frame relay\nservices, each selected to match a specific network need for a certain set of circuits. Would you say\nthis was a well-designed network? Explain.\n25. It is said that frame relay services and dedicated-circuit services are somewhat similar from the\nperspective of the network designer. Why?\nEXERCISES\nA. Find out the data rates and costs of T-carrier services in your area.\nB. Find out the data rates and costs of packet-switched and dedicated-circuit services in your area.\nC. Investigate the WAN of a company in your area. Draw a network map.\nD. Using Figure 9-10:\na. Suppose that the example used a layer 2 VPN protocol called L2TP. Draw the messages and the\npackets they would contain.", "source": "Page 318", "chapter_title": "Chapter 11"}
{"id": "0e8467ef805c-1", "text": "packets they would contain.\nb. Suppose that the Web server was an email server. Draw the messages from the email server to\nthe employee\u2019s computer. Show what packets would be in the message.\nc. Suppose the office connects to its ISP using metro Ethernet. What packets would be in the\nmessage from the office router to the ISP?\nd. Suppose the employee connects to the ISP using a layer 2 protocol called XYZ. What packets\nwould be in the message from the employee\u2019s router to the ISP?\nE. Select one SDWAN vendor and describe the products it offers.\nMINICASES\nI. Cookies Are Us Cookies Are Us runs a series of 100 cookie stores across the midwestern United\nStates and central Canada. At the end of each day, the stores send sales and inventory data to\nheadquarters, which uses the data to ship new inventory and plan marketing campaigns. The\ncompany has decided to move to a new WAN. What type of a WAN architecture and WAN service\nwould you recommend? Why?\nII. MegaCorp MegaCorp is a large manufacturing firm that operates five factories in Dallas, four\nfactories in Los Angeles, and five factories in Albany, New York. It operates a tightly connected order", "source": "Page 318", "chapter_title": "Chapter 11"}
{"id": "c75268cdeb20-0", "text": "management system that coordinates orders, raw materials, and inventory across all 14 factories.\nWhat type of WAN architecture and WAN service would you recommend? Why?\nIII. Sunrise Consultancy Sunrise Consultancy is a medium-sized consulting firm that operates 17\noffices around the world (Dallas, Chicago, New York, Atlanta, Miami, Seattle, Los Angeles, San Jose,\nToronto, Montreal, London, Paris, Sao Paulo, Singapore, Hong Kong, Sydney, and Mumbai). They\nhave been using Internet connections to exchange email and files, but the volume of traffic has\nincreased to the point that they now want to connect the offices via a WAN. Volume is low but\nexpected to grow quickly once they implement a new knowledge management system. What type of a\nWAN topology and WAN service would you recommend? Why?\nIV. Cleveland Transit Reread Management Focus 9-1. What other alternatives do you think Cleveland\nTransit considered? Why do you think they did what they did?\nV. Marietta City Schools Reread Management Focus 9-2. What alternatives do you think Marietta\nCity Schools considered? Why do you think they did what they did?\nTECH UPDATES\nIn every chapter, we will offer a couple of ideas to investigate. Pick one of these topics to investigate.\nTopic A: Password Cracking\nPassword cracking is done by either repeatedly guessing the password, usually through a computer\nalgorithm in which the computer tries numerous combinations until the password is successfully\ndiscovered. What are the top three ways password cracking can be done? What tools can one download\nfrom the Internet to do password cracking? How fast are these tools? What are the most common\npasswords? Demonstrate in real time two password cracking techniques.\nTopic B: Blockchain and Cryptocurrency\nBitcoin is the name of the best-known cryptocurrency, the one for which blockchain technology was", "source": "Page 319", "chapter_title": "Chapter 11"}
{"id": "a0ca3beb31ce-1", "text": "Bitcoin is the name of the best-known cryptocurrency, the one for which blockchain technology was\ninvented. Blockchain is, quite simply, a digital, decentralized ledger that keeps a record of all transactions\nthat take place across a peer-to-peer network. This seems like a very good idea, yet banks while open to\nblockchain seem to have strong opinions about cryptocurrency. Why do think this is happening? Who is\nSatoshi Nakamoto? Investigate the origins of cryptocurrency, its history, and predictions for the future.\nDeliverables\nYour job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title Slide\n2. Short description of the topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use a lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along\n5. How does it relate to material covered in class so far (and in the future)\n6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 9A", "source": "Page 319", "chapter_title": "Chapter 11"}
{"id": "5cc60c9c31f6-0", "text": "Examining Wide Area Networks\nThere are millions of WANs in the world. Some are run by common carriers and are available to the\npublic. Others are private networks run by organizations for their internal use only. Thousands of these\nnetworks have been documented on the Web.\nExplore the Web to find networks offered by common carriers and compare the types of network circuits\nthey have. Now do the same for public and private organizations to see what they have. Figure 9-14 shows\nthe network map for Zayo, a large common carrier (see www.zayo.com). This figure shows the circuits\nrunning at 100 Gbps that connect major cities in the United States. Zayo has a much larger network that\nincludes portions that run slower than 100 Gbps, but the network has hundreds of sites and is too hard to\nshow in one figure.\nFIGURE 9-14 100 Gbps network for a U.S. Internet service provider\nDeliverable\n1. Print or copy two different WAN maps. Does the WAN use only one type of circuits, or are there a mix\nof technologies in use?\nHANDS-ON ACTIVITY 9B\nExamining VPNs with Wireshark\nIf you want to see VPNs in action and understand how they protect your data as they move over the\nInternet, you can sniff your packets with Wireshark. To do this lab, you\u2019ll have to have a VPN you can use.\nThis will normally be available from your school.\nIn this exercise, you\u2019ll use Wireshark to sniff the packets with and without the VPN. Before you start,\nyou\u2019ll need to download and install Wireshark, a packet sniffer software package, on your computer.\n1. Start the VPN software on your computer.\n2. Start a Web browser (e.g., Internet Explorer) and go to a website.", "source": "Page 320", "chapter_title": "Chapter 11"}
{"id": "8880c8c74e86-1", "text": "2. Start a Web browser (e.g., Internet Explorer) and go to a website.\n3. Start Wireshark and click on the Capture menu item. This will open up a new menu (see the very top\nof Figure 9-15). Click on Interfaces.\n4. This will open a new window that will enable you to select which interface you want to capture\npackets from. Figure 9-15 shows you the three interfaces I have on my computer. The first interface is", "source": "Page 320", "chapter_title": "Chapter 11"}
{"id": "057fafb6fc8c-0", "text": "a dial-up modem that I never use. The second interface (labeled \u201cBroadcom NetXtreme Gigabit\nEthernet Driver\u201d) is my Ethernet local area network. It has the IP address of 192.168.1.104. The third\ninterface (labeled \u201cWN (PPP/SLIP) Interface\u201d) is the VPN tunnel; it has an IP address of\n156.56.198.144 and only appears when you start the VPN software and log into a VPN gateway. If you\ndo a WhoIs on this IP address (see Chapter 5 for WhoIs), you will see that this IP address is owned by\nIndiana University. When I logged into my VPN software, it assigned this IP address to the tunnel so\nthat all IP packets that leave my computer over this tunnel will appear to be from a computer on a\nsubnet on the Indiana University campus that is connected to the VPN gateway. Your computer will\nhave different interfaces and IP addresses because your network is different than mine, but the\ninterfaces should be similar.", "source": "Page 321", "chapter_title": "Chapter 11"}
{"id": "28ae3676426e-0", "text": "FIGURE 9-15 Starting Wireshark\nFIGURE 9-16 Viewing encrypted packets\n5. Start by capturing packets on your regular Ethernet interface. In my case, this is the second interface.\nClick on the Start button beside the Ethernet driver (which is 192.168.1.104 on my computer).\n6. Go to your Web browser and use it to load a new Web page, which will cause some packets to move\nthrough your network.\n7. A screen similar to that in Figure 9-16 will appear. After a few seconds, go back to Wireshark and click\nthe Interface menu item and then click Stop.\n8. The top window in this figure shows the packets that are leaving the computer through the tunnel.\nClick on a packet to look at it. The middle window in this figure shows what\u2019s inside the packet. We\nsee an Ethernet frame, an IP packet, a UDP datagram, and an Encapsulating Security Payload packet\n(which is the ESP packet). Notice that you cannot see anything inside the ESP packet because its", "source": "Page 322", "chapter_title": "Chapter 11"}
{"id": "953631447c5e-0", "text": "contents are encrypted. All packets in this tunnel will only flow to and from my computer\n(192.168.1.104) and the VPN gateway (156.56.245.15).\n9. Now we want to look at the packets that are sent by your computer into the VPN tunnel. No one else\ncan see these packets. You can see them only because they are on your computer and you\u2019re looking at\nthem as they move from your traditional network software to your VPN software.\n10. Click on the Wireshark Capture menu item and click Interfaces.\n11. Click on the Start button beside your VPN interface, which in my case in Figure 9-15 is the button in\nfront of 156.56.198.144.\n12. Go to your Web browser and use it to load a new Web page, which will cause some packets to move\nthrough your network.\n13. A screen similar to that in Figure 9-17 will appear. After a few seconds, go back to Wireshark and click\nthe Interface menu item, and then click Stop.\n14. The top window in Figure 9-17 shows the packets that are entering the VPN tunnel. Click on an HTTP\npacket to look at it (you may need to scroll to find one). The middle window in this figure shows\nwhat\u2019s inside the packet. We see an Ethernet frame, an IP packet, a TCP segment, and an HTTP\nrequest (for a page called/enterprise/ at the server www.tatacommunications.com). We can see these\nbecause they have not yet entered the VPN software to be encrypted. These are the packets that would\nnormally be sent over the Internet if we have not started the VPN software. Like all normal Internet\nmessages, they can be read by anyone with sniffer software such as Wireshark.\nDeliverables", "source": "Page 323", "chapter_title": "Chapter 11"}
{"id": "4fa816ef4dd5-1", "text": "Deliverables\n1. What layer 2, 3, and 4 protocols are used on your network to transmit an HTTP packet without a\nVPN?\n2. What layer 2, 3, and 4 protocols are used on your network to transmit an HTTP packet when your\nVPN is active?\n3. Look inside the VPN tunnel as was done in step 14. What layer 2, 3, and 4 protocols are used inside\nthe encrypted packet?\nHANDS-ON ACTIVITY 9C\nExamining VPNs with Tracert\nTracert is a useful tool for seeing how VPNs affect routing. To do this lab, you\u2019ll have to have a VPN you\ncan use. This will normally be available from your school.\nTracert is a simple command that comes preinstalled on all Windows and Mac computers. Tracert enables\nyou to see the route that an IP packet takes as it moves over the Internet from one computer to another.\nDo this activity when you are not on campus.\nTracert is a command line command, so you first need to start the CMD window. Click Start, then Run,\nand then type CMD and press enter. This will open the command window, which is usually a small\nwindow with a black background. You can change the size and shape of this window, but it is not as\nflexible as a usual window.\nWe will first trace the route from your computers to two other computers without using the VPN. So make\nsure your VPN is not connected.\nWe\u2019ll start by tracing the route from your computer to a computer on the campus of the site you VPN into.\nIn my case, I VPN into my university, which is Indiana University. I can choose to trace the route to any\ncomputer on campus. I\u2019ll choose our main Web server (www.iu.edu). At the command prompt, type", "source": "Page 323", "chapter_title": "Chapter 11"}
{"id": "14d039e644da-2", "text": "tracert and the URL of a computer on your campus.\nThe top half of Figure 9-18 shows the route from my computer to www.iu.edu. There are 18 hops and it\ntakes about 35 ms. The first hop does not report information because this feature is turned off in the\nrouter at my house for security reasons. You can see that my ISP is Comcast (hop 6). If you compare this", "source": "Page 323", "chapter_title": "Chapter 11"}
{"id": "0c781e588a7f-0", "text": "to the tracert at the end of Chapter 5, you\u2019ll notice that my ISP changed (and thus the route into the\nInternet changed) between the time I wrote Chapter 5 and this chapter; Comcast bought Insight in my\ntown of Bloomington, Indiana.", "source": "Page 324", "chapter_title": "Chapter 11"}
{"id": "9f6628d0cdc5-0", "text": "FIGURE 9-17 Packets that enter the VPN tunnel\nFIGURE 9-18 Tracert without a VPN\nNow trace the route from your computer to another computer on the Internet. The bottom of Figure 9-18\nshows the route from my computer to www.google.com. There are 17 hops, and it takes about 35 ms.\nYou\u2019ll see that the routes to IU and Google are the same until step 6, and then they diverge.\nNext we want to see what happens when you have a VPN connection. Start your VPN software and\nconnect into the VPN gateway at your school.\nTrace the route from your computer to the same computer as in step 3. At the command prompt, type\ntracert and the URL of a computer on your campus.", "source": "Page 325", "chapter_title": "Chapter 11"}
{"id": "7df96a1979c0-0", "text": "The top half of Figure 9-19 shows the route from my computer to www.iu.edu. There are two hops and it\ntakes about 35 ms. The VPN is in operation and is transparent to my networking software, which thinks it\nis on the same subnet as the VPN gateway. Therefore, it thinks there is just one hop from my computer to\nthe subnet\u2019s gateway, the VPN gateway. You\u2019ll see that the time is still about 35 ms, so the packet is still\ntraveling the same 18 hops to get there; it\u2019s just that the tracert packet is encapsulated and doesn\u2019t see all\nthe hops through the VPN tunnel.\nNow do a tracert to the same computer as you did in step 5. The bottom of Figure 9-19 shows the route\nfrom my computer to www.google.com. There are nine hops and it takes about 43 ms. Of course, the first\nhop is really 17 hops and 35 ms; this is again hidden from view. As we explained in the text, when the VPN\nis connected, all packets go from your computer to the VPN gateway on your campus before being routed\nto the final destination. You can see from this figure that this adds additional hops and time to packets\nthat are not going to your campus, compared to not using the VPN. You can also see that once the packets\nleave the VPN gate-way, they are ordinary packets; they are no longer encrypted and protected from view.\nFIGURE 9-19 Tracert with a VPN\nThe VPN provides security only to and from the VPN gateway on your campus, not beyond it. Therefore,\nyou should use your VPN if you have security concerns to and from campus (e.g., someone sniffing your\npackets). But if most of your work is going to be off campus, then the VPN increases the time it takes to", "source": "Page 326", "chapter_title": "Chapter 11"}
{"id": "37af3b405a43-1", "text": "send and receive packets and only provides security protection over the last section from your computer to\nyour school\u2019s campus. Using the VPN may not be worth the additional response time it imposes on you.\nDeliverables\n1. What are the routes from your computer to your campus Web server with and without the VPN?\n2. What are the routes from your computer to www.google.com with and without the VPN?\nHANDS-ON ACTIVITY 9D\nApollo Residence Network Design", "source": "Page 326", "chapter_title": "Chapter 11"}
{"id": "c92ab95044a2-0", "text": "Apollo is a luxury residence hall that will serve honor students at your university. We described the\nresidence in Hands-On Activities at the end of Chapters 7 and 8.\nThe university has recognized that work is going virtual, with more and more organizations building\nvirtual teams with members drawn from different parts of the organization who work together from\ndifferent cities, instead of meeting face-to-face. It has joined together with five universities across the\nUnited States and Canada (located in Boston, Los Angeles, Atlanta, Dallas, and Toronto) to form a\nconsortium of universities that will build virtual team experiences into their programs.\nThe universities have decided to start with their honors programs, and each has created a required course\nthat involves its students working with students at the other universities to complete a major project. The\nstudents will use collaboration software such as email, chat, Google Docs, Skype, and WebEx to provide\ntext, audio, and video communication. These tools can be used over the Internet, but to ensure that there\nare no technical problems, the universities have decided to build a separate private WAN that connects\nthe six honors residences on each university campus (in the five cities listed, plus your university).\nWAN Service Data Rate Monthly Cost\nT1\n1.5 Mbps\n$400\nT3\n45 Mbps\n$1,500\nSONET OC-1\n52 Mbps\n$1,800\nSONET OC-3\n155 Mbps\n$2,800\nMPLS\n1.5 Mbps\n$450\nMPLS\n45 Mbps\n$1,700\nMPLS\n52 Mbps\n$2,000\nMPLS\n155 Mbps\n$3,000\nEthernet\n1 Mbps\n$300\nEthernet\n5 Mbps\n$400\nEthernet\n10 Mbps\n$500\nEthernet\n20 Mbps\n$700\nEthernet\n50 Mbps\n$900\nEthernet\n100 Mbps", "source": "Page 327", "chapter_title": "Chapter 11"}
{"id": "08c5a397a545-1", "text": "20 Mbps\n$700\nEthernet\n50 Mbps\n$900\nEthernet\n100 Mbps\n$1,500\nEthernet\n200 Mbps\n$2,500\nInternet VPN\n25 Mbps\n$75\nInternet VPN\n50 Mbps\n$100\nInternet VPN\n100 Mbps\n$125\nInternet VPN\n150 Mbps\n$150\nInternet VPN\n200 Mbps\n$175\nFIGURE 9-20 Monthly costs for WAN services\nDeliverable\nYour team was hired to design the WAN for this six-university residence network. Figure 9-20 provides a\nlist of possible WAN services you can use. Specify what services you will use at each location and how the\nsix locations will be connected. Provide the estimated monthly operating cost of the network.", "source": "Page 327", "chapter_title": "Chapter 11"}
{"id": "146a2324422d-0", "text": "CHAPTER 10\nTHE INTERNET\nThis chapter examines the Internet in more detail to explain how it works and why it is a network of\nnetworks. The chapter also examines Internet access technologies, such as DSL and cable modem, as well\nas the possible future of the Internet.\nOBJECTIVES\nUnderstand the overall design of the Internet\nBe familiar with DSL, cable modem, and fiber to the home\nBe familiar with possible future directions of the Internet\nOUTLINE\n10.1 Introduction\n10.2 How the Internet Works\n10.2.1 Basic Architecture\n10.2.2 Connecting to an ISP\n10.2.3 The Internet Today\n10.3 Internet Access Technologies\n10.3.1 Digital Subscriber Line\n10.3.2 Cable Modem\n10.3.3 Fiber to the Home\n10.4 The Future of the Internet\n10.4.1 Internet Governance\n10.4.2 Building the Future\n10.5 Implications for Cyber Security\nSummary\n10.1 INTRODUCTION\nThe Internet is the most used network in the world, but it is also one of the least understood. There is no\none network that is the Internet. Instead, the Internet is a network of networks\u2014a set of separate and\ndistinct networks operated by various national and state government agencies, nonprofit organizations,\nand for-profit corporations. The Internet exists only to the extent that these thousands of separate\nnetworks agree to use Internet protocols and to exchange data packets among one another.\nWhen you are on the Internet, your computer (iPad, smartphone, etc.) is connected to the network of an\nInternet service provider (ISP) that provides network services for you. Messages flow between your client\ndevice and the ISP\u2019s network. Suppose you request a Web page on CNN.com, a website that is outside of\nyour ISP\u2019s network. Your HTTP request flows from your device through your ISP\u2019s network and through", "source": "Page 328", "chapter_title": "Chapter 11"}
{"id": "b9528c1d7258-1", "text": "your ISP\u2019s network. Your HTTP request flows from your device through your ISP\u2019s network and through\nother networks that link your ISP\u2019s network to the network of the ISP that provides Internet services for\nCNN. Each of these networks is separate and charges its own customers for Internet access but permits\ntraffic from other networks to flow through them. In many ways, the Internet is like the universe (see\nFigure 10-1). Each of us works in our own planet with its own rules (i.e., ISP) but each planet is", "source": "Page 328", "chapter_title": "Chapter 11"}
{"id": "54556cff0e3b-0", "text": "interconnected with all the others.\nThe Internet is simultaneously a strict, rigidly controlled club in which deviance from the rules is not\ntolerated and a freewheeling, open marketplace of ideas. All networks that connect to the Internet must\nrigidly conform to an unyielding set of standards for the transport and network layers; without these\nstandards, data communication would not be possible. At the same time, content and new application\nprotocols are developed freely and without restriction, and quite literally anyone in the world is allowed to\ncomment on proposed changes.\nFIGURE 10-1 The Internet is a lot like the universe\u2014many independent systems linked together\nSource: NASA.\nIn this chapter, we first explain how the Internet really works and look inside the Seattle Internet\nexchange point, at which more than 150 separate Internet networks meet to exchange data. We then turn\nour attention to how you as an individual can access the Internet and what the Internet may look like in\nthe future. Many experts have predicted we will have high-speed wireless Internet access in a few years.\nHowever, none of these predictions have come to pass. We may have wireless Internet access in our\nhomes, but for the foreseeable future, Internet access to our homes will require a wire.", "source": "Page 329", "chapter_title": "Chapter 11"}
{"id": "0d7258752dac-0", "text": "10.2 HOW THE INTERNET WORKS\n10.2.1 Basic Architecture\nThe Internet is hierarchical in structure. At the top are the very large national Internet service\nproviders (ISPs), such as AT&T and Sprint, that are responsible for large Internet networks. These\nnational ISPs, called tier 1 ISPs, connect together and exchange data at Internet exchange points\n(IXPs) (Figure 10-2). For example, AT&T, Sprint, Verizon, Qwest, Level 3, and Global Crossing are all\ntier 1 ISPs that have a strong presence in North America.\nIn the early 1990s, when the Internet was still primarily run by the U.S. National Science Foundation\n(NSF), the NSF established four main IXPs in the United States to connect the major tier 1 ISPs (the 1990s\nname for an IXP was network exchange point or NAP). When the NSF stopped funding the Internet, the\ncompanies running these IXPs began charging the ISPs for connections, so today the IXPs in the United\nStates are all not-for-profit organizations or commercial enterprises run by various common carriers such\nas AT&T and Sprint. As the Internet has grown, so too has the number of IXPs; today there are several\ndozen IXPs in the United States with more than a hundred more spread around the world.\nIXPs were originally designed to connect only large tier 1 ISPs. These ISPs in turn provide services for\ntheir customers and also to regional ISPs (sometimes called tier 2 ISPs) such as Comcast or BellSouth.\nThese tier 2 ISPs rely on tier 1 ISPs to transmit their messages to ISPs in other countries. Tier 2 ISPs, in\nturn, provide services to their customers and to local ISPs (sometimes called tier 3 ISPs) who sell", "source": "Page 330", "chapter_title": "Chapter 11"}
{"id": "4e0c75b01ceb-1", "text": "Internet access to individuals. As the number of ISPs grew, smaller IXPs emerged in most major cities to\nlink the networks of these regional ISPs.\nFIGURE 10-2 Basic Internet architecture. ISP = Internet service provider; IXP = Internet exchange point\nBecause most IXPs and ISPs are now run by commercial firms, many of the early restrictions on who\ncould connect to whom have been lifted. Most now openly solicit business from all tiers of ISPs and even\nlarge organizations. Regional and local ISPs often will have several connections into other ISPs to provide", "source": "Page 330", "chapter_title": "Chapter 11"}
{"id": "7dfd9c441981-0", "text": "backup connections in case one Internet connection fails. In this way, they are not dependent on just one\nhigher-level ISP.\nIn general, ISPs at the same level do not charge one another for transferring messages they exchange.\nThat is, a national tier 1 ISP does not charge another national tier 1 ISP to transmit its messages. This is\ncalled peering. Figure 10-2 shows several examples of peering. It is peering that makes the Internet work\nand that has led to the belief that the Internet is free. This is true to some extent, but higher-level ISPs\nnormally charge lower-level ISPs to transmit their data (e.g., a tier 1 will charge a tier 2 and a tier 2 will\ncharge a tier 3). And, of course, any ISP will charge individuals like us for access!\nIn October 2005, an argument between two national ISPs shut down 45 million websites for a week. The\ntwo ISPs had a peering agreement, but one complained that the other was sending it more traffic than it\nshould, so it demanded payment and stopped accepting traffic, leaving large portions of the network\nisolated from the rest of the Internet. The dispute was resolved, and they began accepting traffic from\neach other and the rest of the Internet again.\nIn Figure 10-2, each of the ISPs is an autonomous system, as defined in Chapter 5. Each ISP is\nresponsible for running its own interior routing protocols and for exchanging routing information via the\nBorder Gateway Protocol (BGP) exterior routing protocol (see Chapter 5) at IXPs and at any other\nconnection points between individual ISPs.\n10.2.2 Connecting to an ISP\nEach of the ISPs is responsible for running its own network that forms part of the Internet. ISPs make\nmoney by charging customers to connect to their part of the Internet. Local ISPs charge individuals for", "source": "Page 331", "chapter_title": "Chapter 11"}
{"id": "841aa214d83a-1", "text": "money by charging customers to connect to their part of the Internet. Local ISPs charge individuals for\naccess, whereas national and regional ISPs (and sometimes local ISPs) charge larger organizations for\naccess.\nEach ISP has one or more points of presence (POP). A POP is simply the place at which the ISP\nprovides services to its customers. To connect into the Internet, a customer must establish a circuit from\nhis or her location into the ISP POP. For individuals, this is often done using a DSL modem or cable\nmodem, as we discuss in the next section. Companies can use these same technologies, or they can use the\nWAN technologies we discussed in the previous chapter. Once connected, the user can begin sending\nTCP/IP packets from his or her computer to the POP.\nMANAGEMENT FOCUS 10-1\nInside the Seattle Internet Exchange Point\nThe Seattle Internet Exchange (SIX) was established as a nonprofit organization in April 1997 by two\nsmall ISPs with offices in Seattle\u2019s Westin Building. The ISPs had discovered that to send data to\neach other\u2019s network in the same building, their data traveled to Texas and back. They decided to\npeer and installed a 10Base-T Ethernet hub connecting their two networks so that traffic flowed\nbetween them much more quickly.\nIn June 1997, a third small ISP joined and connected its network into the hub. Gradually word\nspread and other small ISPs began to connect. In May 1998, the first tier 1 ISP connected its\nnetwork, and traffic grew enough so that the old 10 Mbps hub was replaced by a 10/100 Ethernet\nswitch. As an aside, we\u2019ll note that the switch you have in your house or apartment today probably\nhas more capacity than this switch. In February 1999, Microsoft connected its network, and traffic", "source": "Page 331", "chapter_title": "Chapter 11"}
{"id": "ab9f3864b9ce-2", "text": "took off again. In September 2001, the 10/100 Ethernet switch was replaced by a 10/100/1000\nEthernet switch.\nThe current configuration is a set of two large switches in the Westin building and two smaller\nswitches (which are still immense by corporate standards) in nearby buildings connected together\nwith Ethernet circuits running at up to 800 Gbps. There are another eight GbE switches located\nelsewhere in Seattle and other cities in the United States.\nToday, SIX offers several types of Ethernet connections to its clients. The first 1 Gbps connection has", "source": "Page 331", "chapter_title": "Chapter 11"}
{"id": "9c434e811c2e-0", "text": "a one-time connection fee of $100 with subsequent 1 Gbps connections costing a one-time fee of\n$1,500. Faster connections have a monthly fee (10 Gbps costs $180/month and 100 Gbps\n$900/month). Of course, you have to pay a common carrier to provide a network circuit into the\nWestin Building and then pay the Westin Building a small fee to run a fiber cable from the building\u2019s\nMDF to the SIX network facility. Traffic averages between 800 Gbps and 1,5 Tbps across the SIX\nnetwork.\nMore than 150 ISPs (e.g., AT&T, Verizon, Bell Canada, and Saskatchewan Telecommunications) and\ncorporations (e.g., Akamai, Google, Facebook, and Yahoo) are members of SIX. About half of the\nmembers are open to peering with anyone who joins SIX. The rest, mostly tier 1 ISPs and well-\nknown corporations, are selective or restrictive in their peering agreements, which means that they\nare already well connected into the Internet and want to ensure that any new peering agreements\nmake business sense.\nSource: Adapted from Settle Internet Exchange. www.seattleix.net.\nIt is important to note that the customer must pay for both Internet access (paid to the ISP) and for the\ncircuit connecting from the customer\u2019s location to the POP (usually paid to the local exchange carrier [e.g.,\nBellSouth and AT&T], but sometimes the ISP also can provide circuits). For a T1 connection, for example,\na company might pay the local exchange carrier $250 per month to provide the T1 circuit from its offices\nto the ISP POP and also pay the ISP $250 per month to provide the Internet access.\nAn ISP POP is connected to the other POPs in the ISP\u2019s network. Any messages destined for other", "source": "Page 332", "chapter_title": "Chapter 11"}
{"id": "8fb52d82791d-1", "text": "customers of the same ISP would flow within the ISP\u2019s own network. In most cases, the majority of\nmessages entering the POP are sent outside of the ISP\u2019s network and thus must flow through the ISP\u2019s\nnetwork to the nearest IXP and, from there, into some other ISP\u2019s network.\nThis can be less efficient than one might expect. For example, suppose you are connected to the Internet\nvia a local tier 3 ISP in Minneapolis and request a Web page from another organization in Minneapolis. A\nshort distance, right? Maybe not. If the other organization uses a different local tier 3 ISP, which, in turn,\nuses a different regional tier 2 ISP for its connection into the Internet, the message may have to travel all\nthe way to the nearest IXP, which could be in Chicago, Dallas, or New York, before it can move between\nthe two separate parts of the Internet.\n10.2.3 The Internet Today\nFigure 10-3 shows the North American backbone of a major ISP as it existed while we were writing this\nbook; it will have changed by the time you read this. As you can see, it has many Internet circuits across\nthe United States and Canada. Many interconnect in Chicago, where many ISPs connect into the Chicago\nIXP. It also connects into major IXPs in Reston, Virginia; Miami; Los Angeles; San Jose; Palo Alto;\nVancouver; Calgary; Toronto; and Montreal.\nToday, the backbone circuits of the major U.S. national ISPs operate at SONET OC-192 (10 Gbps). A few\nare now experimenting with OC-768 (80 Gbps), and several are in the planning stages with OC-3072 (160\nGbps). This is good because the amount of Internet traffic has been growing rapidly.\nAs traffic increases, ISPs can add more and faster circuits relatively easily, but where these circuits come", "source": "Page 332", "chapter_title": "Chapter 11"}
{"id": "f40ad666a95b-2", "text": "As traffic increases, ISPs can add more and faster circuits relatively easily, but where these circuits come\ntogether at IXPs, bottlenecks are becoming more common. Network vendors such as Cisco and Juniper\nare making larger and larger switches capable of handling these high-capacity circuits, but it is a daunting\ntask. When circuit capacities increase by 100%, switch manufacturers also must increase their capacities\nby 100%. It is simpler to go from a 622 Mbps circuit to a 10 Gbps circuit than to go from a 20 Gbps switch\nto a 200 Gbps switch.", "source": "Page 332", "chapter_title": "Chapter 11"}
{"id": "0e642e7b0d99-0", "text": "FIGURE 10-3 A typical Internet backbone of a major ISP\n10.3 INTERNET ACCESS TECHNOLOGIES\nThere are many ways in which individuals and organizations can connect to an ISP. Most individuals use\nDSL or cable modem. As we discussed in the preceding section, many organizations lease T1, T3, or\nEthernet circuits into their ISPs. DSL and cable modem technologies are commonly called broadband\ntechnologies because they provide high-speed communications.\nIt is important to understand that Internet access technologies are used only to connect from one location\nto an ISP. Unlike the WAN technologies in the previous chapter, Internet access technologies cannot be\nused for general-purpose networking from any point to any point. In this section, we discuss three\nprincipal Internet access technologies (DSL, cable modem, and fiber to the home). Of course, many users\nconnect to the Internet using Wi-Fi on their laptops from public access points in coffee shops, hotels, and\nairports. Since we discussed Wi-Fi in Chapter 7, we won\u2019t repeat it here.\n10.3.1 Digital Subscriber Line\nDigital subscriber line (DSL) is a family of point-to-point technologies designed to provide high-\nspeed data transmission over traditional telephone lines. The reason for the limited capacity on\ntraditional telephone circuits lies with the telephone and the switching equipment at the end offices. The\nactual cable in the local loop from a home or office to the telephone company end office is capable of\nproviding much higher data transmission rates. So DSL usually requires just changing the telephone\nequipment, not rewiring the local loop, which is what has made it so attractive.\nArchitecture DSL uses the existing local loop cable but places different equipment on the customer\npremises (i.e., the home or office) and in the telephone company end office. The equipment that is\ninstalled at the customer location is called the customer premises equipment (CPE). Figure 10-4", "source": "Page 333", "chapter_title": "Chapter 11"}
{"id": "b30b1467941c-1", "text": "shows one common type of DSL installation. (There are other forms.) The CPE in this case includes a line\nsplitter that is used to separate the traditional voice telephone transmission from the data transmissions.\nThe line splitter directs the telephone signals into the normal telephone system so that if the DSL\nequipment fails, voice communications are unaffected.\nThe line splitter also directs the data transmissions into a DSL modem, which is sometimes called a DSL\nrouter. This is both a modem and a frequency division multiplexing (FDM) multiplexer (see Chapter 3).", "source": "Page 333", "chapter_title": "Chapter 11"}
{"id": "fb8a02649a0d-0", "text": "The DSL modem produces Ethernet packets so it can be connected directly into a computer or to a router\nand can serve the needs of a small network. Most DSL companies targeting home users combine all of\nthese devices (and a wireless access point) into one device so that consumers just have to install one box,\nrather than separate line splitters, modems, routers, switches, and access points.\nFigure 10-4 also shows the architecture within the local carrier\u2019s end office (i.e., the telephone company\noffice closest to the customer premises). The local loops from many customers enter and are connected to\nthe main distribution facility (MDF). The MDF works similarly to the CPE line splitter; it splits the\nvoice traffic from the data traffic and directs the voice traffic to the voice telephone network and the data\ntraffic to the DSL access multiplexer (DSLAM). The DSLAM demultiplexes the data streams and\nconverts them into digital data, which are then distributed to the ISPs. Some ISPs are collocated, in that\nthey have their POPs physically in the telephone company end offices. Other ISPs have their POPs located\nelsewhere.\nTypes of DSL\nThere are many different types of DSL. The most common type today is asymmetric DSL (ADSL).\nADSL uses FDM (see Chapter 3) to create three separate channels over the one local loop circuit. One\nchannel is the traditional voice telephone circuit. A second channel is a relatively high-speed data channel\ndownstream from the carrier\u2019s end office to the customer. The third channel is a slightly slower data\nchannel upstream from the customer to the carrier\u2019s end office. ADSL is called asymmetric because its two\ndata channels have different speeds. Each of the two data channels is further multiplexed using time\ndivision multiplexing so they can be subdivided.", "source": "Page 334", "chapter_title": "Chapter 11"}
{"id": "8c0dbd863e6f-1", "text": "division multiplexing so they can be subdivided.\nFIGURE 10-4 DSL architecture. DSL = digital subscriber line; ISP = Internet service provider; POP =\npoint of presence\nThe size of the two digital channels depends on the distance from the CPE to the end office. The shorter\nthe distance, the higher the speed, because with a shorter distance, the circuit suffers less attenuation and", "source": "Page 334", "chapter_title": "Chapter 11"}
{"id": "e3ece5b2c0fa-0", "text": "higher-frequency signals can be used, providing a greater bandwidth for modulation. Figure 10-5 lists the\ncommon types of DSL, although some providers offer faster speeds, such as 100 Mbps down and 20 Mbps\nup.\n10.3.2 Cable Modem\nOne alternative to DSL is the cable modem, a digital service offered by cable television companies. The\nData over Cable Service Interface Specification (DOCSIS) standard is the dominant one. DOCSIS\nis not a formal standard but is the one used by most vendors of hybrid fiber coax (HFC) networks (i.e.,\ncable networks that use both fiber-optic and coaxial cable). As with DSL, these technologies are changing\nrapidly.\nFIGURE 10-5 Some typical digital subscriber line data rates\nArchitecture\nCable modem architecture is very similar to DSL\u2014with one very important difference. DSL is a point-to-\npoint technology, whereas cable modems use shared multipoint circuits. With cable modems, each user\nmust compete with other users for the available capacity. Furthermore, because the cable circuit is a\nmultipoint circuit, all messages on the circuit go to all computers on the circuit. If your neighbors were\nhackers, they could use pocket sniffers such as Wireshark (see Chapter 4) to read all messages that travel\nover the cable, including yours.\nFigure 10-6 shows the most common architecture for cable modems. The cable TV circuit enters the\ncustomer premises through a cable splitter that separates the data transmissions from the TV\ntransmissions and sends the TV signals to the TV network and the data signals to the cable modem. The\ncable modem (both a modem and frequency division multiplexer) translates from the cable data into\nEthernet packets, which then are directed into a computer to a router for distribution in a small network.", "source": "Page 335", "chapter_title": "Chapter 11"}
{"id": "8b15ac59e63a-1", "text": "As with DSL, cable modem companies usually combine all of these separate devices into one or two\ndevices to make it easier for the home consumer to install.\nThe cable TV wiring entering the customer premises is a standard coaxial cable. A typical segment of cable\nis shared by anywhere from 300 to 1,000 customers, depending on the cable company that installed the\ncable. These 300\u20131,000 customers share the available data capacity, but, of course, not all customers who\nhave cable TV will choose to install cable modems. This coax cable runs to a fiber node, which has an\noptical-electrical (OE) converter to convert between the coaxial cable on the customer side and fiber-\noptic cable on the cable TV company side. Each fiber node serves as many as half a dozen separate coaxial\ncable runs.", "source": "Page 335", "chapter_title": "Chapter 11"}
{"id": "6ccf88269671-0", "text": "FIGURE 10-6 Cable modem architecture. ISP = Internet service provider; POP = point of presence\nThe fiber nodes are in turn connected to the cable company distribution hub (sometimes called a\nheadend) through two separate circuits: an upstream circuit and a downstream circuit. The upstream\ncircuit, containing data traffic from the customer, is connected into a cable modem termination\nsystem (CMTS). The CMTS contains a series of cable modems/multiplexers and converts the data from\ncable modem protocols into protocols needed for Internet traffic, before passing them to a router\nconnected to an ISP POP. Often, the cable company is a regional ISP, but sometimes it just provides\nInternet access to a third-party ISP.\nThe downstream circuit to the customer contains both ordinary video transmissions from the cable TV\nvideo network and data transmissions from the Internet. Downstream data traffic enters the distribution\nhub from the ISP POP and is routed through the CMTS, which produces the cable modem signals. This\ntraffic is then sent to a combiner, which combines the Internet data traffic with the ordinary TV video\ntraffic and sends it back to the fiber node for distribution.\nTypes of Cable Modems\nThe DOCSIS standard provides many types of cable modems. The maximum speed is about 200 Mbps\ndownstream and about 200 Mbps upstream, although most cable TV companies provide at most 50 Mbps\ndownstream and 10 Mbps upstream. Cable modems can be configured to limit capacity, so the most\ncommon speeds offered by most cable providers range from 10 to 75 Mbps downstream and from 1 to 15\nMbps upstream. Of course, this capacity is shared, so an individual user will only see this when no other\ncomputers on his or her segment are active.\nMANAGEMENT FOCUS 10-2\nInternet Speed Test", "source": "Page 336", "chapter_title": "Chapter 11"}
{"id": "bdccef52ab01-0", "text": "The speed of your Internet connection depends on many things, such as your computer\u2019s settings,\nthe connection from your computer to your ISP, and the connections your ISP has into the Internet.\nMany Internet sites enable you to test how fast your Internet connection actually is. Our favorite is\nspeedtest.net\n10.3.3 Fiber to the Home\nFiber to the home (FTTH) is exactly what it sounds like: running fiber-optic cable into the home. The\ntraditional set of hundreds of copper telephone lines that run from the telephone company switch office is\nreplaced by one fiber-optic cable that is run past each house or office in the neighborhood. Data are\ntransmitted down the signal fiber cable using wavelength division multiplexing (WDM), providing\nhundreds or thousands of separate channels. FTTH is only available to about a quarter of the homes in the\nUnited States and Canada, but it is growing.\nArchitecture\nFTTH architecture is very similar to DSL and cable modem. At each subscriber location, an optical\nnetwork unit (ONU) (also called an optical network terminal [ONT]) acts like a DSL modem or cable\nmodem and converts the signals in the optical network into an Ethernet format. The ONU acts as an\nEthernet switch and can also include a router. FTTH is a dedicated point-to-point service like DSL, not a\nshared multipoint service like cable modem.\nProviders of fiber to the home can use either active optical networking or passive optical networking to\nconnect the ONU in the customer\u2019s home. Active networking means that the optical devices require\nelectrical power and works in much the same way as traditional electronic switches and routers. Passive\noptical networking devices require no electrical current and thus are quicker and easier to install and\nmaintain than traditional electrical-based devices, but because they are passive, the optical signal fades\nquickly, giving a maximum range of about 10 miles.", "source": "Page 337", "chapter_title": "Chapter 11"}
{"id": "9ed4fe5f81b0-1", "text": "quickly, giving a maximum range of about 10 miles.\nTypes of FTTH\nThere are many types of FTTH, and because FTTH is a new technology, these types are likely to evolve as\nFTTH enters the market and becomes more widely adopted. Most common carriers offer 1 Gbps services\u2014\nthat is 1 Gbps both up and down.\n10.4 THE FUTURE OF THE INTERNET\n10.4.1 Internet Governance\nBecause the Internet is a network of networks, no one organization operates the Internet. The closest\nthing the Internet has to an owner is the Internet Society (internetsociety.org). The Internet Society is\nan open-membership professional society with about 150 organizational members and 65,000 individual\nmembers in more than 100 countries, including corporations, government agencies, and foundations that\nhave created the Internet and its technologies. Because membership is open, anyone, including students,\nis welcome to join and vote on key issues facing the Internet.\nIts mission is to ensure \u201cthe open development, evolution and use of the Internet for the benefit of all\npeople throughout the world.\u201d It works in three general areas: public policy, education, and standards. In\nterms of public policy, the Internet Society participates in the national and international debates on\nimportant issues such as censorship, copyright, privacy, and universal access. It delivers training and\neducation programs targeted at improving the Internet infrastructure in developing nations. Its most\nimportant activity lies in the development and maintenance of Internet standards. It works through four\ninterrelated standards bodies: the Internet Engineering Task Force, Internet Engineering Steering Group,\nInternet Architecture Board, and Internet Research Task Force.\nThe Internet Engineering Task Force (IETF) (www.ietf.org) is a large, open international\ncommunity of network designers, operators, vendors, and researchers concerned with the evolution of the", "source": "Page 337", "chapter_title": "Chapter 11"}
{"id": "5feda3bde9f3-2", "text": "community of network designers, operators, vendors, and researchers concerned with the evolution of the\nInternet architecture and the smooth operation of the Internet. The IETF works through a series of", "source": "Page 337", "chapter_title": "Chapter 11"}
{"id": "fad58765013b-0", "text": "working groups, which are organized by topic (e.g., routing, transport, and security). The request for\ncomments (RFCs) that form the basis for Internet standards are developed by the IETF and its working\ngroups.\nClosely related to the IETF is the Internet Engineering Steering Group (IESG). The IESG is\nresponsible for technical management of IETF activities and the Internet standards process. It\nadministers the process according to the rules and procedures that have been ratified by the Internet\nSociety trustees. The IESG is directly responsible for the actions associated with entry into and movement\nalong the Internet \u201cstandards track,\u201d including final approval of specifications as Internet standards. Each\nIETF working group is chaired by a member of the IESG.\nWhereas the IETF develops standards and the IESG provides the operational leadership for the IETF\nworking groups, the Internet Architecture Board (IAB) provides strategic architectural oversight.\nThe IAB attempts to develop conclusions on strategic issues (e.g., top-level domain names, use of\ninternational character sets) that can be passed on as guidance to the IESG or turned into published\nstatements or simply passed directly to the relevant IETF working group. In general, the IAB does not\nproduce polished technical proposals but rather tries to stimulate action by the IESG or the IETF that will\nlead to proposals that meet general consensus. The IAB appoints the IETF chairperson and all IESG\nmembers, from a list provided by the IETF nominating committee. The IAB also adjudicates appeals when\nsomeone complains that the IESG has failed.\nThe Internet Research Task Force (IRTF) operates much like the IETF: through small research\ngroups focused on specific issues. Whereas IETF working groups focus on current issues, IRTF research", "source": "Page 338", "chapter_title": "Chapter 11"}
{"id": "9855796b998b-1", "text": "groups work on long-term issues related to Internet protocols, applications, architecture, and technology.\nThe IRTF chairperson is appointed by the IAB.\nTECHNICAL FOCUS 10-1\nRegistering an Internet Domain Name\nUntil the 1990s, there was only a moderate number of computers on the Internet. One organization\nwas responsible for registering domain names (sets of application layer addresses) and assigning IP\naddresses for each top-level domain (e.g., .COM). Network Solutions, for example, was the sole\norganization responsible for domain name registrations for the .COM, .NET, and .ORG domains. In\nOctober 1998, the Internet Corporation for Assigned Names and Numbers (ICANN) was\nformed to assume responsibility for the IP address space and domain name system management.\nIn spring 1999, ICANN established the Shared Registration System (SRS) that enabled many\norganizations to perform domain name registration and address assignment using a shared\ndatabase. More than 1,000 organizations are now accredited by ICANN as registrars and are\npermitted to use the SRS. Each registrar has the right to assign names and addresses in one or more\ntop-level domains. For a list of registrars and the domains they serve, see www.internic.com.\nIf you want to register a new domain name and obtain an IP address, you can contact any accredited\nregistrar for that top-level domain. One of the oldest privately operated registrars is register.com.\nEach registrar follows the same basic process for registering a name and assigning an address, but\neach may charge a different amount for its services. To register a name, you must first check to see if\nit is available (i.e., that no one else has registered it). If the name has already been registered, you\ncan find out who owns it and perhaps attempt to buy it from the owner.", "source": "Page 338", "chapter_title": "Chapter 11"}
{"id": "5d0b640f1b95-2", "text": "can find out who owns it and perhaps attempt to buy it from the owner.\nIf the domain name is available, you will need to provide the IP address of the DNS server that will\nbe used to store all IP addresses in the domain. Most large organizations have their own DNS\nservers, but small companies and individuals often use the DNS of their ISP.\n10.4.2 Building the Future\nThe Internet is changing. New applications and access technologies are being developed at lightning pace.\nBut these innovations do not change the fundamental structure of the Internet. It has evolved more slowly", "source": "Page 338", "chapter_title": "Chapter 11"}
{"id": "8021ad67650b-0", "text": "because the core technologies (TCP/IP) are harder to change gradually; it is difficult to change one part of\nthe Internet without changing the attached parts.\nMany organizations in many different countries are working on dozens of different projects in an attempt\nto design new technologies for the next version of the Internet. The two primary American projects\nworking on the future Internet got started at about the same time in 1996. The U.S. National Science\nFoundation provided $100 million to start the Next Generation Internet\u00ae (NGI) program, and 34\nuniversities got together to start what turned into Internet2\u00ae. Internet2 comprises about 400\nuniversities, corporations, government agencies, and organizations from more than 100 countries with a\nprimary focus to develop advanced networking as well as other innovative technologies for research and\neducation.\nInternet2\u00ae Figure 10-7 shows the major high-speed circuits in the Internet2\u00ae network. All the circuits in\nare at least OC-192 (10 Gbps). Many circuits are 100 Gbps, with 1 Tbps circuits being tested.\nThe access points are called gigapops, so named because they provide a POP at gigabit speeds. Gigapops\nalso usually provide a wider range of services than traditional IXPs, which are primarily just data\nexchange points. All of the gigapops provide connections at layer 1, the physical layer. Many of the\ngigapops also provide layer 2 connections (usually Ethernet) and layer 3 connections (usually IPv6).\nTypical connection fees range from $6,000 per year for 1 Gbps to $165,000 per year for 100 Gbps.\nBesides providing very-high-speed Internet connections, these networks are intended to experiment with\nnew protocols that 1 day may end up on the future Internet. For example, most circuits run IPv6 as the", "source": "Page 339", "chapter_title": "Chapter 11"}
{"id": "2d0cf09f7b4b-1", "text": "primary network layer protocol rather thanInternet2\u00aeIPv4. Most are also working on new ways to provide\nquality of service (QoS) and multicasting. is also developing new applications for a high-speed Internet,\nsuch as tele-immersion and videoconferencing.\nFIGURE 10-7 Internet2 network map\nReproduced by permission of Internet2\u00ae\n10.5 IMPLICATIONS FOR CYBER SECURITY", "source": "Page 339", "chapter_title": "Chapter 11"}
{"id": "35359156652d-0", "text": "As Internet speeds have gotten faster for the average user who has a DSL or cable modem connection in\nhis or her house, security at home has become increasingly important. The irony is that attackers break\ninto home computers not to attack them, but to use them to attack others in what is called a distributed\ndenial-of-service attack (DDOS). As we will discuss in the next chapter, the attacker plants DDOS software\non an unsuspecting user\u2019s home computer. Once the attacker has installed it on thousands of computers,\nhe activates all of them and they begin sending billions of messages to the website the attacker has\ntargeted. This site is so flooded with messages that normal users can\u2019t access it, and it becomes\nunavailable. And, of course, the user\u2019s own Internet is so flooded with outgoing messages that he or she\ncan\u2019t use the Internet, although that is just collateral damage to the attacker.\nDDOS software is most often contained in a video, a song, or a free application that the unsuspecting user\nhas downloaded. However, as the Internet of Things is growing and more consumer products are\nbecoming \u201csmart\u201d (e.g., TVs, thermostats, light bulbs), attackers are beginning to shift their attacks to\nthese devices because users often don\u2019t bother to update them as regularly as they update their computers\nor mobile phones. Typically, attackers find a bug (called a security hole) in a commonly used device such\nas a smart TV. They write software to search the Internet to find these devices and use the bug to trick the\ndevice into accepting the DDOS software.\nInterestingly, university students who live in dorms are a prime target. Most universities have very large\nInternet connections, so that a DDOS attack launched from within a university can do a lot more damage\nthan one launched from a home. There are many computers and smart devices in university dorms, often", "source": "Page 340", "chapter_title": "Chapter 11"}
{"id": "0e884d5a8aed-1", "text": "more than you would find in a typical classroom building, so it is a target-rich environment. Students\nusually are not as careful about security as professional university staff, so their devices are often softer\ntargets than university-managed computers.\nSUMMARY\nHow the Internet Works The Internet is a set of separate networks, ranging from large national\nISPs to midsize regional ISPs to small local ISPs, that connect with one another at IXPs. IXPs charge\nthe ISPs to connect, but similar-sized ISPs usually do not charge each other to exchange data. Each\nISP has a set of POP through which it charges its users (individuals, businesses, and smaller ISPs) to\nconnect to the Internet. Users connect to a POP to get access to the Internet. This connection may be\nvia DSL, cable modem, or a WAN circuit such as T1 or Ethernet.\nDSL DSL enables users to connect to an ISP POP over a standard point-to-point telephone line. The\ncustomer installs a DSL modem that connects via Ethernet to his or her computer system. The\nmodem communicates with a DSLAM at the telephone company office, which sends the data to the\nISP POP. ADSL is the most common type of DSL and often provides 24 Mbps downstream and 3\nMbps upstream.\nCable Modem Cable modems use a shared multipoint circuit that runs through the cable TV cable.\nThey also provide the customer with a modem that connects via Ethernet to his or her computer\nsystem. The modem communicates with a CMTS at the cable company office, which sends the data to\nthe ISP POP. The DOCSIS standard is the dominant standard, but there are no standard data rates\ntoday. Typical downstream speeds range between 10 and 75 Mbps, and typical upstream speeds range\nbetween 1 and 15 Mbps.", "source": "Page 340", "chapter_title": "Chapter 11"}
{"id": "ad44c77e7900-2", "text": "between 1 and 15 Mbps.\nFiber to the Home FTTH is a new technology that is not widely implemented. It uses fiber-optic\ncables to provide high-speed data services (e.g., 100 Mbps to 1 Gbps) to homes and offices.\nThe Future of the Internet The closest the Internet has to an owner is the Internet Society, which\nworks on public policy, education, and Internet standards. Standards are developed through four\nrelated organizations governed by the Internet Society. The IETF develops the actual standards\nthrough a series of working groups. The IESG manages IETF activities. The IAB sets long-term\nstrategic directions, and the IRTF works on future issues through working groups in much the same\nway as the IETF. Many different organizations are currently working on the next generation of the\nInternet, including Internet2.", "source": "Page 340", "chapter_title": "Chapter 11"}
{"id": "2ae933ca1580-0", "text": "KEY TERMS\nasymmetric DSL (ADSL)\nautonomous system\nbroadband technologies\ncable modem\ncable modem termination system (CMTS)\ncustomer premises equipment (CPE)\nData over Cable Service Interface Specification (DOCSIS)\ndigital subscriber line (DSL)\ndistribution hub\nDSL access multiplexer (DSLAM)\nDSL modem\nfiber to the home (FTTH)\ngigapop\nhybrid fiber coax (HFC)\nInternet Architecture Board (IAB)\nInternet Corporation for Assigned Names and Numbers (ICANN)\nInternet Engineering Steering Group (IESG)\nInternet Engineering Task Force (IETF)\nInternet exchange point (IXP)\nInternet Research Task Force (IRTF)\nInternet service provider (ISP)\nInternet Society\nInternet2\u00ae\nline splitter\nlocal loop\nmain distribution facility (MDF)\nnational ISPs\nNext Generation Internet (NGI)\noptical-electrical (OE) converter\noptical network unit (ONU)\npeering\npoint of presence (POP)\nregional ISP\nrequest for comment (RFC)\ntier 1 ISP\ntier 2 ISP\ntier 3 ISP", "source": "Page 341", "chapter_title": "Chapter 11"}
{"id": "72412558c666-0", "text": "QUESTIONS\n1. What is the basic structure of the Internet?\n2. Explain how the Internet is a network of networks.\n3. What is an IXP?\n4. What is a POP?\n5. Explain one reason why you might experience long response times in getting a Web page from a\nserver in your own city.\n6. What types of circuits are commonly used to build the Internet today? Internet2\u00ae What type of\ncircuits are commonly used to build?\n7. Compare and contrast cable modem and DSL.\n8. Explain how DSL works.\n9. How does a DSL modem differ from a DSLAM?\n10. Explain how ADSL works.\n11. Explain how a cable modem works.\n12. What is an OE converter? A CMTS?\n13. Which is better, cable modem or DSL? Explain.\n14. Explain how FTTH works.\n15. What are some future technologies that might change how we access the Internet?\n16. What are the principal organizations responsible for Internet governance, and what do they do?\n17. How is the IETF related to the IRTF?\n18. What is the principal American organization working on the future of the Internet?\n19. What is Internet2\u00ae?\n20. What is a gigapop?\n21. Today, there is no clear winner in the competition for broadband Internet access. What technology or\ntechnologies do you think will dominate in 2 years\u2019 time? Why?\n22. Would you be interested in subscribing to 1 Gbps FTTH (i.e., 1 Gbps both up and down) for a monthly\nprice of $150? Why or why not?\n23. Many experts predicted that small, local ISPs would disappear as regional and national ISPs began\noffering local access. This hasn\u2019t happened. Why?\nEXERCISES", "source": "Page 342", "chapter_title": "Chapter 11"}
{"id": "55f44386ea2c-1", "text": "offering local access. This hasn\u2019t happened. Why?\nEXERCISES\nA. Describe the current network structure of Internet2\u00ae.\nB. Provide the service details (e.g., pricing and data rates) for at least one high-speed Internet access\nservice provider in your area.\nC. Some people are wiring their homes for with Cat 5e for 1000Base-T. Suppose a friend who is building\na house asks you what\u2014if any\u2014wired network to put inside the house and what Internet access\ntechnology to use. What would you recommend?\nD. Provide service details (e.g., pricing and data rates) for FTTH in your area or a large city such as New\nYork or Los Angeles.\nE. Report the prices and available connections for one IXP, such as the Seattle IXP.", "source": "Page 342", "chapter_title": "Chapter 11"}
{"id": "6854047c32d9-0", "text": "MINICASES\nI. Cathy\u2019s Collectibles Your cousin Cathy runs a part-time business out of her apartment. She buys\nand sells collectibles such as antique prints, baseball cards, and cartoon cells and has recently\ndiscovered the Web with its many auction sites. She has begun buying and selling on the Web by\nbidding on collectibles at lesser-known sites and selling them at a profit at more well-known sites.\nShe downloads and uploads lots of graphics (pictures of the items she\u2019s buying and selling). She asks\nyou for advice. Figure 10-8 shows some of the available Internet services and their prices. Explain the\ndifferences in these services and make a recommendation.\nII. Surfing Sam Sam likes to surf the Web for fun, to buy things, and to research for his classes. Figure\n10-8 shows some of the available Internet services and their prices. Explain the differences in these\nservices and make a recommendation.\nIII. Cookies Are Us Cookies Are Us runs a series of 100 cookie stores across the midwestern United\nStates and central Canada. At the end of each day, the stores express-mail a USB drive of sales and\ninventory data to headquarters, which uses the data to ship new inventory and plan marketing\ncampaigns. They have decided to move data over a WAN or the Internet. What type of a WAN\ntopology and service (see Chapter 9) or Internet connection would you recommend? Figure 10-8\nshows some of the available Internet services and their prices, whereas Figure 9-20 in the previous\nchapter shows the WAN circuits.\nIV. Organic Foods Organic Foods operates organic food stores in Toronto. The store operates like a\ntraditional grocery store but offers only organically grown produce and meat, plus a wide array of\nhealth food products. Organic Foods sells memberships, and its 3,000 members receive a discount on", "source": "Page 343", "chapter_title": "Chapter 11"}
{"id": "3a93de1fa802-1", "text": "all products they buy. There are also special member events and sales promotions each month.\nOrganic Foods wants to open a new Internet site that will enable it to email its members monthly and\nprovide up-to-date information and announcements about new products, sales promotions, and\nmember events on its website. It has two options. First, it could develop the software on its own\nserver in its office and connect the office (and the server) to the Internet via DSL, T1, or similar\nconnection from its offices to an ISP (see Chapter 9, and Figure 9-20). Alternately, it could use\nAmazon or other cloud providers to host the website on its servers and just connect the office to the\nISP for Internet service. Figure 10-8 shows some of the available Internet services and their prices.\nWeb hosting would cost $100\u2013$300 per month, depending on the traffic. Which would you\nrecommend, and what size of an Internet connection would you recommend? Justify your choice.\nService\nData Rate\nMonthly Cost\nDown\nUp\nDSL\n3 Mbps\n512 Kbps\n$40\n6 Mbps\n640 Kbps\n$50\n50 Mbps\n50 Mbps\n$70\nCable Modem\n25 Mbps\n20 Mbps\n$60\n100 Mbps\n50 Mbps\n$80\n100 Mbps 100 Mbps\n$125\n150 Mbps 150 Mbps\n$150\n200 Mbps 200 Mbps\n$175\nFTTH\n1 Gbps\n1 Gbps\n$150\nFIGURE 10-8 Internet prices\nTECH UPDATES\nIn every chapter, we will offer a couple of ideas to investigate. Pick one of these topics to investigate.\nTopic A: Stuxnet", "source": "Page 343", "chapter_title": "Chapter 11"}
{"id": "5d7c88712187-0", "text": "Stuxnet is an extremely sophisticated computer worm that exploited multiple previously unknown\nWindows zero-day vulnerabilities to infect computers and spread. Its purpose was not just to infect PCs\nbut to cause real-world physical effects. It targets the types of industrial control systems (ICS) that are\ncommonly used in infrastructure supporting facilities (i.e., power plants, water treatment facilities, gas\nlines, etc.). How does Stuxnet work? Who created it? Does it still pose a threat?\nTopic B: The Dark Web and Tor\nThe Dark Web is part of the Internet that is not visible to the search engines we use every day and can only\nbe access by a special browser, called Tor. How did the Dark Web start? How created Tor and why? How\ndoes Tor work? Who pays for Tor (for the development and maintenance of its network of servers)? How\ncome governments cannot (or will not) shut it down? How is the Dark Web connected to cryptocurrency?\nSo many questions\u2026 Hopefully, you can provide answers to these questions.\nDeliverables\nYour job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title Slide\n2. Short description of the topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use a lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along\n5. How does it relate to material covered in class so far (and in the future)\n6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 10A\nSeeing the Internet", "source": "Page 344", "chapter_title": "Chapter 11"}
{"id": "94ec23d6c8e1-1", "text": "HANDS-ON ACTIVITY 10A\nSeeing the Internet\nThe Internet is a network of networks. One way to see this is by using the VisualRoute software.\nVisualRoute is a commercial package but provides a demonstration on its website. Go to visualroute.com\nand register to use their free service.\nThen enter a URL and watch as the route from your computer to the destination is traced and graphed.\nFigure 10-9 shows the route from my house in Indiana to the City University of Hong Kong.", "source": "Page 344", "chapter_title": "Chapter 11"}
{"id": "8b4a82555511-0", "text": "FIGURE 10-9 Visual trace route\nAnother interesting site is the Internet Traffic Report (www.internettrafficreport.com). This site shows\nhow busy the parts of the Internet are in real time. The main page enables you to see the current status of\nthe major parts of the world, including a \u201ctraffic index\u201d that rates performance on a 100-point scale. You\ncan also see the average response time at key Internet NAPs, MAEs, and peering points (at least those that\nhave agreed to be monitored), which is an average of 135 milliseconds. It also shows the global packet loss\nrates\u2014the percentage of packets discarded due to transmission errors (an average of 3% today).", "source": "Page 345", "chapter_title": "Chapter 11"}
{"id": "a1d7d5e6436c-0", "text": "FIGURE 10-10 Internet traffic reports\nBy clicking on a region of the world, you can see the same statistics for routers in that region. If you click\non a specific router, you can see a graph of its performance over the past 24 hours. Figure 10-10 shows the\nstatistics for one router operated by Sprint.\nYou can also get traffic reports for Internet2\u00ae at noc. net.internet2.edu/i2network/live-network-\nstatus.html.Internet2\u00ae. The \u201cweathermap,\u201d as calls it, shows traffic in both directions because the circuits\nare full duplex. You can also click on any circuit to see a graph of traffic over the last 24 hours.\nDeliverables\n1. Trace the route from your computer to CNN.com and to the University of Oxford www.ox.ac.uk\n2. Use the Internet traffic report to find the average response time and packet loss in Asia, Australia,\nand North America. Pick a router in North America and report its typical response time for the past\n24 hours.\n3. How busy are the Internet2\u00ae links from Chicago to Atlanta right now? What was the peak traffic on", "source": "Page 346", "chapter_title": "Chapter 11"}
{"id": "c4402084bf02-0", "text": "these circuits over the last 24 hours?\nHANDS-ON ACTIVITY 10B\nMeasuring Your Speed\nThe download and upload speeds you get on the Internet depend partly on the type of Internet access you\nhave. The speeds also depend on how your ISP is connected to other ISPs, how busy the Internet is today,\nand how busy the website you\u2019re working with is. The last two factors (Internet traffic and Web traffic at\nthe server) are beyond your control. However, you can choose what type of Internet connection you have\nand who your ISP is.\nMany sites on the Internet can test the speed of your Internet connection. Our favorite speed site is\nspeedtest.net. Speedtest.net has lots of advertising; ignore it (and any \u201cwindows scan\u201d offer) and just do\nthe speed test. You begin by selecting a server for the test. I selected a server in Nova Scotia and tested\nhow fast the connection was between it and my computer in Indiana, which is connected to the Internet\nusing Comcast\u2019s cable modem service. Figure 10-11 shows that my download speed was 28.86 Mbps and\nmy upload speed was 5.63 Mbps. I ran the same test to a server closer to my computer in Indiana and got\nabout the same speeds. The speeds to a server in Mexico were about 1.5 Mbps down and 1.0 up.\nDeliverable\nTest the upload and download speeds to a server close to your computer and to one far away from you.\nFIGURE 10-11 A speed test on my computer in Indiana\nHANDS-ON ACTIVITY 10C\nApollo Residence Network Design\nApollo is a luxury residence hall that will serve honor students at your university. We described the\nresidence in Hands-On Activities at the end of Chapters 7 and 8.", "source": "Page 347", "chapter_title": "Chapter 11"}
{"id": "5cf454307b95-0", "text": "Your university has a good Internet2\u00aeconnection to the Internet through the high-speed network, which\nyou\u2019ll recall is a network that connects about 400 research and education organizations around the world\nover some very-high-speed Internet circuits. While much of the Internet traffic from the university goes to\nand comes from theInternet2\u00ae, other universities and organizations that are part of a substantial portion\nof traffic goes to and comes from the commercial Internet. This is especially true for traffic generated by\nundergraduate students who make up the majority of the intended population of the Apollo Residence.\nTherefore, the university has decided to build a second connection into the Internet for primary use by the\nstudents of the Apollo Residence. This Internet connection will also provide a backup connection for\nInternet2\u00ae, the university\u2019s main Internet connection, just in case it experiences problems.\nDeliverable\nYour team was hired to select the Internet circuit. Figure 10-8 provides a list of possible Internet services\nyou can use. Specify what service(s) you will use. Provide the estimated monthly operating cost of the\ncircuit(s).", "source": "Page 348", "chapter_title": "Chapter 11"}
{"id": "a31450ecdabf-0", "text": "PART THREE NETWORK MANAGEMENT", "source": "Page 349", "chapter_title": "Chapter 11"}
{"id": "5c47287b28a3-0", "text": "CHAPTER 11\nNETWORK SECURITY\nThis chapter describes why networks need security and how to provide it. The first step in any security\nplan is risk assessment, understanding the key assets that need protection, and assessing the risks to each.\nA variety of steps can be taken to prevent, detect, and correct security problems due to disruptions,\ndestruction, disaster, and unauthorized access.\nOBJECTIVES\nBe familiar with the major threats to network security\nBe familiar with how to conduct a risk assessment\nUnderstand how to ensure business continuity\nUnderstand how to prevent intrusion\nOUTLINE\n11.1 Introduction\n11.1.1 Why Networks Need Security\n11.1.2 Types of Security Threats\n11.1.3 Network Controls\n11.2 Risk Assessment\n11.2.1 Develop Risk Measurement Criteria\n11.2.2 Inventory IT Assets\n11.2.3 Identify Threats\n11.2.4 Document Existing Controls\n11.2.5 Identify Improvements\n11.3 Ensuring Business Continuity\n11.3.1 Virus Protection\n11.3.2 Denial-of-Service Protection\n11.3.3 Theft Protection\n11.3.4 Device Failure Protection\n11.3.5 Disaster Protection\n11.4 Intrusion Prevention\n11.4.1 Security Policy\n11.4.2 Perimeter Security and Firewalls\n11.4.3 Server and Client Protection\n11.4.4 Encryption\n11.4.5 User Authentication\n11.4.6 Preventing Social Engineering\n11.4.7 Intrusion Prevention Systems", "source": "Page 350", "chapter_title": "Chapter 11"}
{"id": "dc4cc3f81826-0", "text": "11.4.8 Intrusion Recovery\n11.5 Best Practice Recommendations\n11.6 Implications for Your Cyber Security\nSummary\n11.1 INTRODUCTION\nBusiness and government have always been concerned with physical and information security. They have\nprotected physical assets with locks, barriers, guards, and the military since organized societies began.\nThey have also guarded their plans and information with coding systems for at least 3,500 years. What\nhas changed in the last 50 years is the introduction of computers and the Internet.\nThe rise of the Internet has completely redefined the nature of information security. Now companies face\nglobal threats to their networks and, more importantly, to their data. Malware such as viruses and\nransomware has long been a problem, but credit card theft and identity theft, two of the fastest-growing\ncrimes, pose an immense liability to firms who fail to protect their customers\u2019 data. Laws have been slow\nto catch up, despite the fact that breaking into a computer in the United States\u2014even without causing\ndamage\u2014is a federal crime punishable by a fine and/or imprisonment. Nonetheless, we have a new kind\nof transborder cybercrime against which laws may apply but that will be very difficult to enforce. The\nUnited States and Canada may extradite and allow prosecution of digital criminals operating within their\nborders, but investigating, enforcing, and prosecuting transnational cybercrime across different borders is\nmuch more challenging. And even when someone is caught, he or she faces a lighter sentence than a bank\nrobber.\nComputer security has become increasingly important with the Sarbanes-Oxley Act (SOX) and the Health\nInsurance Portability and Accountability Act (HIPAA). However, despite these measures, the number of\nsecurity incidents is growing by about 30% per year. In 2016, about 50 million passwords were stolen. A", "source": "Page 351", "chapter_title": "Chapter 11"}
{"id": "9bcf55f5c119-1", "text": "survey of 1,500 U.S. adults found that 51% had experienced some form of a cybersecurity incident in 2016.\nThese incidents included not only malware such as viruses but also industrial espionage, fraud, extortion\n(ransomware), and identity theft. In the early days of the Internet, creating a virus and breaking into\nwebsites was mainly done by young adults craving excitement. Those days are gone. Today\u2019s goal is\nmoney.\nYou probably heard on the news that the large companies Zappos and Target had been victims of\ncyberattacks and that millions of the credit card information of millions of their customers had been\nstolen. However, a company of any size can be the target of an attack. According to Symantec, more than\n50% of all targeted companies had fewer than 2,500 employees because they often have weaker security.\nMany organizations, private and public, focus on helping individuals, organizations, and governments to\nprotect themselves from criminals operating on the Internet (cybercriminals). These include CERT\n(Computer Emergency Response Team) at Carnegie Mellon University, APWG (Anti-Phishing Working\nGroup), the Russian-based Kaspersky Lab, McAfee, and Symantec.\nThere are three main reasons why there has been an increase in computer security over the past few years.\nFirst, in the past, hacking into somebody\u2019s computer was considered to be a hobby, but today being a\ncybercriminal is a profession. There are professional organizations that one can hire to break into\ncomputer networks of specific targets to steal information. We are not talking about ethical hacking (when\na company hires another company to test its security) but rather hackers who, for a fee, will steal credit\ncards, personal information, or intellectual property. These attacks are called targeted attacks, in which", "source": "Page 351", "chapter_title": "Chapter 11"}
{"id": "cda05d9c692d-2", "text": "cards, personal information, or intellectual property. These attacks are called targeted attacks, in which\ncybercriminals not only try to exploit technical vulnerabilities but also try to \u201chack the human\u201d via social\nengineering or phishing emails. These targeted attacks can be very sophisticated, and any organization\ncan become a victim because every organization has data that can be of value to cybercriminals.\nSecond, hacktivism (the use of hacking techniques to bring attention to a larger political or social goal) has\nbecome more common. Hacktivism combines illegal hacking techniques with digital activism and usually\ntargets large organizations and governments by sabotaging or defacing their public websites to bring\nattention to the hackers\u2019 social or political cause. For example, the group called Anonymous has taken", "source": "Page 351", "chapter_title": "Chapter 11"}
{"id": "a232b3ed4bda-0", "text": "down websites owned by Visa and MasterCard to protest their denial of payments to WikiLeaks. This type\nof threat is not as pervasive as that from cybercriminals, but it has increased in the past few years.\nThird, the increase in mobile devices offers a very fertile environment for exploitation. More and more\nfrequently, we access our bank accounts, buy items on Amazon, and use our business data through our\nmobile devices, so cybercriminals are now targeting these mobile devices. These types of attacks are often\neasier to develop because mobile security is typically weaker than computer security, so they offer a\npotentially high yield.\nThese trends will increase the value of personal data, and, therefore, the potential threat to our privacy\nand the privacy of businesses will increase. It is thus very important for businesses and also individuals to\nunderstand their assets, potential threats to these assets, and the way they can protect them. We explore\nthese in the next section of this chapter.\n11.1.1 Why Networks Need Security\nIn recent years, organizations have become increasingly dependent on data communication networks for\ntheir daily business communications, database information retrieval, distributed data processing, and the\ninternetworking of LANs. The rise of the Internet with opportunities to connect computers and mobile\ndevices anywhere in the world has significantly increased the potential vulnerability of the organization\u2019s\nassets. Emphasis on network security also has increased as a result of well-publicized security break-ins\nand as government regulatory agencies have issued security-related pronouncements.\nThe losses associated with security failures can be huge. An average data breach costs about $3.5 million,\nbut this is just the tip of the iceberg. The potential loss of consumer confidence from a well-publicized\nsecurity break-in can cost much more in lost business. More important than these, however, are the\npotential losses from the disruption of application systems that run on computer networks. As", "source": "Page 352", "chapter_title": "Chapter 11"}
{"id": "3ab79910ffe8-1", "text": "potential losses from the disruption of application systems that run on computer networks. As\norganizations have come to depend on computer systems, computer networks have become \u201cmission-\ncritical.\u201d Bank of America, one of the largest banks in the United States, estimates that it would cost the\nbank $50 million if its computer networks were unavailable for 24 hours. Other large organizations have\nproduced similar estimates.\nProtecting customer privacy and the risk of identity theft also drive the need for increased network\nsecurity. In 2016, the European Union passed a strong data privacy law, called the General Data\nProtection Regulation (GDPR), on data protection and privacy in the European Union. GDPR also\naddresses the transfer of private information outside of the EU thus influencing international business. In\nthe United States, organizations have begun complying with the data protection requirements of HIPAA\nand a California law providing fines up to $250,000 for each unauthorized disclosure of customer\ninformation (e.g., if someone were to steal 100 customer records, the fine could be $25 million).\nAs you might suspect, the value of the data stored on most organizations\u2019 networks and the value provided\nby the application systems in use far exceeds the cost of the networks themselves. For this reason, the\nprimary goal of network security is to protect organizations\u2019 data and application software, not the\nnetworks themselves.\n11.1.2 Types of Security Threats\nFor many people, security means preventing intrusion, such as preventing an attacker from breaking into\nyour computer. Security is much more than that, however. There are three primary goals in providing\nsecurity: confidentiality, integrity, and availability (also known as CIA). Confidentiality refers to the\nprotection of organizational data from unauthorized disclosure of customer and proprietary data.\nIntegrity is the assurance that data have not been altered or destroyed. Availability means providing", "source": "Page 352", "chapter_title": "Chapter 11"}
{"id": "8c07813af724-2", "text": "Integrity is the assurance that data have not been altered or destroyed. Availability means providing\ncontinuous operation of the organization\u2019s hardware and software so that staff, customers, and suppliers\ncan be assured of no interruptions in service.\nThere are many potential threats to confidentiality, integrity, and availability. In general, security threats\ncan be classified into two broad categories: ensuring business continuity and preventing unauthorized\naccess.\nEnsuring business continuity refers primarily to ensuring availability, with some aspects of data\nintegrity. There are three main threats to business continuity. Disruptions are the loss of or reduction in", "source": "Page 352", "chapter_title": "Chapter 11"}
{"id": "afde8c1944b5-0", "text": "network service. Disruptions may be minor and temporary. For example, a network switch might fail or a\ncircuit may be cut, causing part of the network to cease functioning until the failed component can be\nreplaced. Some users may be affected, but others can continue to use the network. Some disruptions may\nalso be caused by or result in the destruction of data. For example, a virus may destroy files, or the \u201ccrash\u201d\nof a hard disk may cause files to be destroyed. Other disruptions may be catastrophic. Natural (or human-\nmade) disasters may occur that destroy host computers or large sections of the network. For example,\nhurricanes, fires, floods, earthquakes, mudslides, tornadoes, or terrorist attacks can destroy large parts of\nthe buildings and networks in their path.\nPreventing unauthorized access, also referred to as intrusion, refers primarily to confidentiality, but\nalso integrity, as an intruder may change important data. Intrusion is often viewed as external attackers\ngaining access to organizational data files and resources from across the Internet. However, almost half of\nall intrusion incidents involve employees. An intrusion may have only minor effects. A curious intruder\nmay simply explore the system, gaining knowledge that has little value. A more serious intruder may be a\ncompetitor bent on industrial espionage who could attempt to gain access to information on products\nunder development, or the details and price of a bid on a large contract, or a thief trying to steal customer\ncredit card numbers or information to carry out identity theft. Worse still, the intruder could change files\nto commit fraud or theft or could destroy the information to injure the organization.\nMANAGEMENT FOCUS 11-1\nSame Old Same Old\nNo matter the industry, every company should consider itself to be a target of cybercrime\u2014Target", "source": "Page 353", "chapter_title": "Chapter 11"}
{"id": "019eff472f39-1", "text": "No matter the industry, every company should consider itself to be a target of cybercrime\u2014Target\nlearned this the hard way in December 2013. Russian hacker(s) were able to install malware on the\ncompany\u2019s point-of-sale systems (cash registers) and steal the credit card information of more than\n40 million individuals.\nHackers probably got access to Target\u2019s network using the credentials of an HVAC vendor.\nInvestigators said that the malware installed on the point-of-sale systems was neither sophisticated\nnor novel and was detected by two security systems that Target had installed on its network. Why\ndidn\u2019t security specialists listen to the warnings from their security software? Target, just like any\nother company, gets bombarded by thousands of attacks each day, and the likelihood of one of them\ngetting through increases each day\u2014just a simple logic of probability. Although some attacks are\nsophisticated, most of them are well known. One can say, same old same old. Cyberattackers are\nplaying the game of numbers\u2014the more persistent they are in their attacks, the more likely they will\nget inside a network and gain access to critical information such as credit card numbers.\nThis only reminds us that cybersecurity is a global problem and that everybody who uses the Internet\ncan be and probably is under attack. Therefore, learning about security and investing in it is\nnecessary to survive and strive in the Internet era.\nSource: Adapted from \u201cMissed Alarms and 40 Million Stolen Credit Card Numbers: How Target Blew It,\u201d by Michael Riley, Ben\nElgin, Dune Lawrence, and Carol Matlack, Bloomberg Businessweek (www.businessweek.com) and Krebs on Security\n(krebsonsecuirty.com).\n11.1.3 Network Controls\nDeveloping a secure network means developing controls. Controls are software, hardware, rules, or", "source": "Page 353", "chapter_title": "Chapter 11"}
{"id": "a87b9c6c1477-2", "text": "Developing a secure network means developing controls. Controls are software, hardware, rules, or\nprocedures that reduce or eliminate the threats to network security. Controls prevent, detect, and/or\ncorrect whatever might happen to the organization because of threats facing its computer-based systems.\nPreventive controls mitigate or stop a person from acting or an event from occurring. For example, a\npassword can prevent illegal entry into the system, or a set of second circuits can prevent the network\nfrom crashing. Preventive controls also act as a deterrent by discouraging or restraining someone from\nacting or proceeding because of fear or doubt. For example, a guard or a security lock on a door may deter\nan attempt to gain illegal entry.", "source": "Page 353", "chapter_title": "Chapter 11"}
{"id": "774daceb71b2-0", "text": "Detective controls reveal or discover unwanted events. For example, software that looks for illegal\nnetwork entry can detect these problems. They also document an event, a situation, or an intrusion,\nproviding evidence for subsequent action against the individuals or organizations involved or enabling\ncorrective action to be taken. For example, the same software that detects the problem must report it\nimmediately so that someone or some automated process can take corrective action.\nCorrective controls remedy an unwanted event or an intrusion. Either computer programs or humans\nverify and check data to correct errors or fix a security breach so it will not recur in the future. They also\ncan recover from network errors or disasters. For example, the software can recover and restart the\ncommunication circuits automatically when there is a data communication failure.\nThe remainder of this chapter discusses the various controls that can be used to prevent, detect, and\ncorrect threats. We also present a general risk assessment framework for identifying the threats and their\nassociated controls. This framework provides a network manager with a good view of the current threats\nand any controls that are in place to mitigate the occurrence of threats.\nNonetheless, it is important to remember that it is not enough just to establish a series of controls;\nsomeone or some department must be accountable for the control and security of the network. This\nincludes being responsible for developing controls, monitoring their operation, and determining when\nthey need to be updated or replaced.\nControls must be reviewed periodically to be sure that they are still useful and must be verified and tested.\nVerifying ensures that the control is present, and testing determines whether the control is working as\noriginally specified.\nIt is also important to recognize that there may be occasions in which a person must temporarily override\na control, for instance, when the network or one of its software or hardware subsystems is not operating", "source": "Page 354", "chapter_title": "Chapter 11"}
{"id": "84a033826e65-1", "text": "properly. Such overrides should be tightly controlled, and there should be a formal procedure to\ndocument this occurrence should it happen.\n11.2 RISK ASSESSMENT\nThe first step in developing a secure network is to conduct a risk assessment. There are several\ncommonly used risk assessment frameworks that provide strategies for analyzing and prioritizing the\nsecurity risks to information systems and networks. A risk assessment should be simple so that both\ntechnical and nontechnical readers can understand it. After reading a risk assessment, anyone should be\nable to see which systems and network components are at high risk for attack or abuse and which are at\nlow risk. Also, the reader should be able to see what controls have been implemented to protect him or her\nand what new controls need to be implemented.\nThree risk assessment frameworks are commonly used:\n1. Operationally Critical Threat, Asset, and Vulnerability Evaluation (OCTAVE) from the Computer\nEmergency Readiness Team\n2. Control Objectives for Information and Related Technology (COBIT) from the Information Systems\nAudit and Control Association\n3. Risk Management Guide for Information Technology Systems (NIST guide) from the National\nInstitute of Standards and Technology\nEach of these frameworks offers a slightly different process with a different focus. However, they share\nfive common steps:\n1. Develop risk measurement criteria\n2. Inventory IT assets\n3. Identify threats\n4. Document existing controls\n5. Identify improvements", "source": "Page 354", "chapter_title": "Chapter 11"}
{"id": "ac406eca13f8-0", "text": "11.2.1 Develop Risk Measurement Criteria\nRisk measurement criteria are the measures used to evaluate the way a security threat could affect the\norganization. For example, suppose that a hacker broke in and stole customer credit card information\nfrom a company server. One immediate impact to the organization is financial, because some customers\nare likely to stop shopping, at least in the short term. Depending where the company is located, there may\nalso be some legal impact because some countries and/or states have laws concerning the unauthorized\nrelease of personal information. There also may be longer-term impacts on the company\u2019s reputation.\nEach organization needs to develop its own set of potential business impacts, but the five most commonly\nconsidered impact areas are financial (revenues and expenses), productivity (business operations),\nreputation (customer perceptions), safety (the health of customers and employees), and legal\n(potential for fines and litigation). However, some organizations add other impacts and not all\norganizations use all of these five because some may not apply. It is important to remember that these\nimpacts are for information systems and networks, so although safety is important to most organizations,\nthere may be little impact on safety from information systems and network problems.\nOnce the impact areas have been identified, the next step is to prioritize them. Not all impact areas are\nequally important to all organizations. Some areas may be a high priority, some medium, and some low.\nFor example, for a hospital, safety may be the highest priority and financial the lowest. In contrast, for a\nrestaurant, information systems and networks may pose a low (or nonexistent) safety risk (because they\nare not involved in food safety) but a high priority reputation risk (if, for example, credit card data were\nstolen). There may be a temptation to say every impact is a high priority, but this is the same as saying", "source": "Page 355", "chapter_title": "Chapter 11"}
{"id": "dcf7dcae989c-1", "text": "that all impacts are medium, because you cannot distinguish between them when it comes time to take\naction.\nThe next step is to develop specific measures of what could happen in each impact area and what we\nwould consider a high, medium, and low impact. For example, one financial impact could be a decrease\nin sales. What would we consider a low financial impact in terms of a decrease in sales: 1%? 2%? What\nwould be a high impact on sales? These are business decisions, not technology decisions, so they should\nbe made by the business leaders.\nFigure 11-1 has sample risk measurement criteria for a Web-based bookstore. As you can see, only four of\nthe impact areas apply for this company, because information systems and network security problems\nwould not harm the safety of employees or customers. However, it would be a different case if this were a\npharmaceutical company. A threat, such as malware, could cause changes in how a drug is prepared,\npotentially harming customers (patients) and also employees.\nAs Figure 11-1 suggests, our fictional Web-based book company believes that financial and reputation\nimpacts have high priority, whereas productivity and legal impacts are medium. This figure also provides\nmetrics for assessing the impact of each risk. For example, our fictitious company considers it a low\nfinancial impact if their sales were to drop by 2% because of security problems. The financial impact\nwould be high if they were to lose more than 10% of sales.\nImpact\nArea\nPriority Low Impact\nMedium Impact\nHigh Impact\nFinancial\nHigh\nSales drop by less than\n2%\nSales drop by 2\u201310%\nSales drop by more than\n10%\nProductivity Medium Increase in annual\noperating expenses by\nless than 3%\nIncrease in annual\noperating expenses between\n3% and 6%", "source": "Page 355", "chapter_title": "Chapter 11"}
{"id": "63d974e7cc89-2", "text": "Increase in annual\noperating expenses between\n3% and 6%\nIncrease in annual\noperating expenses by\nmore than 6%\nReputation\nHigh\nDecrease in number of\ncustomers by less than\n2%\nDecrease in number of\ncustomers by 2\u201315%\nDecrease in number of\ncustomers by more than\n15%\nLegal\nMedium Incurring fines or legal\nfees less than $10,000\nIncurring fines or legal fees\nbetween $10,000 and\n$60,000\nIncurring fines or legal\nfees exceeding $60,000\nFIGURE 11-1 Sample risk measurement criteria for a Web-based bookstore", "source": "Page 355", "chapter_title": "Chapter 11"}
{"id": "4262600ab58b-0", "text": "Hardware\nServers, such as mail servers, Web servers, DNS servers, DHCP servers, and\nLAN file servers\nClient computers\nDevices such as switches and routers\nCircuits\nLocally operated circuits such as LANs and backbones\nContracted circuits such as WAN circuits\nInternet access circuits\nNetwork software\nServer operating systems and system settings\nApplication software such as mail server and Web server software\nClient software\nOperating systems and system settings\nApplication software such as word processors\nOrganizational data\nDatabases with organizational records\nMission-critical\napplications\nFor example, for an Internet bank, its website is mission-critical\nFIGURE 11-2 Types of assets. DNS = Domain Name Service; DHCP = Dynamic Host Control Protocol;\nLAN = local area network; WAN = wide area network\n11.2.2 Inventory IT Assets\nAn asset is something of value and can be either hardware, software, data, or applications. Figure 11-2\ndefines six common categories of IT assets.\nAn important type of asset is the mission-critical application, which is an information system that is\ncritical to the survival of the organization. It is an application that cannot be permitted to fail, and if it\ndoes fail, the network staff drops everything else to fix it. For example, for an Internet bank that has no\nbrick-and-mortar branches, the website is a mission-critical application. If the website crashes, the bank\ncannot conduct business with its customers. Mission-critical applications are usually clearly identified so\nthat their importance is not overlooked.\nThe next most important type of asset is the organization\u2019s data. For example, suppose someone were to\ndestroy a mainframe computer worth $10 million. The computer could be replaced simply by buying a\nnew one. It would be expensive, but the problem would be solved in a few weeks. Now suppose someone", "source": "Page 356", "chapter_title": "Chapter 11"}
{"id": "125749c2e834-1", "text": "were to destroy all the student records at your university so that no one would know what courses anyone\nhad taken or their grades. The cost would far exceed the cost of replacing a $10 million computer. The\nlawsuits alone would easily exceed $10 million, and the cost of staff to find and reenter paper records\nwould be enormous and certainly would take more than a few weeks.\nOnce all assets are identified, they need to be rated for importance. To order them, you need to answer\nquestions such as, what would happen if this information asset\u2019s confidentiality, integrity, or accessibility\nwere compromised? This will allow you to assess the importance of this asset as low, medium, or high.\nYou need also to document each asset, not just information assets, and briefly describe why each asset is\ncritical to the organization. Finally, the owners of each asset are recorded. Figure 11-3 summarizes some\ntypical assets found in most organizations.\nTECHNICAL FOCUS 11-1\nBasic Control Principles of a Secure Network\nThe less complex a control, the better.\nA control\u2019s cost should be equivalent to the identified risk. It often is not possible to ascertain\nthe expected loss, so this is a subjective judgment in many cases.\nPreventing a security incident is always preferable to detecting and correcting it after it occurs.\nAn adequate system of internal controls is one that provides \u201cjust enough\u201d security to protect", "source": "Page 356", "chapter_title": "Chapter 11"}
{"id": "e2806d051a47-0", "text": "the network, taking into account both the risks and costs of the controls.\nAutomated controls (computer-driven) always are more reliable than manual controls that\ndepend on human interaction.\nControls should apply to everyone, not just a few select individuals.\nWhen a control has an override mechanism, make sure that it is documented and that the\noverride procedure has its own controls to avoid misuse.\nInstitute the various security levels in an organization based on \u201cneed to know.\u201d If you do not\nneed to know, you do not need to access the network or the data.\nThe control documentation should be confidential.\nNames, uses, and locations of network components should not be publicly available.\nControls must be sufficient to ensure that the network can be audited, which usually means\nkeeping historical transaction records.\nWhen designing controls, assume that you are operating in a hostile environment.\nAlways convey an image of high security by providing education and training.\nMake sure the controls provide the proper separation of duties. This applies especially to those\nwho design and install the controls and those who are responsible for everyday use and\nmonitoring.\nIt is desirable to implement entrapment controls in networks to identify attackers who gain\nillegal access.\nWhen a control fails, the network should default to a condition in which everyone is denied\naccess. A period of failure is when the network is most vulnerable.\nControls should still work even when only one part of a network fails. For example, if a\nbackbone network fails, all LANs connected to it should still be operational, with their own\nindependent controls providing protection.\nDon\u2019t forget the LAN. Security and disaster recovery planning has traditionally focused on host\nmainframe computers and WANs. However, LANs now play an increasingly important role in\nmost organizations but are often overlooked by central site network managers.\nAlways assume your opponent is smarter than you.", "source": "Page 357", "chapter_title": "Chapter 11"}
{"id": "1a31b4559f00-1", "text": "Always assume your opponent is smarter than you.\nAlways have insurance as the last resort should all controls fail.\n11.2.3 Identify Threats\nA threat is any potential occurrence that can do harm, interrupt the systems using the network, or cause\na monetary loss to the organization.\nFigure 11-4 summarizes the most common types of threats and their likelihood of occurring based on\nseveral surveys in recent years. This figure shows the percentage of organizations experiencing each threat\nin a typical year but not whether the threat caused damage. For example, 100% of companies reported\nexperiencing one or more malware attacks such as viruses or ransomware, but in most cases, their\nantivirus software prevented any problems. Another common threat is information theft, whether by\nphishing (where an attacker sends an email to trick employees into revealing their passwords), or other\nmeans such as via a security hole or social engineering. Other less common threats are the theft of\nequipment, device failure, denial of service, sabotage (where an attacker changes data), or a natural\ndisaster such as a fire or flood.\nAsset\nImportance Most\nImportant\nSecurity\nRequirement\nDescription\nOwner(s)", "source": "Page 357", "chapter_title": "Chapter 11"}
{"id": "959b6ee5ee90-0", "text": "Customer\ndatabase\nHigh\n\u2022\nConfidentiality\n\u2022 Integrity\n\u2022 Availability\nThis database contains all customers\u2019 records,\nincluding address and credit card information.\nVP of\nMarketing\nCIO\nWeb server High\n\u2022\nConfidentiality\n\u2022 Integrity\n\u2022 Availability\nThis is used by our customers to place orders. It is\nvery important that it would be available 24/7.\nCIO\nMail server Medium\n\u2022\nConfidentiality\n\u2022 Integrity\n\u2022 Availability\nThis is used by employees for internal\ncommunication. It is very important that no one\nintercepts this communication as sensitive\ninformation is shared via email.\nCIO\nFinancial\nrecords\nHigh\n\u2022\nConfidentiality\n\u2022 Integrity\n\u2022 Availability\nThese records are used by the C-level executives\nand also by the VP of operations. It is imperative\nthat nobody else but the C-team be able to access\nthis mission information.\nCFO\nEmployees\u2019\ncomputers\nLow\n\u2022\nConfidentiality\n\u2022 Integrity\n\u2022 Availability\nEach employee is assigned to a cubical that has a\ndesktop computer in it. Employees provide\ncustomer service and support for our website\nusing these computers.\nDivision\ndirectors\nFIGURE 11-3 Sample inventory of assets for a Web-based bookstore\nFIGURE 11-4 Likelihood of a threat\nThe actual probability of a threat to your organization depends on your business. A bank, for example, is\nmore likely to be a target of phishing than a family-owned store. The most frequent targets are healthcare\nproviders, financial services firms, and government agencies, likely because they have the most valuable\ndata.\nThe next step is to create threat scenarios. A threat scenario describes how an asset can be", "source": "Page 358", "chapter_title": "Chapter 11"}
{"id": "e2209ea6a0a9-0", "text": "compromised by one specific threat. An asset can be compromised by more than one threat, so it is\ncommon to have more than one threat scenario for each asset. For example, the confidentiality, integrity,\nand/or availability of the client data database in Figure 11-3 can be compromised by an attacker stealing\ninformation (confidentiality), an attacker changing information (integrity), or a natural disaster\ndestroying information or the hardware on which it is stored (availability).\nWhen preparing a threat scenario, we name the asset, describe the threat, explain the consequence\n(violation of confidentiality, integrity, or availability), and estimate the likelihood of this threat happening\n(high, medium, or low).\nFigure 11-5 provides an example of a threat scenario for one asset (the customer database) of a Web-based\nbookstore. The top half of the threat scenario describes the risk associated with the asset from the threat,\nwhile the bottom half (shaded in color) describes the existing controls that have been implemented to\nprotect the asset from this threat. This step focuses on the top half of the threat scenario, whereas the next\nstep (Section 11.2.4) describes the bottom half.\nA threat scenario begins with the name of the asset and the threat being considered. The threat is\ndescribed and the likelihood of its occurrence is assessed as high, medium, or low. Then the potential\nimpact is identified, whether this is confidentiality, integrity, or availability. Some threats could have\nmultiple impacts.\nNext, the consequences of the threat are assessed, using the impact areas identified in step 1 and their\npriority (e.g., reputation, financial, productivity, safety, and legal). We identify the impact that each\nscenario could have on each priority area, high, medium, or low, using the risk measurement criteria", "source": "Page 359", "chapter_title": "Chapter 11"}
{"id": "26dc0b057375-1", "text": "defined in step 1. We calculate an impact score by multiplying the priority of each area by the impact the\nthreat would have, using a 1 for a low value, a 2 for a medium value, and a 3 for a high value, and\nsumming all the results to produce an impact score.\nFinally, we can calculate the relative risk score by multiplying the impact score by the likelihood (using 1\nfor low likelihood, 2 for medium likelihood, and 3 for high likelihood).\nFigure 11-5 shows that the risk score for information theft from the customer database is 50. The absolute\nnumber does not really tell us anything. Instead, we compare the risk scores among all the different threat\nscenarios to help us identify the most important risks we face.\nFigure 11-6 shows the threat scenario for a tornado strike against our customer database. Take a moment\nand compare the two threat scenarios. You can see that the tornado risk score is 14, which shows that\ninformation theft is a greater risk than a tornado.\nIn these examples, we have used only three values (high, medium, and low) to assess likelihood, priority,\nand impact. Some organizations use more complex scoring systems. And nothing says that likelihood,\npriority, and impact have to use the same scales. Some organizations use 5-point scales for priority, 7-\npoint scales for impact, and 100-point scales for likelihood.\n11.2.4 Document Existing Controls\nOnce the specific assets, threat scenarios, and their risk scores have been identified, you can begin to work\non the risk control strategy, which is the way an organization intends to address a risk. In general, an\norganization can accept the risk, mitigate it, share it, or defer it. If an organization decides to accept a", "source": "Page 359", "chapter_title": "Chapter 11"}
{"id": "60d674662807-2", "text": "risk, it means the organization will be taking no action to address it and accept the stated consequences.\nIn general, these risks have very low impact on the organization.\nRisk mitigation involves implementation of some type of a control to counter the threat or to minimize\nthe impact. An organization can implement several types of controls, such as using antivirus software,\nimplementing state-of-the-art firewalls, or providing security training for employees.\nAn organization can decide to share the risk. In this case, it purchases insurance against the risk. For\nexample, you share a risk for getting into a car accident. It is quite unlikely that you will be in a car\naccident, but if it were to happen, you want to make sure that the insurance company can step in and pay\nfor all the damages. Similarly, an organization may decide to purchase insurance against information theft\nor damage from a tornado. Sharing and mitigation can be done simultaneously.\nFinally, the organization can defer the risk. This usually happens when there is a need to collect additional", "source": "Page 359", "chapter_title": "Chapter 11"}
{"id": "f1dcf406448c-0", "text": "information about the threat and the risk. These risks are usually not imminent and, if they were to occur,\nwould not significantly impact the organization.", "source": "Page 360", "chapter_title": "Chapter 11"}
{"id": "a0f8ed600a13-0", "text": "FIGURE 11-5 Threat scenario for theft of customer information", "source": "Page 361", "chapter_title": "Chapter 11"}
{"id": "1ea63d3165a5-0", "text": "FIGURE 11-6 Threat scenario for destruction of customer information by a tornado\nFor each threat scenario, the risk control strategy needs to be specified. If the organization decides to\nmitigate and/or share the risk, specific controls need to be listed. The next two sections in this chapter\ndescribe numerous controls that can be used to mitigate the security risks organizations face.\nOnce the existing controls have been documented, an overall assessment of their adequacy is done. This\nassessment produces a value that is relative to the risk, such as high adequacy (meaning the controls are\nexpected to strongly control the risks in the threat scenario), medium adequacy (meaning some", "source": "Page 362", "chapter_title": "Chapter 11"}
{"id": "074aebb63fa3-0", "text": "improvements are possible), or low adequacy (meaning improvements are needed to effectively mitigate\nor share the risk). Once again, some organizations use more complex scales such as a letter grade (A, A\u2212,\nA+, B, etc.) or 100-point scales.\nThe bottom sections of the threat scenarios in Figures 11-5 and 11-6 show the strategy, controls, and their\nadequacy for both threat scenarios. For the theft of information, the Web-based bookstore has already\nimplemented several risk mitigation strategies: encryption, a firewall, personnel policies, training, and\nautomatic screen lock. For the tornado, the company implemented a database backup and a disaster\nrecovery plan. Both have been assessed as medium adequacy.\nAt this point, you may or may not understand the controls described in these figures. However, after you\nread the rest of the chapter, you will understand what each control is and how it works to mitigate the risk\nfrom the threat.\n11.2.5 Identify Improvements\nThe final step in risk assessment\u2014and its ultimate goal\u2014is to identify what improvements are needed.\nMost organizations face so many threats that they cannot afford to mitigate all of them to the highest\nlevel. They need to focus first on the highest risks; the threat scenarios with the highest risk scores are\ncarefully examined to ensure that there is at least a medium level of control adequacy. Besides, the most\nimportant assets\u2019 security requirements (labeled as high in Figure 11-3) are adequately protected.\nAdditional controls that could be implemented to improve the risk mitigation are considered, as are ways\nto share the risk. As mentioned earlier, Sections 11.3 and 11.4 describe many different controls that can be\nimplemented to mitigate the risks associated with the loss of business continuity and unauthorized access.", "source": "Page 363", "chapter_title": "Chapter 11"}
{"id": "dee4aeb8601b-1", "text": "implemented to mitigate the risks associated with the loss of business continuity and unauthorized access.\nThe second focus is on threat scenarios whose mitigation controls have low adequacy. Ideally, these will\nall be low-risk threats, but they are examined to ensure the level of expenditure matches the level of risk.\n11.3 ENSURING BUSINESS CONTINUITY\nBusiness continuity means that the organization\u2019s data and applications will continue to operate even in\nthe face of disruption, destruction, or disaster. A business continuity plan has two major parts: the\ndevelopment of controls that will prevent these events from having a major impact on the organization,\nand a disaster recovery plan that will enable the organization to recover if a disaster occurs. In this\nsection, we discuss controls designed to prevent, detect, and correct these threats. We focus on the major\nthreats to business continuity: viruses, theft, denial of service attacks, device failure, and disasters.\nBusiness continuity planning is sometimes overlooked because intrusion is more often the subject of news\nreports.\n11.3.1 Virus Protection\nSpecial attention must be paid to preventing malware such as computer viruses and ransomware.\nSome are harmless and just cause nuisance messages, but others are serious, such as those that destroy\ndata if you don\u2019t pay the ransom. In most cases, disruptions or the destruction of data are local and affect\nonly a small number of computers. Such disruptions are usually fairly easy to deal with; the virus is\nremoved and the network continues to operate. Ransomware can cause widespread destruction.\nMost malware attaches itself to other programs or USB drives. As those files execute or the USB is\naccessed, the malware spreads. Macro viruses, viruses that are contained in documents, emails, or\nspreadsheet files, can spread when an infected file is simply opened. Some viruses change their\nappearances as they spread, making detection more difficult.", "source": "Page 363", "chapter_title": "Chapter 11"}
{"id": "a639a2247de3-2", "text": "appearances as they spread, making detection more difficult.\nA worm is a special type of virus that spreads itself without human intervention. Many viruses attach\nthemselves to a file and require a person to copy the file, but a worm copies itself from computer to\ncomputer. Worms spread when they install themselves on a computer and then send copies of themselves\nto other computers, sometimes by emails, sometimes via security holes in software. (Security holes are\ndescribed later in this chapter.)\nThe best way to prevent the spread of viruses is to install antivirus software such as that by Symantec.\nMost organizations automatically install antivirus software on their computers, but many people fail to", "source": "Page 363", "chapter_title": "Chapter 11"}
{"id": "45aa6f50f569-0", "text": "install them on their home computers. Antivirus software is only as good as its last update, so it is critical\nthat the software is updated regularly. Be sure to set your software to update automatically.\nMANAGEMENT FOCUS 11-2\nAuditors Are Your Friend\nSecurity is now a major business issue, not just a technical one. Since bad security can have a major\nimpact on a firm\u2019s financial performance, cybersecurity is now a key part of most financial audits.\nMost technical people focus on the technology first, and documentation second. How much attention\ndid you spend on documenting your code in your programming class?\nIn contrast, auditors focus first on documentation and repeatable business processes. It is not\ndocumented, it never happened.\nWhile this may sound like oil and water that never mix\u2014with the resulting problems\u2014it can be a\nvery positive situation if managed properly. Auditors require the technical staff to double-check and\nprove that important security controls are in place. And the documentation they require can help\nwhen technical staff leave and are replaced with new people.\nAuditors have also prompted some important improvements in security. Software vendors now\nprovide software that not only ensures security but also provides documentation on what controls\nare in place, which is useful for auditors and the technical security team. Interestingly, some\nsoftware now starts with the documentation for auditors and then once the desired system has been\ndocumented, it implements it throughout the firm (this is desktop management software as\ndescribed in the next chapter).\nMalware is often spread by downloading files from the Internet, so do not copy or download files of\nunknown origin (e.g., music, videos, screen savers), or at least check every file you do download. Always\ncheck all files for malware before using them (even those from friends!). Researchers estimate that 10 new", "source": "Page 364", "chapter_title": "Chapter 11"}
{"id": "9b9a7d5d6e3e-1", "text": "viruses are developed every day, so it is important to frequently update the virus information files that are\nprovided by the antivirus software.\n11.3.2 Denial-of-Service Protection\nWith a denial-of-service (DoS) attack (also called a distributed denial-of-service (DDoS)\nattack), an attacker attempts to disrupt the target by flooding it with messages so that it cannot process\nmessages from normal users. The simplest approach is to flood a Web server, DNS server, mail server, and\nso on, with incoming messages. The server attempts to respond to these, but there are so many messages\nthat it cannot.\nOne might expect that it would be possible to filter messages from one source IP so that if one user floods\nthe network, the messages from this person can be filtered out before they reach the Web server being\ntargeted. This could work, but most attackers use tools that enable them to put false source IP addresses\non the incoming messages so that it is difficult to recognize a message as a real message or a DoS message.\nWith a DDoS attack, the attacker breaks into and takes control of thousands computers or smart devices\n(e.g., TVs) and plants software on them called a DDoS agent (or sometimes a zombie or a bot). The\nattacker then uses software called a DDoS handler (sometimes called a botnet) to control the agents.\nThe handler issues instructions to the computers under the attacker\u2019s control, which simultaneously begin\nsending messages to the target site (see Figure 11-7). Some DDoS attacks have sent more than one billion\npackets per second at the target.\nThere are several approaches to preventing DoS and DDoS attacks from affecting the network. The first is\nto configure the main router that connects your network to the Internet (or the firewall, which will be", "source": "Page 364", "chapter_title": "Chapter 11"}
{"id": "5456c32816ba-2", "text": "discussed later in this chapter) to verify that the source address of all incoming messages is in a valid\naddress range for that connection (called traffic filtering). For example, if an incoming message has a\nsource address from inside your network, then it is obviously a false address. This ensures that only", "source": "Page 364", "chapter_title": "Chapter 11"}
{"id": "8e7bd2230381-0", "text": "messages with valid addresses are permitted into the network, although it requires more processing in the\nrouter and thus slows incoming traffic.\nA second approach is to configure the main router (or firewall) to limit the number of incoming packets\nthat could be DoS/DDoS attack packets that it allows to enter the network, regardless of their source\n(called traffic limiting). Technical Focus 11-2 describes some of the types of DoS/DDoS attacks and the\npackets used. Such packets have the same content as legitimate packets that should be permitted into the\nnetwork. It is a flood of such packets that indicates a DoS/DDoS attack, so by discarding packets over a\ncertain number that arrive each second, one can reduce the impact of the attack. The disadvantage is that\nduring an attack, some valid packets from regular customers will be discarded, so they will be unable to\nreach your network. Thus, the network will continue to operate, but some customer packets (e.g., Web\nrequests, emails) will be lost.\nFIGURE 11-7 A distributed denial-of-service attack\nFIGURE 11-8 Traffic analysis reduces the impact of denial-of-service attacks\nA third and more sophisticated approach is to use a special-purpose security device, called a traffic", "source": "Page 365", "chapter_title": "Chapter 11"}
{"id": "8de3e64a43d9-0", "text": "anomaly detector, that is installed in front of the main router (or firewall) to perform traffic analysis.\nThis device monitors normal traffic patterns and learns what normal traffic looks like. Most DoS/DDoS\nattacks target a specific server or device so when the anomaly detector recognizes a sudden burst of\nabnormally high traffic destined for a specific server or device, it quarantines those incoming packets but\nallows normal traffic to flow through into the network. This results in minimal impact on the network as a\nwhole. The anomaly detector reroutes the quarantined packets to a traffic anomaly analyzer (see\nFigure 11-8). The anomaly analyzer examines the quarantined traffic, attempts to recognize valid source\naddresses and \u201cnormal\u201d traffic, and selects which of the quarantined packets to release into the network.\nThe detector can also inform the router owned by the ISP that is sending the traffic into the organization\u2019s\nnetwork to reroute the suspect traffic to the anomaly analyzer, thus avoiding the main circuit leading into\nthe organization. This process is never perfect, but it is significantly better than the other approaches.\nMANAGEMENT FOCUS 11-3\nDDoS Attacks for Hire?\nAlthough the idea of DDoS is not new, they have increased by 1,000% since 2010, partially because\nyou can now hire a hacker who will attack anyone you like for a fee. On hacker forums, hackers\nadvertise their ability to take websites down. All you need to do is to reach them via a message on\nthis forum and negotiate the fee.\nDDoS attacks are also used as a test for hackers wanting to join these hacker groups. The leader of a\nhacker group will give a target website to an aspiring member, and the hacker has to prove that he or\nshe can bring the website down. The target websites are selected based on the security measures they", "source": "Page 366", "chapter_title": "Chapter 11"}
{"id": "c4f0b4dd4c88-1", "text": "she can bring the website down. The target websites are selected based on the security measures they\nhave to protect themselves against attacks, so this task can be simple or quite complex based on the\ntest target selected.\nDDoS attacks are here to stay because they are no longer a hobby but a source of income for\ncybercriminals. Attackers are now able to bombard a target at more than 300 Gbps.\nSource: Adapted from \u201cThe New Normal: 200\u2013400 Gbps DDoS Attacks,\u201d Krebs on Security (krebsonsecurity.com).\nTECHNICAL FOCUS 11-2\nInside a DoS Attack\nA DoS attack typically involves the misuse of standard TCP/IP protocols or connection processes so\nthat the target for the DoS attack responds in a way designed to create maximum trouble. Five\ncommon types of attacks include the following:\nICMP Attacks The network is flooded with ICMP echo requests (i.e., pings) that have a\nbroadcast destination address and a faked source address of the intended target. Because it is a\nbroadcast message, every computer on the network responds to the faked source address so that\nthe target is overwhelmed by responses. Because there are often dozens of computers in the\nsame broadcast domain, each message generates dozens of messages at the target.\nUDP Attacks This attack is similar to an ICMP attack, except that it uses UDP echo requests\ninstead of ICMP echo requests.\nTCP SYN Floods The target is swamped with repeated SYN requests to establish a TCP\nconnection, but when the target responds (usually to a faked source address), there is no\nresponse. The target continues to allocate TCP control blocks, expects each of the requests to be\ncompleted, and gradually runs out of memory.\nUNIX Process Table Attacks This is similar to a TCP SYN flood, but instead of TCP SYN", "source": "Page 366", "chapter_title": "Chapter 11"}
{"id": "c406525d6530-2", "text": "UNIX Process Table Attacks This is similar to a TCP SYN flood, but instead of TCP SYN\npackets, the target is swamped by UNIX open connection requests that are never completed.\nThe target allocates open connections and gradually runs out of memory.", "source": "Page 366", "chapter_title": "Chapter 11"}
{"id": "adb5d50a0e71-0", "text": "Finger of Death Attacks This is similar to the TCP SYN flood, but instead, the target is\nswamped by finger requests that are never disconnected.\nDNS Recursion Attacks The attacker sends DNS requests to DNS servers (often within the\ntarget\u2019s network) but spoofs the from address so the requests appear to come from the target\ncomputer that is overwhelmed by DNS responses. DNS responses are larger packets than ICMP,\nUDP, or SYN responses, so the effects can be stronger.\nSource: Adapted from \u201cWeb Site Security and Denial of Service Protection,\u201d www.nwfusion.com.\nAnother possibility under discussion by the Internet community as a whole is to require Internet service\nproviders (ISPs) to verify that all incoming messages they receive from their customers have valid source\nIP addresses. This would prevent the use of fake IP addresses and enable users to easily filter out DDoS\nmessages from a given address and make it much harder for a DDoS attack to succeed. Because small- to\nmedium-sized businesses often have poor security and are the unwilling accomplices in DDoS attacks,\nmany ISPs are beginning to impose security restrictions on them, such as requiring firewalls to prevent\nunauthorized access (firewalls are discussed later in this chapter).\n11.3.3 Theft Protection\nOne often overlooked security risk is theft. Computers and network equipment are commonplace items\nthat have a good resale value. Several industry sources estimate that more than $1 billion is lost to\ncomputer theft each year, with many of the stolen items ending up on Internet auction sites (e.g., eBay).\nPhysical security is a key component of theft protection. Most organizations require anyone entering\ntheir offices to go through some level of physical security. For example, most offices have security guards\nand require all visitors to be authorized by an organization employee. Universities are one of the few", "source": "Page 367", "chapter_title": "Chapter 11"}
{"id": "d643083015a9-1", "text": "and require all visitors to be authorized by an organization employee. Universities are one of the few\norganizations that permit anyone to enter their facilities without verification. Therefore, you\u2019ll see most\ncomputer equipment and network devices protected by locked doors or security cables so that someone\ncannot easily steal them (see Figure 11-9).\nOne of the most common targets for theft is laptop computers. More laptop computers are stolen from\nemployees\u2019 homes, cars, and hotel rooms than any other device. Airports are another common place for\nlaptop theft. It is hard to provide physical security for traveling employees, but most organizations provide\nregular reminders to their employees to take special care when traveling with laptops. Nonetheless, they\nare still the most commonly stolen device.", "source": "Page 367", "chapter_title": "Chapter 11"}
{"id": "48b504c262bb-0", "text": "FIGURE 11-9 Security cables protecting computers\n11.3.4 Device Failure Protection\nEventually, every computer network device, cable, or leased circuit will fail. It\u2019s just a matter of time.\nSome computers, devices, cables, and circuits are more reliable than others, but every network manager\nhas to be prepared for failure.\nThe best way to prevent a failure from impacting business continuity is to build redundancy into the\nnetwork. For any network component that would have a major impact on business continuity, the network\ndesigner provides a second, redundant component. For example, if the Internet connection is important\nto the organization, the network designer ensures that there are at least two connections into the Internet\n\u2014each provided by a different common carrier so that if one common carrier\u2019s network goes down, the\norganization can still reach the Internet via the other common carrier\u2019s network. This means, of course,\nthat the organization now requires two routers to connect to the Internet, because there is little use in\nhaving two Internet connections if they both run through the same router; if that one router goes down,\nhaving a second Internet connection provides no value.\nThis same design principle applies to the organization\u2019s internal networks. If the core backbone is\nimportant (and it usually is), then the organization must have two core backbones, each served by\ndifferent devices. Each distribution backbone that connects to the core backbone (e.g., a building\nbackbone that connects to a campus backbone) must also have two connections (and two routers) into the\ncore backbone.\nThe next logical step is to ensure that each access layer LAN also has two connections into the distribution\nbackbone. Redundancy can be expensive, so at some point, most organizations decide that not all parts of\nthe network need to be protected. Most organizations build redundancy into their core backbone and their", "source": "Page 368", "chapter_title": "Chapter 11"}
{"id": "0770bc10ea98-1", "text": "the network need to be protected. Most organizations build redundancy into their core backbone and their\nInternet connections but are very careful in choosing which distribution backbones (i.e., building\nbackbones) and access layer LANs will have redundancy.\nOnly those building backbones and access LANs that are truly important will have redundancy. This is\nwhy a risk assessment is important because it is too expensive to protect the entire network. Most\norganizations only provide redundancy in mission-critical backbones and LANs (e.g., those that lead to\nservers).", "source": "Page 368", "chapter_title": "Chapter 11"}
{"id": "6e1c32bc0cf1-0", "text": "Redundancy also applies to servers. Most organizations use a server farm, rather than a single server so\nthat if one server fails, the other servers in the server farm continue to operate and there is little impact.\nSome organizations use fault-tolerant servers that contain many redundant components so that if one\nof its components fails, it will continue to operate.\nRedundant array of independent disks (RAID) is a storage technology that, as the name suggests,\nis made of many separate disk drives. When a file is written to a RAID device, it is written across several\nseparate, redundant disks.\nThere are several types of RAID. RAID 0 uses multiple disk drives and therefore is faster than traditional\nstorage, because the data can be written or read in parallel across several disks, rather than sequentially\non the same disk. RAID 1 writes duplicate copies of all data on at least two different disks; this means that\nif one disk in the RAID array fails, there is no data loss because there is a second copy of the data stored\non a different disk. This is sometimes called disk mirroring because the data on one disk is copied (or\nmirrored) onto another. RAID 2 provides error checking to ensure no errors have occurred during the\nreading or writing process. RAID 3 provides a better and faster error checking process than RAID 2. RAID\n4 provides slightly faster read access than RAID 3 because of the way it allocates the data to different disk\ndrives. RAID 5 provides slightly faster read and write access because of the way it allocates the error\nchecking data to different disk drives. RAID 6 can survive the failure of two drives with no data loss.\nPower outages are one of the most common causes of network failures. An uninterruptible power\nsupply (UPS) is a device that detects power failures and permits the devices attached to it to operate as", "source": "Page 369", "chapter_title": "Chapter 11"}
{"id": "865032dc749a-1", "text": "long as its battery lasts. UPS for home use are inexpensive and often provide power for up to 15 minutes\u2014\nlong enough for you to save your work and shut down your computer. UPS for large organizations often\nhave batteries that last for an hour and permit mission-critical servers, switches, and routers to operate\nuntil the organization\u2019s backup generator can be activated.\n11.3.5 Disaster Protection\nA disaster is an event that destroys a large part of the network and computing infrastructure in one part of\nthe organization. Disasters are usually caused by natural forces (e.g., hurricanes, floods, earthquakes,\nfires), but some can be human-made (e.g., arson, bombs, terrorism).\nAvoiding Disaster\nIdeally, you want to avoid a disaster, which can be difficult. For example, how do you avoid an\nearthquake? There are, however, some commonsense steps you can take to avoid the full impact of a\ndisaster from affecting your network. The most fundamental is again redundancy; store critical data in at\nleast two very different places, so if a disaster hits one place, your data are still safe.\nOther steps depend on the disaster to be avoided. For example, to avoid the impact of a flood, key network\ncomponents and data should never be located near rivers or in the basement of a building. To avoid the\nimpact of a tornado, key network components and data should be located underground. To reduce the\nimpact of fire, a fire suppression system should be installed in all key data centers. To reduce the impact\nof terrorist activities, the location of key network components and data should be kept a secret and should\nbe protected by security guards.\nDisaster Recovery\nA critical element in correcting problems from a disaster is the disaster recovery plan, which should\naddress various levels of response to a number of possible disasters and should provide for partial or", "source": "Page 369", "chapter_title": "Chapter 11"}
{"id": "ea09c7056f5a-2", "text": "address various levels of response to a number of possible disasters and should provide for partial or\ncomplete recovery of all data, application software, network components, and physical facilities. A\ncomplete disaster recovery plan covering all these areas is beyond the scope of this text. Figure 11-10\nprovides a summary of many key issues. A good example of a disaster recovery plan is MIT\u2019s business\ncontinuity plan at web.mit.edu/security/www/pubplan.htm. Some firms prefer the term business\ncontinuity plan.\nA good disaster recovery plan should include the following:\nThe name of the decision-making manager who is in charge of the disaster recovery operation. A", "source": "Page 369", "chapter_title": "Chapter 11"}
{"id": "bef0510e411a-0", "text": "second manager should be indicated in case the first manager is unavailable.\nStaff assignments and responsibilities during the disaster.\nA preestablished list of priorities that states what is to be fixed first.\nLocation of alternative facilities operated by the company or a professional disaster recovery\nfirm and procedures for switching operations to those facilities using backups of data and\nsoftware.\nRecovery procedures for the data communication facilities (backbone network, metropolitan\narea network, wide area network, and local area network), servers, and application systems.\nThis includes information on the location of circuits and devices, whom to contact for\ninformation, and the support that can be expected from vendors, along with the name and\ntelephone number of the person at each vendor to contact.\nAction to be taken in case of partial damage or threats such as bomb threats, fire, water or\nelectrical damage, sabotage, civil disorders, and vendor failures.\nManual processes to be used until the network is functional.\nProcedures to ensure adequate updating and testing of the disaster recovery plan.\nStorage of the data, software, and the disaster recovery plan itself in a safe area where they\ncannot be destroyed by a catastrophe. This area must be accessible, however, to those who need\nto use the plan.\nFIGURE 11-10 Elements of a disaster recovery plan\nThe most important elements of the disaster recovery plan are backup and recovery controls that\nenable the organization to recover its data and restart its application software should some portion of the\nnetwork fail. The simplest approach is to make backup copies of all organizational data and software\nroutinely and to store these backup copies off-site. Most organizations make daily backups of all critical\ninformation, with less important information (e.g., email files) backed up weekly. Backups used to be\ndone on tapes that were physically shipped to an off-site location, but more and more, companies are", "source": "Page 370", "chapter_title": "Chapter 11"}
{"id": "452fbe88ee2a-1", "text": "using their WAN connections to transfer data to remote locations (it\u2019s faster and cheaper than moving\ntapes). Backups should always be encrypted (encryption is discussed later in the chapter) to ensure that\nno unauthorized users can access them.\nContinuous data protection (CDP) is another option that firms are using in addition to or instead of\nregular backups. With CDP, copies of all data and transactions on selected servers are written to CDP\nservers as the transaction occurs. CDP is more flexible than traditional backups that take snapshots of\ndata at specific times or than disk mirroring, which duplicates the contents of a disk from second to\nsecond. CDP enables data to be stored miles from the originating server and time-stamps all transactions\nto enable organizations to restore data to any specific point in time. For example, suppose a virus brings\ndown a server at 2:45 p.m. The network manager can restore the server to the state it was in at 2:30 p.m.\nand simply resume operations as though the virus had not hit.\nBackups and CDP ensure that important data are safe, but they do not guarantee the data can be used.\nThe disaster recovery plan should include a documented and tested approach to recovery. The recovery\nplan should have specific goals for different types of disasters. For example, if the main database server\nwas destroyed, how long should it take the organization to have the software and data back in operation\nby using the backups? Conversely, if the main data center was completely destroyed, how long should it\ntake? The answers to these questions have very different implications for costs. Having a spare network\nserver or a server with extra capacity that can be used in the event of the loss of the primary server is one\nthing. Having a spare data center ready to operate within 12 hours (for example) is an entirely different\nproposition.", "source": "Page 370", "chapter_title": "Chapter 11"}
{"id": "3e4911753d7f-2", "text": "proposition.\nMany organizations have a disaster recovery plan, but only a few test their plans. A disaster recovery\ndrill is much like a fire drill in that it tests the disaster recovery plan and provides staff the opportunity to\npractice little-used skills to see what works and what doesn\u2019t work before a disaster happens and the staff\nmust use the plan for real. Without regular disaster recovery drills, the only time a plan is tested is when it\nmust be used. For example, when an island-wide blackout shut down all power in Bermuda, the backup", "source": "Page 370", "chapter_title": "Chapter 11"}
{"id": "4ef3fd084676-0", "text": "generator in the British Caymanian Insurance office automatically took over and kept the company\noperating. However, the key-card security system, which was not on the generator, shut down, locking out\nall employees and forcing them to spend the day at the beach. No one had thought about the security\nsystem and the plan had not been tested.\nOrganizations are usually much better at backing up important data than are individual users. When did\nyou last back up the data on your computer? What would you do if your computer was stolen or\ndestroyed? There is an inexpensive alternative to CDP for home users. Online backup services such as\nmozy.com enable you to back up the data on your computer to their server on the Internet. You download\nand install client software that enables you to select what folders to back up. After you back up the data for\nthe first time, which takes a while, the software will run every few hours and automatically back up all\nchanges to the server, so you never have to think about backups again. If you need to recover some or all\nof your data, you can go to their website and download it.\nMANAGEMENT FOCUS 11-4\nDisaster Recovery Hits Home\n\u201cThe building is on fire\u201d were the first words she said as I answered the phone. It was just before\nnoon and one of my students had called me from her office on the top floor of the business school at\nthe University of Georgia. The roofing contractor had just started what would turn out to be the\nworst fire in the region in more than 20 years, although we didn\u2019t know it then. I had enough time to\ngather up the really important things from my office on the ground floor (memorabilia, awards, and\npictures from 10 years in academia) when the fire alarm went off. I didn\u2019t bother with the computer;", "source": "Page 371", "chapter_title": "Chapter 11"}
{"id": "4117274aa531-1", "text": "all the files were backed up off-site.\nTen hours, 100 firefighters, and 1.5 million gallons of water later, the fire was out. Then our work\nbegan. The fire had completely destroyed the top floor of the building, including my 20-computer\nnetworking lab. Water had severely damaged the rest of the building, including my office, which, I\nlearned later, had been flooded by almost 2 feet of water at the height of the fire. My computer and\nvirtually all the computers in the building were damaged by the water and unusable.\nMy personal files were unaffected by the loss of the computer in my office; I simply used the backups\nand continued working\u2014after making new backups and giving them to a friend to store at his house.\nThe Web server I managed had been backed up to another server on the opposite side of campus 2\ndays before (on its usual weekly backup cycle), so we had lost only 2 days\u2019 worth of changes. In less\nthan 24 hours, our website was operational; I had our server\u2019s files mounted on the university\nlibrary\u2019s Web server and redirected the university\u2019s DNS server to route traffic from our old server\naddress to our new temporary home.\nUnfortunately, the rest of our network did not fare as well. The Business School\u2019s primary Web\nserver had been backed up to tape the night before, and though the tapes were stored off-site, the\ntape drive was not; the tape drive was destroyed and no one else on campus had one that could read\nthe tapes; it took 5 days to get a replacement and reestablish the website. Within 30 days we were\noperating from temporary offices with a new network, and 90% of the office computers and their\ndata had been successfully recovered.", "source": "Page 371", "chapter_title": "Chapter 11"}
{"id": "08e5259b0c77-2", "text": "data had been successfully recovered.\nLiving through a fire changes a person. I\u2019m more careful now about backing up my files, and I move\nmuch more quickly when a fire alarm sounds.\nSource: Alan Dennis.\nDisaster Recovery Outsourcing\nMost large organizations have a two-level disaster recovery plan. When they build networks, they build\nenough capacity and have enough spare equipment to recover from a minor disaster such as loss of a\nmajor server or a portion of the network (if any such disaster can truly be called minor). This is the first\nlevel. Building a network that has sufficient capacity to quickly recover from a major disaster such as the", "source": "Page 371", "chapter_title": "Chapter 11"}
{"id": "11e3f0b6a2d4-0", "text": "loss of an entire data center is beyond the resources of most firms. Therefore, most large organizations\nrely on professional disaster recovery firms to provide this second-level support for major disasters.\nMany large firms outsource their disaster recovery efforts by hiring disaster recovery firms that\nprovide a wide range of services. At the simplest, disaster recovery firms provide secure storage for\nbackups. Full services include a complete networked data center that clients can use when they experience\na disaster. Once a company declares a disaster, the disaster recovery firm immediately begins recovery\noperations using the backups stored on-site and can have the organization\u2019s entire data network back in\noperation on the disaster recovery firm\u2019s computer systems within hours. Full services are not cheap, but\ncompared to the potential millions of dollars that can be lost per day from the inability to access critical\ndata and application systems, these systems quickly pay for themselves in time of disaster.\n11.4 INTRUSION PREVENTION\nIntrusion is the second main type of security problem and the one that tends to receive the most attention.\nNo one wants an intruder breaking into his or her network.\nFour types of intruders may attempt to gain unauthorized access to computer networks. The first are\ncasual intruders who have only a limited knowledge of computer security. They simply cruise along the\nInternet trying to access any computer they come across. Their unsophisticated techniques are the\nequivalent of trying doorknobs, and, until recently, only those networks that left their front doors\nunlocked were at risk. Unfortunately, a variety of hacking tools are now available on the Internet that\nenable even novices to launch sophisticated intrusion attempts. Novice attackers who use such tools are\nsometimes called script kiddies.\nThe second type of intruders are experts in security, but their motivation is the thrill of the hunt. They", "source": "Page 372", "chapter_title": "Chapter 11"}
{"id": "06bc1cb36395-1", "text": "break into computer networks because they enjoy the challenge and enjoy showing off for friends or\nembarrassing the network owners. These intruders are called hackers and often have a strong\nphilosophy against ownership of data and software. Most cause little damage and make little attempt to\nprofit from their exploits, but those who do can cause major problems. Hackers who cause damage are\noften called crackers.\nThe third type of intruder is the most dangerous. They are professional hackers who break into corporate\nor government computers for specific purposes, such as espionage, fraud, or intentional destruction. The\nU.S. Department of Defense (DoD), which routinely monitors attacks against U.S. military targets, has\nuntil recently concluded that most attacks are individuals or small groups of hackers in the first two\ncategories. While some of their attacks have been embarrassing (e.g., defacement of some military and\nintelligence websites), there have been no serious security risks. However, in the late 1990s, the DoD\nnoticed a small but growing set of intentional attacks that they classify as exercises, exploratory attacks\ndesigned to test the effectiveness of certain software attack weapons. Therefore, they established an\ninformation warfare program and a new organization responsible for coordinating the defense of\nmilitary networks under the U.S. Space Command.\nThe fourth type of intruder is also very dangerous. These are organization employees who have legitimate\naccess to the network but who gain access to information they are not authorized to use. This information\ncould be used for their own personal gain, sold to competitors, or fraudulently changed to give the\nemployee extra income. Many security break-ins are caused by this type of intruder.\nThe key principle in preventing intrusion is to be proactive. This means routinely testing your security\nsystems before an intruder does. Many steps can be taken to prevent intrusion and unauthorized access to", "source": "Page 372", "chapter_title": "Chapter 11"}
{"id": "a0e382e362dd-2", "text": "systems before an intruder does. Many steps can be taken to prevent intrusion and unauthorized access to\norganizational data and networks, but no network is completely safe. The best rule for high security is to\ndo what the military does: Do not keep extremely sensitive data online. Data that need special security are\nstored in computers isolated from other networks. In the following sections, we discuss the most\nimportant security controls for preventing intrusion and for recovering from intrusion when it occurs.\n11.4.1 Security Policy\nIn the same way that a disaster recovery plan is critical to controlling risks due to disruption, destruction,\nand disaster, a security policy is critical to controlling risk due to intrusion. The security policy should\nclearly define the important assets to be safeguarded and the important controls needed to do that. It", "source": "Page 372", "chapter_title": "Chapter 11"}
{"id": "e636e588266c-0", "text": "should have a section devoted to what employees should and should not do. Also, it should contain a clear\nplan for routinely training employees\u2014particularly end-users with little computer expertise\u2014on key\nsecurity rules and a clear plan for routinely testing and improving the security controls in place (Figure 11-\n11). A good set of examples and templates is available at www.sans.org/resources/policies.\n11.4.2 Perimeter Security and Firewalls\nIdeally, you want to stop external intruders at the perimeter of your network so that they cannot reach the\nservers inside. There are three basic access points into most networks: the Internet, LANs, and WLANs.\nRecent surveys suggest that the most common access point for intrusion is the Internet connection (70%\nof organizations experienced an attack from the Internet), followed by LANs and WLANs (30%). External\nintruders are most likely to use the Internet connection, whereas internal intruders are most likely to use\nthe LAN or WLAN. Because the Internet is the most common source of intrusions, the focus of perimeter\nsecurity is usually on the Internet connection, although physical security is also important.\nA good security policy should include the following:\nThe name of the decision-making manager who is in charge of security\nAn incident reporting system and a rapid-response team to respond to security breaches in\nprogress\nA risk assessment with priorities as to which assets are most important\nEffective controls placed at all major access points into the network to prevent or deter access by\nexternal agents\nEffective controls placed within the network to ensure that internal users cannot exceed their\nauthorized access\nUse of minimum number of controls possible to reduce management time and to provide the\nleast inconvenience to users\nAn acceptable use policy that explains to users what they can and cannot do, including\nguidelines for accessing others\u2019 accounts, password security, email rules, and so on", "source": "Page 373", "chapter_title": "Chapter 11"}
{"id": "27f8b6edeff6-1", "text": "guidelines for accessing others\u2019 accounts, password security, email rules, and so on\nA procedure for monitoring changes to important network components (e.g., routers, DNS\nservers)\nA plan to routinely train users regarding security policies and build awareness of security risks\nA plan to routinely test and update all security controls that includes monitoring of popular\npress and vendor reports of security holes\nAn annual audit and review of the security practices\nFIGURE 11-11 Elements of a security policy\nFIGURE 11-12 Using a firewall to protect networks\nA firewall is commonly used to secure an organization\u2019s Internet connection. A firewall is a router or\nspecial-purpose device that examines packets flowing into and out of a network and restricts access to the\norganization\u2019s network. The network is designed so that a firewall is placed on every network connection\nbetween the organization and the Internet (Figure 11-12). No access is permitted except through the\nfirewall. Some firewalls can detect and prevent denial-of-service attacks as well as unauthorized access", "source": "Page 373", "chapter_title": "Chapter 11"}
{"id": "fb75c5574eea-0", "text": "attempts. Three commonly used types of firewalls are packet-level firewalls, application-level firewalls,\nand network address translation (NAT) firewalls.\nPacket-Level Firewalls\nA packet-level firewall examines the source and destination address of every network packet that\npasses through it. It only allows packets into or out of the organization\u2019s networks that have acceptable\nsource and destination addresses. In general, the addresses are examined only at the transport layer (TCP\nport ID) and the network layer (IP address). Each packet is examined individually, so the firewall does not\nknow what packets came before. It simply chooses to permit entry or exit based on the contents of the\npacket itself. This type of firewall is the simplest and least secure because it does not monitor the contents\nof the packets or why they are being transmitted and typically does not log the packets for later analysis.\nThe network manager writes a set of rules (called an access control list [ACL]) for the packet-level\nfirewall so it knows what packets to permit into the network and what packets to deny entry. Remember\nthat the IP packet contains the source IP address and the destination address and that the TCP segment\nhas the destination port number that identifies the application-layer software to which the packet is going.\nMost application layer software on servers uses standard TCP port numbers. The Web (HTTP) uses port\n80, whereas email (SMTP) uses port 25.\nSuppose that the organization had a public Web server with an IP address of 128.192.44.44 and an email\nserver with an address of 128.192.44.45 (see Figure 11-13). The network manager wants to make sure that\nno one outside of the organization can change the contents of the Web server (e.g., by using telnet or\nFTP). The ACL could be written to include a rule that permits the Web server to receive HTTP packets", "source": "Page 374", "chapter_title": "Chapter 11"}
{"id": "a1b27b651a03-1", "text": "from the Internet (but other types of packets would be discarded). For example, the rule would say if the\nsource address is anything, the destination IP address is 128.192.44.44, and the destination TCP port is\n80, then permit the packet into the network; see the ACL on the firewall in Figure 11-13. Likewise, we\ncould add a rule to the ACL that would permit SMTP packets to reach the email server: If the source\naddress is anything, the destination is 128.192.44.45 and the destination TCP port is 25, then permit the\npacket through (see Figure 11-13). The last line in the ACL is usually a rule that says to deny entry to all\nother packets that have not been specifically permitted (some firewalls come automatically configured to\ndeny all packets other than those explicitly permitted, so this command would not be needed). With this\nACL, if an external intruder attempted to use telnet (port 23) to reach the Web server, the firewall would\ndeny entry to the packet and simply discard it.\nAlthough source IP addresses can be used in the ACL, they often are not used. Most hackers have software\nthat can change the source IP address on the packets they send (called IP spoofing), so using the source\nIP address in security rules is not usually worth the effort. Some network managers do routinely include a\nrule in the ACL that denies entry to all packets coming from the Internet that have a source IP address of a\nsubnet inside the organization because any such packets must have a spoofed address and therefore\nobviously are an intrusion attempt.", "source": "Page 374", "chapter_title": "Chapter 11"}
{"id": "4d454b61852f-0", "text": "FIGURE 11-13 How packet-level firewalls work\nApplication-Level Firewalls\nAn application-level firewall is more expensive and more complicated to install and manage than a\npacket-level firewall because it examines the contents of the application-level packet and searches for\nknown attacks (see Security Holes later in this chapter). Application-layer firewalls have rules for each\napplication they can process. For example, most application-level firewalls can check Web packets\n(HTTP), email packets (SMTP), and other common protocols. In some cases, special rules must be written\nby the organization to permit the use of application software it has developed.\nRemember from Chapter 5 that TCP uses connection-oriented messaging in which a client first establishes\na connection with a server before beginning to exchange data. Application-level firewalls can use stateful\ninspection, which means that they monitor and record the status of each connection and can use this\ninformation in making decisions about what packets to discard as security threats.\nMany application-level firewalls prohibit external users from uploading executable files. In this way,\nintruders (or authorized users) cannot modify any software unless they have physical access to the\nfirewall. Some refuse changes to their software unless it is done by the vendor. Others also actively\nmonitor their own software and automatically disable outside connections if they detect any changes.\nNetwork Address Translation Firewalls\nNetwork address translation (NAT) is the process of converting between one set of public IP\naddresses that are viewable from the Internet and a second set of private IP addresses that are hidden\nfrom people outside of the organization. NAT is transparent, in that no computer knows it is happening.\nAlthough NAT can be done for several reasons, the most common reasons are IPv4 address conservation\nand security. If external intruders on the Internet can\u2019t see the private IP addresses inside your\norganization, they can\u2019t attack your computers. Most routers and firewalls today have NAT built into", "source": "Page 375", "chapter_title": "Chapter 11"}
{"id": "1988fdf4e1f7-1", "text": "organization, they can\u2019t attack your computers. Most routers and firewalls today have NAT built into\nthem, even inexpensive routers designed for home use.\nThe NAT firewall uses an address table to translate the private IP addresses used inside the organization\ninto proxy IP addresses used on the Internet. When a computer inside the organization accesses a\ncomputer on the Internet, the firewall changes the source IP address in the outgoing IP packet to its own\naddress. It also sets the source port number in the TCP segment to a unique number that it uses as an\nindex into its address table to find the IP address of the actual sending computer in the organization\u2019s\ninternal network. When the external computer responds to the request, it addresses the message to the\nfirewall\u2019s IP address. The firewall receives the incoming message, and after ensuring the packet should be\npermitted inside, changes the destination IP address to the private IP address of the internal computer", "source": "Page 375", "chapter_title": "Chapter 11"}
{"id": "fba80a748719-0", "text": "and changes the TCP port number to the correct port number before transmitting it on the internal\nnetwork.\nThis way systems outside the organization never see the actual internal IP addresses, and thus they think\nthere is only one computer on the internal network. Most organizations also increase security by using\nprivate internal addresses. For example, if the organization has been assigned the Internet 128.192.55.X\naddress domain, the NAT firewall would be assigned an address such as 128.192.55.1. Internal computers,\nhowever, would not be assigned addresses in the 128.192.55.X subnet. Instead, they would be assigned\nunauthorized Internet addresses such as 10.3.3.55 (addresses in the 10.X.X.X domain are not assigned to\norganizations but instead are reserved for use by private intranets). Because these internal addresses are\nnever used on the Internet but are always converted by the firewall, this poses no problems for the users.\nEven if attackers discover the actual internal IP address, it would be impossible for them to reach the\ninternal address from the Internet because the addresses could not be used to reach the organization\u2019s\ncomputers.\nFirewall Architecture\nMany organizations use layers of NAT, packet-level, and application-level firewalls (Figure 11-14). Packet-\nlevel firewalls are used as an initial screen from the Internet into a network devoted solely to servers\nintended to provide public access (e.g., Web servers, public DNS servers). This network is sometimes\ncalled the DMZ (demilitarized zone). DMZ is a physical or logical subnetwork that exposes an\norganization\u2019s external-facing servers (such as Web Server, DNS Server, Mail Server) to the Internet. The\nprimary purpose of the DMZ is to provide another layer of security to the LAN. Therefore, the packet-level", "source": "Page 376", "chapter_title": "Chapter 11"}
{"id": "eb025b5c3a6c-1", "text": "firewall in front of the DMZ will permit Web requests and similar access to the DMZ network servers but\nwill deny FTP access, for example, to these servers from the Internet because no one except internal users\nshould have the right to modify the servers. Each major portion of the organization\u2019s internal networks\nhas its own NAT firewall to grant (or deny) access based on rules established by that part of the\norganization.\nThis figure also shows how a packet sent by a client computer inside one of the internal networks\nprotected by a NAT firewall would flow through the network. The packet created by the client has the\nclient\u2019s source address and the source port number of the process on the client that generated the packet\n(an HTTP packet going to a Web server, as you can tell from the destination port address of 80). When the\npacket reaches the firewall, the firewall changes the source address on the IP packet to its own address\nand changes the source port number to an index it will use to identify the client computer\u2019s address and\nport number. The destination address and port number are unchanged. The firewall then sends the packet\non its way to the destination. When the destination Web server responds to this packet, it will respond\nusing the firewall\u2019s address and port number. When the firewall receives the incoming packets, it will use\nthe destination port number to identify what IP address and port number to use inside the internal\nnetwork, change the inbound packet\u2019s destination and port number, and send it into the internal network\nso it reaches the client computer.\nPhysical Security\nOne important element to prevent unauthorized users from accessing an internal LAN is physical\nsecurity: preventing outsiders from gaining access into the organization\u2019s offices, server room, or network\nequipment facilities. Both main and remote physical facilities should be secured adequately and have the\nproper controls. Good security requires implementing the proper access controls so that only authorized", "source": "Page 376", "chapter_title": "Chapter 11"}
{"id": "1cdc97ca92a3-2", "text": "proper controls. Good security requires implementing the proper access controls so that only authorized\npersonnel can enter closed areas where servers and network equipment are located or access the network.\nThe network components themselves also have a level of physical security. Computers can have locks on\ntheir power switches or passwords that disable the screen and keyboard.", "source": "Page 376", "chapter_title": "Chapter 11"}
{"id": "13eba68f8eac-0", "text": "FIGURE 11-14 A typical network design using firewalls\nIn the previous section, we discussed the importance of locating backups and servers at separate (off-site)\nlocations. Some companies have also argued that by having many servers in different locations, you can\nreduce your risk and improve business continuity. Does having many servers disperse risk, or does it\nincrease the points of vulnerability? A clear disaster recovery plan with an off-site backup and server\nfacility can disperse risk, like distributed server systems. Distributed servers offer many more physical\nvulnerabilities to an attacker: more machines to guard, upgrade, patch, and defend. Many times these\ndispersed machines are all part of the same logical domain, which means that breaking into one of them\noften can give the attacker access to the resources of the others. It is our feeling that a well-backed-up,\ncentralized data center can be made inherently more secure than a proliferated base of servers.\nProper security education, background checks, and the implementation of error and fraud controls are\nalso very important. In many cases, the simplest means to gain access is to become employed as a janitor\nand access the network at night. In some ways this is easier than the previous methods because the\nintruder only has to insert a listening device or computer into the organization\u2019s network to record\nmessages. Three areas are vulnerable to this type of unauthorized access: wireless LANs, network cabling,\nand network devices.\nWireless LANs are the easiest target for eavesdropping because they often reach beyond the physical\nwalls of the organization. Chapter 7 discussed the techniques of WLAN security, so we do not repeat them\nhere.\nNetwork cables are the next easiest target for eavesdropping because they often run long distances and\nusually are not regularly checked for tampering. The cables owned by the organization and installed", "source": "Page 377", "chapter_title": "Chapter 11"}
{"id": "accc5e92db5c-0", "text": "within its facility are usually the first choice for eavesdropping. It is 100 times easier to tap a local cable\nthan it is to tap an interexchange channel because it is extremely difficult to identify the specific circuits\nbelonging to any one organization in a highly multiplexed switched interexchange circuit operated by a\ncommon carrier. Local cables should be secured behind walls and above ceilings, and telephone\nequipment and switching rooms (wiring closets) should be locked and their doors equipped with alarms.\nThe primary goal is to control physical access by employees or vendors to the connector cables and\nmodems. This includes restricting their access to the wiring closets in which all the communication wires\nand cables are connected.\nTECHNICAL FOCUS 11-3\nData Security Requires Physical Security\nThe general consensus is that if someone can physically get to your server for some period of time,\nthen all of your information on the computer (except perhaps strongly encrypted data) is available to\nthe attacker.\nWith a Windows server, the attacker simply boots the computer from the CD drive with a Knoppix\nversion of Linux. (Knoppix is Linux on a CD.) If the computer won\u2019t boot from the CD, the attacker\nsimply changes the BIOS to make it boot from the CD. Knoppix finds all the drivers for the specific\ncomputer and gives you a Linux desktop that can fully read all of the NTFS or FAT32 files.\nBut what about Windows password access? Nothing to it. Knoppix completely bypasses it. The\nattacker can then read, copy, or transmit any of the files on the Windows machine. Similar attacks\nare also possible on a Linux or Unix server, but they are slightly more difficult.\nCertain types of cable can impair or increase security by making eavesdropping easier or more difficult.", "source": "Page 378", "chapter_title": "Chapter 11"}
{"id": "1af15ef6bf79-1", "text": "Obviously, any wireless network is at extreme risk for eavesdropping because anyone in the area of the\ntransmission can easily install devices to monitor the radio or infrared signals. Conversely, fiber-optic\ncables are harder to tap, thus increasing security. Some companies offer armored cable that is virtually\nimpossible to cut without special tools. Other cables have built-in alarm systems. The U.S. Air Force, for\nexample, uses pressurized cables that are filled with gas. If the cable is cut, the gas escapes, pressure\ndrops, and an alarm is sounded.\nNetwork devices such as switches and routers should be secured in a locked wiring closet. As discussed in\nChapter 7, all messages within a given local area network are actually received by all computers on the\nWLAN, although they only process those messages addressed to them. It is rather simple to install a\nsniffer program that records all messages received for later (unauthorized) analysis. A computer with a\nsniffer program could then be plugged into an unattended switch to eavesdrop on all message traffic. A\nsecure switch makes this type of eavesdropping more difficult by requiring a special authorization code\nto be entered before new computers can be added.\n11.4.3 Server and Client Protection\nSecurity Holes\nEven with physical security and firewalls, the servers and client computers on a network may not be safe\nbecause of security holes. A security hole is simply a bug that permits unauthorized access. Many\ncommonly used operating systems have major security holes well known to potential intruders. Many\nsecurity holes have been documented and \u201cpatches\u201d are available from vendors to fix them, but network\nmanagers may be unaware of all the holes or simply forget to update their systems with new patches\nregularly.\nA complete discussion of security holes is beyond the scope of this book. Many security holes are highly", "source": "Page 378", "chapter_title": "Chapter 11"}
{"id": "e05234184846-2", "text": "A complete discussion of security holes is beyond the scope of this book. Many security holes are highly\ntechnical; for example, sending a message designed to overflow a memory buffer, thereby placing a short\ncommand into a very specific memory area that performs some function. Others are rather simple, but not\nobvious. For example, the attacker sends a message that lists the server\u2019s address as both the sender and", "source": "Page 378", "chapter_title": "Chapter 11"}
{"id": "3dde17557c4e-0", "text": "the destination, so the server repeatedly sends messages to itself until it crashes.\nMANAGEMENT FOCUS 11-5\nFake Antivirus?\nThe world of computer viruses is constantly evolving and becoming more and more advanced. At the\nbeginning of Internet, viruses were designed to do funny things (such as turn text on your screen\nupside down), but today they are designed to get your money and private information. Once a virus\nis installed on a computer, it will interact with a remote computer and transfer sensitive data to that\ncomputer. Antivirus software was developed to prevent viruses from being installed on computers.\nHowever, not all antivirus software is made equal.\nThere are many antivirus software companies that offer to scan your computer for free. Yes, for free!\nAn old saying relates that if something sounds too good to be true, it probably is. Free antivirus\nsoftware is not an exception. Chester Wisniewky, at SophosLabs, explains that once you have\ndownloaded a free antivirus on to your computer, you have actually downloaded malware. Once you\nlaunch this software on your computer, it looks and behaves like a legitimate antivirus. Many of\nthese free antivirus software packages are fully multilingual. The software has a very user-friendly\nGUI (graphical user interface) that looks and behaves like a legitimate antivirus. However, once you\nstart scanning your computer, it will mark legitimate files on your computer as worms and Trojans\nand will give you a warning that your computer is infected. A regular user gets scared at this point\nand allows the software to remove the infected files. What is really happening is that malware is\ninstalled on your computer that will scan for any sensitive information and send this information to\na host.\nRather than trying to get a free antivirus, spend money on a legitimate product such as Sophos,", "source": "Page 379", "chapter_title": "Chapter 11"}
{"id": "4781e4d3c748-1", "text": "Symantec, or McAfee. Popular news magazines, such as PC Magazine, provide annual reviews of\nlegitimate antivirus software and also the free antivirus. Your best protection against exploits of this\nkind is education.\nSources: \u201cWhich Antivirus Is the Best\u201d (www. pcantivirusreviews.com); \u201cFake Antivirus: What Are They and How Do You Avoid\nThem?\u201d by Cassie Bodnar (blog.kaspersky.com).\nOnce a security hole is discovered, it is quickly circulated through the Internet. The race begins between\nhackers and security teams; hackers share their discovery with other hackers and security teams share the\ndiscovery with other security teams. CERT is the central clearinghouse for major Internet-related security\nholes, so the CERT team quickly responds to reports of new security problems and posts alerts and\nadvisories on the Web and emails them to those who subscribe to its service. The developer of the\nsoftware with the security hole usually works quickly to fix the security hole and produces a patch that\ncorrects the hole. This patch is then shared with customers so they can download and apply it to their\nsystems to prevent hackers from exploiting the hole to break in. Attacks that take advantage of a newly\ndiscovered security hole before a patch is developed are called zero-day attacks. One problem is that\nmany network managers do not routinely respond to such security threats and immediately download and\ninstall the patch. Often it takes many months for patches to be distributed to most sites. Do you regularly\ninstall all the Windows or Mac updates on your computer?\nOther security holes are not really holes but simply policies adopted by computer vendors that open the\ndoor for security problems, such as computer systems that come with a variety of preinstalled user\naccounts. These accounts and their initial passwords are well documented and known to all potential\nattackers. Network managers sometimes forget to change the passwords on these well-known accounts,", "source": "Page 379", "chapter_title": "Chapter 11"}
{"id": "aa2ff9421bcb-2", "text": "attackers. Network managers sometimes forget to change the passwords on these well-known accounts,\nthus enabling an attacker to slip in.\nOperating Systems\nThe American government requires certain levels of security in the operating systems and network\noperating systems it uses for certain applications. The minimum level of security is C2. Most major\noperating systems (e.g., Windows) provide at least C2. Most widely used systems are striving to meet the", "source": "Page 379", "chapter_title": "Chapter 11"}
{"id": "956803c30965-0", "text": "requirements of much higher security levels such as B2. Very few systems meet the highest levels of\nsecurity (A1 and A2).\nThere has been a long running debate about whether the Windows operating system is less secure than\nother operating systems such as Linux. Every new attack on Windows systems ignites the debate;\nWindows detractors repeat \u201cI told you so\u201d while Windows defenders state that this happens mostly\nbecause Windows is the obvious system to attack since it is the most commonly used operating system\nand because of the hostility of the Windows detractors themselves.\nThere is a critical difference in what applications can do in Windows and in Linux. Linux (and its ancestor\nUnix) was first written as a multiuser operating system in which different users had different rights. Only\nsome users were system administrators and had the rights to access and make changes to the critical parts\nof the operating system. All other users were barred from doing so.\nTECHNICAL FOCUS 11-4\nExploiting a Security Hole\nTo exploit a security hole, the hacker has to know it\u2019s there. So how does a hacker find out? It\u2019s\nsimple in the era of automated tools.\nFirst, the hacker has to find the servers on a network. The hacker could start by using network\nscanning software to systematically probe every IP address on a network to find all the servers on the\nnetwork. At this point, the hacker has narrowed the potential targets to a few servers.\nSecond, the hacker needs to learn what services are available on each server. To do this, he or she\ncould use port scanning software to systematically probe every TCP/IP port on a given server. This\nwould reveal which ports are in use and thus what services the server offers. For example, if the\nserver has software that responds to port 80, it is a Web server, while if it responds to port 25, it is a", "source": "Page 380", "chapter_title": "Chapter 11"}
{"id": "cd4595058bba-1", "text": "mail server.\nThird, the hacker would begin to seek out the exact software and version number of the server\nsoftware providing each service. For example, suppose the hacker decides to target mail servers.\nThere are a variety of tools that can probe the mail server software, and based on how the server\nsoftware responds to certain messages, determine which manufacturer and version number of\nsoftware is being used.\nFinally, once the hacker knows which package and version number the server is using, the hacker\nuses tools designed to exploit the known security holes in the software. For example, some older mail\nserver software packages do not require users to authenticate themselves (e.g., by a user id and\npassword) before accepting SMTP packets for the mail server to forward. In this case, the hacker\ncould create SMTP packets with fake source addresses and use the server to flood the Internet with\nspam (i.e., junk mail). In another case, a certain version of a well-known e-commerce package\nenabled users to pass operating system commands to the server simply by including a UNIX pipe\nsymbol (|) and the command to the name of a file name to be uploaded; when the system opened the\nuploaded file, it also executed the command attached to it.\nIn contrast, Windows (and its ancestor DOS) was first written as an operating system for a single personal\ncomputer, an environment in which the user was in complete control of the computer and could do\nanything he or she liked. As a result, Windows applications regularly access and make changes to critical\nparts of the operating system. There are advantages to this. Windows applications can do many powerful\nthings without the user needing to understand them. These applications can be very rich in features, and,\nmore important, they can appear to the user to be very friendly and easy to use. Everything appears to run", "source": "Page 380", "chapter_title": "Chapter 11"}
{"id": "efa8c2f60d70-2", "text": "\u201cout-of-the-box\u201d without modification. Windows has built these features into the core of their systems.\nAny major rewrite of Windows to prevent this would most likely cause significant incompatibilities with\nall applications designed to run under previous versions of Windows. To many, this would be a high price\nto pay for some unseen benefits called \u201csecurity.\u201d", "source": "Page 380", "chapter_title": "Chapter 11"}
{"id": "c592f5a213fa-0", "text": "But there is a price for this friendliness. Hostile applications can easily take over the computer and\nliterally do whatever they want without the user knowing. Simply put, there is a trade-off between ease of\nuse and security. Increasing needs for security demand more checks and restrictions, which translates\ninto less friendliness and fewer features. It may very well be that there is an inherent and permanent\ncontradiction between the ease of use of a system and its security.\nTrojan Horses\nOne important tool in gaining unauthorized access is a Trojan horse. Trojans are remote access\nmanagement consoles (sometimes called rootkits) that enable users to access a computer and manage it\nfrom afar. If you see free software that will enable you to control your computer from anywhere, be\ncareful; the software may also permit an attacker to control your computer from anywhere! Trojans are\nmore often concealed in other software that unsuspecting users download over the Internet (their name\nalludes to the original Trojan horse). Music and video files shared on Internet music sites are common\ncarriers of Trojans. When the user downloads and plays a music file, it plays normally and the attached\nTrojan software silently installs a small program that enables the attacker to take complete control of the\nuser\u2019s computer, so the user is unaware that anything bad has happened. The attacker then simply\nconnects to the user\u2019s computer and has the same access and controls as the user. Many Trojans are\ncompletely undetectable by the very best antivirus software.\nOne of the first major Trojans was Back Orifice, which aggressively attacked Windows servers. Back\nOrifice gave the attacker the same functions as the administrator of the infected server, and then some:\ncomplete file and network control, device and registry access, with packet and application redirection. It\nwas every administrator\u2019s worst nightmare, and every attacker\u2019s dream.", "source": "Page 381", "chapter_title": "Chapter 11"}
{"id": "80a694f8a063-1", "text": "was every administrator\u2019s worst nightmare, and every attacker\u2019s dream.\nMore recently, Trojans have morphed into tools such as MoSucker and Optix Pro. These attack consoles\nnow have one-button clicks to disable firewalls, antivirus software, and any other defensive process that\nmight be running on the victim\u2019s computer. The attacker can choose what port the Trojan runs on, what it\nis named, and when it runs. They can listen in to a computer\u2019s microphone or look through an attached\ncamera\u2014even if the device appears to be off. Figure 11-15 shows a menu from one Trojan that illustrates\nsome of the \u201cfun stuff\u201d that an attacker can do, such as opening and closing the CD tray, beeping the\nspeaker, or reversing the mouse buttons so that clicking on the left button actually sends a right click.\nNot only have these tools become powerful, but they are also very easy to use\u2014much easier to use than the\nnecessary defensive countermeasures to protect oneself from them. And what does the near future hold\nfor Trojans? We can easily envision Trojans that schedule themselves to run at, say 2:00 a.m., choosing a\nrandom port, emailing the attacker that the machine is now \u201copen for business\u201d at port # NNNNN. The\nattackers can then step in, do whatever they want to do, run a script to erase most of their tracks, and then\nsign out and shut off the Trojan. Once the job is done, the Trojan could even erase itself from storage.\nScary? Yes. And the future does not look better.", "source": "Page 381", "chapter_title": "Chapter 11"}
{"id": "2cc486427825-0", "text": "FIGURE 11-15 One menu on the control console for the Optix Pro Trojan\nSpyware, adware, and DDoS agents are three types of Trojans. DDoS agents were discussed in the\nprevious section. As the name suggests, spyware monitors what happens on the target computer. Spyware\ncan record keystrokes that appear to be userids and passwords so the intruder can gain access to the user\u2019s\naccount (e.g., bank accounts). Adware monitors a user\u2019s actions and displays pop-up advertisements on\nthe user\u2019s screen. For example, suppose you clicked on the website for an online retailer. Adware might\npop-up a window for a competitor, or, worse still, redirect your browser to the competitor\u2019s website. Many\nantivirus software packages now routinely search for and remove spyware, adware, and other Trojans and\nspecial-purpose antispyware software is available (e.g., Spybot). Some firewall vendors are now adding\nanti-Trojan logic to their devices to block any transmissions from infected computers from entering or\nleaving their networks.\n11.4.4 Encryption\nOne of the best ways to prevent intrusion is encryption, which is a means of disguising information by\nthe use of mathematical rules known as algorithms. Actually, cryptography is the more general and\nproper term. Encryption is the process of disguising information, whereas decryption is the process of\nrestoring it to readable form. When information is in readable form, it is called plaintext; when in\nencrypted form, it is called ciphertext.\nEncryption can be used to encrypt files stored on a computer or to encrypt data in transit between\ncomputers. Many firms use both because encrypting files is done using a simple setting on the operating\nsystem. For example, if you use Windows, you can encrypt your data to protect it if your laptop is stolen.", "source": "Page 382", "chapter_title": "Chapter 11"}
{"id": "b4ca8f4fca2c-1", "text": "Likewise, most websites use encryption on data in transit either by using VPNs (see Chapter 10) or using\nencrypted Web protocols such as HTTPS.\nThere are two fundamentally different types of encryption: symmetric and asymmetric. With symmetric", "source": "Page 382", "chapter_title": "Chapter 11"}
{"id": "d24ab89f3b44-0", "text": "encryption, the key used to encrypt a message is the same as the one used to decrypt it. With\nasymmetric encryption, the key used to decrypt a message is different from the key used to encrypt it.\nMANAGEMENT FOCUS 11-6\nRansomware Becomes Profitable\nRansomware is a special type of malware that takes a victim\u2019s data hostage and demands a ransom\nto release it. It usually begins when a user downloads a file containing the ransomware or runs a\nscript on a website. The ransomware encrypts all the files on the victim\u2019s computer with a key\nunknown to the victim, so he or she cannot access the files. The attacker then demands a ransom\nthat must be paid within a day or two or all the files will be deleted.\nThe ransom is usually a modest amount (e.g., $750) so that the victim is more likely to pay it than\nattempt to try to fix the problem. The ransom is often paid in bitcoins to the attacker in a country\nthat does not prosecute computer criminals.\nMost victims are individual users, because they are less sophisticated than companies and it is easier\nto extort money from an individual than a company. Nonetheless, ransomware attackers have\ntargeted servers owned by a variety of small- and medium-sized businesses and demanded higher\nransom amounts. Professional service firms such as doctors, dentists, and lawyers have been\nincreasingly targeted, presumably because they have more to lose and can afford to pay higher\nransoms.\nThe FBI estimates that U.S. firms suffer losses of about $1 billion per year, once you factor in the cost\nto re-create data and recover from the damage done, including lost business. Most ransomware\nattacks are not reported to the FBI, and the FBI only considers attacks on U.S. firms, so this is only\nthe tip of the iceberg.\nSingle-Key Encryption", "source": "Page 383", "chapter_title": "Chapter 11"}
{"id": "c07f8d3d1aaf-1", "text": "the tip of the iceberg.\nSingle-Key Encryption\nSymmetric encryption (also called single-key encryption) has two parts: the algorithm and the key,\nwhich personalizes the algorithm by making the transformation of data unique. Two pieces of identical\ninformation encrypted with the same algorithm but with different keys produce completely different\nciphertexts. With symmetric encryption, the communicating parties must share the one key. If the\nalgorithm is adequate and the key is kept secret, acquisition of the ciphertext by unauthorized personnel is\nof no consequence to the communicating parties.\nGood encryption systems do not depend on keeping the algorithm secret. Only the keys need to be kept\nsecret. The key is a relatively small numeric value (in terms of the number of bits). The larger the key, the\nmore secure the encryption because large \u201ckey space\u201d protects the ciphertext against those who try to\nbreak it by brute-force attacks\u2014which simply means trying every possible key.\nThere should be a large enough number of possible keys that an exhaustive brute-force attack would take\ninordinately long or would cost more than the value of the encrypted information. Because the same key is\nused to encrypt and decrypt, symmetric encryption can cause problems with key management; keys\nmust be shared among the senders and receivers very carefully. Before two computers in a network can\ncommunicate using encryption, both must have the same key. This means that both computers can then\nsend and read any messages that use that key. Companies often do not want one company to be able to\nread messages they send to another company, so this means that there must be a separate key used for\ncommunication with each company. These keys must be recorded but kept secure so that they cannot be\nstolen. Because the algorithm is known publicly, the disclosure of the key means the total compromise of\nencrypted messages. Managing this system of keys can be challenging.", "source": "Page 383", "chapter_title": "Chapter 11"}
{"id": "378acf6a57cd-2", "text": "encrypted messages. Managing this system of keys can be challenging.\nOne commonly used symmetric encryption technique is the Data Encryption Standard (DES), which\nwas developed in the mid-1970s by the U.S. government in conjunction with IBM. DES is standardized by\nthe National Institute of Standards and Technology (NIST). The most common form of DES uses a 56-bit\nkey, which experts can break in less than a day (i.e., experts with the right tools can figure out what a", "source": "Page 383", "chapter_title": "Chapter 11"}
{"id": "c34c5ed854f2-0", "text": "message encrypted using DES says without knowing the key in less than 24 hours). DES is no longer\nrecommended for data needing high security, although some companies continue to use it for less\nimportant data.\nTriple DES (3DES) is a newer standard that is harder to break. As the name suggests, it involves using\nDES three times, usually with three different keys to produce the encrypted text, which produces a\nstronger level of security because it has a total of 168 bits as the key (i.e., 3 times 56 bits).\nThe NIST\u2019s new standard, called Advanced Encryption Standard (AES), has replaced DES. AES has\nkey sizes of 128, 192, and 256 bits. NIST estimates that using the most advanced computers and\ntechniques available today, it will require about 150 trillion years to crack AES by brute force. As\ncomputers and techniques improve, the time requirement will drop, but AES seems secure for the\nforeseeable future; the original DES lasted 20 years, so AES may have a similar life span.\nAnother commonly used symmetric encryption algorithm is RC4, developed by Ron Rivest of RSA Data\nSecurity, Inc. RC4 can use a key up to 256 bits long but most commonly uses a 40-bit key. It is faster to\nuse than DES but suffers from the same problems from brute-force attacks: Its 40-bit key can be broken\nby a determined attacker in a day or two.\nToday, the U.S. government considers encryption to be a weapon and regulates its export in the same way\nit regulates the export of machine guns or bombs. Present rules prohibit the export of encryption\ntechniques with keys longer than 64 bits without permission, although exports to Canada and the\nEuropean Union are permitted, and American banks and Fortune 100 companies are now permitted to", "source": "Page 384", "chapter_title": "Chapter 11"}
{"id": "cb25f407201c-1", "text": "European Union are permitted, and American banks and Fortune 100 companies are now permitted to\nuse more powerful encryption techniques in their foreign offices. This policy made sense when only\nAmerican companies had the expertise to develop powerful encryption software. Today, however, many\nnon-American companies are developing encryption software that is more powerful than American\nsoftware that is limited only by these rules. Therefore, the American software industry is lobbying the\ngovernment to change the rules so that they can successfully compete overseas.\nPublic Key Encryption\nThe most popular form of asymmetric encryption (also called public key encryption) is RSA, which\nwas invented at MIT in 1977 by Rivest, Shamir, and Adleman, who founded RSA Data Security in 1982.\nThe patent expired in 2000, so many new companies entered the market and public key software dropped\nin price. The RSA technique forms the basis for today\u2019s public key infrastructure (PKI).\nPublic key encryption is inherently different from symmetric single-key systems like DES. Because public\nkey encryption is asymmetric, there are two keys. One key (called the public key) is used to encrypt the\nmessage and a second, very different private key is used to decrypt the message. Keys are often 512 bits,\n1,024 bits, or 2,048 bits in length.\nPublic key systems are based on one-way functions. Even though you originally know both the contents of\nyour message and the public encryption key, once it is encrypted by the one-way function, the message\ncannot be decrypted without the private key. One-way functions, which are relatively easy to calculate in\none direction, are impossible to \u201cuncalculate\u201d in the reverse direction. Public key encryption is one of the\nmost secure encryption techniques available, excluding special encryption techniques developed by\nnational security agencies.\nPublic key encryption greatly reduces the key management problem. Each user has its public key that is", "source": "Page 384", "chapter_title": "Chapter 11"}
{"id": "a343d171167c-2", "text": "Public key encryption greatly reduces the key management problem. Each user has its public key that is\nused to encrypt messages sent to it. These public keys are widely publicized (e.g., listed in a telephone-\nbook-style directory)\u2014that\u2019s why they\u2019re called \u201cpublic\u201d keys. In addition, each user has a private key that\ndecrypts only the messages that were encrypted by its public key. This private key is kept secret (that\u2019s\nwhy it\u2019s called the \u201cprivate\u201d key). The net result is that if two parties wish to communicate with each other,\nthere is no need to exchange keys beforehand. Each knows the other\u2019s public key from the listing in a\npublic directory and can communicate encrypted information immediately. The key management problem\nis reduced to the on-site protection of the private key.", "source": "Page 384", "chapter_title": "Chapter 11"}
{"id": "27aeafc827db-0", "text": "FIGURE 11-16 Secure transmission with public key encryption\nFigure 11-16 illustrates how this process works. All public keys are published in a directory. When\nOrganization A wants to send an encrypted message to Organization B, it looks through the directory to\nfind its public key. It then encrypts the message using B\u2019s public key. This encrypted message is then sent\nthrough the network to Organization B, which decrypts the message using its private key.\nAuthentication\nPublic key encryption also permits the use of digital signatures through a process of authentication.\nWhen one user sends a message to another, it is difficult to legally prove who actually sent the message.\nLegal proof is important in many communications, such as bank transfers and buy/sell orders in currency\nand stock trading, which normally require legal signatures. Public key encryption algorithms are\ninvertible, meaning that text encrypted with either key can be decrypted by the other. Normally, we\nencrypt with the public key and decrypt with the private key. However, it is possible to do the inverse:\nencrypt with the private key and decrypt with the public key. Because the private key is secret, only the\nreal user could use it to encrypt a message. Thus, a digital signature or authentication sequence is used as\na legal signature on many financial transactions. This signature is usually the name of the signing party\nplus other key-contents such as unique information from the message (e.g., date, time, or dollar amount).\nThis signature and the other key-contents are encrypted by the sender using the private key. The receiver\nuses the sender\u2019s public key to decrypt the signature block and compares the result to the name and other\nkey contents in the rest of the message to ensure a match.", "source": "Page 386", "chapter_title": "Chapter 11"}
{"id": "ae3fbd0e6f66-0", "text": "FIGURE 11-17 Authenticated and secure transmission with public key encryption\nFigure 11-17 illustrates how authentication can be combined with public encryption to provide a secure\nand authenticated transmission with a digital signature. The plaintext message is first encrypted using\nOrganization A\u2019s private key and then encrypted using the Organization\u2019s B public key. It is then", "source": "Page 387", "chapter_title": "Chapter 11"}
{"id": "e91df5be1eea-0", "text": "transmitted to B. Organization B first decrypts the message using its private key. It sees that part of the\nmessage (the key-contents) is still in ciphertext, indicating it is an authenticated message. B then decrypts\nthe key-contents part of the message using A\u2019s public key to produce the plaintext message. Since only A\nhas the private key that matches A\u2019s public key, B can safely assume that A sent the message.\nThe only problem with this approach lies in ensuring that the person or organization who sent the\ndocument with the correct private key is actually the person or organization it claims to be. Anyone can\npost a public key on the Internet, so there is no way of knowing for sure who they actually are. For\nexample, it would be possible for someone to create a website and claim to be \u201cOrganization A\u201d when in\nfact the person is really someone else.\nThis is where the Internet\u2019s PKI becomes important. The PKI is a set of hardware, software, organizations,\nand polices designed to make public key encryption work on the Internet. PKI begins with a certificate\nauthority (CA), which is a trusted organization that can vouch for the authenticity of the person or\norganization using authentication (e.g., VeriSign). A person wanting to use a CA registers with the CA and\nmust provide some proof of identity. There are several levels of certification, ranging from a simple\nconfirmation from a valid email address to a complete police-style background check with an in-person\ninterview. The CA issues a digital certificate that is the requestor\u2019s public key encrypted using the CA\u2019s\nprivate key as proof of identity. This certificate is then attached to the user\u2019s email or Web transactions, in\naddition to the authentication information. The receiver then verifies the certificate by decrypting it with", "source": "Page 388", "chapter_title": "Chapter 11"}
{"id": "bb65d9a079a7-1", "text": "addition to the authentication information. The receiver then verifies the certificate by decrypting it with\nthe CA\u2019s public key\u2014and must also contact the CA to ensure that the user\u2019s certificate has not been\nrevoked by the CA.\nFor higher security certifications, the CA requires that a unique \u201cfingerprint\u201d be issued by the CA for each\nmessage sent by the user. The user submits the message to the CA, who creates the unique fingerprint by\ncombining the CA\u2019s private key with the message\u2019s authentication key contents. Because the user must\nobtain a unique fingerprint for each message, this ensures that the CA has not revoked the certificate\nbetween the time it was issued and the time the message was sent by the user.\nEncryption Software\nPretty Good Privacy (PGP) is a freeware public key encryption package developed by Philip\nZimmermann that is often used to encrypt email. Users post their public key on Web pages, for example,\nand anyone wishing to send them an encrypted message simply cuts and pastes the key off the Web page\ninto the PGP software, which encrypts and sends the message.\nSecure Sockets Layer (SSL) is an encryption protocol widely used on the Web. It operates between the\napplication-layer software and the transport layer (in what the OSI model calls the presentation layer).\nSSL encrypts outbound packets coming out of the application layer before they reach the transport layer\nand decrypts inbound packets coming out of the transport layer before they reach the application layer.\nWith SSL, the client and the server start with a handshake for PKI authentication and for the server to\nprovide its public key and preferred encryption technique to the client (usually RC4, DES, 3DES, or AES).\nThe client then generates a key for this encryption technique, which is sent to the server encrypted with\nthe server\u2019s public key. The rest of the communication then uses this encryption technique and key.", "source": "Page 388", "chapter_title": "Chapter 11"}
{"id": "d1580295f713-2", "text": "the server\u2019s public key. The rest of the communication then uses this encryption technique and key.\nIP Security Protocol (IPSec) is another widely used encryption protocol. IPSec differs from SSL in\nthat SSL is focused on Web applications, whereas IPSec can be used with a much wider variety of\napplication layer protocols. IPSec sits between IP at the network layer and TCP/UDP at the transport\nlayer. IPSec can use a wide variety of encryption techniques, so the first step is for the sender and receiver\nto establish the technique and key to be used. This is done using the Internet Key Exchange (IKE).\nBoth parties generate a random key and send it to the other using an encrypted authenticated PKI\nprocess, and then put these two numbers together to produce the key. The encryption technique is also\nnegotiated between the two, often being 3DES. Once the keys and techniques have been established, IPSec\ncan begin transmitting data.\nIP Security Protocol can operate in either transport mode or tunnel mode for VPNs. In IPSec transport\nmode, IPSec encrypts just the IP payload, leaving the IP packet header unchanged so it can be easily\nrouted through the Internet. In this case, IPSec adds an additional packet (either an Authentication\nHeader [AH] or an Encapsulating Security Payload [ESP]) at the start of the IP packet that provides\nencryption information for the receiver.", "source": "Page 388", "chapter_title": "Chapter 11"}
{"id": "11bcc41a35a0-0", "text": "In IPSec tunnel mode, IPSec encrypts the entire IP packet and must, therefore, add an entirely new IP\npacket that contains the encrypted packet as well as the IPSec AH or ESP packets. In tunnel mode, the\nnewly added IP packet just identifies the IPSec encryption agent at the next destination, not the final\ndestination; once the IPSec packet arrives at the encryption agent, the encrypted packet is VPN decrypted\nand sent on its way. In tunnel mode, attackers can only learn the endpoints of the VPN tunnel, not the\nultimate source and destination of the packets.\n11.4.5 User Authentication\nOnce the network perimeter and the network interior have been secured, the next step is to ensure that\nonly authorized users are permitted into the network and into specific resources in the interior of the\nnetwork. This is called user authentication.\nThe basis of user authentication is the user profile for each user\u2019s account that is assigned by the\nnetwork manager. Each user\u2019s profile specifies what data and network resources he or she can access and\nthe type of access (read-only, write, create, delete).\nUser profiles can limit the allowable log-in days, time of day, physical locations, and the allowable number\nof incorrect log-in attempts. Some will also automatically log a user out if that person has not performed\nany network activity for a certain length of time (e.g., the user has gone to lunch and has forgotten to log\noff the network). Regular security checks throughout the day when the user is logged in can determine\nwhether a user is still permitted access to the network. For example, the network manager might have\ndisabled the user\u2019s profile while the user is logged in, or the user\u2019s account may have run out of funds.\nCreating accounts and profiles is simple. When a new staff member joins an organization, that person is", "source": "Page 389", "chapter_title": "Chapter 11"}
{"id": "34ffcd3e4c8a-1", "text": "Creating accounts and profiles is simple. When a new staff member joins an organization, that person is\nassigned a user account and profile. One security problem is the removal of user accounts when someone\nleaves an organization. Often, network managers are not informed of the departure and accounts remain\nin the system. For example, an examination of the user accounts at the University of Georgia found 30%\nbelonged to staff members no longer employed by the university. If the staff member\u2019s departure was not\nfriendly, there is a risk that he or she may attempt to access data and resources and use them for personal\ngain, or destroy them to get back at the organization. Many systems permit the network manager to assign\nexpiration dates to user accounts to ensure that unused profiles are automatically deleted or deactivated,\nbut these actions do not replace the need to notify network managers about an employee\u2019s departure as\npart of the standard human resources procedures.\nTECHNICAL FOCUS 11-5\nCracking a Password\nTo crack Windows passwords, you just need to get a copy of the security account manager (SAM) file\nin the WINNT directory, which contains all the Windows passwords in an encrypted format. If you\nhave physical access to the computer, that\u2019s sufficient. If not, you might be able to hack in over the\nnetwork. Then, you just need to use a Windows-based cracking tool such as L0phtCrack. Depending\non the difficulty of the password, the time needed to crack the password via brute force could take\nminutes or up to a day.\nOr that\u2019s the way it used to be. Recently the Cryptography and Security Lab in Switzerland\ndeveloped a new password-cracking tool that relies on very large amounts of RAM. It then does\nindexed searches of possible passwords that are already in memory. This tool can cut cracking times", "source": "Page 389", "chapter_title": "Chapter 11"}
{"id": "1a09d37aa1b1-2", "text": "indexed searches of possible passwords that are already in memory. This tool can cut cracking times\nto less than 1/10 of the time of previous tools. Keep adding RAM and mHertz and you could reduce\nthe crack times to 1/100 that of the older cracking tools. This means that if you can get your hands\non the Windows-encrypted password file, then the game is over. It can literally crack complex\npasswords in Windows in seconds.\nIt\u2019s different for Linux, Unix, or Apple computers. These systems insert a 12-bit random \u201csalt\u201d to the\npassword, which means that cracking their passwords will take 4,096 (2^12) times longer to do. That\nmargin is probably sufficient for now, until the next generation of cracking tools comes along.\nMaybe.", "source": "Page 389", "chapter_title": "Chapter 11"}
{"id": "191a6f7f3c8a-0", "text": "So what can we say from all of this? That you are 4,096 times safer with Linux? Well, not necessarily.\nBut what we may be able to say is that strong password protection, by itself, is an oxymoron. We\nmust combine it with other methods of security to have reasonable confidence in the system.\nMANAGEMENT FOCUS 11-7\nMaking Strong Passwords\nThe keys to users\u2019 accounts are passwords\u2014we all know this. But most people are more worried\nabout forgetting a password than about having someone break-in to their computer account because\nthe risk of forgetting is more real\u2014we\u2019ve all forgotten a password. The risk of a break-in is less real\nbecause most people haven\u2019t had someone break-in. As a result, most people choose passwords that\nare easy to remember, rather than secure passwords.\nResearch shows that the most commonly used passwords are as follows:\nThe word \u201cpassword\u201d\nKeyboard patterns such as \u201cqwerty\u201d and \u201c12345678\u201d\nSports such as \u201cfootball\u201d and \u201cbaseball\u201d\nNames from movies such as \u201cgandolf\u201d and \u201cleia\u201d\nOther common passwords are related to the individual, such as names of the person\u2019s spouse,\nchildren or pets, important numbers such as birthdays or phone numbers, or place names such as\ncities. We often reuse the same password at different websites.\nThe stronger the password, the more secure your account. But what does it mean to have a \u201cstrong\u201d\npassword? Some organizations impose rules for passwords, such as requiring uppercase letters,\nnumbers, and special characters. Does this make for stronger passwords?\nIt turns out that making strong passwords is simple. Strong passwords are long passwords. Length\nmatters and everything else is really not that important. The strongest password is actually a\npassphrase that contains at least 20 characters. You can increase the strength by adding a few", "source": "Page 390", "chapter_title": "Chapter 11"}
{"id": "bf35f6d37c7a-1", "text": "passphrase that contains at least 20 characters. You can increase the strength by adding a few\nnumbers somewhere. This will then become a very easy password to remember but a very difficult\none to crack.\nGeneral rules:\nUse passphrases, not passwords. Choose four easily remembered words along with a few\nnumbers, but don\u2019t choose a common phrase such as \u201cto be or not to be.\u201d\nDon\u2019t use the same passphrase everywhere. Instead, create a general passphrase that you\ncustomize. For example, count the number of times the letter \u201ca\u201d appears in the website URL\nand add that number to the end of your usual passphrase to create a unique passphrase just for\nthat site.\nAlways choose a unique passphrase for every high-risk site, such as your bank.\nGaining access to an account can be based on something you know, something you have, or\nsomething you are.\nPasswords\nThe most common approach is something you know, usually a password. Before users can log in, they\nneed to enter a password. Unfortunately, passwords are often poorly chosen, enabling intruders to guess\nthem and gain access. Some organizations have moved to passphrases which, as the name suggests, are\na series of words separated by spaces. Management Focus 11-7 offers some suggestions on how to create a\nstrong password that is easy to remember.", "source": "Page 390", "chapter_title": "Chapter 11"}
{"id": "8775165d3710-0", "text": "Password managers such as Dashlane and LastPass are becoming more common, but are still not\nwidely adopted. A password manager is a browser add-in or app that stores website passwords. When you\ncreate an account on a new website, the password manager asks if you want to store the password. When\nyou return to a website whose password is stored, a button appears next to the password box that you can\nclick and the password manager fills in the userid and password.\nAll the passwords are stored on the password manager website, not on any device, so it is simple to install\nthe add-in or app on any device. All passwords are protected by a master password that you must enter\nbefore you can use the password manager, although you can have the password manager \u201ctrust\u201d a device\nfor several days at a time, so you do not have to login every day. If a device is stolen, you can easily login to\nthe password manager website and change your master password, which then requires any trusted device\nto login again.\nTwo-Factor Authentication\nRequiring passwords provides, at best, midlevel security (much like locking your doors when you leave the\nhouse); it won\u2019t stop the professional intruder, but it will slow amateurs. Nonetheless, most organizations\ntoday use only passwords. About a third of organizations go beyond this and are requiring users to enter a\npassword in conjunction with something they have, which is called two-factor authentication because\nthe password is the first factor and the object is the second. For example, an automated teller machine\n(ATM) uses two-factor authentication by requiring you have your ATM card and know your PIN.\nTwo-factor authentication commonly employs the user\u2019s mobile phone. The user installs an app on his or\nher mobile phone (Duo is a common one) and adds this app information to his or her account. When the", "source": "Page 391", "chapter_title": "Chapter 11"}
{"id": "9820133a4ca2-1", "text": "user logs in, the software sends an alert to the app, which asks the user to confirm or deny the login (see\nFigure 11-18). This greatly increases security, because an attacker must physically have the user\u2019s mobile\nphone and be able to login to it, as well and knowing the user\u2019s password.\nAnother approach is one-time passwords. The user connects into his or her account as usual, and after\nthe user\u2019s password is accepted, the system generates a one-time password (sometimes called an access\ncode), which is emailed or texted to the user using information that is stored in the user\u2019s account. The\nuser must enter this password to gain access, otherwise the login is blocked. This is sometimes used when\na user logs in from a computer that he or she has not used before to ensure that someone else is not trying\nto access the user\u2019s account with a stolen password.\nWith any of these two-factor authentication systems, an attacker must know the user\u2019s account name and\npassword and have access to a second item that belongs to the user, whether it is a physical item like a\nphone or a logical item such as an email account.", "source": "Page 391", "chapter_title": "Chapter 11"}
{"id": "545fb86adcea-0", "text": "FIGURE 11-18 Two-factor authentication with the Duo app for mobile phones\nBiometrics", "source": "Page 392", "chapter_title": "Chapter 11"}
{"id": "c2f24cc28908-0", "text": "In high-security applications, a user may be required to present something he or she is, such as a finger,\nhand, or the retina of the eye for scanning by the system. These biometric systems scan the user to\nensure that the user is the sole individual authorized to access the network account. About 15% of\norganizations now use biometrics. Although most biometric systems are developed for high-security\nusers, several low-cost biometric systems are now on the market. Many mobile phones use fingerprints to\nunlock them.\nCentral Authentication\nOne long-standing problem has been that users are often assigned user profiles and passwords on several\ndifferent computers. Each time a user wants to access a new server, he or she must supply his or her\npassword. This is cumbersome for the users and even worse for the network manager who must manage\nall the separate accounts for all the users.\nMore and more organizations are adopting central authentication (also called network\nauthentication, single sign-on, or directory services), in which a log-in server is used to authenticate the\nuser. Instead of logging into a file server or application server, the user logs into the authentication\nserver. This server checks the user ID and password against its database and, if the user is an authorized\nuser, issues a certificate (also called credentials). Whenever the user attempts to access a restricted\nservice or resource that requires a user ID and password, the user is challenged, and his or her software\npresents the certificate to the authentication server (which is revalidated by the authentication server at\nthe time). If the authentication server validates the certificate, then the service or resource lets the user in.\nIn this way, the user no longer needs to enter his or her password to be authenticated to each new\nresource or service he or she uses. This also ensures that the user does not accidentally give out his or her", "source": "Page 393", "chapter_title": "Chapter 11"}
{"id": "fc62dec0db63-1", "text": "password to an unauthorized service\u2014it provides mutual authentication of both the user and the service\nor resource. The most commonly used authentication protocol is Kerberos, developed at MIT (see\nweb.mit.edu/kerberos/www).\nAlthough many systems use only one authentication server, it is possible to establish a series of\nauthentication servers for different parts of the organization. Each server authenticates clients in its\ndomain but can also pass authentication credentials to authentication servers in other domains.\n11.4.6 Preventing Social Engineering\nOne of the most common ways for attackers to break into a system, even master hackers, is through social\nengineering, which refers to breaking security simply by asking. For example, attackers routinely phone\nunsuspecting users and, imitating someone such as a technician or senior manager, ask for a password.\nUnfortunately, too many users want to be helpful and simply provide the requested information. At first,\nit seems ridiculous to believe that someone would give his or her password to a complete stranger, but a\nskilled social engineer is like a good con artist: he\u2014and most social engineers are men\u2014can manipulate\npeople.\nMost security experts no longer test for social engineering attacks; they know from experience that social\nengineering will eventually succeed in any organization and therefore assume that attackers can gain\naccess at will to normal user accounts. Training end users not to divulge passwords may not eliminate\nsocial engineering attacks, but it may reduce their effectiveness so that hackers give up and move on to\neasier targets. Acting out social engineering skits in front of users often works very well; when employees\nsee how they can be manipulated into giving out private information, it becomes more memorable and\nthey tend to become much more careful.\nPhishing is a very common type of social engineering. The attacker simply sends an email to millions of\nusers telling them that their bank account has been shut down due to an unauthorized access attempt and", "source": "Page 393", "chapter_title": "Chapter 11"}
{"id": "0d2d9b542439-2", "text": "users telling them that their bank account has been shut down due to an unauthorized access attempt and\nthat they need to reactivate it by logging in. The email contains a link that directs the user to a fake\nwebsite that appears to be the bank\u2019s website. After the user logs into the fake site, the attacker has the\nuser\u2019s user ID and password and can break into his or her account at will. Clever variants on this include\nan email informing you that a new user has been added to your PayPal account, stating that the IRS has\nissued you a refund and you need to verify your social security number, or offering a mortgage at very low\nrate for which you need to provide your social security number and credit card number.", "source": "Page 393", "chapter_title": "Chapter 11"}
{"id": "d5743d860371-0", "text": "TECHNICAL FOCUS 11-6\nInside Kerberos\nKerberos, the most commonly used central authentication protocol, uses symmetric encryption\n(usually DES). Kerberos is used by a variety of central authentication services, including Windows\nactive directory services. When you log in to a Kerberos-based system, you provide your user ID and\npassword to the Kerberos software on your computer. This software sends a request containing the\nuser ID but not the password to the Kerberos authentication server (called the Key Distribution\nCenter [KDC]).\nThe KDC checks its database for the user ID, and if it finds it, then it accepts the log-in and does two\nthings. First, it generates a service ticket (ST) for the KDC that contains information about the KDC,\na time stamp, and, most importantly, a unique session key (SK1), which will be used to encrypt all\nfurther communication between the client computer and the KDC until the user logs off. SK1 is\ngenerated separately for each user and is different every time the user logs in. Now, here\u2019s the clever\npart: The ST is encrypted using a key based on the password that matches the user ID. The client\ncomputer can only decrypt the ST if it knows the password that matches the user ID used to log in. If\nthe user enters an incorrect password, the Kerberos software on the client can\u2019t decrypt the ST and\nasks the user to enter a new password. This way, the password is never sent over the network.\nSecond, the KDC creates a Ticket-Granting Ticket (TGT). The TGT includes information about the\nclient computer and a time stamp that is encrypted using a secret key known only to the KDC and\nother validated servers. The KDC sends the TGT to the client computer encrypted with SK1, because", "source": "Page 394", "chapter_title": "Chapter 11"}
{"id": "241ee57f9d5b-1", "text": "all communications between the client and the server are encrypted with SK1 (so no one else can\nread the TGT). The client decrypts the transmission to receive the TGT, but because the client does\nnot know the KDC\u2019s secret key, it cannot decrypt the contents of the TGT. From now until the user\nlogs off, the user does not need to provide his or her password again; the Kerberos client software\nwill use the TGT to gain access to all servers that require a password.\nThe first time a user attempts to use a server that requires a password, that server directs the user\u2019s\nKerberos software to obtain a ST for it from the KDC. The user\u2019s Kerberos software sends the TGT to\nthe KDC along with information about which server the user wants to access (remember that all\ncommunications between the client and the KDC are encrypted with SK1). The KDC checks to make\nsure that the user has not logged off, and if the TGT is validated, the KDC sends the client an ST for\nthe desired server and a new session key (SK2) that the client will use to communicate with that\nserver, both of which have been encrypted using SK1. The ST contains authentication information\nand SK2, both of which have been encrypted using the secret key known only to the KDC and the\nserver.\nThe client presents a log-in request (which specifies the user ID, a time and date stamp, and other\ninformation) that has been encrypted with SK2 and the ST to the server. The server decrypts the ST\nusing the KDC\u2019s secret key to find the authentication information and SK2. It uses the SK2 to decrypt\nthe log-in request. If the log-in request is valid after decrypting with SK2, the server accepts the log-", "source": "Page 394", "chapter_title": "Chapter 11"}
{"id": "8634ff0dce2c-2", "text": "in and sends the client a packet that contains information about the server that has been encrypted\nwith SK2. This process authenticates the client to the server and also authenticates the server to the\nclient. Both now communicate using SK2. Notice that the server never learns the user\u2019s password.\n11.4.7 Intrusion Prevention Systems\nIntrusion prevention systems (IPSs) are designed to detect an intrusion and take action to stop it.\nThere are two general types of IPS, and many network managers choose to install both. The first type is a\nnetwork-based IPS. With a network-based IPS, an IPS sensor is placed on key network circuits. An\nIPS sensor is simply a device running a special operating system that monitors all network packets on that\ncircuit and reports intrusions to an IPS management console. The second type of IPS is the host-\nbased IPS, which, as the name suggests, is a software package installed on a host or server. The host-\nbased IPS monitors activity on the server and reports intrusions to the IPS management console.", "source": "Page 394", "chapter_title": "Chapter 11"}
{"id": "132215f0f939-0", "text": "There are two fundamental techniques that these types of IPSs can use to determine that an intrusion is in\nprogress; most IPSs use both techniques. The first technique is misuse detection, which compares\nmonitored activities with signatures of known attacks. Whenever an attack signature is recognized, the\nIPS issues an alert and discards the suspicious packets. The problem, of course, is keeping the database of\nattack signatures up to date as new attacks are invented.\nMANAGEMENT FOCUS 11-8\nSocial Engineering Wins Again\nDanny had collected all the information he needed to steal the plans for the new product. He knew\nthe project manager\u2019s name (Bob Billings), phone number, department name, office number,\ncomputer user ID, and employee number, as well as the project manager\u2019s boss\u2019s name. These had\ncome from the company website and a series of innocuous phone calls to helpful receptionists. He\nhad also tricked the project manager into giving him his password, but that hadn\u2019t worked because\nthe company used one-time passwords using a time-based token system called Secure ID. So, after\ngetting the phone number of the computer operations room from another helpful receptionist, all he\nneeded was a snowstorm.\nLate one Friday night, a huge storm hit and covered the roads with ice. The next morning, Danny\ncalled the computer operations room:\nDanny:\n\u201cHi, this is Bob Billings in the Communications Group. I left my Secure ID in my desk and I need\nit to do some work this weekend. There\u2019s no way I can get into the office this morning. Could you\ngo down to my office and get it for me? And then read my code to me so I can log in?\u201d\nOperations:\n\u201cSorry, I can\u2019t leave the Operations Center.\u201d\nDanny:\n\u201cDo you have a Secure ID yourself?\u201d\nOperations:\n\u201cThere\u2019s one here we keep for emergencies.\u201d", "source": "Page 395", "chapter_title": "Chapter 11"}
{"id": "61be52f5da14-1", "text": "Operations:\n\u201cThere\u2019s one here we keep for emergencies.\u201d\nDanny:\n\u201cListen. Can you do me a big favor? Could you let me borrow your Secure ID? Just until it\u2019s safe to\ndrive in?\u201d\nOperations:\n\u201cWho are you again?\u201d\nDanny:\n\u201cBob Billings. I work for Ed Trenton.\u201d\nOperations:\n\u201cYeah, I know him.\u201d\nDanny:\n\u201cMy office is on the second floor (2202B). Next to Roy Tucker. It\u2019d be easier if you could just get\nmy Secure ID out of my desk. I think it\u2019s in the upper left drawer.\u201d (Danny knew the guy wouldn\u2019t\nwant to walk to a distant part of the building and search someone else\u2019s office.)", "source": "Page 395", "chapter_title": "Chapter 11"}
{"id": "c40dbb8195cf-0", "text": "Operations:\n\u201cI\u2019ll have to talk to my boss.\u201d\nAfter a pause, the operations technician came back on and asked Danny to call his manager on his\ncell phone. After talking with the manager and providing some basic information to \u201cprove\u201d he was\nBob Billings, Danny kept asking about having the operations technician go to \u201chis\u201d office.\nFinally, the manager decided to let Danny use the Secure ID in the Operations Center. The manager\ncalled the technician and gave permission for him to tell \u201cBob\u201d the one-time password displayed on\ntheir Secure ID any time he called that weekend. Danny was in.\nSource: Adapted from Kevin Mitnick and William Simon, The Art of Deception, John Wiley and Sons, 2002.\nThe second fundamental technique is anomaly detection, which works well in stable networks by\ncomparing monitored activities with the \u201cnormal\u201d set of activities. When a major deviation is detected\n(e.g., a sudden flood of ICMP ping packets, an unusual number of failed log-ins to the network manager\u2019s\naccount), the IPS issues an alert and discards the suspicious packets. The problem, of course, is false\nalarms when situations occur that produce valid network traffic that is different from normal (e.g., on a\nheavy trading day on Wall Street, e-trade receives a larger than normal volume of messages).\nFIGURE 11-19 Intrusion prevention system (IPS). DMZ = demilitarized zone; DNS = Domain Name\nService; NAT = network address translation\nIntrusion prevention systems are often used in conjunction with other security tools such as firewalls\n(Figure 11-19). In fact, some firewalls are now including IPS functions. One problem is that the IPS and its\nsensors and management console are a prime target for attackers. Whatever IPS is used, it must be very", "source": "Page 396", "chapter_title": "Chapter 11"}
{"id": "97098343da92-1", "text": "secure against attack. Some organizations deploy redundant IPSs from different vendors (e.g., a network-\nbased IPS from one vendor and a host-based IPS from another) to decrease the chance that the IPS can be", "source": "Page 396", "chapter_title": "Chapter 11"}
{"id": "23825a3d3006-0", "text": "hacked.\nAlthough IPS monitoring is important, it has little value unless there is a clear plan for responding to a\nsecurity breach in progress. Every organization should have a clear response planned if a break-in is\ndiscovered. Many large organizations have emergency response \u201cSWAT\u201d teams ready to be called into\naction if a problem is discovered. The best example is CERT, which is the Internet\u2019s emergency response\nteam. CERT has helped many organizations establish such teams.\nResponding to an intrusion can be more complicated than it at first seems. For example, suppose the IPS\ndetects a DoS attack from a certain IP address. The immediate reaction could be to discard all packets\nfrom that IP address; however, in the age of IP spoofing, the attacker could fake the address of your best\ncustomer and trick you into discarding packets from it.\n11.4.8 Intrusion Recovery\nOnce an intrusion has been detected, the first step is to identify how the intruder gained unauthorized\naccess and prevent others from breaking in the same way. Some organizations will simply choose to close\nthe door on the attacker and fix the security problem. About 30% of organizations take a more aggressive\nresponse by logging the intruder\u2019s activities and working with police to catch the individuals involved.\nOnce identified, the attacker will be charged with criminal activities and/or sued in civil court. Several\nstates and provinces have introduced laws requiring organizations to report intrusions and theft of\ncustomer data, so the percentage of intrusions reported and prosecuted will increase.\nA whole new area called computer forensics has recently opened up. Computer forensics is the use of\ncomputer analysis techniques to gather evidence for criminal and/or civil trials. The basic steps of\ncomputer forensics are similar to those of traditional forensics, but the techniques are different. First,\nidentify potential evidence. Second, preserve evidence by making backup copies and use those copies for", "source": "Page 397", "chapter_title": "Chapter 11"}
{"id": "d754ba9e7810-1", "text": "identify potential evidence. Second, preserve evidence by making backup copies and use those copies for\nall analysis. Third, analyze the evidence. Finally, prepare a detailed legal report for use in prosecutions.\nAlthough companies are sometimes tempted to launch counterattacks (or counterhacks) against\nintruders, this is illegal.\nSome organizations have taken their own steps to snare intruders by using entrapment techniques. The\nobjective is to divert the attacker\u2019s attention from the real network to an attractive server that contains\nonly fake information. This server is often called a honey pot. The honey pot server contains highly\ninteresting, fake information available only through illegal intrusion to \u201cbait\u201d the intruder. The honey pot\nserver has sophisticated tracking software to monitor access to this information that allows the\norganization and law enforcement officials to trace and legally document the intruder\u2019s actions.\nPossession of this information then becomes final legal proof of the intrusion.\n11.5 BEST PRACTICE RECOMMENDATIONS\nThis chapter provides numerous suggestions on business continuity planning and intrusion prevention.\nGood security starts with a clear disaster recovery plan and a solid security policy. Probably the best\nsecurity investment is user training: training individual users on data recovery and ways to defeat social\nengineering. But this doesn\u2019t mean that technologies aren\u2019t needed either.\nFigure 11-20 shows the most commonly used security controls. In the coming years, we expect two-factor\nauthentication and encryption to become much more popular.\nEven so, rarely does a week pass without a new warning of a major vulnerability. Leave a server\nunattended for two weeks, and you may find that you have five critical patches to install.", "source": "Page 397", "chapter_title": "Chapter 11"}
{"id": "f9685bddade3-0", "text": "FIGURE 11-20 Commonly used security controls\nPeople are now asking, \u201cWill it end?\u201d Is (in)security just a permanent part of the information systems\nlandscape? In a way, yes. The growth of information systems, along with the new and dangerous ability to\nreach into them from around the world, has created new opportunities for criminals. Mix the possibilities\nof stealing valuable, marketable information with the low possibilities for getting caught and punished,\nand we would expect increasing numbers of attacks.\nPerhaps the question should be: Does it have to be this bad? Unquestionably, we could be protecting\nourselves better. We could better enforce security policies and restrict access. But all of this has a cost.\nAttackers are writing and distributing a new generation of attack tools right before us\u2014tools that are very\npowerful, more difficult to detect, and very easy to use. Usually, such tools are much easier to use than\ntheir defensive countermeasures.\nThe attackers have another advantage, too. Whereas the defenders have to protect all vulnerable points all\nthe time to be safe, the attacker just has to break into one place one time to be successful.\nSo what may we expect in the future in \u201csecure\u201d organizational environments? We would expect to see\nstrong desktop management, including the use of thin clients. Centralized desktop management, in\nwhich individual users are not permitted to change the settings on their computers, may become common,\nalong with regular reimaging of computers to prevent Trojans and viruses and to install the most recent\nsecurity patches. All external software downloads will likely be prohibited.\nA Day in the Life: Network Security Manager\n\u201cManaging security is a combination of detective work and prognostication about the future.\u201d\nA network security manager spends much of his or her time doing three major things. First, much\ntime is spent looking outside the organization by reading and researching potential security holes", "source": "Page 398", "chapter_title": "Chapter 11"}
{"id": "99e5f1fed484-1", "text": "time is spent looking outside the organization by reading and researching potential security holes\nand new attacks because the technology and attack opportunities change so fast. It is important to\nunderstand new attack threats, new scripting tools used to create viruses, remote access Trojans and", "source": "Page 398", "chapter_title": "Chapter 11"}
{"id": "280983854237-0", "text": "other harmful software, and the general direction in which the hacking community is moving. Much\nimportant information is contained at websites such as those maintained by CERT (www.cert.org)\nand SANS (www.sans.org). This information is used to create new versions of standard computer\nimages that are more robust in defeating attacks and to develop recommendations for the\ninstallation of application security patches. It also means that he or she must update the\norganization\u2019s written security policies and inform users of any changes.\nSecond, the network security manager looks inward toward the networks he or she is responsible for.\nHe or she must check the vulnerability of those networks by thinking like a hacker to understand\nhow the networks may be susceptible to attack, which often means scanning for open ports and\nunguarded parts of the networks and looking for computers that have not been updated with the\nlatest security patches. It also means looking for symptoms of compromised machines such as new\npatterns of network activity or unknown services that have been recently opened on a computer.\nThird, the network security manager must respond to security incidents. This usually means\n\u201cfirefighting\u201d\u2014quickly responding to any security breach, identifying the cause, collecting forensic\nevidence for use in court, and fixing the computer or software application that has been\ncompromised.\nSource: With thanks to Kenn Crook.\nContinuous content filtering, in which all incoming packets (e.g., Web, email) are scanned, may become\ncommon, thus significantly slowing down the network. All server files and communications with client\ncomputers would be encrypted, further slowing down transmissions.\nFinally, all written security policies would be rigorously enforced. Violations of security policies might\neven become a \u201ccapital offense\u201d (i.e., meaning one violation and you are fired).\nWe may look forlornly back to the early days of the Internet when we could \u201cdo anything\u201d as its Golden\nDays.", "source": "Page 399", "chapter_title": "Chapter 11"}
{"id": "62f24a70647f-1", "text": "Days.\n11.6 IMPLICATIONS FOR YOUR CYBER SECURITY\nCyber security was once an esoteric field of interest to only a few dedicated professionals. Today, it is the\nfastest-growing area in information systems.\nThe good news is there are plenty of job opportunities. Experts estimate that by 2020 there will be one\nmillion unfilled jobs because companies won\u2019t be able to hire enough people to meet their needs. Many of\nthese jobs will require advanced training and years of experience, but about a third of them will be entry\nlevel positions.\nThe bad news is that you as a user will have to be more concerned with security than ever before, not only\nin your professional life but also in your personal life. We have several recommendations to help you\nmanage your personal cyber security.\nSubscribe to an automatic backup service to ensure you never lose data. We recommend Mozy and\nCarbonite.\nEnsure your computer\u2019s operating system and antivirus software are set to automatic update. Same for\nyour mobile phone and any smart devices like smart TVs.\nUse passphrases rather than short passwords, and sign-up for two-factor authentication on any important\nwebsite that offers it, such as your bank. Install and use a password manager.\nPut a passphrase on your laptop and a pin or fingerprint on your phone. Statistics show that an average\nperson will lose (or have stolen) two to three phones and laptops over their working life. Put an app on\nyour phone that enables it to be wiped or disabled remotely, because access to your data is worth far more\nthan the cost of the phone. For example, do you have a banking or payment app on your phone?\nNever click on a link in an email, no matter who sent it. More than 90% of emails containing links are", "source": "Page 399", "chapter_title": "Chapter 11"}
{"id": "3a7c5411411c-2", "text": "phishing attacks, so if an email has a link, it is a strong indicator that it is an attack. Instead, ignore the\nemail or use Google to find the URL you want.", "source": "Page 399", "chapter_title": "Chapter 11"}
{"id": "f9ec1aa44b6b-0", "text": "Never click on a pop-up warning that appears on a website (especially if it says something scary like your\ncomputer has a virus). It is trying to trick you into letting the website install malware (a virus or\nransomware); any button you click will install the malware, regardless of what the button says. Instead,\nclose the browser or turn off your computer.\nNever give out your passphrase to anyone. More than 99% of people who ask for your passphrase are\nattackers. Hang up the phone immediately; don\u2019t bother to say bye. If they are in your home or office, ask\nthem to step outside while you make a personal call and then lock the door and call the company IT help\ndesk. Real IT support staff will avert their eyes when you type your passphrase so they can\u2019t see what you\ntype.\nSUMMARY\nTypes of Security Threats In general, network security threats can be classified into one of two\ncategories: (1) business continuity and (2) intrusions. Business continuity can be interrupted by\ndisruptions that are minor and temporary, but some may also result in the destruction of data.\nNatural (or human-made) disasters may occur that destroy host computers or large sections of the\nnetwork. Intrusion refers to intruders (external attackers or organizational employees) gaining\nunauthorized access to files. The intruder may gain knowledge, change files to commit fraud or theft,\nor destroy information to injure the organization.\nRisk Assessment Developing a secure network means developing controls that reduce or eliminate\nthreats to the network. Controls prevent, detect, and correct whatever might happen to the\norganization when its computer-based systems are threatened. The first step in developing a secure\nnetwork is to conduct a risk assessment. This is done by identifying the key assets and threats and\ncomparing the nature of the threats to the controls designed to protect the assets. A company can pick", "source": "Page 400", "chapter_title": "Chapter 11"}
{"id": "5d98e3560727-1", "text": "one of several risk assessment frameworks that are considered to be industry standards.\nBusiness Continuity The major threats to business continuity are viruses, theft, DOS attacks,\ndevice failure, and disasters. Installing and regularly updating antivirus software is one of the most\nimportant and commonly used security controls. Protecting against DOS attacks is challenging and\noften requires special hardware. Theft is one of the most often overlooked threats and can be\nprevented by good physical security, especially the physical security of laptop computers. Devices fail,\nso the best way to prevent network outages is to ensure that the network has redundant circuits and\ndevices (e.g., switches and routers) on mission-critical network segments (e.g., the Internet\nconnection and core backbone). Avoiding disasters can take a few commonsense steps, but no\ndisaster can be completely avoided; most organizations focus on ensuring important data are backed\nup off-site and having a good, tested disaster recovery plan.\nIntrusion Prevention Intruders can be organization employees or external hackers who steal data\n(e.g., customer credit card numbers) or destroy important records. A security policy defines the key\nstakeholders and their roles, including what users can and cannot do. Firewalls often stop intruders\nat the network perimeter by permitting only authorized packets into the network, by examining\napplication layer packets for known attacks, and/or by hiding the organization\u2019s private IP addresses\nfrom the public Internet. Physical and dial-up security are also useful perimeter security controls.\nPatching security holes\u2014known bugs in an operating system or application software package\u2014is\nimportant to prevent intruders from using these to break in. Single key or public key encryption can\nprotect data in transit or data stored on servers. User authentication ensures only authorized users\ncan enter the network and can be based on something you know (passwords), something you have", "source": "Page 400", "chapter_title": "Chapter 11"}
{"id": "baebb162a96e-2", "text": "can enter the network and can be based on something you know (passwords), something you have\n(two-factor authentication), or something you are (biometrics). Preventing social engineering, where\nhackers trick users into revealing their passwords, is very difficult. Intrusion prevention systems are\ntools that detect known attacks and unusual activity and enable network managers to stop an\nintrusion in progress. Intrusion recovery involves correcting any damaged data, reporting the\nintrusion to the authorities, and taking steps to prevent the other intruders from gaining access the\nsame way.\nKEY TERMS", "source": "Page 400", "chapter_title": "Chapter 11"}
{"id": "2465e9ad058d-0", "text": "accept\naccess control list (ACL)\naccount\nAdvanced Encryption Standard (AES)\nadware\nalgorithm\nanomaly detection\nantivirus software\napplication-level firewall\nasset\nasymmetric encryption\nauthentication server\nauthentication\navailability\nbackup control\nbiometric system\nbrute-force attack\nbusiness continuity\ncentral authentication\ncertificate authority (CA)\ncertificate\nciphertext\ncomputer forensics\nconfidentiality\ncontinuous data protection (CDP)\ncontrols\ncorrective control\ncracker\nData Encryption Standard (DES)\nDDoS agent\nDDoS handler\ndecryption\ndefer\ndenial-of-service (DoS) attack\ndesktop management\ndetective control\ndisaster recovery drill\ndisaster recovery firm\ndisaster recovery plan", "source": "Page 401", "chapter_title": "Chapter 11"}
{"id": "13a5a728c1a0-0", "text": "disk mirroring\ndistributed denial-of-service (DDoS) attack\neavesdropping\nencryption\nentrapment\nfault-tolerant server\nfinancial\nfinancial impact\nfirewall\nhacker\nhoney pot\nhost-based IPS\nimpact score\ninformation warfare\nintegrity\nInternet Key Exchange (IKE)\nintrusion prevention systems (IPSs)\nIP Security Protocol (IPSec)\nIP spoofing\nIPS management console\nIPS sensor\nIPSec transport mode\nIPSec tunnel mode\nKerberos\nkey management\nkey\nlegal\nmalware\nmission-critical application\nmisuse detection\nmitigate\nNAT firewall\nnetwork address translation (NAT)\nnetwork-based IPS\none-time password\nonline backup\npacket-level firewall\npassphrase\npassword manager", "source": "Page 402", "chapter_title": "Chapter 11"}
{"id": "daf663771a83-0", "text": "password\npatch\nphishing\nphysical security\nplaintext\nPretty Good Privacy (PGP)\npreventive control\nPreventing unauthorized access\nprivate key\nproductivity\npublic key encryption\npublic key infrastructure (PKI)\npublic key\nransomware\nRC4\nrecovery control\nredundancy\nredundant array of independent disks (RAID)\nreputation\nrisk assessment frameworks\nrisk assessment\nrisk control strategy\nrisk mitigation\nrisk score\nrootkit\nRSA\nsafety\nSecure Sockets Layer (SSL)\nsecure switch\nsecurity hole\nsecurity policy\nshare\nsniffer program\nsocial engineering\nsomething you are\nsomething you have\nsomething you know\nspyware\nsymmetric encryption", "source": "Page 403", "chapter_title": "Chapter 11"}
{"id": "b5acf3811916-0", "text": "threat scenario\nthreat\ntraffic analysis\ntraffic anomaly analyzer\ntraffic anomaly detector\ntraffic filtering\ntraffic limiting\ntriple DES (3DES)\nTrojan horse\ntwo-factor authentication\nuninterruptible power supply (UPS)\nuser authentication\nuser profile\nvirus\nworm\nzero-day attack\nQUESTIONS\n1. What factors have brought an increased emphasis on network security?\n2. Briefly outline the steps required to complete a risk assessment.\n3. Name and describe the main impact areas. Who should be responsible for assessing what is meant by\nlow/medium/high impact for each of the impact areas? Explain your answer.\n4. What are some of the criteria that can be used to rank security risks?\n5. What are the most common security threats? What are the most critical? Why?\n6. Explain the purpose of threat scenarios. What are the steps in preparing threat scenarios?\n7. What is the purpose of the risk score, and how is it calculated?\n8. What are the possible risk control strategies? How do we pick which one to use?\n9. Why is it important to identify improvements that are needed to mitigate risks?\n10. What is the purpose of a disaster recovery plan? What are the five major elements of a typical disaster\nrecovery plan?\n11. What is a computer virus? What is ransomware?\n12. Explain how a denial-of-service attack works.\n13. How does a denial-of-service attack differ from a distributed denial-of-service attack?\n14. What is a disaster recovery firm? When and why would you establish a contract with them?\n15. What is online backup?\n16. People who attempt intrusion can be classified into several different categories. Describe them.\n17. There are many components in a typical security policy. Describe three important components.\n18. What are the major aspects of intrusion prevention?", "source": "Page 404", "chapter_title": "Chapter 11"}
{"id": "df7d1183778a-1", "text": "18. What are the major aspects of intrusion prevention?\n19. How do you secure the network perimeter?\n20. What is physical security, and why is it important?", "source": "Page 404", "chapter_title": "Chapter 11"}
{"id": "4a177d968aee-0", "text": "21. What is eavesdropping in a computer security sense?\n22. What is a sniffer?\n23. What is a firewall?\n24. How do the different types of firewalls work?\n25. What is IP spoofing?\n26. What is a NAT firewall, and how does it work?\n27. What is a security hole, and how do you fix it?\n28. Explain how a Trojan horse works.\n29. Compare and contrast symmetric and asymmetric encryption.\n30. Describe how symmetric encryption and decryption work.\n31. Describe how asymmetric encryption and decryption work.\n32. What is key management?\n33. How does DES differ from 3DES? From AES?\n34. Compare and contrast DES and public key encryption.\n35. Explain how authentication works.\n36. What is PKI, and why is it important?\n37. What is CA?\n38. How does PGP differ from SSL?\n39. How does SSL differ from IPSec?\n40. What are the three major ways of authenticating users? What are the pros and cons of each\napproach?\n41. What are the different types of two factor authentication methods and how do they work?\n42. Explain how a biometric system can improve security. What are the problems with it?\n43. Why is the management of user profiles an important aspect of a security policy?\n44. What is social engineering? Why does it work so well?\n45. What techniques can be used to reduce the chance that social engineering will be successful?\n46. What is an IPS?\n47. How does IPS anomaly detection differ from misuse detection?\n48. What is computer forensics?\n49. What is a honey pot?\n50. A few security consultants have said that fast Internet and wireless technologies are their best friends.\nExplain.", "source": "Page 405", "chapter_title": "Chapter 11"}
{"id": "da91076313b1-1", "text": "Explain.\n51. Most hackers start their careers breaking into computer systems as teenagers. What can we as a\ncommunity of computer professionals do to reduce the temptation to become a hacker?\n52. Some experts argue that CERT\u2019s posting of security holes on its website causes more security break-\nins than it prevents and should be stopped. What are the pros and cons of both sides of this\nargument? Do you think CERT should continue to post security holes?\n53. What is one of the major risks of downloading unauthorized copies of music files from the Internet\n(aside from the risk of fines and lawsuits)?\n54. Although it is important to protect all servers, some servers are more important than others. What\nserver(s) are the most important to protect and why?", "source": "Page 405", "chapter_title": "Chapter 11"}
{"id": "c1ba1dfab206-0", "text": "EXERCISES\nA. Conduct a risk assessment of your organization\u2019s networks. Some information may be confidential, so\nreport what you can.\nB. Investigate and report on the activities of CERT (the Computer Emergency Response Team).\nC. Investigate the capabilities and costs of a disaster recovery service.\nD. Investigate the capabilities and costs of a firewall.\nE. Investigate the capabilities and costs of an IPS.\nF. Investigate the capabilities and costs of an encryption package.\nG. Investigate the capabilities and costs of an online backup service.\nH. Is the DMZ dead? Investigate the use of DMZ in organizations. What lessons can organizations learn\nfrom the DMZ mechanism?\nMINICASES\nI. Belmont State Bank Belmont State Bank is a large bank with hundreds of branches that are\nconnected to a central computer system. Some branches are connected over dedicated circuits and\nothers use Multiprotocol Label Switching (MPLS). Each branch has a variety of client computers and\nATMs connected to a server. The server stores the branch\u2019s daily transaction data and transmits it\nseveral times during the day to the central computer system. Tellers at each branch use a four-digit\nnumeric password, and each teller\u2019s computer is transaction-coded to accept only its authorized\ntransactions. Perform a risk assessment.\nII. Western Bank Western Bank is a small, family-owned bank with six branches spread over the\ncounty. It has decided to move onto the Internet with a website that permits customers to access their\naccounts and pay bills. Design the key security hardware and software the bank should use.\nIII. Classic Catalog Company, Part 1 Classic Catalog Company runs a small but rapidly growing\ncatalog sales business. It outsourced its Web operations to a local ISP for several years, but as sales", "source": "Page 406", "chapter_title": "Chapter 11"}
{"id": "c6789d05c286-1", "text": "over the Web have become a larger portion of its business, it has decided to move its website onto its\nown internal computer systems. It has also decided to undertake a major upgrade of its own internal\nnetworks. The company has two buildings, an office complex and a warehouse. The two-story office\nbuilding has 60 computers. The first floor has 40 computers, 30 of which are devoted to telephone\nsales. The warehouse, located 400 feet across the company\u2019s parking lot from the office building, has\nabout 100,000 square feet, all on one floor. The warehouse has 15 computers in the shipping\ndepartment located at one end of the warehouse. The company is about to experiment with using\nwireless handheld computers to help employees more quickly locate and pick products for customer\norders. Based on traffic projections for the coming year, the company plans to use a T1 connection\nfrom its office to its ISP. It has three servers: the main Web server, an email server, and an internal\napplication server for its application systems (e.g., orders, payroll). Perform a risk assessment.\nIV. Classic Catalog Company, Part 2 Read MINICASES III above. Outline a brief business continuity\nplan, including controls to reduce the risks in advance as well as a disaster recovery plan.\nV. Classic Catalog Company, Part 3 Read MINICASES III above. Outline a brief security policy and\nthe controls you would implement to control unauthorized access.\nVI. Classic Catalog Company, Part 4 Read MINICASES III above. What patching policy would you\nrecommend for Classic Catalog?\nVII. Personal Password Storage and Protection To help us not forget our many passwords, there\nare several companies that provide password managers. Find the top five password manager\nprograms, compare their features and costs, and make a presentation of your findings to your\nclassmates.", "source": "Page 406", "chapter_title": "Chapter 11"}
{"id": "a74c15173506-0", "text": "TECH UPDATES\nIn every chapter, we will offer a couple of ideas to investigate. Pick one of these topics to investigate.\nTopic A: Black, White, and Grey Hat Hackers\nThere are many different types of hackers\u2014some who illegally hack companies for financial gain, some\nwho the company hires to hack their own system (the \u201cgood guys\u201d), and those in between. What are some\nreal examples of each case and why might a company hire a hacker to infiltrate their own system? Where\ncan you learn to hack? How lucrative is it? What kinds of different attacks may a hacker employ?\nTopic B: Top Cybersecurity Programs and Certifications\nThere is a cybersecurity skill gap. Research suggests that in five years, there will be 3.5 million unfilled\ncybersecurity jobs. This deficit of skills is likely to become a growing matter of public concern. Where can\nyou get an education? Or certification? What skills are needed? How much does it pay?\nDeliverables\nYour job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title Slide\n2. Short description of the topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use a lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along\n5. How does it relate to material covered in class so far (and in the future)\n6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 11A\nSecuring Your Computer\nThis chapter has focused on security, including risk analysis, business continuity, and intrusion", "source": "Page 407", "chapter_title": "Chapter 11"}
{"id": "327cddf040a7-1", "text": "This chapter has focused on security, including risk analysis, business continuity, and intrusion\nprevention. At first glance, you may think security applies to corporate networks, not your network.\nHowever, if you have a LAN at your house or apartment, or even if you just own a desktop or laptop\ncomputer, security should be one of your concerns. There are so many potential threats to your business\ncontinuity\u2014which might be your education\u2014and to intrusion into your computer(s) that you need to take\naction.\nYou should perform your own risk analysis, but this section provides a brief summary of some simple\nactions you should take that will greatly increase your security. Do this this week; don\u2019t procrastinate. Our\nfocus is on Windows security, because most readers of this book use Windows computers, but the same\nadvice (but different commands) applies to Apple computers.\nBusiness Continuity\nIf you run your own business, then ensuring business continuity should be a major focus of your efforts.\nBut even if you are \u201cjust\u201d an employee or a student, business continuity is important. What would happen\nif your hard disk failed just before the due date for a major report?\n1. The first and most important security action you can take is to configure Windows to perform", "source": "Page 407", "chapter_title": "Chapter 11"}
{"id": "04872ca22d85-0", "text": "automatic updates. This will ensure you have the latest patches and updates installed.\n2. The second most important action is to buy and install antivirus software such as that from\nSymantec. Be sure to configure it for regular updates too. If you perform just these two actions, you\nwill be relatively secure from viruses, but you should scan your system for viruses on a regular basis,\nsuch as the first of every month, when you pay your rent or mortgage.\n3. Spyware is another threat. You should buy and install antispyware software that provides the same\nprotection that antivirus software does for viruses. Spybot is a good package. Be sure to configure this\nsoftware for regular updates and scan your system on a regular basis.\n4. One of the largest sources of viruses, spyware, and adware are free software and music/video files\ndownloaded from the Internet. Simply put, don\u2019t download any file unless it is from a trusted vendor\nor distributor of software and files.\n5. Develop a disaster recovery plan. You should plan today for what you would do if your computer were\ndestroyed. What files would you need? If there are any important files that you wouldn\u2019t want to lose\n(e.g., reports you\u2019re working on, key data, or precious photos), you should develop a backup and\nrecovery plan for them. The simplest is to copy the files to a shared directory on another computer on\nyour LAN. But this won\u2019t enable you to recover the files if your apartment or house was destroyed by\nfire, for example. A better plan is to subscribe to a free online backup service such as mozy.com or\ncarbonite.com (think CDP on the cheap). If you don\u2019t use such a site, buy a large USB drive, copy your", "source": "Page 408", "chapter_title": "Chapter 11"}
{"id": "6dea23cf38ac-1", "text": "files to it, and store it off-site in your office or at a friend\u2019s house. A plan is only good if it is followed,\nso your data should be regularly backed up, such as doing so the first of every month.\nDeliverables\n1. Perform risk analysis for your home network.\n2. Prepare a disaster recovery plan for your home network.\n3. Research antivirus and antispyware software that you can purchase for your home network.\nHANDS-ON ACTIVITY 11B\nHow to Set Up Encryption on Your Computer\nIf you want to protect the data on your computer, you need to encrypt it. Encryption is widely used on the\nInternet these days\u2014when you are making a purchase on Amazon or another retailer, your computer\nencrypts your credit card information before it gets transferred over the Internet.\nShould you encrypt the data on your computer? The answer is yes. What if your computer gets stolen?\nYou might say that your computer is password protected. Well, breaking into a password-protected\ncomputer is extremely easy. Should you then encrypt only your files, or should you encrypt the entire\ndrive? If you only encrypt your files, if your computer gets stolen, the criminal will not be able to read your\nfiles but will still be able to install anything on your computer and see all the nonencrypted files. If you\nencrypt the entire drive, it would make it extremely difficult for anybody even to boot your computer\nwithout the password. However, if you ever forget your password or your drive gets corrupted, you\nprobably wouldn\u2019t be able to retrieve your data files at all. That\u2019s why it\u2019s important to set up data recovery\nfeatures specific to your operating system such as your Microsoft account for Windows and iCloud for\nApple products.\nWindows\n1. Open your file explorer and navigate to your drives. From here, right-click on the drive that you", "source": "Page 408", "chapter_title": "Chapter 11"}
{"id": "f5fc141c912b-2", "text": "would like to encrypt and press Turn on BitLocker (Figure 11-21).", "source": "Page 408", "chapter_title": "Chapter 11"}
{"id": "a368805673aa-0", "text": "FIGURE 11-21 BitLocker\n2. Choose the new encryption mode (Figure 11-22).", "source": "Page 409", "chapter_title": "Chapter 11"}
{"id": "11a67bdbaad5-0", "text": "FIGURE 11-22 Selecting the encryption mode\n3. Begin encryption (Figure 11-23)", "source": "Page 410", "chapter_title": "Chapter 11"}
{"id": "e3206671a1e1-0", "text": "FIGURE 11-23 Starting the encryption\nMac\n1. Navigate to the Apple logo at the top right of your screen. Open the Apple menu and press System\nPreferences (Figure 11-24).\n2. Type FileVault at the search bar in the top right and click return (Figure 11-25).\n3. Press Turn on FileVault and wait while the drive is encrypted (this may take a while, this is best to\nleave and complete overnight) (Figure 11-26).", "source": "Page 411", "chapter_title": "Chapter 11"}
{"id": "a24eccdb558b-0", "text": "FIGURE 11-24 System Preferences for a Mac\nDeliverable\nEncrypt a folder on your home computer. Show a screenshot of the encrypted folder.\nHANDS-ON ACTIVITY 11C\nEncryption Lab\nThe purpose of this lab is to practice encrypting and decrypting email messages using a standard called\nPGP (Pretty Good Privacy) that is implemented at https://8gwifi.org/pgpencdec.jsp (links to an external\nsite). You may generate your public keys here: https://www.igolder.com/pgp/generate-key/.\n1. Open https://www.igolder.com/pgp/generate-key/ (links to an external site) and generate your PGP\nkey pair\u2014your personal private and public keys (Figure 11-27). Save these in a note file; an example\nwith the password and private key removed is shown below:", "source": "Page 412", "chapter_title": "Chapter 11"}
{"id": "cc674af6676e-0", "text": "FIGURE 11-25 Searching system preferences\nFIGURE 11-26 Security & Privacy: FileVault", "source": "Page 413", "chapter_title": "Chapter 11"}
{"id": "4c8ab47006b1-0", "text": "FIGURE 11-27 PGP key generator\n2. Next, open https://8gwifi.org/pgpencdec.jsp (links to an external site) and create an encrypted\nmessage with your public key (Figure 11-28). It should look something like this with the recipients\npublic key in the public key field:\n3. If you were sent a message, you could decrypt it by clicking the decrypt radio button on the site and\nputting in you private key and passphrase that you set up before (Figure 11-29).\nDeliverables\nCreate your key pair. Post your public key to a folder/discussion board as specified by your professor.\nCopy the public key of your professor. Send your instructor an encrypted message that contains\ninformation about your favorite food, hobbies, places to travel, and so on (Figure 11-30).\nYour professor will send you a response that will be encrypted. Decrypt the email and print its\ncontent so that you can submit a hard copy in class.\nHANDS-ON ACTIVITY 11D\nApollo Residence Network Design\nApollo is a luxury residence hall that will serve honors students at your university. We described the\nresidence in Hands-On Activities at the end of the previous chapters. The university is concerned about\ncyber security and wants to ensure that the Apollo Residence had good business continuity and is well\nprotected against intrusion. It needs to ensure that the network design protects both its residence\noperations and the students who live in Apollo. The university is well aware that half of all intrusion\nattempts come from inside the organization, which in this case means its own students.", "source": "Page 414", "chapter_title": "Chapter 11"}
{"id": "3f6462e41565-0", "text": "FIGURE 11-28 PGP encryption\nDeliverable\nYour team was hired to design the network security for the residence. Using the network design from the\nprevious chapters, decide what security hardware, software, and services you will buy. Figure 11-31\nprovides a list of possibilities.", "source": "Page 415", "chapter_title": "Chapter 11"}
{"id": "b9b52a25850d-0", "text": "FIGURE 11-29 PGP decryption", "source": "Page 416", "chapter_title": "Chapter 11"}
{"id": "85a0f9a260db-0", "text": "FIGURE 11-30 Selecting a recipient of an encrypted message", "source": "Page 417", "chapter_title": "Chapter 11"}
{"id": "bfe00b8e318b-0", "text": "FIGURE 11-31 Security hardware, software, and services", "source": "Page 418", "chapter_title": "Chapter 11"}
{"id": "7c3cc72c33d0-0", "text": "CHAPTER 12\nNETWORK MANAGEMENT\nNetwork managers perform two key tasks: (1) designing new networks and network upgrades and (2)\nmanaging the day-to-day operation of existing networks. The previous chapters have examined network\ndesign, so this chapter focuses on day-to-day network management, discussing the things that must be\ndone to ensure that the network functions properly, although we do discuss some special-purpose\nequipment designed to improve network performance. Our focus is on the network management\norganization and the basic functions that a network manager must perform to operate a successful\nnetwork.\nOBJECTIVES\nUnderstand what is required to manage the day-to-day operation of networks\nBe familiar with the network management organization\nUnderstand configuration management\nUnderstand performance and fault management\nBe familiar with end-user support\nBe familiar with cost management\nOUTLINE\n12.1 Introduction\n12.2 Designing for Network Performance\n12.2.1 Managed Networks\n12.2.2 Managing Network Traffic\n12.2.3 Reducing Network Traffic\n12.3 Configuration Management\n12.3.1 Configuring the Network and Client Computers\n12.3.2 Documenting the Configuration\n12.4 Performance and Fault Management\n12.4.1 Network Monitoring\n12.4.2 Failure Control Function\n12.4.3 Performance and Failure Statistics\n12.4.4 Improving Performance\n12.5 End User Support\n12.5.1 Resolving Problems\n12.5.2 Providing End User Training\n12.6 Cost Management\n12.6.1 Sources of Costs\n12.6.2 Reducing Costs\n12.7 Implications for Cyber Security", "source": "Page 419", "chapter_title": "Chapter 11"}
{"id": "093eede33f9e-0", "text": "Summary\n12.1 INTRODUCTION\nNetwork management is the process of operating, monitoring, and controlling the network to ensure it\nworks as intended and provides value to its users. The primary objective of the data communications\nfunction is to move application-layer data from one location to another in a timely fashion and to provide\nthe resources that allow this transfer to occur. This transfer of information may take place within a single\ndepartment, between departments in an organization, or with entities outside the organization across\nprivate networks or the Internet.\nWithout a well-planned, well-designed network and without a well-organized network management staff,\noperating the network becomes extremely difficult. Unfortunately, many network managers spend most of\ntheir time firefighting\u2014dealing with breakdowns and immediate problems. If managers do not spend\nenough time on planning and organizing the network and networking staff, which are needed to predict\nand prevent problems, they are destined to be reactive rather than proactive in solving problems.\nMANAGEMENT FOCUS 12-1\nWhat Do Network Managers Do?\nIf you were to become a network manager, some of your responsibilities and tasks would be the\nfollowing:\nManage the day-to-day operations of the network.\nProvide support to network users.\nEnsure the network is operating reliably.\nEvaluate and acquire network hardware, software, and services.\nManage the network technical staff.\nManage the network budget, with emphasis on controlling costs.\nDevelop a strategic (long-term) networking and voice communications plan to meet the\norganization\u2019s policies and goals.\nKeep abreast of the latest technological developments in computers, data communications\ndevices, network software, and the Internet.\nKeep abreast of the latest technological developments in telephone technologies and network\nservices.\nAssist senior management in understanding the business implications of network decisions and\nthe role of the network in business operations.\n12.2 DESIGNING FOR NETWORK PERFORMANCE", "source": "Page 420", "chapter_title": "Chapter 11"}
{"id": "e41c7e0fd6ae-1", "text": "the role of the network in business operations.\n12.2 DESIGNING FOR NETWORK PERFORMANCE\nAt the end of the previous chapters, we have discussed the best practice design for LANs, backbones,\nWANs, and WLANs and examined how different technologies and services offered different effective data\nrates at different costs. In the backbone and WAN chapters, we also examined different topologies and\ncontrasted the advantages and disadvantages of each. So at this point, you should have a good\nunderstanding of the best choices for technologies and services and how to put them together into a good\nnetwork design. In this section, we examine several higher-level concepts used to design the network for\nthe best performance.\n12.2.1 Managed Networks", "source": "Page 420", "chapter_title": "Chapter 11"}
{"id": "297674932880-0", "text": "The single most important element that contributes to the performance of a network is a managed\nnetwork that uses managed devices. Managed devices are standard devices, such as switches and\nrouters, that have small onboard computers to monitor the traffic that flows through the device as well as\nthe status of the device and other devices connected to it. You\u2019ll recall that we discussed SDWAN\ntechnology in Chapter 9. An SDWAN is one example of a managed network. Most network management\nsoftware provides SDWAN capabilities, but there is also dedicated SDWAN software that only manages\nthe WAN.\nManaged devices perform their normal functions (e.g., routing, switching) and also provide three\nadditional capabilities. First, they record data on the traffic they process. These data are sent to the\nnetwork management console either every few seconds or when the device receives a special control\nmessage requesting the data. These data enable the network manager to see which circuits are busy and\nnot busy, both for real-time management and longer-term network planning and design.\nSecond, managed devices monitor the status of other devices around them and can send an alarm\nmessage to the network management console if they detect a critical situation such as a failing device or a\nhuge increase in traffic. These alarms are configurable so the network manager can define whatever\ncriteria he or she likes. The alarms can be sent from the management console to the manager\u2019s mobile\nphone or other devices, so no one has to be at the console to receive the alarms.\nThird, managed devices and the management console software can be programed to take action when\ncertain events occurs. For example, a managed device can be configured to detect if a nearby device is no\nlonger responding, and if so, to send an alarm and automatically reroute around the failed device.\nIn this way, network problems can be detected and reported by the devices themselves before problems", "source": "Page 421", "chapter_title": "Chapter 11"}
{"id": "33c9e9163a70-1", "text": "In this way, network problems can be detected and reported by the devices themselves before problems\nbecome serious. In the case of the failing network card, a managed device could record the increased\nnumber of retransmissions required to successfully transmit messages and inform the network\nmanagement software of the problem. A managed switch is often able to detect the faulty transmissions\nfrom a failing network card, disable the incoming circuit so that the card could not send any more\nmessages, and issue an alarm to the network manager. In either case, finding and fixing problems is much\nsimpler, requiring minutes, not hours.\nNetwork Management Software\nA managed network requires both hardware and software: managed devices (e.g., switches, routers, APs)\nto monitor, collect, and transmit traffic reports and problem alerts; and network management software to\nstore, organize, and analyze these reports and alerts. Managed devices are more expensive than\nunmanaged devices because they have a CPU and software built into them. When we build a managed\nnetwork, we normally buy all managed devices, rather than cutting costs by buying some managed devices\nand some unmanaged devices, although some organizations do install a mix of managed and unmanaged\ndevices to cut costs. In this case, the managed devices are usually placed on the backbone and unmanaged\ndevices in the access layer. There are three fundamentally different types of network management\nsoftware.\nDevice management software (sometimes called point management software) is designed to provide\ninformation about the specific devices on a network. It enables the network manager to monitor\nimportant devices such as servers, routers, and switches to report configuration information, traffic\nvolumes, and error conditions for each device. Figure 12-1 shows a sample display from a device\nmanagement software package running at Indiana University. This figure shows the amount of traffic on", "source": "Page 421", "chapter_title": "Chapter 11"}
{"id": "5d42b19d1943-2", "text": "management software package running at Indiana University. This figure shows the amount of traffic on\nthe university\u2019s core backbone network. This chart is in color, which is hard to see in a black-and-white\nbook. The chart shows that traffic is generally under control, with most circuits running at 10% or less of\ncapacity. A few circuits are running at between 20% and 50% of capacity (e.g., the circuits between\nbr2.ictc and br2.bldc). You can see that all circuits are full duplex because there are different traffic\namounts in each direction.\nSystem management software (sometimes called enterprise management software or a network\nmanagement framework) provides the same configuration, traffic, and error information as device\nmanagement systems but can analyze the device information to diagnose patterns, not just display\nindividual device problems. This is important when a critical device fails (e.g., a router into a high-traffic\nbuilding). With device management software, all of the devices that depend on the failed device will", "source": "Page 421", "chapter_title": "Chapter 11"}
{"id": "5af14ff10729-0", "text": "attempt to send warning messages to the network administrator. One failure often generates several\ndozen problem reports, called an alarm storm, making it difficult to pinpoint the true source of the\nproblem quickly. The dozens of error messages are symptoms that mask the root cause. System\nmanagement software tools correlate the individual error messages into a pattern to find the true cause,\nwhich is called root cause analysis, and then report the pattern to the network manager. Rather than\nfirst seeing pages and pages of error messages, the network manager instead is informed of the root cause\nof the problem.\nApplication management software also builds on the device management software, but instead of\nmonitoring systems, it monitors applications. In many organizations, there are mission-critical\napplications that should get priority over other network traffic. For example, real-time order-entry\nsystems used by telephone operators need priority over email. Application management systems track\ndelays and problems with application layer packets and inform the network manager if problems occur.\nFIGURE 12-1 Device management software used on Indiana University\u2019s core backbone network\nNetwork Management Standards\nOne important problem is ensuring that hardware devices from different vendors can understand and\nrespond to the messages sent by the network management software of other vendors. By this point in the\nbook, the solution should be obvious: standards. A number of formal and de facto standards have been\ndeveloped for network management. These standards are application layer protocols that define the type\nof information collected by network devices and the format of control messages that the devices\nunderstand.\nThe most commonly used network management protocol is Simple Network Management Protocol\n(SNMP). Each SNMP device (e.g., router, switch, server) has an agent that collects information about\nitself and the messages it processes and stores that information in a database called the management", "source": "Page 422", "chapter_title": "Chapter 11"}
{"id": "4da96a836ed9-0", "text": "information base (MIB). The network manager\u2019s management station that runs the network\nmanagement software has access to the MIB. Using this software, the network manager can send\ncontrol messages to individual devices or groups of devices asking them to report the information stored\nin their MIB.\nMost SNMP devices have the ability for remote monitoring (RMON). Most first-generation SNMP\ntools reported all network monitoring information to one central network management database. Each\ndevice would transmit updates to its MIB on the server every few minutes, greatly increasing network\ntraffic. RMON SNMP software enables MIB information to be stored on the device itself or on distributed\nRMON probes that store MIB information closer to the devices that generate it. The data are not\ntransmitted to the central server until the network manager requests, thus reducing network traffic\n(Figure 12-2).\nFIGURE 12-2 Network management with Simple Network Management Protocol (SNMP). MIB =\nmanagement information base\nNetwork information is recorded based on the data link layer protocols, network layer protocols, and\napplication layer protocols so that network managers can get a very clear picture of the exact types of\nnetwork traffic. Statistics are also collected based on network addresses so the network manager can see\nhow much network traffic any particular computer is sending and receiving. A wide variety of alarms can\nbe defined, such as instructing a device to send a warning message if certain items in the MIB exceed\ncertain values (e.g., if circuit utilization exceeds 50%).\nAs the name suggests, SNMP is a simple protocol with a limited number of functions. One problem with\nSNMP is that many vendors have defined their own extensions to it. So the network devices sold by a", "source": "Page 423", "chapter_title": "Chapter 11"}
{"id": "35a5a17e7c36-0", "text": "vendor may be SNMP compliant, but the MIBs they produce contain additional information that can be\nused only by network management software produced by the same vendor. Therefore, although SNMP\nwas designed to make it easier to manage devices from different vendors, in practice, this is not always the\ncase.\nMANAGEMENT FOCUS 12-2\nNetwork Management at ZF Lenksysteme\nZF Lenksysteme manufactures steering systems for cars and trucks. It is headquartered in southern\nGermany but has offices and plants in France, England, the United States, Brazil, India, China, and\nMalaysia. Its network has about 300 servers and 600 devices (e.g., routers, switches).\nZF Lenksysteme had a network management system, but when a problem occurred with one device,\nnearby devices also issued their own alarms. The network management software did not recognize\nthe interactions among the devices, and the resulting alarm storm meant that it took longer to\ndiagnose the root cause of the problem.\nThe new HP network management system monitors and controls the global network from one\ncentral location with only three staff. All devices and servers are part of the system, and\ninterdependencies are well defined, so alarm storms are a thing of the past. The new system has cut\ncosts by 50% and also has extended network management into the production line. The robots on\nthe production line now use TCP/IP networking, so they can be monitored like any other device.\nSources: ZF Lenksysteme, HP Case studies, hp.com.\n12.2.2 Managing Network Traffic\nMost approaches to improving network performance attempt to maximize network speed. Another\napproach is to manage where and how we route traffic to improve network performance. This section\nexamines two tools designed to better manage traffic with the ultimate goal of improving network\nperformance.\nLoad Balancing", "source": "Page 424", "chapter_title": "Chapter 11"}
{"id": "695a78d172ea-1", "text": "performance.\nLoad Balancing\nAs we mentioned in Chapter 7 on the design of the data center, servers are typically placed together in\nserver farms or clusters, which sometimes have hundreds of servers that perform the same task. In\nthis case, it is important to ensure that when a request arrives at the server farm, it is immediately\nforwarded to a server that is not busy\u2014or is the least busy.\nA special device called a load balancer or virtual server acts as a traffic manager at the front of the\nserver farm (Figure 12-3). All requests are directed to the load balancer at its IP address. When a request\nhits the load balancer, it forwards it to one specific server using the server\u2019s IP address. Sometimes a\nsimple round-robin formula is used (requests go to each server one after the other in turn); in other cases,\nmore complex formulas track how busy each server actually is. If a server crashes, the load balancer stops\nsending requests to it, and the network continues to operate without the failed server. Load balancing\nmakes it simple to add servers (or remove servers) without affecting users. You simply add or remove the\nserver(s) and change the software configuration in the load balancer; no one is aware of the change.\nPolicy-Based Management\nWith policy-based management (sometimes called application shaping or traffic shaping), the\nnetwork manager uses special software to set priority policies for network traffic that take effect when the\nnetwork becomes busy. For example, the network manager might say that order processing and\nvideoconferencing get the highest priority (order processing because it is the lifeblood of the company and\nvideoconferencing because poor response time will have the greatest impact on it).\nThe policy management is usually implemented as a combination of hardware and software. A special\ndevice called a traffic shaper is installed at a key point (usually between a building backbone and the", "source": "Page 424", "chapter_title": "Chapter 11"}
{"id": "15a4b0e8e4ac-0", "text": "campus backbone). The software to manage this device also configures the network devices behind it\nusing the quality of service (QoS) capabilities in TCP/IP and/or VLANs to give certain applications the\nhighest priority when the devices become busy. Policy-based management requires managed devices that\nsupport QoS.\nFIGURE 12-3 Network with load balancer\n12.2.3 Reducing Network Traffic\nA more radical approach to improving performance is to reduce the amount of traffic on the network. This\nmay seem quite difficult at first glance\u2014after all, how can we reduce the number of Web pages people\nrequest? We can\u2019t reduce all types of network traffic, but if we limit high-capacity users and move the\nmost commonly used data closer to the users who need it, we can reduce traffic enough to have an impact\non network performance. This section discusses three different tools that can be used.\nCapacity Management\nCapacity management devices, sometimes called bandwidth limiter or bandwidth shapers,\nmonitor traffic and can slow down traffic from users who consume a lot of network capacity. Capacity\nmanagement is related to policy-based management but is simpler in that it only looks at the source of the\ntraffic (i.e., the source IP address) rather than the nature of the traffic (e.g., videoconferencing, email,\nWeb pages). These devices are installed at key points in the network, such as between a backbone and the\ncore network. Figure 12-4 shows the control panel for one device made by Net Equalizer.\nContent Caching\nThe basic idea behind content caching is to store other people\u2019s Web data closer to your users. With\ncontent caching, you install a content engine (also called a cache engine) close to your Internet\nconnection and install special content management software on the router (Figure 12-5). The router", "source": "Page 425", "chapter_title": "Chapter 11"}
{"id": "1d62a948d53e-1", "text": "connection and install special content management software on the router (Figure 12-5). The router\ndirects all outgoing Web requests and the files that come back in response to those requests to the cache", "source": "Page 425", "chapter_title": "Chapter 11"}
{"id": "ef2c514d340a-0", "text": "engine. The content engine stores the request and the static files that are returned in response (e.g.,\ngraphics files, banners). The content engine also examines each outgoing Web request to see if it is\nrequesting static content that the content engine has already stored. If the request is for content already in\nthe content engine, it intercepts the request and responds directly itself with the stored file but makes it\nappear as though the request came from the URL specified by the user. The user receives a response\nalmost instantaneously and is unaware that the content engine responded. The content engine is\ntransparent.\nFIGURE 12-4 Capacity management software", "source": "Page 426", "chapter_title": "Chapter 11"}
{"id": "3bb182897051-0", "text": "FIGURE 12-5 Network with content engine\nAlthough not all Web content will be in the content engine\u2019s memory, content from many of the most\ncommonly accessed sites on the Internet will be, for example, yahoo.com, google.com, and amazon.com.\nThe contents of the content engine reflect the most common requests for each individual organization that\nuses it and changes over time as the pattern of pages and files changes. Each page or file also has a limited\nlife in the cache before a new copy is retrieved from the original source so that pages that occasionally\nchange will be accurate.\nBy reducing outgoing traffic (and incoming traffic in response to requests), the content engine enables the\norganization to purchase a smaller WAN circuit into the Internet. So not only does content caching\nimprove performance, but it can also reduce network costs if the organization produces a large volume of\nnetwork requests.\nContent Delivery\nContent delivery, pioneered by Akamai, is a special type of Internet service that works in the opposite\ndirection. Rather than storing other people\u2019s Web files closer to their own internal users, a content\ndelivery provider stores Web files for its clients closer to their potential users. Akamai, for example,\noperates almost 10,000 Web servers located near the busiest Internet IXPs and other key places around\nthe Internet. These servers contain the most commonly requested Web information for some of the\nbusiest sites on the Internet (e.g., yahoo.com, monster.com, ticketmaster.com).\nWhen someone accesses a Web page of one of Akamai\u2019s customers, special software on the client\u2019s Web\nserver determines if there is an Akamai server containing any static parts of the requested information\n(e.g., graphics, advertisements, banners) closer to the user. If so, the customer\u2019s Web server redirects\nportions of the request to the Akamai server nearest the user.", "source": "Page 427", "chapter_title": "Chapter 11"}
{"id": "7bcb25e0dc97-1", "text": "portions of the request to the Akamai server nearest the user.\nThe user interacts with the customer\u2019s website for dynamic content or HTML pages with the Akamai", "source": "Page 427", "chapter_title": "Chapter 11"}
{"id": "ef976e215fb7-0", "text": "server providing static content. In Figure 12-6, for example, when a user in Singapore requests a Web\npage from yahoo.com, the main yahoo.com server farm responds with the dynamic HTML page. This page\ncontains several static graphic files. Rather than provide an address on the yahoo.com site, the Web page\nis dynamically changed by the Akamai software on the yahoo.com site to pull the static content from the\nAkamai server in Singapore. If you watch the bottom action bar closely on your Web browser while some\nof your favorite sites are loading, you\u2019ll see references to Akamai\u2019s servers. On any given day, 15\u201320% of\nall Web traffic worldwide comes from an Akamai server.\nFIGURE 12-6 Network with content delivery\nAkamai servers benefit both the users and the organizations that are Akamai\u2019s clients, as well as many\nISPs and all Internet users not directly involved with the Web request. Because more\nMANAGEMENT FOCUS 12-3\nContent Delivery at Best Buy\nBest Buy operates more than 1,150 retail electronic stores across the United States and Canada and\nhas an extensive online Web store offering more than 600,000 products. Its Web store hosts more\nthan 4,000 million visits a year, more than all of its 1,150 physical stores combined.\nBest Buy wanted to improve its Web store to better customer experience and reduce operating costs.\nAkamai\u2019s extensive content delivery presence in North America enabled Best Buy to improve the\nspeed of its Web transactions by 80%, resulting in substantial increases in sales. The shift to content\ndelivery has also reduced the traffic to its own servers by more than 50%, reducing its operating", "source": "Page 428", "chapter_title": "Chapter 11"}
{"id": "7aa18d8c5bcb-0", "text": "costs. How does Akamai do this? Check out this video for a brief explanation:\nhttps://www.youtube.com/watch?\nv=w6AcfTE5rVQ&list=PLYDvXrgDLAbUqIQXZtgFkBDRoiLGbs87X&index=8.\nSource: Adapted from Akamai Helps Best Buy, Akamai case studies, akamai.com.\nWeb content is now processed by the Akamai server and not the client organization\u2019s more distant Web\nserver, the user benefits from a much faster response time; in Figure 12-6, for example, more requests\nnever have to leave Singapore. The client organization benefits because it serves its users with less traffic\nreaching its Web server; Yahoo!, for example, need not spend as much on its server farm or the Internet\nconnection into its server farm. In our example, the ISPs providing the circuits across the Pacific benefit\nbecause now less traffic flows through their network\u2014traffic that is not paid for because of Internet\npeering agreements. Likewise, all other Internet users in Singapore (as well as users in the United States\naccessing websites in Singapore) benefit because there is now less traffic across the Pacific, and response\ntimes are faster.\n12.3 CONFIGURATION MANAGEMENT\nWe now turn our attention to the four basic management tasks that comprise network management. The\nfirst is configuration management. Configuration management means managing the network\u2019s\nhardware and software configuration, documenting it, and ensuring it is updated as the configuration\nchanges.\n12.3.1 Configuring the Network and Client Computers\nOne of the most common configuration activities is adding and deleting user accounts. When new users\nare added to the network, they are usually categorized as being a member of some group of users (e.g.,\nfaculty, students, accounting department, personnel department). Each user group has its own access", "source": "Page 429", "chapter_title": "Chapter 11"}
{"id": "521d8619f944-1", "text": "faculty, students, accounting department, personnel department). Each user group has its own access\nprivileges, which define what file servers, directories, and files they can access and provide a standard log-\nin script. The log-in script specifies what commands are to be run when the user first logs in (e.g., setting\ndefault directories, connecting to public disks, running menu programs).\nAnother common activity is updating the software on the client computers attached to the network. Every\ntime a new application system is developed or updated (or, for that matter, when a new version is\nreleased), each client computer in the organization must be updated. Traditionally, this has meant that\nsomeone from the networking staff has had to go to each client computer and manually install the\nsoftware, either from CDs or by downloading over the network. For a small organization, this is time\nconsuming but not a major problem. For a large organization with hundreds or thousands of client\ncomputers (possibly with a mixture of Windows and Apples), this can be a nightmare.\nDesktop management, sometimes called electronic software delivery or automated software delivery,\nis one solution to the configuration problem. Desktop management enables network managers to install\nsoftware on client computers over the network without physically touching each client computer. Most\ndesktop management packages provide application-layer software for the network server and all client\ncomputers. The server software communicates directly with the desktop management software on the\nclients and can be instructed to download and install certain application packages on each client at some\npredefined time (e.g., at midnight on a Saturday). Microsoft and many antivirus software vendors use this\napproach to deliver updates and patches to their software.\nDesktop management greatly reduces the cost of configuration management over the long term because it\neliminates the need to update each and every client computer manually. It also automatically produces\nand maintains accurate documentation of all software installed on each client computer and enables", "source": "Page 429", "chapter_title": "Chapter 11"}
{"id": "b8804621975e-2", "text": "and maintains accurate documentation of all software installed on each client computer and enables\nnetwork managers to produce a variety of useful reports. However, desktop management increases cost in\nthe short term because it costs money (typically $25 per client computer) and requires network staff to\ninstall it manually on each client computer. Desktop Management Interface (DMI) is the emerging\nstandard for desktop management.\n12.3.2 Documenting the Configuration", "source": "Page 429", "chapter_title": "Chapter 11"}
{"id": "ec9a0f98be73-0", "text": "Configuration documentation includes information about network hardware, network software, user and\napplication profiles, and network documentation. The most basic information about network\nhardware is a set of network configuration diagrams that document the number, type, and placement of\nnetwork circuits (whether organization owned or leased from a common carrier), network servers,\nnetwork devices (e.g., hubs, routers), and client computers. For most organizations, this is a large set of\ndiagrams: one for each LAN, BN, and WAN. Figure 12-7 shows a diagram of network devices in one office\nlocation.\nThese diagrams must be supplemented by documentation on each individual network component (e.g.,\ncircuit, hub, server). Documentation should include the type of device, serial number, vendor, date of\npurchase, warranty information, repair history, telephone number for repairs, and any additional\ninformation or comments the network manager wishes to add. For example, it would be useful to include\ncontact names and telephone numbers for the individual network managers responsible for each separate\nLAN within the network and common carrier telephone contact information. (Whenever possible,\nestablish a national account with the common carrier rather than dealing with individual common\ncarriers in separate states and areas.)\nA similar approach can be used for network software. This includes the network operating system and any\nspecial-purpose network software. For example, it is important to record which network operating system\nwith which version or release date is installed on each network server. The same is true for application\nsoftware. Sharing software on networks can greatly reduce costs, although it is important to ensure that\nthe organization is not violating any software license rules.\nFIGURE 12-7 Network configuration diagram", "source": "Page 430", "chapter_title": "Chapter 11"}
{"id": "0e3882e91c70-0", "text": "Software documentation can also help in negotiating site licenses for software. Many users buy software\non a copy-by-copy basis, paying the retail price for each copy. It may be cheaper to negotiate the payment\nof one large fee for an unlimited-use license for widely used software packages instead of paying on a per-\ncopy basis.\nThe third type of documentation is the user and application profiles, which should be automatically\nprovided by the network operating system or additional vendor or third-party software agreements. These\nshould enable the network manager to easily identify the files and directories to which each user has\naccess and each user\u2019s access rights (e.g., read-only, edit, delete). Equally important is the ability to access\nthis information in the \u201copposite\u201d direction, that is, to be able to select a file or directory and obtain a list\nof all authorized users and their access rights.\nIn addition, other documentation must be routinely developed and updated pertaining to the network.\nThis includes network hardware and software manuals, application software manuals, standards manuals,\noperations manuals for network staff, vendor contracts and agreements, and licenses for software. The\ndocumentation should include details about performance and fault management (e.g., preventive\nmaintenance guidelines and schedules, disaster recovery plan, and diagnostic techniques), end user\nsupport (e.g., applications software manuals, vendor support telephone numbers), and cost management\n(e.g., annual budgets, repair costs for each device). The documentation should also include any legal\nrequirements to comply with local or federal laws, control, or regulatory bodies.\nMaintaining documentation is usually a major issue for most organizations. Have you written programs?\nHow well did you document them? Many technicians hate documentation because it is not \u201cfun\u201d and\ndoesn\u2019t provide immediate value the same way that solving problems does. Therefore, it is often\noverlooked, so when someone leaves the organization, the knowledge of the network leaves with him or\nher.", "source": "Page 431", "chapter_title": "Chapter 11"}
{"id": "a202fbb95abf-1", "text": "her.\n12.4 PERFORMANCE AND FAULT MANAGEMENT\nPerformance management means ensuring the network is operating as efficiently as possible,\nwhereas fault management means preventing, detecting, and correcting faults in the network circuits,\nhardware, and software (e.g., a broken device or improperly installed software). Fault management and\nperformance management are closely related because any faults in the network reduce performance. Both\nrequire network monitoring, which means keeping track of the operation of network circuits and\ndevices to ensure they are functioning properly and to determine how heavily they are used.\n12.4.1 Network Monitoring\nMost large organizations and many smaller ones use network management software to monitor and\ncontrol their networks. One function provided by these systems is to collect operational statistics from the\nnetwork devices. For small networks, network monitoring is often done by one person, aided by a few\nsimple tools.\nIn large networks, network monitoring becomes more important. Large networks that support\norganizations operating 24 hours a day are often mission critical, which means a network problem can\nhave serious business consequences. For example, consider the impact of a network failure for a common\ncarrier such as AT&T or for the air traffic control system. These networks often have a dedicated network\noperations center (NOC) that is responsible for monitoring and fixing problems. Such centers are\nstaffed by a set of skilled network technicians that use sophisticated network management software. When\na problem occurs, the software immediately detects the problems and sends an alarm to the NOC. Staff\nmembers in the NOC diagnose the problem and can sometimes fix it from the NOC (e.g., restarting a\nfailed device). Other times, when a device or circuit fails, they must change routing tables to route traffic\naway from the device and dispatch a technician to fix it.\nA Day in the Life: Network Policy Manager", "source": "Page 431", "chapter_title": "Chapter 11"}
{"id": "88dfd686932e-2", "text": "A Day in the Life: Network Policy Manager\nAll large organizations have formal policies for the use of their networks (e.g., wireless LAN access,", "source": "Page 431", "chapter_title": "Chapter 11"}
{"id": "03cf28d21a64-0", "text": "password, server space). Most large organizations have a special policy group devoted to the creation\nof network policies, many of which are devoted to network security. The job of the policy officer is to\nsteer the policy through the policy-making process and ensure that all policies are in the best\ninterests of the organization as a whole. Although policies are focused inside the organization,\npolicies are influenced by events both inside and outside the organization. The policy manager\nspends a significant amount of time working with outside organizations such as the U.S. Department\nof Homeland Security, CIO and security officer groups, and industry security consortiums. The goal\nis to make sure all policies (especially security policies) are up to date and provide a good balance\nbetween costs and benefits.\nA typical policy begins with networking staff writing a summary containing the key points of the\nproposed policy. The policy manager takes the summary and uses it to develop a policy that fits the\nstructure required for organizational policies (e.g., date, rationale, scope, responsible individuals,\nand procedures). This policy manager works with the originating staff to produce an initial draft of\nthe proposed policy. Once everyone in the originating department and the policy office are satisfied\nwith the policy, it is provided to an advisory committee of network users and network managers for\ndiscussion. Their suggestions are then incorporated into the policy, or an explanation is provided as\nto why the suggestions will not be incorporated in the policy.\nAfter several iterations, a policy becomes a draft policy and is posted for comment from all users\nwithin the organization. Comments are solicited from interested individuals, and the policy may be\nrevised. Once the draft is finalized, the policy is then presented to senior management for approval.\nOnce approved, the policy is formally published, and the organization charged with implementing\nthe policy begins to use it to guide its operations.\nSource: With thanks to Mark Bruhn.", "source": "Page 432", "chapter_title": "Chapter 11"}
{"id": "2413b71b9fa8-1", "text": "Source: With thanks to Mark Bruhn.\nMANAGEMENT FOCUS 12-4\nNetwork Management Salaries\nNetwork management is not easy, but it doesn\u2019t pay too badly. Here are some typical jobs and their\nrespective annual salaries:\nNetwork Vice President $150,000\nNetwork Manager\n90,000\nTelecom Manager\n77,000\nLAN Administrator\n70,000\nWAN Administrator\n75,000\nNetwork Designer\n80,000\nNetwork Technician\n60,000\nTechnical Support Staff\n50,000\nTrainer\n50,000\nFigure 12-8 shows part of the NOC at Indiana University (this is only about one-third of it). The NOC is\nstaffed 24 hours a day, 7 days a week to monitor the university\u2019s networks. The NOC also has\nresponsibility for managing portions of several very-high-speed networks, including Internet2 (see\nManagement Focus Box 12-5).\nSome types of management software operate passively, collecting the information, and reporting it back to\nthe central NOC. Others are active, in that they routinely send test messages to the servers or application\nbeing monitored (e.g., an HTTP Web page request) and record the response times. The network\nmanagement software discussed in Section 12.2.2 is commonly used for network monitoring.", "source": "Page 432", "chapter_title": "Chapter 11"}
{"id": "f74440bac84a-0", "text": "Performance tracking is important because it enables the network manager to be proactive and respond to\nperformance problems before users begin to complain. Poor network reporting leads to an organization\nthat is overburdened with current problems and lacks time to address future needs. Management requires\nadequate reports if it is to address future needs.\nFIGURE 12-8 Part of the Network Operations Center at Indiana University\n12.4.2 Failure Control Function\nFailure control requires developing a central control philosophy for problem reporting, whether the\nproblems are first identified by the NOC or by users calling into the NOC or a help desk. Whether problem\nreporting is done by the NOC or the help desk, the organization should maintain a central telephone\nnumber for network users to call when any problem occurs in the network. As a central troubleshooting\nfunction, only this group or its designee should have the authority to call hardware or software vendors or\ncommon carriers.\nMany years ago, before the importance (and cost) of network management was widely recognized, most\nnetworks ignored the importance of fault management. Network devices were \u201cdumb\u201d in that they did\nonly what they were designed to do (e.g., routing packets) but did not provide any network management\ninformation.\nFor example, suppose a network interface card fails and begins to transmit garbage messages randomly.\nNetwork performance immediately begins to deteriorate because these random messages destroy the\nmessages transmitted by other computers, which need to be retransmitted. Users notice a delay in\nresponse time and complain to the network support group, which begins to search for the cause. Even if\nthe network support group suspects a failing network card (which is unlikely, unless such an event has\noccurred before), locating the faulty card is very difficult and time consuming.\nMost network managers today are installing managed devices that perform their functions (e.g., routing,", "source": "Page 433", "chapter_title": "Chapter 11"}
{"id": "ef2ba14a50b2-1", "text": "Most network managers today are installing managed devices that perform their functions (e.g., routing,\nswitching) and also record data on the messages they process (see Section 12.2.1). Finding and fixing the\nfault is much simpler, requiring minutes, not hours.\nMANAGEMENT FOCUS 12-5", "source": "Page 433", "chapter_title": "Chapter 11"}
{"id": "bd1a67d699c2-0", "text": "Internet2 Weather Map\nInternet2 is a high-performance backbone that connects about 400 Internet2 institutions in more\nthan 100 countries. The current network is primarily a 10 Gbps fiber-optic network.\nThe network is monitored 24 hours a day, 7 days a week from the network operations center (NOC)\nlocated on the campus of Indiana University. The NOC oversees problem, configuration, and change\nmanagement; network security; performance and policy monitoring; reporting; quality assurance;\nscheduling; and documentation. The center provides a structured environment that effectively\ncoordinates operational activities with all participants and vendors related to the function of the\nnetwork.\nThe NOC uses multiple network management software running across several platforms. One of the\ntools used by the NOC that is available to the general public is the Internet2 Weather Map\n(noc.net.internet2.edu). Each of the major circuits connecting the major Internet2 gigapops is shown\non the map. Each link has two parts, showing the utilization of the circuits to and from each pair.\nSource: Adapted from Internet2 Network NOC (noc.net.internet2.edu).\nNumerous software packages are available for recording fault information (Remedy is one of the most\npopular ones). The reports they produce are known as trouble tickets. The software packages assist the\nhelp desk personnel so they can type the trouble report immediately into a computerized failure analysis\nprogram. They also automatically produce various statistical reports to track how many failures have\noccurred for each piece of hardware, circuit, or software package. Automated trouble tickets are better\nthan paper because they allow management personnel to gather problem and vendor statistics. There are\nfour main reasons for trouble tickets: problem tracking, problem statistics, problem-solving methodology,\nand management reports.\nProblem tracking allows the network manager to determine who is responsible for correcting any", "source": "Page 434", "chapter_title": "Chapter 11"}
{"id": "e48bdea30b78-1", "text": "and management reports.\nProblem tracking allows the network manager to determine who is responsible for correcting any\noutstanding problems. This is important because some problems often are forgotten in the rush of a very\nhectic day. In addition, anyone might request information on the status of a problem. The network\nmanager can determine whether the problem-solving mechanism is meeting predetermined schedules.\nFinally, the manager can be assured that all problems are being addressed. Problem tracking also can\nassist in problem resolution. Are problems being resolved in a timely manner? Are overdue problems\nbeing flagged? Are all resources and information available for problem solving?\nProblem statistics are important because they are a control device for the network managers as well as\nfor vendors. With this information, a manager can see how well the network is meeting the needs of end\nusers. These statistics also can be used to determine whether vendors are meeting their contractual\nmaintenance commitments. Finally, they help to determine whether problem-solving objectives are being\nmet.\nProblem prioritizing helps ensure that critical problems get priority over less important ones. For\nexample, a network support staff member should not work on a problem on one client computer if an\nentire circuit with dozens of computers is waiting for help. Moreover, a manager must know whether\nproblem-resolution objectives are being met. For example, how long is it taking to resolve critical\nproblems?\nManagement reports are required to determine network availability, product and vendor reliability\n(mean time between failures), and vendor responsiveness. Without them, a manager has nothing more\nthan a \u201cbest guess\u201d estimate for the effectiveness of either the network\u2019s technicians or the vendor\u2019s\ntechnicians. Regardless of whether this information is typed immediately into an automated trouble ticket\npackage or recorded manually in a bound notebook-style trouble log, the objectives are the same.\nThe purposes of the trouble log are to record problems that must be corrected and to keep track of", "source": "Page 434", "chapter_title": "Chapter 11"}
{"id": "5a1d459a52bd-2", "text": "The purposes of the trouble log are to record problems that must be corrected and to keep track of\nstatistics associated with these problems. For example, the log might reveal that there were 37 calls for\nsoftware problems (3 for one package, 4 for another package, and 30 for a third software package), 26\ncalls for cable modem problems evenly distributed among 2 vendors, 49 calls for client computers, and 2\ncalls to the common carrier that provides the network circuits. These data are valuable when the design\nand analysis group begins redesigning the network to meet future requirements.", "source": "Page 434", "chapter_title": "Chapter 11"}
{"id": "68207beecbd4-0", "text": "TECHNICAL FOCUS 12-1\nTechnical Reports\nTechnical reports that are helpful to network managers are those that provide summary information,\nas well as details that enable the managers to improve the network. Technical details include the\nfollowing:\nCircuit use\nUsage rate of critical hardware such as host computers, front-end processors, and servers\nFile activity rates for database systems\nUsage by various categories of client computers\nResponse time analysis per circuit or per computer\nVoice versus data usage per circuit\nQueue-length descriptions, whether in the host computer, in the front-end processor, or at\nremote sites\nDistribution of traffic by time of day, location, and type of application software\nFailure rates for circuits, hardware, and software\nDetails of any network faults\n12.4.3 Performance and Failure Statistics\nMany different types of failure and recovery statistics can be collected. The most obvious performance\nstatistics are those discussed earlier: how many packets are being moved on what circuits and what the\nresponse time is. Failure statistics also tell an important story.\nOne important failure statistic is availability, the percentage of time the network is available to users. It\nis calculated as the number of hours per month the network is available divided by the total number of\nhours per month (i.e., 24 hours per day \u00d7 30 days per month = 720 hours). The downtime includes\ntimes when the network is unavailable because of faults and routine maintenance and network upgrades.\nMost network managers strive for 99\u201399.5% availability, with downtime scheduled after normal working\nhours.\nThe mean time between failures (MTBF) is the number of hours or days of continuous operation\nbefore a component fails. Obviously, devices with higher MTBF are more reliable.\nWhen faults occur, and devices or circuits go down, the mean time to repair (MTTR) is the average", "source": "Page 435", "chapter_title": "Chapter 11"}
{"id": "a22b61098cce-1", "text": "number of minutes or hours until the failed device or circuit is operational again. The MTTR is composed\nof these separate elements:\nThe mean time to diagnose (MTTD) is the average number of minutes until the root cause of the\nfailure is correctly diagnosed. This is an indicator of the efficiency of problem management personnel in\nthe NOC or help desk who receive the problem report.\nThe mean time to respond (MTTR) is the average number of minutes or hours until service personnel\narrive at the problem location to begin work on the problem. This is a valuable statistic because it\nindicates how quickly vendors and internal groups respond to emergencies. Compilation of these figures\nover time can lead to a change of vendors or internal management policies or, at the minimum, can exert\npressure on vendors who do not respond to problems promptly.\nTECHNICAL FOCUS 12-2", "source": "Page 435", "chapter_title": "Chapter 11"}
{"id": "8e1fc57ac3da-0", "text": "Elements of a Trouble Report\nWhen a problem is reported, the trouble log staff members should record the following:\nTime and date of the report\nName and telephone number of the person who reported the problem\nThe time and date of the problem (and the time and date of the call)\nLocation of the problem\nThe nature of the problem\nWhen the problem was identified\nWhy and how the problem happened\nFinally, after the vendor or internal support group arrives on the premises, the last statistic is the mean\ntime to fix (MTTF). This figure tells how quickly the staff is able to correct the problem after they arrive.\nA very long time to fix in comparison with the time of other vendors may indicate faulty equipment\ndesign, inadequately trained customer service technicians, or even the fact that inexperienced personnel\nare repeatedly sent to fix problems.\nFor example, suppose your Internet connection at home stops working. You call your ISP, and they fix it\nover the phone in 15 minutes. In this case, the MTTRepair is 15 minutes, and it is hard to separate the\ndifferent parts (MTTD, MTTR, and MTTF). Suppose you call your ISP and spend 60 minutes on the phone\nwith them, and they can\u2019t fix it over the phone; instead, the technician arrives the next day (18 hours later)\nand spends 1 hour fixing the problem. In this case, MTTR = 1 hour + 18 hours + 1 hour = 20 hours.\nTECHNICAL FOCUS 12-3\nManagement Reports\nManagement-oriented reports that are helpful to network managers and their supervisors provide\nsummary information for overall evaluation and for network planning and design. Details include\nthe following:\nGraphs of daily/weekly/monthly usage, number of errors, or whatever is appropriate to the\nnetwork", "source": "Page 436", "chapter_title": "Chapter 11"}
{"id": "a9a5e31f83a2-1", "text": "network\nNetwork availability (uptime) for yesterday, the last 5 days, the last month, or any other\nspecific period\nPercentage of hours per week the network is unavailable because of network maintenance and\nrepair\nFault diagnosis\nWhether most response times are less than or equal to 2 seconds for online real-time traffic\nWhether management reports are timely and contain the most up-to-date statistics\nPeak volume statistics as well as average volume statistics per circuit\nComparison of activity between today and a similar previous period\nThe MTBF can be influenced by the original selection of vendor-supplied equipment. The MTTD relates\ndirectly to the ability of network personnel to isolate and diagnose failures and can often be improved by\ntraining. The MTTR (respond) can be influenced by showing vendors or internal groups how good or bad\ntheir response times have been in the past. The MTTF can be affected by the technical expertise of internal\nor vendor staff and the availability of spare parts on site.", "source": "Page 436", "chapter_title": "Chapter 11"}
{"id": "36f63f977fe0-0", "text": "Another set of statistics that should be gathered are those collected daily by the network operations group,\nwhich uses network management software. These statistics record the normal operation of the network,\nsuch as the number of errors (retransmissions) per communication circuit. Statistics also should be\ncollected on the daily volume of transmissions (characters per hour) for each communication circuit, each\ncomputer, or whatever is appropriate for the network. It is important to closely monitor usage rates, the\npercentage of the theoretical capacity that is being used. These data can identify computers/devices or\ncommunication circuits that have higher-than-average error or usage rates, and they may be used for\npredicting future growth patterns and failures. A device or circuit that is approaching maximum usage\nobviously needs to be upgraded.\nTECHNICAL FOCUS 12-4\nInside a Service-Level Agreement\nThere are many elements to a solid service-level agreement (SLA) with a common carrier. Some\nof the important ones include the following:\nNetwork availability, measured over a month as the percentage of time the network is available\n(e.g., [total hours\u2014hours unavailable]/total hours) should be at least 99.5%.\nAverage round-trip permanent virtual circuit (PVC) delay, measured over a month as the\nnumber of seconds it takes a message to travel over the PVC from sender to receiver, should be\nless than 110 milliseconds, although some carriers will offer discounted services for SLA\nguarantees of 300 milliseconds or less.\nPVC throughput, measured over a month as the number of outbound packets sent over a PVC\ndivided by the inbound packets received at the destination (not counting packets over the\ncommitted information rate, which are discard eligible), should be above 99%\u2014ideally, 99.99%.\nMean time to respond, measured as a monthly average of the time from inception of trouble", "source": "Page 437", "chapter_title": "Chapter 11"}
{"id": "bbb4b8b2e6f4-1", "text": "Mean time to respond, measured as a monthly average of the time from inception of trouble\nticket until repair personnel are on site, should be 4 hours or less.\nMean time to fix, measured as a monthly average of the time from the arrival of repair personnel\non site until the problem is repaired, should be 4 hours or less.\nSource: Adapted from \u201cCarrier Service-Level Agreements,\u201d International Engineering Consortium Tutorial, www.iec.org,\nFebruary.\n12.4.4 Improving Performance\nThe chapters on LANs, BNs, and WANs discussed several specific actions that could be taken to improve\nnetwork performance for each of those types of networks. There are also several general activities to\nimprove performance that cut across the different types of networks.\nMost organizations establish service-level agreements (SLAs) with their common carriers and Internet\nservice providers. An SLA specifies the exact type of performance and fault conditions that the\norganization will accept. For example, the SLA might state that network availability must be 99% or\nhigher and that the MTBF for T1 circuits must be 120 days or more. In many cases, SLA includes\nmaximum allowable response times. The SLA also states what compensation the service provider must\nprovide if it fails to meet the SLA. Some organizations are also starting to use an SLA internally to define\nrelationships between the networking group and its organizational \u201ccustomers.\u201d\n12.5 END USER SUPPORT\nProviding end user support means solving whatever problems users encounter while using the\nnetwork. There are three main functions within end user support: resolving network faults, resolving user\nproblems, and training. We have already discussed how to resolve network faults, and now we focus on\nresolution of user problems and end user training.", "source": "Page 437", "chapter_title": "Chapter 11"}
{"id": "66187634999f-0", "text": "12.5.1 Resolving Problems\nProblems with user equipment (as distinct from network equipment) usually stem from three major\nsources. The first is a failed hardware device. These are usually the easiest to fix. A network technician\nsimply fixes the device or installs a new part.\nThe second type of problem is a lack of user knowledge. These problems can usually be solved by\ndiscussing the situation with the user and taking that person through the process step by step. This is the\nnext easiest type of problem to solve and can often be done by email or over the telephone, although not\nall users are easy to work with. Problematic users are sometimes called ID ten-T errors, written ID10T.\nThe third type of problem is one with the software, software settings, or an incompatibility between the\nsoftware and network software and hardware. In this case, there may be a bug in the software, or the\nsoftware may not function properly on a certain combination of hardware and software. Solving these\nproblems may be difficult because they require expertise with the specific software package in use and\nsometimes require software upgrades from the vendor.\nResolving either type of software problem begins with a request for assistance from the help desk.\nRequests for assistance are usually handled in the same manner as network faults. A trouble log is\nmaintained to document all incoming requests and the manner in which they are resolved. The staff\nmember receiving the request attempts to resolve the problem in the best manner possible. Staff members\nshould be provided with a set of standard procedures or scripts for soliciting information from the user\nabout problems. In large organizations, this process may be supported by special software.\nThere are often several levels to the problem-resolution process. The first level is the most basic. All staff\nmembers working at the help desk should be able to resolve most of these. Most organizations strive to", "source": "Page 438", "chapter_title": "Chapter 11"}
{"id": "7a27e8b10d0c-1", "text": "members working at the help desk should be able to resolve most of these. Most organizations strive to\nresolve between 75% and 85% of requests at this first level in less than an hour. If the request cannot be\nresolved, it is escalated to the second level of problem resolution. Escalation is a normal part of the\nprocess and not something that is \u201cbad.\u201d Staff members who handle second-level support have specialized\nskills in certain problem areas or with certain types of software and hardware. In most cases, problems are\nresolved at this level. Some large organizations also have a third level of resolution in which specialists\nspend many hours developing and testing various solutions to the problem, often in conjunction with staff\nmembers from the vendors of network software and hardware.\nMANAGEMENT FOCUS 12-6\nNetwork Manager Job Requirements\nBeing a network manager is not easy. We reviewed dozens of job postings for the key\nresponsibilities, skills, and education desired by employers. The responsibilities listed as follows\nwere commonly mentioned.\nResponsibilities\nDetermine network needs and design technical solutions to address business requirements.\nProcure and manage vendor relations with providers of equipment and services.\nDeploy new network components and related network systems and services, including the\ncreation of test plans and procedures, documentation of the operation, maintenance and\nadministration of any new systems or services, and training.\nDevelop, document, and enforce standards, procedures, and processes for the operation and\nmaintenance of the network and related systems.\nManage the efficiency of operations of the current network infrastructure, including analyzing\nnetwork performance and making configuration adjustments as necessary.\nAdminister the network servers and the network-printing environment.\nEnsure network security, including the development of applicable security, server, and desktop\nstandards, and monitoring processes to ensure that mission-critical processes are operational.", "source": "Page 438", "chapter_title": "Chapter 11"}
{"id": "bc62f2f6fcce-0", "text": "Manage direct reports and contractors. This includes task assignments, performance\nmonitoring, and regular feedback. Hire, train, evaluate, and terminate staff and contractors\nunder the direction of company policies and processes.\nAssist business in the definition of new product/service offerings and the capabilities and\nfeatures of the systems to deliver those products and services to customers.\nSkills Required\nStrong technology skills in a variety of technologies\nLAN/WAN networking experience working with routers and switches\nExperience with Internet access solutions, including firewalls and VPN\nNetwork architecture design and implementation experience\nInformation security experience\nPersonnel management experience\nProject management experience\nExperience working in a team environment\nAbility to work well in an unstructured environment\nExcellent problem-solving and analytical skills\nEffective written and oral communication skills\nEducation\nBachelor\u2019s degree in an information technology field\nSecurity Certification\nMicrosoft MCSE Certification preferred\nCisco CCNA Certification preferred\n12.5.2 Providing End User Training\nEnd user training is an ongoing responsibility of the network manager. Training is a key part in the\nimplementation of new networks or network components. It is also important to have an ongoing training\nprogram because employees may change job functions and new employees require training to use the\norganization\u2019s networks.\nTraining usually is conducted through in-class, one-on-one instruction and online self-paced courses. In-\nclass training should focus on the 20% of the network functions that the user will use 80% of the time\ninstead of attempting to cover all network functions. By getting in-depth instruction on the fundamentals,\nusers become confident about what they need to do. The training should also explain how to locate\nadditional information from online support, documentation, or the help desk.\n12.6 COST MANAGEMENT\nOne of the most challenging areas of network management over the past few years has been cost\nmanagement. Data traffic has been growing much more rapidly than has the network management", "source": "Page 439", "chapter_title": "Chapter 11"}
{"id": "221f4678589a-1", "text": "management. Data traffic has been growing much more rapidly than has the network management\nbudget, which has forced network managers to provide greater network capacity at an ever lower cost per\nmegabyte (Figure 12-9). In this section, we examine the major sources of costs and discuss several ways to\nreduce them.\n12.6.1 Sources of Costs\nThe cost of operating a network in a large organization can be very expensive. Figure 12-10 shows a recent\ncost analysis to operate the network for 1 year at Indiana University, a large Big Ten research university", "source": "Page 439", "chapter_title": "Chapter 11"}
{"id": "7bd79d7f6bde-0", "text": "serving 40,000 students and 4,000 faculty and staff. This analysis includes the costs of operating the\nnetwork infrastructure and standard applications such as email and the Web but does not include the\ncosts of other applications such as course management software, registration, student services,\naccounting, and so on. Indiana University has a federal IT governance structure, which means that the\ndifferent colleges and schools on campus also have budgets to hire staff and buy equipment for their\nfaculty and staff. The budget in this figure omits these amounts, so the real costs are probably 50% higher\nthan those shown. Nonetheless, this presents a snapshot of the costs of running a large network.\nThe largest area of costs in network operations is the $7.4 million spent on WAN circuits. Indiana\nUniversity operates many high-speed networks (including Internet2), so these costs are higher than might\nbe expected. This figure also shows the large costs of email, Web services, data storage, and security. The\ncost of end user support is the next largest cost item. This includes training as well as answering users\u2019\nquestions and fixing their problems. The remaining costs are purchasing new and replacement hardware\nand software. But, once again, remember that this does not include the hardware and software purchased\nby individual colleges and schools for their faculty and staff, which does not come from the central IT\nbudget.\nThe total cost of ownership (TCO) is a measure of how much it costs per year to keep one computer\noperating. TCO includes the actual direct cost of repair parts, software upgrades, and support staff\nmembers to maintain the network, install software, administer the network (e.g., create user IDs, back up\nuser data), provide training and technical support, and upgrade hardware and software. It also includes\nthe indirect cost of time \u201cwasted\u201d by the user when problems occur, when the network is down, or when", "source": "Page 440", "chapter_title": "Chapter 11"}
{"id": "5c5ea8922cb7-1", "text": "the user is attempting to learn new software.\nFIGURE 12-9 Network traffic versus network management budgets\nSeveral studies over the past few years by Gartner Group, Inc., a leading industry research firm, suggest\nthat the TCO of a computer is astoundingly high. Most studies suggest that the TCO for typical Windows\ncomputers on a network is about $7,000 per computer per year. In other words, it costs almost five times\nas much each year to operate a computer than it does to purchase it in the first place. Other studies by\nfirms such as IBM and Information Week, an industry magazine, have produced TCO estimates of\nbetween $5,000 and $10,000 per year, suggesting that the Gartner Group\u2019s estimates are reasonable.", "source": "Page 440", "chapter_title": "Chapter 11"}
{"id": "80ceb49ad8d0-0", "text": "Although TCO has been accepted by many organizations, other firms argue against the practice of\nincluding indirect in the calculation. For example, using a technique that includes indirect, the TCO of a\ncoffee machine is more than $50,000 per year\u2014not counting the cost of the coffee or supplies. The\nassumption that getting coffee \u201cwastes\u201d 12 minutes per day multiplied by 5 days per week yields 1 hour per\nweek, or about 50 hours per year, of wasted time. If you assume the coffeepot serves 20 employees who\nhave an average cost of $50 per hour (not an unusually high number), you have a loss of $50,000 per\nyear.\nSome organizations, therefore, prefer to focus on costing methods that examine only the direct costs of\noperating the computers, omitting softer indirect costs such as \u201cwasted\u201d time. Such measures, often called\nnetwork cost of ownership (NCO) or real TCO, have found that NCO ranges between $1,500 and\n$3,500 per computer per year. The typical network management group for a 100-user network would\ntherefore have an annual budget of about $150,000\u2013$350,000. The most expensive item is personnel\n(network managers and technicians), which typically accounts for 50\u201370% of total costs. The second most\nexpensive cost item is WAN circuits, followed by hardware upgrades and replacement parts.\nNetwork Operations\n$14,871,000\nAccount Administration\n275,000\nAuthentication Services\n257,000\nDirectory Services Infrastructure (incl DHCP, DNS)\n746,000\nE-mail and Messaging\n1,434,000\nMainframe and Cluster Operations\n633,000\nMass Data Storage\n1,424,000\nPolicy Management\n75,000\nPrinting\n201,000\nSecurity Administration\n1,270,000\nWAN Operations", "source": "Page 441", "chapter_title": "Chapter 11"}
{"id": "4b5fe3de7f9e-1", "text": "Printing\n201,000\nSecurity Administration\n1,270,000\nWAN Operations\n7,410,000\nWeb Services\n1,146,000\nEnd User Support\n$6,544,000\nDepartmental Technology Support\n553,000\nInstructional Technology Support\n856,000\nStudent Residence Halls Support\n279,000\nStudent Technology Centers Support\n1,288,000\nSupport Center (Help Desk)\n2,741,000\nTraining and Education\n827,000\nClient Hardware\n$3,901,000\nClassroom Technology Equipment and Supplies\n844,000\nStudent Residence Halls Equipment and Supplies\n601,000\nStudent Technology Centers Equipment and Supplies 2,456,000\nApplication Software\n$3,729,000\nSoftware Site Licenses\n2,540,000\nStudent Residence Halls Software\n146,000\nStudent Technology Centers Software\n1,043,000\nTotal\n$29,045,000\nFIGURE 12-10 Annual networking costs at Indiana University", "source": "Page 441", "chapter_title": "Chapter 11"}
{"id": "6146d54e0f67-0", "text": "FIGURE 12-11 Network management personnel costs\nCalculating TCO for universities can be difficult. Do we calculate TCO for the number of computers or the\nnumber of users? Figure 12-10 shows an annual cost of $29 million. If we use the number of users, the\nTCO is about $659 ($29 million divided by 44,000 users). If we use the number of computers, TCO is\n$4,800 ($29 million divided by about 6,000 computers owned by the university).\nThere is one very important message from this pattern of costs. Because the largest cost item is personnel\ntime, the primary focus of cost management lies in designing networks and developing policies to reduce\npersonnel time, not to reduce hardware cost. Over the long term, it makes more sense to buy more\nexpensive equipment if it can reduce the cost of network management.\nFigure 12-11 shows the average breakdown of personnel costs by function. The largest time cost (where\nstaff members spend most of their time) is systems management, which includes configuration, fault, and\nperformance management tasks that focus on the network as a whole. The second largest item is end-user\nsupport.\nNetwork managers usually find it difficult to manage their budgets because networks grow so rapidly.\nThey often find themselves having to defend ever-increasing requests for more equipment and staff. To\ncounter these escalating costs, many large organizations have adopted charge-back policies for users of\nWANs and mainframe-based networks. (A charge-back policy attempts to allocate the costs associated\nwith the network to specific users.) These users must \u201cpay\u201d for their network usage by transferring part of\ntheir budget allocations to the network group. Such policies are seldom used in LANs, making one more\npotential cultural difference between network management styles.\n12.6.2 Reducing Costs", "source": "Page 442", "chapter_title": "Chapter 11"}
{"id": "a2f04bf8c3b4-1", "text": "potential cultural difference between network management styles.\n12.6.2 Reducing Costs\nGiven the huge amounts in TCO or even the substantial amounts spent in NCO, there is considerable\npressure on network managers to reduce costs. Figure 12-12 summarizes five steps to reduce network\ncosts.\nThe first and most important step is to develop standards for client computers, servers, and network\ndevices (i.e., switches, routers). These standards define one configuration (or a small set of\nconfigurations) that are permitted for all computers and devices. Standardizing hardware and software\nmakes it easier to diagnose and fix problems. Also, there are fewer software packages for the network\nsupport staff members to learn. The downside, of course, is that rigid adherence to standards reduces", "source": "Page 442", "chapter_title": "Chapter 11"}
{"id": "911428046f78-0", "text": "innovation.\nFive Steps to Reduce Network Costs\nDevelop standard hardware and software configurations for client computers and\nservers.\nAutomate as much of the network management function as possible by deploying a\nsolid set of network management tools.\nReduce the costs of installing new hardware and software by working with\nvendors.\nCentralize help desks.\nMove to thin-client or cloud-based architectures.\nFIGURE 12-12 Reducing network costs\nMANAGEMENT FOCUS 12-7\nTotal Cost of Ownership in Minnesota\nTotal cost of ownership (TCO) has come to the classroom. As part of a national TCO initiative,\nseveral school districts, including one in Minnesota, recently conducted a real TCO analysis. The\nschool district was a system of eight schools (one high school, one middle school, and six elementary\nschools) serving 4,100 students in kindergarten through grade 12. All schools are connected via a\nframe relay WAN to the district head office.\nCosts were assessed in two major groups: direct costs and indirect costs. The direct costs included\nthe costs of hardware (replacement client computers, servers, networks, and printers and supplies),\nsoftware, internal network staff, and external consultants. The indirect costs included staff training\nand development. \u201cWasted time\u201d was not included in the TCO analysis.\nThe district examined its most recent annual budget and allocated its spending into these categories.\nThe district calculated that it spent about $1.2 million per year to support its 1,200 client computers,\nproviding a TCO of about $1,004 per client computer per year. Figure 12-13 provides a summary of\nthe costs by category.\nA TCO of $1,004 is below average, indicating a well-managed network. The district had implemented\nseveral network management best practices, such as using a standardized set of software, using new", "source": "Page 443", "chapter_title": "Chapter 11"}
{"id": "998bce6b1193-1", "text": "several network management best practices, such as using a standardized set of software, using new\nstandardized hardware, and providing professional development to teachers to reduce support costs.\nOne other major contributing factor was the extremely low salaries paid to the IT technical staff (less\nthan $25,000 per year) because of the district\u2019s rural location. Had the district been located in a\nmore urban area, IT staff costs would have doubled, bringing TCO closer to the lower end of the\nnational average.\nSource: Adapted from \u201cMinnesota District Case Study,\u201d Taking TCO to the Classroom, k12tco.gartner.com.", "source": "Page 443", "chapter_title": "Chapter 11"}
{"id": "40d5d19daeb1-0", "text": "FIGURE 12-13 Total cost of ownership (per client computer per year) for a Minnesota school district\nThe second most important step is to automate as much of the network management process as possible.\nDesktop management can significantly reduce the cost to upgrade when new software is released. It also\nenables faster installation of new computers and faster recovery when software needs to be reinstalled and\nhelps enforce the standards policies. The use of network management software to identify and diagnose\nproblems can significantly reduce time spent in performance and fault management. Likewise, help desk\nsoftware can cut the cost of the end support function. A third step is to do everything possible to reduce\nthe time spent installing new hardware and software. The cost of a network technician\u2019s spending half a\nday to install and configure new computers is often $300\u2013$500. Desktop management is an important\nstep to reducing costs, but careful purchasing can also go a long way. The installation of standard\nhardware and software (e.g., Microsoft Office) by the hardware vendor can significantly reduce costs.\nLikewise, careful monitoring of hardware failures can quickly identify vendors of less reliable equipment\nwho should be avoided in the next purchasing cycle. Traditionally, help desks have been decentralized into\nuser departments. The result is a proliferation of help desks and support staff members, many of whom\ntend to be generalists rather than specialists in one area. Many organizations have found that centralizing\nhelp desks enables them to reduce the number of generalists and provide more specialists in key\ntechnology areas. This results in faster resolution of difficult problems. Centralization also makes it easier\nto identify common problems occurring in different parts of the organization and take actions to reduce\nthem. Finally, many network experts argue that moving to thin-client or cloud-based architectures, just\nWeb browsers on the client (see Chapter 2), can significantly reduce costs. Although this can reduce the", "source": "Page 444", "chapter_title": "Chapter 11"}
{"id": "51e494dc9654-1", "text": "cost to buy software, the real saving lies in the support costs. Because they are restricted to a narrow set of\nfunctions and generally do not need software installations, thin-client architectures become much easier\nto manage. TCO and NCO drop by 20\u201340%. Most organizations anticipate using thin-client and cloud-\nbased architectures selectively in areas where applications are well defined and can easily be restricted.\n12.7 IMPLICATIONS FOR CYBER SECURITY\nNetwork monitoring is important for performance and fault management, but it can also be important for\nsecurity. Network monitoring creates a baseline of \u201cnormal\u201d activity, so when something unusual\nhappens, it is more easily recognized and triggers an investigation. One evening, the networking software\nat Indiana University detected an unusually large amount of traffic flowing out of a computer lab onto the\nInternet. The volume of traffic was unusual, something more typical of a server than the usual client\ncomputers in a computer lab, which most students use to download files from the Internet, not upload. An\nanalysis of the traffic showed that the traffic was mostly MPEG movies; we don\u2019t store movies on client\ncomputers in our labs, so it meant that an attacker had taken over control of the computers.", "source": "Page 444", "chapter_title": "Chapter 11"}
{"id": "50f6a52a6834-0", "text": "An investigation revealed that the attacker had used a brute-force attack to break the administrator\npassword on our lab computers by using software that tried every possible password until it guessed the\nright one. He then stored pirated Japanese anime movies that were being downloaded from all over the\nworld. The fix was simple. First, we changed the configuration on each lab computer to permit only three\nfailed administrator logins before the user was locked out. Then, we deployed desktop management\nsoftware on every lab computer so that every morning each computer reset itself back to image stored on\nthe desktop management server, removing any configuration changes and any files that had been stored\non it the previous day. That way even if someone broke in, the changes would only last for a day before the\ndesktop management software automatically fixed them.\nAnother security incident at Indiana University shows the importance of widespread security awareness,\nboth within the network management organization and the organization itself. One day in late July, a\nsophisticated phishing attack tricked more than 600 faculty and staff into revealing their passphrase. The\nattackers quickly logged into the university\u2019s financial system with the stolen passphrases and changed the\nemployees\u2019 direct deposit information so that their pay checks were deposited into the attackers\u2019 accounts\nin an offshore bank in a country with weak law enforcement.\nThe attack was discovered when an employee noticed that he had not received his direct deposit and\ncalled the university\u2019s financial services department, which quickly routed the call to the help desk. The IT\nstaff responded immediately and, working with financial services staff, identified all the users whose\nbanking information had been recently changed. They reversed all their direct deposits within the 2-day\nlimit for recall under global banking rules, so no one lost any money. University lawyers later determined\nthat if the direct deposit diversion had not been discovered in time, the employees\u2014not the university\u2014", "source": "Page 445", "chapter_title": "Chapter 11"}
{"id": "69c30ef005ea-1", "text": "that if the direct deposit diversion had not been discovered in time, the employees\u2014not the university\u2014\nwould have lost 1 month\u2019s pay because the university was not at fault.\nBoth of these incidents show how important it is for employees to protect their passphrases, especially\nemployees whose accounts have extra privileges, such as network managers and senior administrators.\nThis is challenging because as our university\u2019s CIO puts it, the good guys have to win every single time, but\nthe bad guys only have to win once. And we cannot expect humans to be perfect. So, the university now\nrequires two factor authentication using Duo for all employee logins, whether financial or not, so if\nemployees fall for a phishing attack, there is an extra line of defense.\nAfter the financial attack had been thwarted, the IT staff conducted routine audits of other system activity\nthat followed the phishing attack. Interestingly, they discovered that several unauthorized grade changes\nhad been submitted using the stolen passphrases. These too have been reversed and an investigation is\nongoing.\nSUMMARY\nDesigning for Performance Network management software is critical to the design of reliable,\nhigh-performance networks. This software provides statistics about device utilizations and issues\nalerts when problems occur. SNMP is a common standard for network management software and the\nmanaged devices that support it. Load balancing and policy-based management are tools used to\nbetter manage the flow of traffic. Capacity management, content caching, and content delivery are\nsometimes used to reduce network traffic.\nConfiguration Management Configuration management means managing the network\u2019s\nhardware and software configuration, documenting it, and ensuring the documentation is updated as\nthe configuration changes. The most common configuration management activity is adding and\ndeleting user accounts. The most basic documentation about network hardware is a set of network\nconfiguration diagrams, supplemented by documentation on each individual network component. A", "source": "Page 445", "chapter_title": "Chapter 11"}
{"id": "9f7653d6ff0b-2", "text": "configuration diagrams, supplemented by documentation on each individual network component. A\nsimilar approach can be used for network software. Desktop management plays a key role in\nsimplifying configuration management by automating and documenting the network configurations.\nUser and application profiles should be automatically provided by the network and desktop\nmanagement software. There is a variety of other documentation that must be routinely developed\nand updated, including users\u2019 manuals and organizational policies.\nPerformance and Fault Management Performance management means ensuring the network is\noperating as efficiently as possible. Fault management means preventing, detecting, and correcting", "source": "Page 445", "chapter_title": "Chapter 11"}
{"id": "2a0d6e84c0b5-0", "text": "any faults in the network circuits, hardware, and software. The two are closely related because any\nfaults in the network reduce performance and because both require network monitoring. Today, most\nnetworks use a combination of managed devices to monitor the network and issue alarms and a help\ndesk to respond to user problems. Problem tracking allows the network manager to determine\nproblem ownership or who is responsible for correcting any outstanding problems. Problem statistics\nare important because they are a control device for the network operators as well as for vendors.\nProviding End User Support Providing end user support means solving whatever network\nproblems users encounter. Support consists of resolving network faults, resolving software problems,\nand training. Software problems often stem from lack of user knowledge, fundamental problems with\nthe software, or an incompatibility between the software and the network\u2019s software and hardware.\nThere are often several levels to problem resolution. End user training is an ongoing responsibility of\nthe network manager. Training usually has two parts: in-class instruction and the documentation and\ntraining manuals that the user keeps for reference.\nCost Management As the demand for network services grows, so does its cost. The TCO for typical\nnetworked computers is about $7,000 per year per computer, far more than the initial purchase\nprice. The network management cost (omitting \u201cwasted\u201d time) is between $1,500 and $3,500 per\nyear per computer. The largest single cost item is staff salaries. The best way to control rapidly\nincreasing network costs is to reduce the amount of time taken to perform management functions,\noften by automating as many routine ones as possible.\nKEY TERMS\nagent\nAkamai\nalarm\nalarm storm\napplication management software\napplication shaping\navailability\nbandwidth limiter\nbandwidth shaper\ncache engine\ncapacity management\ncharge-back policy\nclusters\nconfiguration management\ncontent caching\ncontent delivery\ncontent delivery provider\ncontent engine", "source": "Page 446", "chapter_title": "Chapter 11"}
{"id": "b979f6585df2-1", "text": "clusters\nconfiguration management\ncontent caching\ncontent delivery\ncontent delivery provider\ncontent engine\ncost management\ndesktop management\ndevice management software\ndowntime\nend user support", "source": "Page 446", "chapter_title": "Chapter 11"}
{"id": "3461612019b6-0", "text": "fault management\nfirefighting\nhelp desk\nload balancer\nmanaged device\nmanaged network\nmanagement information base (MIB)\nmean time between failures (MTBF)\nmean time to diagnose (MTTD)\nmean time to fix (MTTF)\nmean time to repair (MTTR)\nmean time to respond (MTTR)\nmonitor\nnetwork cost of ownership (NCO)\nnetwork documentation\nnetwork management\nnetwork management software\nnetwork monitoring\nnetwork operations center (NOC)\nperformance management\npolicy-based management\nproblem statistics\nproblem tracking\nreal TCO\nremote monitoring (RMON)\nRMON probes\nroot cause analysis\nservice farm\nservice-level agreement (SLA)\nSimple Network Management Protocol (SNMP)\nsystem management software\ntotal cost of ownership (TCO)\ntraffic shaper\ntraffic shaping\ntrouble ticket\nuptime\nvirtual server\nQUESTIONS", "source": "Page 447", "chapter_title": "Chapter 11"}
{"id": "50cf4a7ff817-0", "text": "1. What skill does a network manager need?\n2. What is firefighting?\n3. Why is combining voice and data a major organizational challenge?\n4. Describe what configuration management encompasses.\n5. People tend to think of software when documentation is mentioned. What is documentation in a\nnetwork situation?\n6. What is desktop management, and why is it important?\n7. What is performance and fault management?\n8. What does a help desk do?\n9. What do trouble tickets report?\n10. Several important statistics related to network uptime and downtime are discussed in this chapter.\nWhat are they, and why are they important?\n11. What is an SLA?\n12. How is network availability calculated?\n13. What is problem escalation?\n14. What are the primary functions of end user support?\n15. What is TCO?\n16. Why is the TCO so high?\n17. How can network costs be reduced?\n18. What do network management software systems do and why are they important?\n19. What is SNMP and RMON?\n20. Compare and contrast device management software, system management software, and application\nmanagement software.\n21. How does a load balancer work?\n22. What is server virtualization?\n23. What is policy-based management?\n24. What is capacity management?\n25. How does content caching differ from content delivery?\n26. How does network cost of ownership (aka real TCO) differ from total cost of ownership? Which is the\nmost useful measure of network costs from the point of view of the network manager? Why?\n27. Many organizations do not have a formal trouble reporting system. Why do you think this is the case?\nEXERCISES\nA. What factors might cause peak loads in a network? How can a network manager determine if they are", "source": "Page 448", "chapter_title": "Chapter 11"}
{"id": "6963771a5e73-1", "text": "important, and how are they taken into account when designing a data communications network?\nB. Today\u2019s network managers face a number of demanding problems. Investigate and discuss three\nmajor issues.\nC. Research the networking budget in your organization and discuss the major cost areas. Discuss\nseveral ways of reducing costs over the long term.\nD. Explore the traffic on the networks managed by the Indiana University NOC as noc.net.internet2.edu.\nCompare the volume of traffic in two networks and how close to capacity the networks are.\nE. Investigate the latest versions of SNMP and RMON and describe the functions that have been added", "source": "Page 448", "chapter_title": "Chapter 11"}
{"id": "89af5f983596-0", "text": "in the latest version of the standard.\nF. Investigate and report on the purpose, relative advantages, and relative disadvantages of two network\nmanagement software tools.\nG. If a common carrier guarantees 99% reliability, how many hours a year will the circuit be down? How\nabout 99.5%, 99.9%, 99.99%? Improved reliability comes with increased cost. What is the minimum\nreliability most firms should consider?\nMINICASES\nI. City School District, Part 1 City School District is a large, urban school district that operates 27\nschools serving 22,000 students from kindergarten through grade 12. All schools are networked into\na regional WAN that connects the schools to the district central office and each other. The district has\na total of 5,300 client computers. The following table shows the annual costs. Calculate the real TCO\n(without wasted time).\nBudget Item\nAnnual Cost\nIT staff salaries\n$7,038,400\nConsultants\n1,340,900\nSoftware\n657,200\nStaff training\n545,900\nClient computers\n2,236,600\nServers\n355,100\nNetwork\n63,600\nSupplies and parts\n2,114,700\nII. City School District, Part 2 Read and complete Minicase I. Examine the TCO by category. Do you\nthink that this TCO indicates a well-run network? What suggestions would you have?\nIII. Central Textiles Central Textiles is a clothing manufacturer that operates 16 plants throughout the\nsouthern United States and in Latin America. The Information Systems Department, which reports to\nthe vice president of finance, operates the central mainframe and LAN at the headquarters building\nin Spartanburg, South Carolina, and the WAN that connects all the plants. The LANs in each plant", "source": "Page 449", "chapter_title": "Chapter 11"}
{"id": "7182521e293a-1", "text": "are managed by a separate IT group at each plant that reports to the plant manager (the plant\nmanagers report to the vice president of manufacturing). The telephone communications system and\nlong-distance agreements are managed by a telecommunications department in the headquarters\nthat reports to the vice president of finance. The CEO of Central Textiles has come to you asking\nabout whether this is the best arrangement, or whether it would make more sense to integrate the\nthree functions under one new department. Outline the pros and cons of both alternatives.\nIV. Indiana University Reread Management Focus 12-5. Take another look at Figure 12-1. If this is a\ntypical traffic pattern, how would you suggest that they improve performance?\nTECH UPDATES\nIn every chapter, we will offer a couple of ideas to investigate. Pick one of these topics to investigate.\nTopic A: Emergence of the 5G Network\nWith major carriers rolling out (or promising to roll out) a 5G network, what does all this mean? What\nexactly is 5G and how will it affect our daily lives? Is every 5G network the same? What is required to\nproduce such a network and why is it only available in the places that it is?\nTopic B: Network Management\nBetween wireless networks in the workplace, cellular networks, and home networks, all must be designed", "source": "Page 449", "chapter_title": "Chapter 11"}
{"id": "3905b933f779-0", "text": "in such a fashion that suits their respective breadth and usage case. How does a manager decide what to\nemploy, how to employ it, and monitor to assure reliability and high performance? What is Network\nManagement Software and how is it used? What is the cost? Does it still need to be monitored by a\nhuman? How so?\nDeliverables\nYour job will be to prepare a presentation/video (7\u201310 minutes long) that addresses the topic and\nprovides information on the following items:\n1. Title Slide\n2. Short description of the topic\n3. Main players\u2014these could be people, processes, software, hardware, etc.\n4. How it works\u2014use a lot of pictures and be as technical as possible; create this part as a tutorial so that\nyour audience can follow along\n5. How does it relate to material covered in class so far (and in the future)\n6. Additional material/books/links where to learn more about this topic\n7. Credits\n8. List of References\n9. Memo addressed to your professor describing all of the above information\nHANDS-ON ACTIVITY 12A\nMonitoring Solar Winds Network\nOne of the key tasks of network management is monitoring the network to make sure everything is\nrunning well. There are many effective network monitoring tools available, and several have\ndemonstrations you can view on the Web. One of my favorites is solarwinds.net. They have a live\ndemonstration of their network management software available at npm.solarwinds.net. Log in with the\nprovided guest access.\nFigure 12-14 shows the top portion of the demo page. It shows a map of the network with circuits and\nlocations color-coded. On the left side of the screen is a list of all nodes showing their status (green for", "source": "Page 450", "chapter_title": "Chapter 11"}
{"id": "e89f558305e1-1", "text": "good, yellow for some problems, and red for major problems), although the colors are hard to see in the\nfigure. The bottom left part of the figure shows the busiest servers. The bottom right of this figure shows\nthe nodes with problems so that a network manager can quickly see problems and act to fix them. For\nexample, the sales switch is down.", "source": "Page 450", "chapter_title": "Chapter 11"}
{"id": "36ec94dc8269-0", "text": "FIGURE 12-14 SolarWinds network management software, used with permission\nFigure 12-15 shows the next part of the page after I scrolled down. We now see two pie charts on the right\nside that show application health (which indicates that the software is an application management\npackage as well as a network management package) and hardware health. You can click on any of the\napplication or hardware categories to see which applications/hardware are in which status category. The\ntable below these two pie charts shows the processes using the most memory, while the pie chart on the\nright shows the busiest circuits (top five conversations). You\u2019ll note that the software is also a\nconfiguration management package because below this pie chart there is a list of the last configuration\nchanges.", "source": "Page 451", "chapter_title": "Chapter 11"}
{"id": "5234d83f1765-0", "text": "FIGURE 12-15 SolarWinds network management software, used with permission\nFigure 12-16 shows the next part of the page. This includes the disk space that is close to capacity and a\nsummary of recent events. This software also integrates the help desk software, so it displays help desk\nrequests that have not yet been completed, in order of priority. At the bottom of the screen is a weather\nradar map because weather often causes network issues.\nThis page is a summary page. Every element on the page can be clicked to go to the detail page to get more\ninformation about any item on the page.", "source": "Page 452", "chapter_title": "Chapter 11"}
{"id": "960c77e1f4ae-0", "text": "FIGURE 12-16 SolarWinds network management software, used with permission\nDeliverables\n1. What problem alerts are currently displayed for the SolarWinds network?\n2. What are the top three nodes by CPU load? What are the top three conversations?\n3. How many applications are in critical condition? Name one.\n4. What is one help desk ticket that has not been completed?\nHANDS-ON ACTIVITY 12B\nMonitoring AT&T\u2019s WAN\nAT&T permits you to monitor their Global IP network. Go to ipnetwork.bgtmo.ip.att.net and click on Take\nA Look At Your Worldwide Network.\nYou\u2019ll see a screen that displays all the circuits at each of the major PoPs in their global IP network. You\ncan select a city and see the round-trip delay (from the city to the other city and back again). It also\ndisplays the percentage of packets that have been lost in transit (due either to errors or overloading of", "source": "Page 453", "chapter_title": "Chapter 11"}
{"id": "6d20efaf351d-0", "text": "circuits).\nThe tabs across the top of the screen (e.g., Network Delay, Network Loss, Averages) show summary data\nacross the entire network.\nDeliverables\n1. What is the current latency and packet loss between Dallas and Austin?\n2. What is the current latency and packet loss between Phoenix and New York?\nHANDS-ON ACTIVITY 12C\nApollo Residence Network Design\nApollo is a luxury residence hall that will serve honors students at your university. We described the\nresidence in Hands-On Activities at the end of Chapters 7\u201311. In this activity, we want you to revisit the\nLAN design (Chapter 7), backbone design (Chapter 8), WAN design (Chapter 8), Internet design (Chapter\n10), and security design (Chapter 11) and then add the design for good network management (this\nchapter).\nDeliverable\nYour team was hired to design the network for the Apollo residence. Design the entire network, including\nLANs, backbones, WAN, Internet, security, and network management. You will need to refer to the\nHands-On Activities in Chapters 7\u201311 as well as this one. Figure 12-17 provides a list of possible hardware\nand software you can add, in addition to the equipment lists in these activities in previous chapters. Note\nthat you can\u2019t just \u201cadd SNMP\u201d to any device; instead, this is the difference in cost between the\n\u201cunmanaged\u201d devices listed in prior chapters and \u201cmanaged\u201d devices we\u2019ve discussed in this chapter.", "source": "Page 454", "chapter_title": "Chapter 11"}
{"id": "073dc1e31390-0", "text": "FIGURE 12-17 Equipment list", "source": "Page 455", "chapter_title": "Chapter 11"}
{"id": "58b19991e078-0", "text": "INDEX\nw1 GbE, 193\u20134\n10 GbE, 193\u20134\n10/100/1000 Ethernet, 193\u20134\n10Base-T, 193\u20134\n100Base-T, 193\u20134\n1000Base-T, 193\u20134\n40 GbE, 193\u20134\n802.11ac, 197\n802.11ax, 197\u20138\n802.11i, 198\n802.11n, 197\nA\naccept, risk, 301\naccess control list (ACL), 138, 234\u20135, 315\naccess layer, 163\naccess points (AP), 187\nassociating with, 195\naccess request technique, 92\naccess VPN, 255\naccount, user, 329\nacknowledgments (ACK), 102, 120\nActive Directory Service (ADS), 189\nactive scanning, 195\nadaptive differential pulse code modulation (ADPCM), 81\u20132\nadaptive routing. See dynamic routing\naddress field, 102\naddressing\naddress resolution, 129\u201331\nserver name resolution, 129\u201331\napplication layer address, 129\nassigning addresses, 124\u20139\nclassless addressing, 126\ndata link layer address, 124\nresolution, 131\ndynamic addressing, 128\u20139", "source": "Page 456", "chapter_title": "Chapter 11"}
{"id": "e00675f858c3-0", "text": "network layer address, 124\nsubnets, 127\u20138\naddress resolution, 129\u201331\nAddress Resolution Protocol (ARP), 131, 151\nAdvanced Encryption Standard (AES), 325\nadware, 323\nAkamai, 360\u20131\nalarm, 353\nmessage, 353\nstorm, 354\nalgorithm, 324\nalternate mark inversion (AMI), 74\nAmerican National Standards Institute (ANSI), 15\nAmerican Standard Code for Information Interchange (ASCII), 71\namplifiers, 96\namplitude, 75\namplitude modulation (AM), 75\namplitude shift keying (ASK), 76\nanalog data, 60\nanalog to digital transmission, 79\u201380\nanalog transmission, 75\nof digital data\ncapacity of a circuit, 78\nmodems, 78\u20139\nmodulation, 75\u20138 (See also individual entry)\nanatomy, routing, 137\u20138\nanomaly detection, 334\nantivirus software, 305, 320\nApollo Residence, 348\u20139\nbackbone networks (BNs), 234\u20136\nInternet, 291\nnetwork management, 385\nwide area network (WAN), 273\napplication architectures, 28\napplication logic, 29\nchoosing, 36\u20137\nclient-based, 29\nclient-server, 30\u20133\ncloud-based, 29", "source": "Page 457", "chapter_title": "Chapter 11"}
{"id": "3f95b45a900e-0", "text": "cloud computing, 28, 33\u20135\ndata access logic, 28\ndata storage, 28\nhost-based, 29\npeer-to-peer (P2P), 35\u20136\npresentation logic, 29\napplication layer, 10, 11, 27\u201358\naddress, 123, 124, 129\ncyber security, implications, 48\u20139\ndesktop videoconferencing, 47\u20138\nelectronic mail (email), 41\nemail working, 41\u20134\nmultipurpose internet mail extension, 45\nSMTP packet, 44\nTelnet, 46\nvideoconferencing, 47\u20138\nWorld Wide Web\nHTTP request, 38\u20139\nHTTP response, 39\u201340\nweb working, 37\u20138\napplication layer address, 123\napplication-level firewall, 316\napplication logic, 29\napplication management software, 354\u20135\napplication security, 48\napplication shaping. See policy-based management\napplication systems, 169\narchitecture DSL, 279\nARP cache, 142\nasset, 298\nassigning addresses, 124\u20139\nassociation, 195\nasymmetric DSL (ADSL), 279\u201380\nasymmetric encryption, 323\nasynchronous transmission, 101\nAT&T, 385\nAttacks tab, 25\nattenuation, 95\u20136\nauthentication, 326. See also user authentication", "source": "Page 458", "chapter_title": "Chapter 11"}
{"id": "401727136d6b-0", "text": "authentication server, 332\nauthoritative name server, 130\nautomated software delivery. See desktop management\nAutomatic Repeat reQuest (ARQ), 99, 120\nautonomous system, 134, 276\nauxiliary port, 137\navailability, 294, 355, 367\navoiding disaster, 310\nB\nbackbone cabling, 64\nbackbone networks (BNs), 3, 7, 8, 220\u201342. See also routed backbones; switched backbones; virtual LANs\n(VLANs)\nbest practice backbone design, 232\u20133\ncyber security, 234\u20135\ndesign, 232\u20133\nperformance improvement, 233\u20134\ncircuit capacity, 234\ndevice performance, 233\u20134\nnetwork demand, 234\nrouted backbones, 224\u20136\nswitched backbones, 221\u20134\nvirtual LAN (VLAN), 227\nbenefits of, 227\u20139\nworking, 229\u201332\nBack Orifice, 322\nbackup controls, 311\nbandwidth, 78\nbandwidth limiter/bandwidth shapers. See capacity management\nbaseline, 168\nbaselining, 169\nbasic modulation, 76\nbaud rate, 78\nbeacon frame, 195\nBest Buy, 361\nbiometric systems, 332\nbipolar signal, 73\nBitLocker, 344\nbit rate, 78", "source": "Page 459", "chapter_title": "Chapter 11"}
{"id": "99743f818ff6-0", "text": "bits per second (bps), 78\nbody, SMTP packet, 44\nBoingo hot spots, 68\nBorder Gateway Protocol (BGP), 135\nborder router, 134\nbottleneck, 172, 208\nBoyle Transportation, 70\nbring your own device (BYOD), 18\nbroadband technologies, 279\nbroadcast messages, 126\nbrowser-based approach, 18\nbrowser-based technologies, 18\nbrute-force attacks, 324\nbuilding backbone network, 163\nbuilding-block network design process, 166\ncost assessment, 166\u20137, 175\nneeds analysis, 166\ntechnology design, 166, 171\u20134\nbuilding entrance, 64\nburst error, 94\nbusiness continuity, ensuring, 294. See also Denial-of-Service (DoS) protection\nDenial-of-Service protection, 305\u20138\ndevice failure protection, 309\u201310\ndisaster protection, 310\u201312\nfault-tolerant servers, 310\ntheft protection, 308\u20139\nvirus protection, 304\u20135\nbusiness continuity plan, 294\nbus topology, 190\nbyte, 71\nC\ncable modem, 280\u20132\narchitecture, 281\u20132\noptical-electrical (OE) converter, 281\ntypes of, 282\ncable modem termination system (CMTS), 282\ncable plan, LAN, 200\ncables, 6", "source": "Page 460", "chapter_title": "Chapter 11"}
{"id": "6995d2475ded-0", "text": "cabling, LAN, 200\ncampus backbone network, 163\nCanadian Radio-Television and Telecommunications Commission (CRTC), 244\ncapacity management, 358\ncapacity of a circuit, 78\ncapacity planning, 171\nCaptain D\u2019s (multicast), 136\ncareer opportunities in communications, 4\nCarrier Sense Multiple Access with Collision Avoidance (CSMA/CA), 194\u20135\nCarrier Sense Multiple Access with Collision Detection (CSMA/CD), 193\ncarrier wave, 75\nCat 5/Cat 5e cable, 88\u20139\ncategorizing network needs, 170\nCat 5e patch cable, 90\ncentral authentication, 332\ncentral distribution facility (CDF), 221\ncentralized routing, 133\ncertificate, 332\ncertificate authority (CA), 327\nchannel, 184\nchannel service unit (CSU), 245\ncharacter, 71\ncharge-back policies, 375\nchassis switch, 221\u20132\nchecksum technique, 98\nchoosing architectures, 36\u20137\nCIA. See confidentiality, integrity, and availability\nciphertext, 326\ncircuit configuration, 61\ncircuit loading, 172\ncircuits, 6, 60\ncapacity, 210\nbackbone networks (BNs), 234\nbandwidth, 78\ndata rate (or bit rate), 78\nWAN, 262\ncapacity, improving, 210\nconfiguration, 61\u20132\ndata flow, 62", "source": "Page 461", "chapter_title": "Chapter 11"}
{"id": "3250efbc4af9-0", "text": "dedicated circuits, 61\ndesigning, 171\u20133\nbottleneck, 172\ncapacity planning, 171\ncircuit loading, 172\nfull-duplex transmission, 62\nhalf-duplex transmission, 62\nloading, 172\nmultiplexing, 62\u20135\nmultipoint circuit, 61\u20132\nnetwork design, 171\u20133\npoint-to-point circuit, 61\nsimplex transmission, 62\nturnpike effect, 172\nmultiplexing, 62\u20135\nCisco Internetwork Operating Systems (IOS), 137\nclassless addressing, 126\nclear to send (CTS), 196\nclient, 6\nclient-based architectures, 29, 30\nclient computer, 183\nclient protection, 320\u20133\nclients and servers, network design, 171\nclient-server architectures, 29, 30\u20133\nn-tier architecture, 31\u20132\nthin clients versus thick clients, 33\nthree-tier architecture, 31, 32, 42\u20134\ntwo-tier architecture, 31, 41\ncloud-based architecture, 29, 33\ncloud computing architectures, 33\u20135, 36\u20137\ncloud computing deployment models, 28\ncloud providers, 28\ncommunity cloud, 28\nhybrid cloud strategy, 28\nprivate cloud, 28\npublic cloud, 28\npure strategy, 28\ncloud computing with Salesforce.com, 36\ncloud Email, 39", "source": "Page 462", "chapter_title": "Chapter 11"}
{"id": "67b5b6e2e054-0", "text": "cloud providers, 28\nclusters, 357\ncoaxial cable, 65\u20136\ncode/coding scheme, 71\ncodecs, 60, 79\ncoding\nbyte, 71\ncharacter, 71\ncode, 71\nscheme, 71\ncollision, 193\ncollision detection (CD), 193\ncollision domain, 190\ncommitted information rate (CIR), 251\u20132\ncommon carriers, 161, 164, 243\nCommon Object Request Broker Architecture (CORBA), 31\ncommunication media\ncoaxial cable, 65\u20136\nfiber-optic cable, 66\u20137\nguided media, 65\nmedia selection factors, 70\u20131\ncost, 70\nerror rates, 71\nsecurity, 70\ntransmission distance, 70\ntransmission speeds, 71\ntype of network, 70\nmicrowave, 68\nradio, 67\nsatellite transmission, 68\u201370\ntwisted pair cable, 65\u20136\ncommunity cloud, 28\ncomponents, LAN\nnetwork circuits, 184\u20135\nnetwork hubs, switches, and access points, 185\u20138\nnetwork interface cards (NIC), 183\nnetwork operating systems (NOS), 188\u20139\ncomputer\nencryption, 344\u20136", "source": "Page 463", "chapter_title": "Chapter 11"}
{"id": "fb68d81490ca-0", "text": "security, 343\u20134\nTCP/IP settings, 140\nComputer Emergency Response Team (CERT), 293\ncomputer forensics, 336\nconfidentiality, 294\nconfidentiality, integrity, and availability (CIA), 294\nconfiguration management, 361\ndesktop management, documentation, 362\u20134\nsoftware documentation, 363\nuser and application profiles, 363\nnetwork and client computers, 361\u20132\nconnectionless messaging, 120, 122\u20133\nconnection-oriented messaging\nfour-way handshake, 122\nthree-way handshake, 120\nconsole port, 137\ncontent caching, 358\u201360\ncontent delivery, 360\ncontent delivery provider, 360\ncontent engine/cache engine, 358\u201360\ncontention, 92\ncontinuous ARQ, 102, 121\u20132\ncontinuous data protection (CDP), 311\ncontrol field, 102\ncontrolled access, 92\u20133\ncontrol plane, 259\ncontrols, 295. See also network controls\ndocument existing, 301\u20134\ncontrols, network\ncorrective controls, 296\ndetective controls, 295\u20136\npreventive controls, 295\ncore layer, 163\ncorrective controls, 296\ncorrupted data, 94\ncost assessment, network design, 166\u20137, 174\u20136\ndeliverables, 180\nrequest for proposal (RFP), 175\nselling the proposal to management, 175\u20136", "source": "Page 464", "chapter_title": "Chapter 11"}
{"id": "8efaa5273f6f-0", "text": "cost management, 373\nreducing costs, 375\u20137\nautomation, 377\nby developing standards, 376\nmoving to thin-client or cloud-based architectures, 377\nreducing the time spent installing new hardware and software, 364\nsources of costs, 373\u20135\ncost, media, 70\ncrackers, 313\ncross-talk, 95\ncryptography, 323\ncustomer premises equipment (CPE), 279\ncut-through switching, 192\ncyber security\napplication layer, 48\u20139\nbackbone networks (BNs), 234\u20135\ndata communications, 20\u20131\ndata link layer, 106\u20137\ninternet, 285\nlocal area networks (LANs), 210\nnetwork design, 176\u20137\nnetwork layer and transport layer, 145\nnetwork management, 377\u20138\nnetwork security, 330\nphysical layer, 83\nwide area network (WAN), 262\ncybersecurity programs and certifications, 342\ncyclic redundancy check (CRC), 98\nD\ndata access logic, 28\ndata center, 163\ndesigning, 203\u20135\ndata communications, 1\u201326\nbasic concepts, 1\u201326\ncareer opportunities, 4\nfuture trends, 18\u201320\nhistory of, 1\u201326\n1800s, 2", "source": "Page 465", "chapter_title": "Chapter 11"}
{"id": "7967e2362603-0", "text": "1900s, 2\nfirst Industrial Revolution, 2\nsecond Industrial Revolution, 2\ndata compression, 79\nData Encryption Standard (DES), 324\ntriple DES (3DES), 325\ndata flow, in circuits, 62\ndatagrams, 117\ndata link layer, 9\u201311, 13, 15, 17, 21, 91\u2013113. See also error control; media access control (MAC)\naddress, 131\ncyber security, 106\u20137\ndata link protocols\nasynchronous transmission, 101\nsynchronous transmission, 101\u20134\nerror control\nerror correction via retransmission, 98\nerror detection, 97\u20138\nerror prevention, 96\u20137\nforward error correction, 98\u20139\nin practice, 99\nsources of errors, 94\u20136\nlogical link control (LLC) sublayer, 91\u20132\nmedia access control (MAC) sublayer, 92\ncontention, 92\ncontrolled access, 92\u20133\nrelative performance, 93\u20134\ntransmission efficiency, 104\u20136\ndata link layer address, 124\nData Link Layer Address Resolution, 131\ndata link protocols\nasynchronous transmission, 101\nEthernet, 102\u20133\nLink Access Protocol-Balanced (LAP-B), 102\npoint-to-point protocol (PPP), 103\u20134\nsynchronous data link control (SDLC), 102\nsynchronous transmission, 101\u20134\nData over Cable Service Interface Specification (DOCSIS) standard, 280\u20131, 282\ndata plane, 259\ndata rate (or bit rate), 78", "source": "Page 466", "chapter_title": "Chapter 11"}
{"id": "5e41410dad1d-0", "text": "data security, physical security, 319\ndata service unit (DSU), 245\ndata storage, 28\nDDoS agents, 306, 323\nDDoS handler, 306\ndecimal values to binary (and vice versa), 156\u20137\ndecryption, 323\ndedicated-circuit networks, 61, 244\u201350\nbasic architecture, 245\u20138\nfull-mesh architecture, 247\nmesh architecture, 247\u20138\npartial-mesh architecture, 247\nring architecture, 246, 247\nservices\nSONET, 249\nT-carrier, 248\u201350\nstar architecture, 246\u20137, 248\nsynchronous optical network (SONET), 249\ndedicated circuits. See point-to-point circuit\ndedicated-circuit services, 248\nde facto standard, 15\ndefer, risk, 301\nde jure standardization process, 15\nacceptance stage, 15\nidentification of choices stage, 15\nspecification stage, 15\ndeliverables, 176\ndemilitarized zone (DMZ), 317\nDenial-of-Service (DoS) protection, 305\u20138\nagent, 306, 323\nattack, 305\u20138\nhandler, 306\ntraffic analysis, 307\ntraffic anomaly analyzer, 307\ntraffic anomaly detector, 307\ntraffic filtering, 306\ntraffic limiting, 306\ndesignated router, 134\ndesign, backbone networks (BNs), 232\u20133", "source": "Page 467", "chapter_title": "Chapter 11"}
{"id": "fa513fac60e8-0", "text": "design, LAN\ndata center, 203\u20135\ne-commerce edge, 206\nSOHO environment, 206\u20137\nuser access with wired Ethernet, 200\nuser access with wireless Ethernet, 200\u20133\ndesign, network\nmanaged networks, 353\u20137\nmanaging network traffic, 357\u20138\nreducing network traffic, 358\u201361\ndesirable requirements, 170\nDesktop-as-a-Service (DaaS), 49\ndesktop management, 337, 362\nDesktop Management Interface (DMI), 362\ndesktop videoconferencing, 47\u20138\ndestination port address, 118\ndestruction, 294\ndetective controls, 295\ndevice, backbone networks (BNs), 233\u20134\ndevice failure protection, 309\u201310\ndevice management software, 354\ndevice performance, WAN, 261\ndigital subscriber line (DSL), 65\narchitecture, 279\nasymmetric DSL (ADSL), 279\nDSL access multiplexer (DSLAM), 279\nlocal loop, 279\nmain distribution facility (MDF), 279\nmodem, 279\ntypes of, 279\ndigital transmission, 65\nof analog data, 60\ninstant messenger transmitting voice data, 81\u20132\ntelephones transmitting voice data, 80\u20131\ntranslating from analog to digital, 79\u201380\nVoice over Internet Protocol (VoIP), 82\nof digital data\nbipolar signaling, 73\ncoding, 71\u20132", "source": "Page 468", "chapter_title": "Chapter 11"}
{"id": "e7e9e1904b83-0", "text": "digital transmission, 73\u20134\nEthernet, 74\u20135\nISO 8859, 71\ntransmission modes, 72\u20133\nunicode, 71\ndirectional antenna, 187\ndisaster protection, 310\u201313. See also intrusion prevention\navoiding disaster, 310\nbackup, 311\ncontinuous data protection (CDP), 311\u201312\ndisaster recovery, 310\u201311\nonline backup services, 312\nrecovery controls, 311\ndisaster recovery drill, 312\ndisaster recovery firms, 313\ndisaster recovery outsourcing, 313\ndisaster recovery plan, 310\u201311, 312\ndiscard eligible (DE), 251\u20132\ndisk mirroring, 310\ndisruptions, 294\ndistance vector dynamic routing, 133\ndistortion, 94\nDistributed Computing Environment (DCE), 31\ndistributed coordination function (DCF), 195\ndistributed denial-of-service (DDoS) attack, 305\ndistribution hub, 282\ndistribution layer, 163\ndistribution list, 41\nDNS recursion attacks, 308\nDNS request, 155\u20136\nDNS response, 155\u20136\ndocumentation, 362\u20134\ndocument existing controls, 301\u20134\ndomain controllers, 189\ndomain names, 125\nDomain Name Service (DNS) server, 129\nworking of, 130\ndouble current signal, 74\ndowntime, 368", "source": "Page 469", "chapter_title": "Chapter 11"}
{"id": "7aa82b95f66c-0", "text": "DSL access multiplexer (DSLAM), 279\nDSL modem, 279\ndual-band access point, 197\ndynamic addressing, 128\u20139\nDynamic Host Configuration Protocol (DHCP), 129\ndynamic routing\ndistance vector dynamic routing, 133\nhops, 133\nlink state dynamic routing, 133\nE\neavesdropping, 319\nechoes, 95\ne-commerce edge, 164, 206\ndesigning, 206\nefficiency, 97\nEIA/TIA 568-B, 64\nelectricity, 72\nElectronic Industries Alliance (EIA), 64\nelectronic mail (email), 41\nemail working, 41\u20134\nmail transfer agent, 41\nmail user agent, 41\nmultipurpose internet mail extension, 45\nSMTP packet, 44\nthree-tier thin client-server architecture, 31, 32, 42\u20134\ntracing your, 53\u20135\ntwo-tier email architecture, 31, 41\nWeb-based email, 42\nworking of, 41\u20134\nelectronic software delivery. See desktop management\neMail Tracker Pro, 53\nEncapsulating Security Payload (ESP) packet, 257\nencapsulation, 14\nencryption, 323\u20138\nasymmetric, 323\nauthentication, 326\u20138\nData Encryption Standard (DES), 324\nmode, selecting/starting, 345", "source": "Page 470", "chapter_title": "Chapter 11"}
{"id": "076678493747-0", "text": "public key, 325\u20136\nsingle-key, 324\nsoftware\nIPSec transport mode, 328\nIPSec tunnel mode, 328\nIP Security Protocol (IPSec), 328\nPretty Good Privacy (PGP), 328\nsymmetric, 323, 324\ntriple DES (3DES), 325\nencryption lab, 346\u20138\nencryption software Pretty Good Privacy (PGP), 328\nend user support, 371\nend user training, 372\u20133\nresolving problems, 371\ntraining, 372\u20133\nEnhanced Interior Gateway Routing Protocol (EIGRP), 136\nenterprise campuses, 163\nenterprise edge, 164\nenterprise management software. See system management software\nentrapment techniques, 336\nequipment room (ER), 64\nerror control, 94\u2013100\nerror correction via retransmission, 98\nerror detection, 97\u20138\nerror prevention, 96\u20137\nforward error correction, 98\u20139\nin practice, 99\nsources of errors, 94\u20136\nwired Ethernet, 208\nerror correction via retransmission, 98\nerror detection, 97\u20138\nchecksum, 98\ncyclic redundancy check (CRC), 98\neven parity, 98\nodd parity, 98\nparity bit, 97\nparity check, 97\nerror prevention, 96\u20137\namplifiers, 96", "source": "Page 471", "chapter_title": "Chapter 11"}
{"id": "305dc9586900-0", "text": "moving cables, 96\nrepeaters, 96\nshielding, 96\nerror rates, 94\nmedia, 70\nerrors, sources of, 94\u20136\nattenuation, 95\u20136\ncross-talk, 95\ndistortion, 94\nechoes, 95\nimpulse noise, 95\nintermodulation noise, 96\nline noise, 94\u20135\nwhite noise or Gaussian noise, 95\nEthernet, 74\u20135, 189\u201390. See also wired Ethernet; wireless Ethernet\nTracePlus, 215\u201316\nEthernet (IEEE 802.3), 102\u20133\ntypes\n10Base-T, 193\u20134\n100Base-T, 193\u20134\n1000Base-T, 193\u20134\n10/100/1000 Ethernet, 193\u20134\nwardriving, 217\u201318\nEthernet II, 103\nEthernet services, WAN, 252\u20133\neven parity, 98\nexterior routing protocols, 134\nextranets, 8\nextranet VPN, 255\nF\nfailure control function, 366\u20138\nhelp desk, 366\nproblem statistics, 367\nproblem tracking, 367\ntrouble tickets, 367\nfailure statistics\navailability, 368\ndowntime, 368", "source": "Page 472", "chapter_title": "Chapter 11"}
{"id": "47212fa7de9d-0", "text": "mean time between failures (MTBF), 368\nmean time to diagnose (MTTD), 369\nmean time to fix (MTTF), 369\nmean time to repair (MTTR), 369\nmean time to respond (MTTR), 369\nfault management. See also performance and fault management\nfailure control function, 366\u20138\nfault-tolerant servers, 310\nFederal Communications Commission (FCC), 244\nfiber node, 281\nfiber-optic cable, 66, 184\nmultimode, 66\nsingle-mode, 67\nfiber to the home (FTTH), 282\u20133\nfile server, 6\nFileVault, 347\nfinancial, business impacts, 297\nfinger of death attacks, 308\nfirefighting, 352\nfirewall, 315\napplication-level, 316\narchitecture, 317\neavesdropping, 319\nnetwork address translation (NAT) firewalls, 316\u201317\npacket-level, 315\u201316\nphysical security, 308, 317\u201319\nto protect networks, 315\nsecure switch, 319\nsniffer program, 319\nflag, 102\nflow control, 121\nforward error correction, 98\u20139\nworking of, 99\nforwarding table, 191\nfour-way handshake, 122\nfractional T1 (FT1), 249\nfragment-free switching, 192\nframe(s), 101, 190\nframe check sequence field, 102", "source": "Page 473", "chapter_title": "Chapter 11"}
{"id": "dfa1f7697f89-0", "text": "frame relay services, WAN, 251\nframe size, 106\nfrequency, 63, 75\nfrequency division multiplexing (FDM), 63, 96\nfrequency modulation (FM), 75, 76\nfrequency shift keying (FSK), 76\nfull-duplex transmission, 62\nfull-mesh architecture, 247\nfunctions\nlinking to the application layer, 118\u201319\nsegmenting, 119\u201320\nsession management, 120\u20133\nG\ngateway, 139\nGaussian noise, 95\ngeographic scope, 168\ngeosynchronous satellite transmission, 68\ngigapops, 284\n5G network, emergence of, 381\nGo-Back-N ARQ, 121\nGreater Cleveland Regional Transit Authority (GCRTA), 251\nguided media, 65\nH\nhackers, 313, 342\nhacking, 293\nhacktivism, 293\nhalf-duplex transmission, 62\nHamming code, 99\nHardware as a Service (HaaS), 35\nhardware layers, 11\nhardware, server performance, 208\u201310\nheadend, 282\nheader, SMTP packet, 44\nHealth Insurance Portability and Accountability Act (HIPAA), 293\nhelp desk, 366\nhidden node problem, 195\u20136\nhierarchical backbones. See routed backbones", "source": "Page 474", "chapter_title": "Chapter 11"}
{"id": "2db7d9eb4baa-0", "text": "high-level data link control (HDLC), 102\nhoney pot, 336\nhops, 133\nhorizontal cabling, 64\nhost-based architectures, 29\nproblems with, 29\nhost-based IPS, 333\nH.320 standard, 48\nH.323 standard, 48\nHTTP request, 38\u20139\nHTTP response, 38\u201340\nhub-based Ethernet, 190\nhub polling, 93\nhubs, 185\u20138\nhuman errors, 94\nhybrid cloud strategy, 28\nhybrid fiber coax (HFC), 281\nHypertext Markup Language (HTML), 39\nHypertext Transfer Protocol (HTTP), 12, 38, 112\u201313, 122, 143\nHTTP request, 38\u20139\nHTTP response, 38\u201340\ninside HTTP request\nrequest body, 38\nrequest header, 38\nrequest line, 38\ninside HTTP response\nresponse body, 40\nresponse header, 40\nresponse status, 39\nI\nICMP attacks, 308\nIEEE 802.3. See also Ethernet (IEEE 802.3)\nIEEE 802.11. See also wireless Ethernet\nIEEE 802.3ac, 102\nIEEE 802.1q standard, 229\nIEEE 802.3, 189. See also Ethernet (IEEE 802.3)\nIEEE 802.11, 194. See also wireless Ethernet\nimpact score, 301", "source": "Page 475", "chapter_title": "Chapter 11"}
{"id": "b4a6d491c760-0", "text": "improvements, identify, 304\nimproving performance, 370\u20131\nimpulse noise, 95\ninformation bits, 105\ninformation frame, 102\ninformation warfare program, 313\nInfrastructure as a Service (IaaS), 35\nInstant Messenger, 81\u20132\ninstant messenger transmitting voice data, 81\u20132\nInstitute of Electrical and Electronics Engineers (IEEE), 17\nintegrity, 294\ninterexchange carrier (IXC), 91, 94, 244\ninterface, 131\nInterior Gateway Routing Protocol (IGRP), 136\ninterior routing protocols, 134\nIntermediate System to Intermediate System (IS-IS), 135\nintermodulation noise, 96\nInternational Organization for Standardization (ISO), 15\nInternational Telecommunications Union-Telecommunications Group (ITU-T), 15\nInternet, 27, 274\u201391\nbasic architecture, 275\u20136\nconnecting to an ISP, 277\u20138\ncyber security, 285\u20136\nfuture of, 274\u20137\nbuilding the future, 284\u20135\ngigapops, 284\nInternet2, 284\nInternet Engineering Task Force (IETF), 283\nInternet governance, 283\u20134\nNext Generation Internet (NGI), 284\ngovernance, 283\u20134\nInternet access technologies\ncable modem, 280\u20132\ndigital subscriber line (DSL), 279\u201380 (See also individual entry)\nfiber to the home (FTTH), 282\u20133\nWiMax, 274\nInternet as we know it today, 22, 25\nInternet today, 278\nISPs, 275, 277\u20138", "source": "Page 476", "chapter_title": "Chapter 11"}
{"id": "3f6e9e3b947a-0", "text": "rise of, 292\u20133\nrouting on the, 134\nspeed test, 282, 290\u20131\nworking of, 275\u20138\nInternet2, 367\nInternet2\u00ae, 284, 285\nInternet access, 164\nInternet access component, 164\nInternet access technologies\nbroadband technologies, 279\ncable modem, 280\u20132\nDigital Subscriber Line (DSL), 279\u201380 (See also individual entry; individual entry)\nfiber to the home (FTTH), 282\u20133\nWiMax, 274\nInternet address classes, 125\nInternet addresses, 125, 129\nInternet Control Message Protocol (ICMP), 135\nInternet Corporation for Assigned Names and Numbers (ICANN), 121, 125, 284\nInternet domain names, 5\nInternet Engineering Steering Group (IESG), 283\nInternet Engineering Task Force (IETF), 16, 17, 283\nInternet exchange points (IXPs), 275\u20136\nInternet Group Management Protocol (IGMP), 137\nInternet Key Exchange (IKE), 328\nInternet Message Access Protocol (IMAP), 41, 42\nInternet model, 9, 10\u201312\napplication layer, 11\ndata link layer, 11\ngroups of layers, 11\u201312\nhardware layers, 11\ninternetwork layers, 11\nnetwork layer, 11\nphysical layer, 11\ntransport layer, 11\nInternet of Things (IoT), 18\u201319\nInternet Protocol (IP), 13, 117\u201318\nInternet Protocol version 4 (IPv4), 117, 118, 125\nInternet Protocol version 6 (IPv6), 117\u201318, 161\nInternet Research Task Force (IRTF), 283", "source": "Page 477", "chapter_title": "Chapter 11"}
{"id": "a5a4d691cca6-0", "text": "Internet Service Provider (ISP), 1, 254, 275, 277\u20138\nautonomous system, 276\nconnecting to, 277\u20138\nlocal ISPs, 275\nnational ISPs, 275\nregional ISPs, 275\nInternet Society, 283\ninternetwork layer, 11\nInternetwork Operating Systems (IOS), 137\nintranets, 8\nintranet VPN, 255\nintrusion, 295\nintrusion prevention, 313\u201314. See also encryption; firewalls\nadware, 323\nclient protection, 320\u20133\ncrackers, 313\nencryption, 323\u20138\nintrusion recovery, 335\u20136\nIPSs, 333\u20135\noperating systems, 321\u20132\nperimeter security and firewalls, 314\u201319\npreventing social engineering, 332\u20133\nproactive principle in, 314\nsecurity holes, 320\nsecurity policy, 314\nserver and client protection, 320\u20133\nserver protection, 320\u20133\nsocial engineering, 332\u20133\nspyware, 323\nTrojan horse, 322\ntypes of intruders, 313\ncasual intruders, 313\nhackers, 313\norganization employees, 313\nprofessional hackers, 313\nuser authentication, 329\u201332\nintrusion prevention systems (IPSs), 333\u20135\nanomaly detection, 334\nhost-based IPS, 333", "source": "Page 478", "chapter_title": "Chapter 11"}
{"id": "ff1fe29d4f03-0", "text": "misuse detection, 334\nnetwork-based IPS, 333\nintrusion recovery, 335\u20136\ncomputer forensics, 336\nentrapment techniques, 336\nhoney pot, 336\ninventory IT assets, 298\nmission-critical application, 298\nIPCONFIG command, 150\nIPCONFIG/DISPLAYDNS command, 151\nIPSec transport mode, 328\nIPSec tunnel mode, 328\nIP Security Protocol (IPSec), 248, 255, 328\nIPSec transport mode, 328\nIPSec tunnel mode, 328\nIP services, WAN, 252\nIPS management console, 333\nIP spoofing, 315\nIPS sensor, 333\nIPv4 private address space, 126\nISO 8859, 71\nISO 13818-2, 48\nK\nKerberos, 332, 333\nkey, 324\nKey Distribution Center (KDC), 333\nkey management, 324\nKilo Hertz (kHz), 73\nknown addresses, 140\u20131\nL\nLAN administrator, 183\nlatency, 192, 261\nlayers, 8\nlayer 2 switches, 186, 191, 220\nlayer 2 tunneling protocol (L2TP), 255\nlayer 2 VPN, 255\nlayer 3 VPN, 255", "source": "Page 479", "chapter_title": "Chapter 11"}
{"id": "c41e50631daf-0", "text": "legal, business impacts, 297\nLempel\u2013Ziv encoding, 79\nlightweight directory access protocol (LDAP), 189\nline noise, 94\nline splitter, 279\nLink Access Protocol\u2013Balanced (LAP-B), 102\nLink Access Protocol for Modems (LAP-M), 121\nlink state dynamic routing, 133\nload balancer, 357\nload balancer/load balancing switch, 203\nlocal area networks (LANs), 7, 8, 163, 182\u2013219, 210, 218\u201319. See also wired Ethernet; wired LANs;\nwireless LANs (WLANs)\nbest practice LAN design, 199\u2013207\ndesigning data center, 203\u20135\ndesigning user access with wired Ethernet, 200\u20133\ne-commerce edge, designing, 206\nnetwork-attached storage (NAS), 205\nSOHO environment designing, 206\u20137\nstorage area network (SAN), 205\ncomponents\naccess points, 185\u20138\nclient computer, 183\ndirectional antenna, 187\nhubs, 185\u20138\nnetwork circuits, 184\u20135\nnetwork hubs, switches, and access points, 185\u20138\nnetwork interface cards (NIC), 183\nnetwork operating systems (NOS), 188\u20139\nnetwork profile, 189\nomnidirectional antennas, 187\nport, 185\npower over Ethernet (POE), 187\nswitches, 185\u20138\ntwisted-pair cable, 185\nuser profile, 189\nwireless access point, 187\ncyber security, 210\ndesign\ndata center, 203\u20135", "source": "Page 480", "chapter_title": "Chapter 11"}
{"id": "b19f1d6553d0-0", "text": "e-commerce edge, 206\nSOHO environment, 206\u20137\nuser access with wired Ethernet, 200\nuser access with wireless Ethernet, 200\u20133\nperformance improvement, 207\u201310\ncircuit capacity, 210\nhardware, 209\u201310\nnetwork demand, reducing, 210\nperformance checklist, 209\nredundant array of inexpensive disks (RAID), 209\nserver performance, 208\u201310\nsymmetric multiprocessing (SMP), 209\u201310\nwired Ethernet\nmedia access control, 192\u20133\ntopology, 190\u20132\ntypes, 193\nwireless Ethernet\nframe layout, 196\nmedia access control, 194\u20135\nsecurity, 198\u20139\ntopology, 194\ntypes, 196\u20138\nlocal exchange carrier (LEC), 244\nlocal loop, 80, 279\nlogical circuit, 60\nlogical link control (LLC) sublayer, 91\u20132\nlogical network design, 168\nlogical topology, 190\nloopback, 125\nlost data, 94\nM\nMAC address, 106\nMAC address filtering, 107, 199\nMAC address spoofing, 107\nmacro viruses, 304\nMac, system preferences for, 346\nmail server, 6\nmail transfer agent, 41", "source": "Page 481", "chapter_title": "Chapter 11"}
{"id": "f84120cb1bc7-0", "text": "mail user agent, 41\nmain distribution facility (MDF), 221, 279\nmalware, 81, 83, 299, 304, 305\nmanaged APs, 202\nmanaged devices, 353\nmanaged networks, 353\u20137\nalarm message, 353\napplication management software, 354\u20135\ndevice management software, 354\nnetwork management software, 354\nsystem management software, 354\nmanagement information base (MIB), 355\nmanagement-oriented reports, 369\nmanagement plane, 259\nmanagement port, 133, 137\nmanagement reports, 367\u20138\nmanaging network traffic, 357\u20138\nManchester encoding, 75\nmandatory requirements, 170\nmapping a small network, 238\u201340\nmassively online, 19\u201320\nmaximum allowable rate (MAR), 251\u20132\nmean time between failures (MTBF), 368\nmean time to diagnose (MTTD), 368\nmean time to fix (MTTF), 369\nmean time to repair (MTTR), 368\nmean time to respond (MTTR), 369\nmedia access control (MAC), 92\naccess request technique, 92\naddress, 124\ncontention, 92\ncontrolled access, 92\u20133\npolling, 93\nrelative performance, 93\u20134\nroll-call polling, 93\nsublayer, 92\nwired Ethernet, 193\nwireless Ethernet, 194\u20136\nmedia selection, 70\u20131", "source": "Page 482", "chapter_title": "Chapter 11"}
{"id": "272f492a9bdd-0", "text": "mesh architecture, 247\u20138\nfull-mesh architecture, 247\npartial-mesh architecture, 247\nmessage transmission using layers, 12\u201314\nmicrowave transmission, 68\nmiddleware, 31\nmission-critical application, 298\nmisuse detection, 334\nmitigate, risk, 301\nmobile wireless, 274\nmodems, 60, 78\u20139\nmodems transmitting data, 78\u20139\ndata compression, 79\nLempel-Ziv encoding, 79\nmodulation, 75\u20138\namplitude modulation (AM), 75\nbasic modulation, 76\nbaud rate, 78\nbit rate, 78\nfrequency modulation (FM), 76\nphase modulation (PM), 76\nquadrature amplitude modulation (QAM), 77\nsending multiple bits simultaneously, 77\nsymbol rate, 78\ntwo-bit amplitude modulation, 77\nmodules, 221\u20132\nmonitor, 364. See also network monitoring\nMoSucker, 322\nmoving cables, 96\nMPEG-2 standard, 48\nMP3 files, 89\nmulticasting, 126, 136\u20137\nmulticast message, 136\nmultimode fiber-optic cables, 66\nmultiplexing, 62\u20135. See also individual entry\nfrequency division multiplexing (FDM), 63\nstatistical time division multiplexing (STDM), 63\ntime division multiplexing (TDM), 63\nwavelength division multiplexing (WDM), 63", "source": "Page 483", "chapter_title": "Chapter 11"}
{"id": "c33f31d2bf96-0", "text": "multipoint circuit, 61\u20132\nmultiprotocol label switching (MPLS), 252\nMultipurpose Internet Mail Extension (MIME), 45\nattachments in, 45\nmultiswitch VLAN, 227\u20138\nmultitenancy, 34\nN\nname servers, 129\nNAT firewall, 317\nnational ISPs, 275\nnative apps, 18\nneeds analysis, network design, 166\u201371\napplication systems, 169\nbaseline, 168\ncategorizing network needs, 170\ndeliverables, 171\ngeographic scope, 168\nlogical network design, 168\nnetwork architecture component, 168\u20139\nnetwork needs, categorizing, 170\ndesirable requirements, 170\nmandatory requirements, 170\nwish-list requirements, 170\nnetwork users, 169\nnegative acknowledgment (NAK), 102, 120\u20131\nnetwork address translation (NAT) firewalls, 316\nnetwork and client computers, 361\u20132\nnetwork and transport layers, 114\u201361. See also addressing; routing\nmessage transmission using layers, 115\nprotocols, 116\u201318\nInternet Protocol (IP), 117\u201318\nTransmission Control Protocol (TCP), 116\u201317\nnetwork architecture components, 163\u20134, 168\u20139\naccess layer, 163\nbuilding backbone network, 163\ncampus backbone, 163\ndistribution layer, 163\nenterprise campuses, 163", "source": "Page 484", "chapter_title": "Chapter 11"}
{"id": "ff7a5f2fb423-0", "text": "network-attached storage (NAS), 205\nnetwork authentication. See central authentication\nnetwork-based IPS, 333\nnetwork cabling, 188\nnetwork controls, 295\u20136\nnetwork cost of ownership (NCO), 374\nnetwork demand, 210\nbackbone networks (BNs), 234\nWAN, 262\nnetwork design, 162\u201381\nbuilding-block network design process, 166\u20137\ncost assessment\ndeliverables, 176\nrequest for proposal (RFP), 175\nselling the proposal to management, 175\u20136\ncyber security, 176\u20137\nneeds analysis\napplication systems, 169\ncategorizing network needs, 170\ndeliverables, 171\nnetwork architecture components, 168\u20139\nnetwork users, 169\nnetwork architecture components, 163\u20134\nnetwork design software, 180\u20131\nSmartDraw software, 180\ntechnology design\ncircuits, 171\u20133\nclients and servers, 171\ndeliverables, 176\nnetwork design tools, 174\ntools, 174\ntraditional network design process, 164\u20135\nnetwork design software, 180\u20131\nnetwork design tools, 174\nnetwork documentation, 362\nnetwork errors, 94\ncorrupted data, 94\nlost data, 94\nnetwork hubs, 185\u20138", "source": "Page 485", "chapter_title": "Chapter 11"}
{"id": "ebeba5a64680-0", "text": "network interface card (NIC), 107, 183\nnetwork interface port, 137\nnetwork layer, 10, 11\nnetwork layer address, 124\nnetwork layer and transport layer, 114\u201361\naddressing\naddress resolution, 129\u201331\nassigning addresses, 124\u20139\ncyber security, 145\nfunctions\nlinking to the application layer, 118\u201319\nsegmenting, 119\u201320\nsession management, 120\u20133\nknown addresses, 140\u20131\nprotocols\nInternet Protocol (IP), 117\u201318\nTransmission Control Protocol (TCP), 116\u201317\nrouting\nanatomy, 137\u20138\nmulticasting, 136\u20137\nprotocols, 134\u20136\ntypes, 132\u20133\nTCP connections, 142\u20133\nTCP/IP and network layers, 143\u20134\nunknown addresses, 141\u20132\nnetwork management, 352\u201385, 377\u20138, 381. See also configuration management; cost management; end\nuser support; fault management; managed networks; performance management\nAT&T, 385\nconfiguration management\ndocumentation, 362\u20134\nnetwork and client computers, 361\u20132\ncost management\nreducing costs, 375\u20137\nsources of costs, 373\u20135\ncyber security, 377\u20138\ndesign\nmanaged networks, 353\u20137\nmanaging network traffic, 357\u20138\nreducing network traffic, 358\u201361", "source": "Page 486", "chapter_title": "Chapter 11"}
{"id": "7d813e16c729-0", "text": "end user support\nresolving problems, 371\u20132\ntraining, 372\u20133\nnetwork managers\njob requirements, 372\nrole, 353\nnetwork traffic, managing, 357\u20138\nload balancing, 354\npolicy-based management, 357\u20138\nperformance and fault management\nfailure control function, 366\u20138\nimproving performance, 370\u20131\nnetwork monitoring, 364\nperformance and failure statistics, 368\u20139\nsoftware, 363\nSolarWinds, 382\u20134\nstandards, 355\nnetwork management framework, 354\nnetwork management software, 354\u20135, 364\nNetwork Management Standards, 355\nnetwork mapping software, 238\nnetwork models, 8\u201314\napplication layer, 10, 11, 13\ndata link layer, 13\nlayers, 8\npros and cons of using, 14\nnetwork layer, 13\nphysical layer, 13\ntransport layer, 13\nnetwork monitoring, 364\nNetwork of Things (NoT), 18\nnetwork operating systems (NOS), 188\u20139\nNOS Client Software, 188\nNOS Server Software, 188\nnetwork operations manager, 226\nnetwork profile, 189\nnetworks, data communications, 5\u20138\ncomponents of, 6\u20137\ncables, 6", "source": "Page 487", "chapter_title": "Chapter 11"}
{"id": "e8741f64181b-0", "text": "circuit, 6\nclient, 6\nfile server, 6\nmail server, 6\npeer-to-peer networks, 6\nrouter, 6\nserver, 6\nswitch, 6\nWeb server, 6\ntypes of, 7\u20138\nbackbone networks (BNs), 7, 8\nlocal area networks (LANs), 7, 8\nwide area networks (WANs), 7, 8\nnetwork security, 292\u2013351. See also controls, network; intrusion prevention; risk assessment; sec urity\nthreats\nbasic control principles of, 299\nbusiness continuity\nDenial-of-Service protection, 305\u20138\ndevice failure protection, 309\u201310\ndisaster protection, 310\u201313\ntheft protection, 308\u20139\nvirus protection, 304\u20135\ncyber security, 338\ndesktop management, 337\nintrusion prevention\nencryption, 323\u20138\nintrusion recovery, 335\u20136\nIPSs, 333\u20135\nperimeter security and firewalls, 314\u201319\nsecurity policy, 314\nserver and client protection, 320\u20133\nsocial engineering, 332\u20133\nuser authentication, 329\u201332\nneed for, 294\nnetwork controls, 295\u20136\nphysical security, 308\u20139\nprinciples, 299\nreasons for, 293\nhacking, 293", "source": "Page 488", "chapter_title": "Chapter 11"}
{"id": "fa576824d1c5-0", "text": "hacktivism, 293\nmobile devices exploitation, 293\nrisk assessment, 296\ndevelop risk measurement criteria, 297\u20138\ndocument existing controls, 301\u20134\nidentify improvements, 304\nidentify threats, 299\u2013301\ninventory IT assets, 298\u20139\nsecurity controls, 336\u20137\nsecurity threats, types of, 294\u20135\nnetwork security manager, 337\nnetwork segmentation, 210\nnetwork server(s), 188\nnetwork standards. See standards, network\nnetwork support technicians, 104\nnetwork traffic\nreducing, 358\u201361\ncapacity management, 358\ncontent caching, 358\u201360\ncontent delivery, 360\nnetwork users, 169\nNext Generation Internet (NGI) program, 284\nNOS client software, 188\nNOS server software, 188\nNSLOOKUP, 151\nn-tier architecture, 31\u20132\nO\nodd parity, 98\nomnidirectional antennas, 187\none-time passwords, 331\nonline backup services, 312\nOpen Database Connectivity (ODBC), 31\nOpen Shortest Path First (OSPF), 135, 136\nOpen Systems Interconnection Reference (OSI) model, 8\u201310\napplication layer, 10\ndata link layer, 9\u201310\nnetwork layer, 10\nphysical layer, 9", "source": "Page 489", "chapter_title": "Chapter 11"}
{"id": "513821309bf3-0", "text": "presentation layer, 10\nsession layer, 10\ntransport layer, 10\noperating systems, 321\u20132\nOperationally Critical Threat, Asset, and Vulnerability Evaluation (OCTAVE), 296\noptical network terminal (ONT). See optical network unit (ONU)\noptical network unit (ONU), 282\nOptix Pro, 323\nOrchestration plane, 259\noverhead bits, 105\noverlay networks, 199\noversampling, 79\nP\npacket assembly/disassembly device (PAD), 250\npacket-level firewall, 315\npacket services, 251\npacket-switched networks, 250\nbasic architecture, 250\u20131\npacket-switched services, 250\nEthernet services, 252\u20133\nframe relay services, 251\u20132\nIP services, 246\nMPLS services, 252\npacket-switched services, 250\nparallel transmission, 72\u20133\nparity bit, 97\nparity checking, 97\u20138\npassive scanning, 195\npassphrases, 330\npassword, 330\ncracking, 329\none-time passwords, 331\nselecting, 330\nstrong, 330\npassword managers, 330\npatch, 320\npatch cables, 221\nCat 5e, 90", "source": "Page 490", "chapter_title": "Chapter 11"}
{"id": "c2cb005e8993-0", "text": "peering, 276\npeer-to-peer (P2P) architectures, 35\u20136\npeer-to-peer networks, 6\nperformance management\nbackbone networks (BNs)\ncircuit capacity, 234\ndevice, 233\u20134\nnetwork demand, 234\nand failure statistics, 368\u201370\nand fault management, 364\nfailure control function, 366\u20138\nimproving performance, 370\u20131\nnetwork monitoring, 364\u20136\nperformance and failure statistics, 368\u201370\nLAN\ncircuit capacity, 210\nnetwork demand, 210\nserver performance, 208\u201310\nWAN\ncircuit capacity, 261\ndevice performance, 261\nnetwork demand, 262\nperimeter security and firewalls, 314\u201319\npermanent virtual circuits (PVCs), 251\nPGP encryption, 349\nPGP key generator, 348\nphase, 75, 76\nphase modulation (PM), 75\u20137, 76, 77\nphase shift keying (PSK), 76\nphishing, 332\nphysical carrier sense method. See distributed coordination function (DCF)\nphysical circuit, 60\nphysical layer, 9, 11, 13, 59\u201390\nanalog transmission of digital data\ncapacity of a circuit, 78\nmodems, 78\u20139\nmodulation, 75\u20138\ncircuits\ncircuit configuration, 61\u20132", "source": "Page 491", "chapter_title": "Chapter 11"}
{"id": "46ec8e4310e5-0", "text": "data flow, 62\nmultiplexing, 62\u20135\ncommunication media\ncoaxial cable, 65\u20136\nfiber-optic cable, 66\u20137\nmicrowave, 68\nradio, 67\nsatellite, 68\u201370\ntwisted pair cable, 65\u20136\ncyber security, 83\ndigital transmission of analog data\nanalog to digital, 79\u201380\nInstant Messenger, 81\u20132\ntelephones, 80\u20131\nVoIP, 82\ndigital transmission of digital data\ncoding, 71\u20132\ndigital transmission, 73\u20134\nEthernet, 74\u20135\ntransmission modes, 72\u20133\nphysical network design, 171\nphysical security, 308\u20139, 317\u201319\nphysical topology, 190\nPING command, 151\nplain old telephone service (POTS), 75\nplaintext, 323\nPlatform as a Service (PaaS), 35\npoint coordination function (PCF), 195\u20136\npoint management software, 354\npoint of presence (POP), 251, 277\u20138\npoint-to-point circuit, 61\npoint-to-point protocol (PPP), 103\u20134, 124\nInternet addresses, 125\npolarity, 72\npolicy-based management, 357\npolling, 93\nhub polling, 93\nroll-call polling, 93\nport, 185", "source": "Page 492", "chapter_title": "Chapter 11"}
{"id": "e04d8417a7a8-0", "text": "port address, 118\u201319\ndestination port address, 118\nsource port address, 118\nPost Office Protocol (POP), 41, 57\u20138\npowerline networking, 207\npower over Ethernet (POE), 187\npresentation logic, 29\nPretty Good Privacy (PGP) software, 328\npreventive controls, 295\nprivate cloud, 28\nprivate IPv4 address space, 126\nprivate key, 325\nprivate line services, 244\nprobe frame, 195\nproblem prioritizing, 367\nproblem statistics, 367\nmanagement reports, 367\u20138\nproblem prioritizing, 367\nproblem tracking, 367\nproductivity, business impacts, 297\npropagation delay, 68\nprotocol, 14, 38\nInternet Protocol (IP), 117\u201318\nrouting, 134\u20136\nTransmission Control Protocol (TCP), 116\u201317\nprotocol data, 28\nProtocol Data Units (PDUs), 12, 21, 55, 91\u20132, 115\nseeing PDUs in messages, 25\u20136\nprotocol stack, 14\npublic cloud, 28\npublic key, 325\npublic key encryption, 325\nsecure transmission with, 326\npublic key infrastructure (PKI), 325, 327\u20138\npublic utilities commission (PUC), 244\npulse amplitude modulation (PAM), 80\npulse code modulation (PCM), 81\npure strategy, 28\nPuTTY, software packages, 46", "source": "Page 493", "chapter_title": "Chapter 11"}
{"id": "3c3091cdf7e8-0", "text": "Q\nquadrature amplitude modulation (QAM), 77\nQuality of Service (QoS), 123\nquantizing error, 79\nR\nrack, 221\nrack-mounted switched backbone network architecture, 222\nradio, 67\nRadio Frequency Identification (RFID), 46\nradio transmission, 67\nraindrop attenuation, 70\nransomware, 304, 324\nRC4, 325\nRealNetworks.com, 79\nreal TCO, 374\nReal-Time Streaming Protocol (RTSP), 123\nReal-Time Transport Protocol (RTP), 123\nreclocking time, 62\nrecovery controls, 311\nreducing costs, 375\u20137\nreducing network traffic, 358\u201361\nredundancy, 309\nredundant array of independent disks (RAID), 204, 209, 302, 310\nregional ISPs, 275\u20136\nrelative performance, 93\u20134\nremote monitoring (RMON), 355\u20136\nrepeaters, 96\nreplication, 130\nreputation, business impacts, 297\nrequest body, HTTP request, 38\nrequest for comments (RFCs), 16, 283\nrequest for proposal (RFP), 175\nrequest header, HTTP request, 38\nrequest line, HTTP request, 38\nrequest to send (RTS), 195\u20136\nreserved addresses, 125\nresolving name server, 130\nResource Reservation Protocol (RSVP), 123", "source": "Page 494", "chapter_title": "Chapter 11"}
{"id": "c792b366ffbe-0", "text": "response body, 40\nresponse header, 40\nresponse status, 39\nresponse status, HTTP response, 39\nretrain/reclocking time, 62\nring architecture, 246, 247\nrisk assessment (network security), 296. See also intrusion prevention\ndevelop risk measurement criteria, 297\u20138\ndocument existing controls, 301\u20134\nframeworks, 296\nidentify improvements, 304\nidentify threats, 299\u2013301\ninventory IT assets, 298\u20139\nrisk measurement criteria, 297\u20138\nfinancial, 297\nlegal, 297\nproductivity, 297\nreputation, 297\nrisk mitigation, 301\nrisk score, 301\nthreats identification, 299\u2013301\nrisk assessment frameworks, 296\nrisk control strategy, 301\nrisk measurement criteria, 297\u20138\nrisk mitigation, 301\nrisk score, 301\nRMON probes, 356\nroll-call polling, 93\nroot cause analysis, 354\nrootkits, 322\nroot servers, 130\nrouted backbones, 224\u20136\narchitecture, 225\nrouters, 6, 131, 221\nrouting, 131\u20138\naccess control list (ACL), 138\nanatomy, 137\u20138\nborder router, 134\ncentralized routing, 133", "source": "Page 495", "chapter_title": "Chapter 11"}
{"id": "3895a8d6b579-0", "text": "designated router, 134\ndynamic routing, 133\non the Internet, 134\nInternet Group Management Protocol (IGMP), 137\nmulticasting, 136\u20137\nnetwork manager connect to, 137\nauxiliary port, 137\nconsole port, 137\nnetwork interface port, 137\nprotocols, 134\u20136\nrouting protocols, 134\u20136\nBorder Gateway Protocol (BGP), 135\nEnhanced Interior Gateway Routing Protocol (EIGRP), 136\nexterior routing protocols, 134\nInterior Gateway Routing Protocol (IGRP), 136\ninterior routing protocols, 134\nIntermediate System to Intermediate System (IS-IS), 135\nInternet Control Message Protocol (ICMP), 135\nOpen Shortest Path First (OSPF), 135\nRouting Information Protocol (RIP), 135\nstatic routing, 133\ntypes, 132\u20133\nRouting Information Protocol (RIP), 136\nRSA. See public key encryption\nS\nsafety, business impacts, 297\nSalesforce.com, cloud computing with, 36\nSarbanes-Oxley Act (SOX), 293\nsatellite transmission, 68\u201370\ngeosynchronous, 68\nscalability, 36\nscanning, 195\nSeattle Internet Exchange (SIX), 277\nsecure sockets layer (SSL), 328\nsecure switch, 319\nsecurity\nmedia, 70\nnetwork (See network security)", "source": "Page 496", "chapter_title": "Chapter 11"}
{"id": "4769423d6f0a-0", "text": "wireless Ethernet, 197\u20138\nsecurity controls, 336\u20137\nsecurity holes, 299, 320, 321\nsecurity policy, 314\nsecurity threats\nbusiness continuity, 294\nconfidentiality, integrity, and availability (CIA), 294\ndisruptions, 294\ntypes of, 294\u20135\nunauthorized access, 295\nsegment, 115\nsegmenting, 119\u201320\nSelective-Repeat ARQ, 121\nselling the proposal to management, 175\u20136\nsending multiple bits simultaneously, 77\nserial transmission, 73\nserver, 6\nserver and client protection, 320\u20133\nserver farms, 31\u20132, 33\u20134, 357\nserver farms or clusters, 357\nserver name resolution, 129\u201331\nserver performance, 208\u201310\nserver protection, 320\u20133\nserver virtualization, 204\nservice-level agreement (SLA), 370\nservices logic, 29\nsession, 120\nsession management, 120\u20133\nacknowledgment (ACK), 120\nconnectionless messaging, 120\nconnection-oriented messaging, 120\ncontinuous ARQ, 121\u20132\nflow control, 121\nforward error correction, working, 99\nHamming code, 99\nnegative acknowledgment (NAK), 120\u20131\nQuality of Service (QoS), 123\nsliding window, 121\nstop-and-wait ARQ, 120\u20131", "source": "Page 497", "chapter_title": "Chapter 11"}
{"id": "bf444a8e0af4-0", "text": "shared circuit. See multipoint circuit\nShared Registration System (SRS), 284\nshare, risk, 301\nshielded twisted-pair (STP) cable, 184\nshielding, 96\nSimple Mail Transfer Protocol (SMTP), 41, 43, 55\u20138, 115\ninside SMTP packet, 44\nSMTP transmission, 43\nSimple Network Management Protocol (SNMP), 355, 356\nsimplex transmission, 62\nsimulation, 174\nsingle-key encryption, 324\nalgorithm, 324\nbrute-force attacks, 324\nkey, 324\nkey management, 324\nsingle-mode fiber-optic cables, 67\nsingle sign-on. See central authentication\nsingle-switch VLAN, 227\nsite survey, 201\nsliding window, 102, 121\nsmall-office, home-office (SOHO), 185\nSOHO environment designing, 206\u20137\nSmartDraw software, 180\nSMTP header, 53\nSMTP packet, 44\nsniffer program, 319\nsocial engineering, 299, 332\u20133\nphishing, 332\u20133\npreventing, 332\u20133\nsoftware, 208\nsoftware as a service (SaaS), 28, 34\u20135, 39\nSoftware Defined WAN (SDWAN), 258\u20139\nUnited Federal Credit Union (UFCU), 260\nsoftware, server performance, 208\nSOHO environment, 206\u20137\nSolarwinds Network, 382\u20134\nSolarWinds network management software, 382\u20134\nsomething you are, 330", "source": "Page 498", "chapter_title": "Chapter 11"}
{"id": "a86e32c97b5c-0", "text": "something you have, 330\nsomething you know, 330\nsource port address, 118\nsources of costs, 373\u20135\nsources of errors, 94\u20136\nspikes, 95\nspyware, 323\nSQL injection, 48\u20139\nStandards, 14\nstandards-making process, 15\u201317\nAmerican National Standards Institute (ANSI), 15\ncommon standards, 17\nde facto standards, 15\nde jure standard, 15\nacceptance stage, 15\nidentification of choices stage, 15\nspecification stage, 15\nInstitute of Electrical and Electronics Engineers (IEEE), 17\nInternational Organization for Standardization (ISO), 15\nInternational Telecommunications Union-Telecommunications Group (ITU-T), 15\nInternet Engineering Task Force (IETF), 16, 17\nnetwork protocols becoming standards, 16\nstandards, network, 14\u201317\ncommon standards, 17\nimportance of, 14\u201315\nstandards-making process, 15\u201317\nstar architecture, 246\u20137, 248\nstart bit, 101\nstart-stop transmission. See asynchronous transmission\nstatic routing, 133\nstatistical time division multiplexing (STDM), 63\nstop-and-wait ARQ, 120\u20131\nstop bit, 101\nstorage area network (SAN), 32, 34, 205\nstore-and-forward switching, 192\nstructured cabling EIA/TIA 568-B, 64\nsubnet mask, 128\nsubnets, 127\u20138\nsubnetted backbones. See routed backbones", "source": "Page 499", "chapter_title": "Chapter 11"}
{"id": "e26bc55b7c75-0", "text": "subnetting, 157\u20139\nsubnetting Class C Addresses, 159\u201361\nsupervisory frame, 102\nswitch, 6, 81\nswitch-based Ethernet, 191\ncut-through switching, 192\nfragment-free switching, 192\nstore and forward switching, 192\nswitched backbones, 221\u20134\nchassis switch, 221\u20132\nlayer-2 switches, 220, 223\nmodules, 222\nrack-mounted, 222\nswitched Ethernet network, 199\nswitched virtual circuits (SVCs), 251\nswitches, 180\u20132, 185\u20138, 221\nswitching, 185\nVLAN switches, 221\nsymbol rate, 60\u20131, 78\nsymmetric encryption, 323, 324\nsymmetric multiprocessing (SMP), 209\u201310\nsynchronization, 101\nsynchronous data link control (SDLC), 102\nsynchronous digital hierarchy (SDH), 249\u201350\nsynchronous optical network (SONET) services, 249\u201350\nsynchronous transmission, 101\u20134\nsystem management software, 354\nT\nT-carrier circuits, 248\nT-carrier services, 248\u20139\nfractional T1 (FT1), 249\nT1 circuit, 249\nT3 circuit, 249\nT1 circuit, 249\nT2 circuit, 249\nT3 circuit, 249\nT4 circuit, 249\nTCP connections, 138\u20139, 142\u20133", "source": "Page 500", "chapter_title": "Chapter 11"}
{"id": "001e5fd845c3-0", "text": "TCP/IP and network layers, 143\u20134\nTCP SYN Floods, 308\ntechnical reports, 368\ntechnology design, 166\ntechnology design, network design\ncircuits, 171\u20133\nclients and servers, 171\ndeliverables, 176\nnetwork design tools, 174\ntelecommunications closet, 64\nTelecommunications Industry Association (TIA), 64\ntelephones transmitting voice data, 80\u20131\ntelephone system, 75, 80\u20131\nTelnet, 46\ntheft protection, 308\u20139\nthick client (fat-client) approach, 33\nthin client approach, 33\nthreat scenarios, 300\nthreats identification, 299\u2013301\nthree-tier architecture, 31, 32, 42\u20134\nthree-tier thin client-server architecture, 42\u20134\nthree-way handshake, 120\nthroughput, 105\nTIA/EIA 568-A, 64\nTicket-Granting Ticket (TGT), 333\ntier 1 ISPs, 275\ntier 2 ISPs, 275\ntier 3 ISPs, 276\ntime-based tokens, 334\ntime division multiplexing (TDM), 63, 96\ntoken, 334\ntoken passing, 93\ntop-level domain (TLD) server, 130\ntopology, 190\nwired Ethernet, 189\u201392\nwireless Ethernet, 194\ntotal cost of ownership (TCO), 373\u20135, 376\nreal TCO, 374\nTracePlus Ethernet, 215\u201316", "source": "Page 501", "chapter_title": "Chapter 11"}
{"id": "5ca791807c40-0", "text": "Tracert\nVPN, 269\u201372\nTRACERT command, 153, 155\ntraditional network design process, 164\u20135\ntraffic analysis, 307\ntraffic anomaly analyzer, 307\ntraffic anomaly detector, 307\ntraffic filtering, 306\ntraffic limiting, 306\ntraffic shaper, 357\ntraffic shaping. See policy-based management\ntraining, end user, 372\u20133\nTransmission Control Protocol (TCP), 13, 112\u201313, 116\u201317\nTransmission Control Protocol/Internet Protocol (TCP/IP), 116, 138\u201344, 150\u20135\nARP command, 151\nDNS cache, 151\u20134\nDNS Request, 155\u20136\nDNS Response, 155\u20136\nexample\nknown addresses, 140\u20131\nTCP connections, 142\u20133\nTCP/IP and network layers, 143\u20134\nunknown addresses, 141\u20132\nIPCONFIG command, 150\nand network layers, 143\u20134\nNSLOOKUP command, 151\nPING command, 151\nTRACERT command, 153, 155\ntransmission distance, media, 70\ntransmission efficiency, 104\u20136\ninformation bits, 105\noverhead bits, 105\nthroughput, 106\ntransmission modes, 72\u20133\nparallel transmission, 72\u20133\nserial transmission, 73\ntransmission speeds, media, 71\ntransport layer, 10, 11, 13\ntransport layer functions, 118\u201323", "source": "Page 502", "chapter_title": "Chapter 11"}
{"id": "c0e4c2d01a24-0", "text": "linking to application layer, 118\u201319\nsegmenting, 119\u201320\nsession management, 120\u20133\nTriple DES (3DES), 325\nTrojan horse, 322\ntrouble tickets, 367\nTunnels, 254\nturnaround time, 62\nturnpike effect, 172\ntwisted pair cable, 65\u20136, 186\ntwo-factor authentication, 331\ntwo-tier architecture, 31, 41\nemail architecture, 41\ntype of network, media, 70\nU\nUDP attacks, 308\nunauthorized access, preventing, 295\nundersea fiber-optic cables, 64\nunicast message, 136\nUnicode, 71\nuniform resource locator (URL), 37\u20138\nuninterruptible power supply (UPS), 310\nunipolar signal, 73\nUnited Federal Credit Union (UFCU), 260\nUnited States of America Standard Code for Information Interchange (USASCII), 71\nUNIX process table attacks, 308\nunknown addresses, 141\u20132\nunshielded twisted-pair (UTP) cable, 184\nuptime, 369\nUSB drive, 83\nU.S. Department of Defense (DoD), 313\nuser access with wired Ethernet, 200\nuser access with wireless Ethernet, 200\u20133\nuser authentication, 329\u201332\nauthentication server, 332\nbiometrics, 332\ncentral authentication, 332\ncertificate, 332", "source": "Page 503", "chapter_title": "Chapter 11"}
{"id": "16fef0bb4b50-0", "text": "Kerberos, 332\none-time passwords, 331\npasswords, 330\nUser Datagram Protocol (UDP), 117, 122\u20133\nuser profile, 329\nV\nV.44 compression, 79\nvideoconferencing, 47\u20138\ndesktop videoconferencing, 47\u20138\nH.320, 48\nH.323, 48\nMPEG-2, 48\nWebcasting, 48\nvirtual carrier sense method. See point coordination function (PCF)\nvirtual carrier sense method. See point coordination function (PCF)\nvirtual LANs (VLANs), 103, 227\nbenefits of, 227\u20139\nLAN switches, 221, 232\nmultiswitch VLAN, 227, 229\nsingle-switch VLAN, 227\nVLAN-based backbone network architecture, 229\nVLAN tag, 231\nworking, 229\u201332\nvirtual private network (VPN), 254\naccess VPN, 255\nbasic architecture, 254\u20135\nextranet VPN, 255\nInternet Service Provider (ISP), 254\nintranet VPN, 255\nlayer-2 VPN, 255\nTracert, 269\u201372\ntunnels, 254\ntypes, 255\nVPN gateway, 254\nVPN software, 254\nwith Wireshark, 266\u20139\nworking, 256\u20138\nvirtual server, 357", "source": "Page 504", "chapter_title": "Chapter 11"}
{"id": "5fceb158e40e-0", "text": "viruses, 324\nvirus protection, 304\u20135\nantivirus software, 305\nmacro viruses, 304\nworm, 305\nVLAN ID, 229, 232\nVLAN switches, 221, 232\nVLAN tag, 231\nVLAN trunks, 231\nVoice over Internet Protocol (VoIP), 18, 82\nVPN gateway, 254\nVPN software, 254\u20135\nW\nwardriving, 198, 217\u201318\nwarwalking, 218\nwavelength division multiplexing (WDM), 63\nWeb-based email, 42\nWeb browser, 37\nWebcasting, 48\nWeb server, 6, 37\nwhite noise, 95\nwide area network (WAN), 7, 8, 164, 243\u201373\nbest practice WAN design, 258\u201360\ncyber security, 262\ndedicated-circuit networks\nbasic architecture, 244\u20138\nSONET services, 249\nT-carrier services, 248\u20139\ndesign, best practice recommendations, 258\u201360\nchoosing WAN Circuits, 259\u201360\nSDWAN, 258\u20139\nexamining, 265\u20136\npacket-switched networks\nbasic architecture, 250\u20131\nEthernet services, 252\u20133\nframe relay services, 251\u20132\nIP services, 246\nMPLS services, 252", "source": "Page 505", "chapter_title": "Chapter 11"}
{"id": "fdc2ef5d7c6e-0", "text": "performance improvement, 261\ncircuit capacity, 261\u20132\ndevice performance, 261\nreducing network demand, 262\nrecommendations, 260\nservices, 259\nvirtual private network (VPN)\nbasic architecture, 254\u20135\ntypes, 255\nworking, 255\u20138\nWi-Fi. See wireless Ethernet\nWi-FI 6, 197\nWi-Fi controller, 202\nWi-Fi light bulb, 199\nWi-Fi Protected Access (WPA), 198\nWiMax (Worldwide Interoperability for Microwave Access), 274\nWired Equivalent Privacy (WEP), 198\nwired Ethernet. See also wired Ethernet; wireless Ethernet\ndesigning user access with, 200\nerror control in, 208\nhub-based Ethernet, 190\nmedia access control, 192\u20133\nswitch-based Ethernet, 191\ntopology, 190\u20132\nlogical topology, 190\nphysical topology, 190\nwired LANs, 182\u2013219\nwireless access point (AP), 6\nwireless Ethernet, 194\nassociating with AP, 195\ndistributed coordination function (DCF), 195\nframe layout, 196\nmedia access control, 194\u20135\npoint coordination function (PCF), 195\u20136\nsecurity, 198\u20139\nMAC address filtering, 199\ntopology, 194\ntypes, 196\u20138\n802.11ac, 197", "source": "Page 506", "chapter_title": "Chapter 11"}
{"id": "0c3026f278a8-0", "text": "802.11ax, 197\u20138\n802.11i, 198\n802.11n, 197\nwireless Internet service provider (WISP), 68\nwireless LANs (WLANs), 18, 182\u2013219, 184\nwireless media, 65\nwireless networks, 381\nWireshark, 111\u201313\nwish-list requirements, 170\nwork area, 64\nWorldwide Interoperability for Microwave Access (WiMax), 274\nWorld Wide Web\nHTTP request, 38\u20139\nHTTP response, 39\u201340\nweb working, 37\u20138\nworm, 305\nWPA2. See 802.11i\nZ\nzero-day attacks, 321\nZF Lenksysteme, network management, 357", "source": "Page 507", "chapter_title": "Chapter 11"}
{"id": "04dac38f8fb3-0", "text": "WILEY END USER LICENSE AGREEMENT\nGo to www.wiley.com/go/eula to access Wiley\u2019s ebook EULA.", "source": "Page 508", "chapter_title": "Chapter 11"}