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+
+
+![ITU logo](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features a globe with a lightning bolt superimposed on it, and the letters 'ITU' in a bold, sans-serif font.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**G.102**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**TRANSMISSION SYSTEMS AND MEDIA**
+
+**GENERAL CHARACTERISTICS OF INTERNATIONAL  
+TELEPHONE CONNECTIONS AND INTERNATIONAL  
+TELEPHONE CIRCUITS**
+
+---
+
+**TRANSMISSION PERFORMANCE OBJECTIVES  
+AND RECOMMENDATIONS**
+
+**ITU-T Recommendation G.102**
+
+(Extract from the *Blue Book*)
+
+---
+
+# NOTES
+
+1 ITU-T Recommendation G.102 was published in Fascicle III.1 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## **TRANSMISSION PERFORMANCE OBJECTIVES AND RECOMMENDATIONS**
+
+*(Geneva, 1980)*
+
+## **1 General**
+
+The CCITT has drawn up (or is in the process of studying) Recommendations concerning transmission impairments and their permissible magnitude with the object of achieving satisfactory performance of the network. Such impairments include for example:
+
+- a) loudness rating (LR) and loss,
+- b) noise,
+- c) attenuation distortion,
+- d) crosstalk,
+- e) single tone interference,
+- f) spurious modulation,
+- g) effects of errors in digital systems.
+
+Some Recommendations state objectives for an impairment with the implicit assumption that other impairments are at their maximum value (e.g. noise and loss).
+
+In many instances the objectives are based primarily on telephony; this however may require special measures to be applied when other, more demanding services (e.g. sound-programme transmission) are to be incorporated within the network or constituent parts thereof.
+
+The following distinctions may be made between different types of objectives:
+
+- 1) performance objectives for networks,
+- 2) performance objectives for circuits, transmission and switching equipment,
+- 3) design objectives for transmission and switching equipment,
+- 4) commissioning objectives for circuits, transmission and switching equipment,
+- 5) maintenance/service limits for circuits, transmission and switching equipment.
+
+## **2 Explanation of a performance objective**
+
+The performance objective for a measurable transmission impairment for networks, entire connections, national systems forming part of international connections, international chains of circuits, individual circuits etc. often describes in statistical terms (mean value, standard deviation, or probability of exceeding stated value, etc.) the value to be aimed at in transmission network and systems planning. It describes the performance which, based for example on subjective or other performance assessment tests, it is desirable to aim at in order to offer the user a satisfactory service.
+
+The items (circuits, systems, equipments) making up the network are normally assumed to have a performance related to that recommended by the performance objectives. Traffic weighting will, in some cases, be applied to calculations.
+
+A powerful set of tools which may be used in analyses concerning network objectives and compliance therewith are the hypothetical reference connections described in Recommendation G.103.
+
+## **3 Explanation of a design objective**
+
+The "design objective" for a measurable transmission impairment (e.g. noise, error-rate, attenuation-distortion) for an item of equipment (e.g. a line system, a telephone exchange) is its value when the item is operating in certain electrical/physical environments which might be defined by such parameters as power supply voltage, signal load, temperature, humidity, etc. Some of these parameters may be the subject of CCITT Recommendations and some may not, and it is for the Administrations to assign values to them when they prepare specifications. A suitable allowance may also be made for aging. The most adverse combination of the specified parameters is often assumed.
+
+The purpose of a "design objective" is to provide a basis for the design of an item with respect to the quantity concerned. The significance of the design objective for an item, and examples of the relative frequency of impairment values, are illustrated in Figures 1/G.102 and 2/G.102 respectively.
+
+Design objectives will in many cases directly form the basis of a specification clause for the development and/or the purchase of equipments.
+
+A powerful set of tools used in connection with applying design objectives are the hypothetical reference (HR) circuits and hypothetical reference (HR) digital paths (see relevant Recommendations in the G.100 and G.700 Series).
+
+## **4 Explanation of a commissioning objective**
+
+The conditions encountered on real circuits and installed equipment may differ from the assumptions valid for the HR circuits and for the design of equipment. Therefore the performance to be expected at the time of commissioning cannot be deduced uniquely from Recommendations relating to HR circuits. Suitable allowances may have to be made for such matters as circuits being made up of equipments of different design, line systems differing substantially in length from a homogeneous section, etc. (see for example Recommendation G.226 [1] for noise on real links).
+
+Commissioning objectives are not normally the subject of CCITT Recommendations.
+
+## **5 Explanations of limits for maintenance purposes**
+
+In service, the performance of an item or assembly of items may deteriorate for various reasons: aging, excessive loading, excessive environmental conditions, operations errors, components failures, etc. and there is an economic penalty in service costs if such deterioration is always to be kept negligibly small. Therefore design objectives are chosen to confer as great a margin as possible to assure a satisfactory in-service performance.
+
+![Figure 1/G.102: Illustration of the significance of design objective for an item. The diagram shows a horizontal axis representing increasing values of impairment (e.g., noise power, error rate, etc.). The axis is divided into three regions: 'Fully acceptable range', 'Tolerable range', and 'Unusable'. Key points on the axis are marked with vertical lines and labels: 'Value when the operating environment is at its optimum (e.g. power supplies producing nominal voltages, temperature at mid-range, etc.). This inherent, irreducible value is zero in some cases.'; 'The design objective, as explained in the text, for the item (e.g. system, exchange, equipment, etc.)'; 'Maximum acceptable value at commissioning for a particular set of operating conditions (may also be the same as the line-up limit)'; 'Maintenance limit at which attention is alerted (e.g. deferred maintenance limit)'; and 'Maintenance limit at which point the item is taken out of service (e.g. prompt maintenance limit)'. A 'Design allowance' is indicated between the optimum value and the design objective. A note states 'Acceptable value at time of commissioning lies within this range'. A bracket on the right indicates 'Increasing values of impairment (e.g. noise power, error rate, etc.)'. A legend at the bottom right distinguishes between 'A value ordinarily not the subject of CCI Recommendations' and 'A value which is ordinarily the subject of CCI Recommendations'. The code 'CCITT - 27 701' is also present.](f9a14fbfecbd7d059226cc93677d721b_img.jpg)
+
+Figure 1/G.102: Illustration of the significance of design objective for an item. The diagram shows a horizontal axis representing increasing values of impairment (e.g., noise power, error rate, etc.). The axis is divided into three regions: 'Fully acceptable range', 'Tolerable range', and 'Unusable'. Key points on the axis are marked with vertical lines and labels: 'Value when the operating environment is at its optimum (e.g. power supplies producing nominal voltages, temperature at mid-range, etc.). This inherent, irreducible value is zero in some cases.'; 'The design objective, as explained in the text, for the item (e.g. system, exchange, equipment, etc.)'; 'Maximum acceptable value at commissioning for a particular set of operating conditions (may also be the same as the line-up limit)'; 'Maintenance limit at which attention is alerted (e.g. deferred maintenance limit)'; and 'Maintenance limit at which point the item is taken out of service (e.g. prompt maintenance limit)'. A 'Design allowance' is indicated between the optimum value and the design objective. A note states 'Acceptable value at time of commissioning lies within this range'. A bracket on the right indicates 'Increasing values of impairment (e.g. noise power, error rate, etc.)'. A legend at the bottom right distinguishes between 'A value ordinarily not the subject of CCI Recommendations' and 'A value which is ordinarily the subject of CCI Recommendations'. The code 'CCITT - 27 701' is also present.
+
+FIGURE 1/G.102
+
+### **Illustration of the significance of design objective for an item**
+
+With transmission impairments, there is often no value which represents a clear boundary between "tolerable" and "unusable" performance and in practice a range of impairments in excess of those provided by design objectives will give satisfactory service to customers. This is the case for telephony but for other services may be different.
+
+Nevertheless it is often expedient to define a particular value of impairment above which the item is deemed to be "unusable" and at which the item will be withdrawn from service at the first opportunity so that remedial action can be taken to restore the performance to comply with some defined limit (e.g. limit for prompt maintenance action).
+
+It is often useful to define a performance limit at which attention is alerted but (perhaps) no action is taken immediately (e.g. limit for deferred maintenance action).
+
+These limits are usually independent of the type of service carried by that particular entity. However, it is sometimes necessary to define a performance limit for a particular type of service, beyond which the customer is no longer offered a satisfactory service quality. This limit may differ for various services; some may coincide with a prompt maintenance limit (service limit).
+
+These limits (and others, if necessary) would fall above the design objective. These limits are illustrated in Figure 1/G.102 and a generic title for them is "maintenance limits".
+
+![Figure 2/G.102: Examples of the relative frequency of impairment values. The graph plots 'Relative frequency of occurrence' on the y-axis against 'values of impairment' on the x-axis. Three curves are shown: Curve 1 (solid line, highest peak), Curve 2 (solid line, lower peak), and Curve 3 (dashed line, lowest peak). The x-axis is divided into three regions: 'Fully acceptable range', 'Tolerable range', and 'Unusable'. A vertical line marks the 'Design objective'. An arrow indicates 'Increasing values of impairment' to the right. The text 'CCITT - 27 710' is in the bottom right corner.](431b8889a0e7f676f0eef40859590349_img.jpg)
+
+Figure 2/G.102: Examples of the relative frequency of impairment values. The graph plots 'Relative frequency of occurrence' on the y-axis against 'values of impairment' on the x-axis. Three curves are shown: Curve 1 (solid line, highest peak), Curve 2 (solid line, lower peak), and Curve 3 (dashed line, lowest peak). The x-axis is divided into three regions: 'Fully acceptable range', 'Tolerable range', and 'Unusable'. A vertical line marks the 'Design objective'. An arrow indicates 'Increasing values of impairment' to the right. The text 'CCITT - 27 710' is in the bottom right corner.
+
+Such curves may be obtained for ensembles of items of equipment at the time of commissioning.
+
+Alternatively curves may be plotted representing the performance of an item during its lifetime.
+
+Curve 1 - Example of relative frequency of occurrence of impairments at time of commissioning in which the design value is met with some margin. A similar distribution might be achieved in service throughout the lifetime of an item of equipment if the effect of environmental conditions etc. is negligible. An example might be the attenuation distortion of transformers.
+
+Curve 2 - Example of the relative frequency of occurrence of impairments at time of commissioning in which the design value is exceeded with some agreed probability because the item of equipment is used in a way which is more demanding than that in the design objectives. An example might be the effect of a repeater spacing of a radio or line system greater than anticipated.
+
+Curve 3 - Example of the relative frequency of occurrence of impairments in service in which the working environment has parameters more onerous than or additional to those specified. Examples might be the effect of excessive loading, component failure or operational errors.
+
+FIGURE 2/G.102
+
+### **Examples of the relative frequency of impairment values**
+
+## **Reference**
+
+- [1] CCITT Recommendation *Noise on a real link*, Vol. III, Rec. G.226.

marked/G/T-REC-G.1082-200904-I_PDF-E/raw.md

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+
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**G.1082**
+
+(04/2009)
+
+SERIES G: TRANSMISSION SYSTEMS AND MEDIA,  
+DIGITAL SYSTEMS AND NETWORKS
+
+Multimedia Quality of Service and performance – Generic  
+and user-related aspects
+
+# --- **Measurement-based methods for improving the robustness of IPTV performance**
+
+Recommendation ITU-T G.1082
+
+## ITU-T G-SERIES RECOMMENDATIONS **TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS**
+
+|                                                                                                                                              |                      |
+|----------------------------------------------------------------------------------------------------------------------------------------------|----------------------|
+| INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS                                                                                             | G.100–G.199          |
+| GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS                                                                  | G.200–G.299          |
+| INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES                                                      | G.300–G.399          |
+| GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES | G.400–G.449          |
+| COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY                                                                                            | G.450–G.499          |
+| TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS                                                                                       | G.600–G.699          |
+| DIGITAL TERMINAL EQUIPMENTS                                                                                                                  | G.700–G.799          |
+| DIGITAL NETWORKS                                                                                                                             | G.800–G.899          |
+| DIGITAL SECTIONS AND DIGITAL LINE SYSTEM                                                                                                     | G.900–G.999          |
+| <b>MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE – GENERIC AND USER-RELATED ASPECTS</b>                                                      | <b>G.1000–G.1999</b> |
+| TRANSMISSION MEDIA CHARACTERISTICS                                                                                                           | G.6000–G.6999        |
+| DATA OVER TRANSPORT – GENERIC ASPECTS                                                                                                        | G.7000–G.7999        |
+| PACKET OVER TRANSPORT ASPECTS                                                                                                                | G.8000–G.8999        |
+| ACCESS NETWORKS                                                                                                                              | G.9000–G.9999        |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+## **Recommendation ITU-T G.1082**
+
+# **Measurement-based methods for improving the robustness of IPTV performance**
+
+## **Summary**
+
+Recommendation ITU-T G.1082 provides a framework for improving the robustness of IPTV performance based on the results of real-time measurements. The primary application of this framework is to control the media and network resources based on the measurement information and according to policy rules to support high quality of experience of IPTV services.
+
+For IPTV services, service providers and network providers may have separate monitoring systems. Measurement information is provided by the monitoring system. This Recommendation first describes the possible measurement information used in different monitoring domains and the information exchanged between providers. It then gives guidance on how to take these factors into account to adjust media and network resources in order to maintain the quality of experience for IPTV services.
+
+## **Source**
+
+Recommendation ITU-T G.1082 was approved on 29 April 2009 by ITU-T Study Group 12 (2009-2012) under Recommendation ITU-T A.8 procedure.
+
+## **Keywords**
+
+IPTV, measurement, QoE, QoS, resource adjustment.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2010
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## CONTENTS
+
+|       |                                                                                                                      | Page |
+|-------|----------------------------------------------------------------------------------------------------------------------|------|
+| 1     | Scope .....                                                                                                          | 1    |
+| 2     | References.....                                                                                                      | 1    |
+| 3     | Definitions .....                                                                                                    | 1    |
+| 4     | Abbreviations and acronyms .....                                                                                     | 1    |
+| 5     | Conventions .....                                                                                                    | 2    |
+| 6     | Overview of the framework of measurement-based methods for improving the robustness of IPTV performance (MMRP) ..... | 2    |
+| 7     | Process of end-to-end quality improvement .....                                                                      | 3    |
+| 7.1   | Monitoring system.....                                                                                               | 4    |
+| 7.2   | Measurement-based resource adjustment function .....                                                                 | 4    |
+| 7.3   | Resource control enforcement .....                                                                                   | 5    |
+| 8     | Measurement information reporting.....                                                                               | 5    |
+| 8.1   | Reported measurement information .....                                                                               | 5    |
+| 8.2   | Intra-domain interactions.....                                                                                       | 7    |
+| 9     | Information exchanged between providers.....                                                                         | 8    |
+| 9.1   | Information provided by SPs.....                                                                                     | 8    |
+| 9.2   | Information provided by NPs .....                                                                                    | 8    |
+| 9.3   | Information exchanged between SPs and NPs .....                                                                      | 8    |
+| 9.4   | Inter-domain interactions.....                                                                                       | 9    |
+| 10    | Measurement-based adaptive resource control for IPTV services .....                                                  | 10   |
+| 10.1  | Media resource control .....                                                                                         | 10   |
+| 10.2  | Network resource control .....                                                                                       | 10   |
+| 11    | Security consideration .....                                                                                         | 11   |
+|       | Appendix I – QoE evaluation in mid-point.....                                                                        | 12   |
+| I.1   | Introduction .....                                                                                                   | 12   |
+| I.2   | Collaboration between SP and NP to evaluate QoE in mid-point.....                                                    | 12   |
+|       | Appendix II – Encoded bit rate adjustment in the head-end system.....                                                | 14   |
+|       | Appendix III – Encoded layer adjustment .....                                                                        | 16   |
+| III.1 | Introduction .....                                                                                                   | 16   |
+| III.2 | Network device adjusts the encoded layer .....                                                                       | 16   |
+| III.3 | STB adjusts the encoded layer .....                                                                                  | 17   |
+|       | Appendix IV – Delivery path adjustment .....                                                                         | 19   |
+|       | Bibliography.....                                                                                                    | 21   |
+
+
+
+## Recommendation ITU-T G.1082
+
+# Measurement-based methods for improving the robustness of IPTV performance
+
+# 1 Scope
+
+This Recommendation describes some methods by which measurement information of IPTV service quality can be used to dynamically control the performance of an IPTV service such as network resource allocation, FEC redundant encoding, delivery path selection or media encoding bit rate if scalable encoding is employed.
+
+This Recommendation defines the subset of QoS/QoE performance parameters to be obtained from the IPTV monitoring system and methods for analysing them to provide media resource and transport network resource control in support of high quality end-to-end delivery of IPTV services.
+
+It also provides guidance on the collaboration between different providers and defines the metrics to be exchanged between them for resource management.
+
+# 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T G.1080] Recommendation ITU-T G.1080 (2008), *Quality of experience requirements for IPTV services*.
+- [ITU-T G.1081] Recommendation ITU-T G.1081 (2008), *Performance monitoring points for IPTV*.
+- [ITU-T Y.1540] Recommendation ITU-T Y.1540 (2007), *Internet protocol data communication service – IP packet transfer and availability performance parameters*.
+
+# 3 Definitions
+
+This Recommendation does not define any special terms.
+
+# 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|          |                           |
+|----------|---------------------------|
+| DiffServ | Differentiated Services   |
+| FEC      | Forward Error Correction  |
+| GOP      | Group Of Pictures         |
+| IP       | Internet Protocol         |
+| IPDV     | IP packet Delay Variation |
+| IPLR     | IP packet Loss Ratio      |
+| IPTD     | IP packet Transfer Delay  |
+
+|       |                                                                            |
+|-------|----------------------------------------------------------------------------|
+| IPTV  | Internet Protocol Television                                               |
+| MMPAP | Monitoring Management and Performance Analysis Platform                    |
+| MMRP  | Measurement-based Methods for improving the Robustness of IPTV Performance |
+| MOS   | Mean Opinion Score                                                         |
+| MPLS  | Multi-Protocol Label Switching                                             |
+| NP    | Network Provider                                                           |
+| QoE   | Quality of Experience                                                      |
+| QoS   | Quality of Service                                                         |
+| RFC   | Request For Comments                                                       |
+| RTCP  | RTP Control Protocol                                                       |
+| RTP   | Real-time Transport Protocol                                               |
+| SLA   | Service Level Agreement                                                    |
+| SP    | Service Provider                                                           |
+| STB   | Set-Top Box                                                                |
+| UDP   | User Datagram Protocol                                                     |
+| VoD   | Video on Demand                                                            |
+
+# 5 Conventions
+
+None.
+
+# 6 Overview of the framework of measurement-based methods for improving the robustness of IPTV performance (MMRP)
+
+In IPTV services, the QoE is a great concern to the end users. The user expects the perceptual quality of IPTV services to be as good as or even better than that of conventional TV service. In order to achieve the user's expectation, a QoS/QoE monitoring system becomes an indispensable part of the IPTV services.
+
+In a conventional monitoring system, the measurement information is only used for evaluating network performance and QoE of end users. However, this information can also be valuable input for providing media resource and transport network resource control in support of high quality of experience of IPTV services. The SP and NP can adjust the media and network resources based on the measurement information. The resource adjustment procedure includes the steps of reporting measurement information, exchanging information between SP and NP, and deciding resource adjustment methods by SP and NP. Figure 1 depicts a reference model for a MMRP system.
+
+![Figure 1 – Reference model. A diagram showing the architecture of an IPTV system with monitoring and control components. At the top, a 'Policy' icon points to two boxes: 'Analysis for media resource control' and 'Analysis for network resource control', which are interconnected. Below this, three main domains are shown: 'Service Provider', 'Network Provider', and 'End user'. The Service Provider contains a VoD server, an Encoder, and a Service server connected to a monitoring point (PT). The Network Provider contains an IP core network and an IP access network, each with a PT. The End user contains an HGW and an STB connected to a PT. Below these domains are two 'Monitoring, Management and Performance Analysis Platform' boxes, one for the Service Provider (SP) and one for the Network Provider (NP), which are also interconnected. Arrows show data flow from the PTs in each domain to their respective MMPAPs. Red lines connect the MMPAPs back to the analysis boxes at the top.](ebff22fb5dd6f50a90e44dca0f82f285_img.jpg)
+
+Figure 1 – Reference model. A diagram showing the architecture of an IPTV system with monitoring and control components. At the top, a 'Policy' icon points to two boxes: 'Analysis for media resource control' and 'Analysis for network resource control', which are interconnected. Below this, three main domains are shown: 'Service Provider', 'Network Provider', and 'End user'. The Service Provider contains a VoD server, an Encoder, and a Service server connected to a monitoring point (PT). The Network Provider contains an IP core network and an IP access network, each with a PT. The End user contains an HGW and an STB connected to a PT. Below these domains are two 'Monitoring, Management and Performance Analysis Platform' boxes, one for the Service Provider (SP) and one for the Network Provider (NP), which are also interconnected. Arrows show data flow from the PTs in each domain to their respective MMPAPs. Red lines connect the MMPAPs back to the analysis boxes at the top.
+
+**Figure 1 – Reference model**
+
+A monitoring system includes monitoring points (labelled PTs) and a monitoring, management and performance analysis platform (MMPAP). MMPAP manages one or multiple domains and collects measurement data from the monitoring points. The MMPAP of the SP collects information from the head-end system and the end-user system. The MMPAP of the NP collects information from backbone and access network domains. Note that the monitoring points located in a service provider's domain have different capabilities from those located in a network provider's domain. Based on the measurement data collected from monitoring points, the MMPAP provides the QoE metrics and other information of IPTV services. If the QoE metrics are below a certain predefined value, which is defined in the policy, it may trigger a network resource adjustment procedure, a media resource adjustment procedure or both. Since one single provider has limited measurement information, the SP and NP may share a set of information to decide on a resource adjustment method. During the procedures, the end users may not perceive the quality degradation of IPTV services.
+
+# 7 Process of end-to-end quality improvement
+
+MMPAP is located in the SP and NP administrative areas. The measurement-based resource adaptive control function collects the information from one or more MMPAP. The media and network resource is adjusted in a centralized model or in a distributed model.
+
+### Centralized model
+
+A single resource adaptive control function is responsible for the management of media and network resources. It collects measurement information from all the MMPAPs. If a MMPAP is
+
+under a different administrative area, it is not easy to aggregate the information and control the resource of entire domains.
+
+### Distributed model
+
+A number of adaptive resource control functions are responsible for the management of media and network resources. Each resource adaptive control function collects measurement information from its associated MMPAP and manages the resource of administrative domains. The measurement information is exchanged between adaptive resource control functions which collaborate with each other for the end-to-end quality maintenance.
+
+This Recommendation describes a distributed model. The SP and NP collect measurement information from their MMPAP and share a part of the measurement information with each other. Based on measurement and auxiliary information, SP and NP first decide which provider is responsible for adjusting the resource. Then, the media and transport network resource is adapted to maintain the end-to-end quality. Figure 2 illustrates this process.
+
+![Figure 2 – Resource control process flowchart](daa4a6fa7e2ba1954258f86b4928eb32_img.jpg)
+
+```
+graph LR; subgraph MS [Monitoring system]; MS1[Collect and analyse measurement data]; MS2[Report measurement information]; end; subgraph MRACF [Measurement-based resource adaptive control function]; MRACF1[Collect measurement information from own monitoring system]; MRACF2[Collect measurement information shared from other providers]; MRACF3[Information analysis based on resource control policy]; end; subgraph RCE [Resource control enforcement]; RCE1[Adjust the resource]; end; MS --> MRACF; MRACF --> RCE;
+```
+
+The diagram illustrates the resource control process flow. It consists of three main components connected sequentially from left to right. The first component is the 'Monitoring system', which contains two sub-functions: 'Collect and analyse measurement data' and 'Report measurement information'. An arrow points from the 'Monitoring system' to the second component, 'Measurement-based resource adaptive control function'. This function contains three sub-functions: 'Collect measurement information from own monitoring system', 'Collect measurement information shared from other providers', and 'Information analysis based on resource control policy'. An arrow points from the 'Measurement-based resource adaptive control function' to the third component, 'Resource control enforcement', which contains the sub-function 'Adjust the resource'.
+
+Figure 2 – Resource control process flowchart
+
+Figure 2 – Resource control process
+
+## 7.1 Monitoring system
+
+The monitoring points collect measurement metrics. The MMPAP entities will process these metrics, e.g., correlate and aggregate metrics, etc., and generate measurement reports. The reporting information obtained by processing metrics extracted from a different domain is described in clause 8.
+
+## 7.2 Measurement-based resource adjustment function
+
+Based on the reported measurement information, the NP and SP first decide the status of the perceived quality. If the measurement information indicates a trend of degradation or occurring degradation, the NP and SP will analyse how to adjust the resource to maintain the perceived quality at an expected level.
+
+Because of the limited ability of the SP and NP, one single provider may not be able to obtain all the information needed for resource control. The SP and NP share information with each other. The SP needs the network resource and network performance information to adjust the media resource. The NP needs the expected or experienced QoE of the user to make sure that the resource adjustment facilitates QoE. The information to be exchanged and methods for exchange are described in clause 9.
+
+The resource control policy instructs the SP and NP what to do. For example, if measurement information indicates mild quality degradation, one provider may adjust the network resource to
+
+improve the experienced quality. If serious degradation occurs, the SP and NP need to enforce the resource adjustment simultaneously. In order to adapt media and network resources, measurement information reported by MMPAP is analysed. Clause 10 describes the measurement-based resource adaptive methods.
+
+## 7.3 Resource control enforcement
+
+The last step is to enforce resource adjustment in media processing devices and network devices to ensure a high quality of experience.
+
+# 8 Measurement information reporting
+
+As shown in Figure 3, there are 5 types of monitoring points, depending on the location. Along with the IPTV services delivery path, the monitoring points, which possess different capabilities, collect the required measurement data.
+
+![Figure 3: Monitoring points (PT1 to PT6) diagram showing the IPTV service delivery path across five domains (A-E) with various monitoring points (PT1-PT5) and a monitoring platform at the bottom.](7e670a2b556b53ea9002dfff3a420e08_img.jpg)
+
+The diagram illustrates the IPTV service delivery path across five domains (A-E) and the locations of monitoring points (PT1 to PT5). The domains are: Domain A (Content provider), Domain B (Service provider (central headend)), Domain C (Service provider (regional headend)), Domain D (Network provider), and Domain E (End user). Monitoring points are indicated by blue boxes with 'PT' labels. A 'Monitoring, management and performance analysis platforms' bar is at the bottom, with orange arrows pointing to it from each domain.
+
+- Domain A (Content provider):** Includes 'Local content acquisition' (PT1), 'Metadata' (PT1), and 'Encoder' (PT1).
+- Domain B (Service provider (central headend)):** Includes 'Encoder' (PT1), 'Transcoder' (PT1), 'Core VoD server' (PT2), and 'Services server' (PT2).
+- Domain C (Service provider (regional headend)):** Includes 'RX' (PT1), 'Encoder' (PT1), and 'VoD server' (PT1).
+- Domain D (Network provider):** Includes 'IP core network' (PT3), 'IP access network' (PT4), and 'Edge VoD server multicast replication point' (PT4).
+- Domain E (End user):** Includes 'Home gateway' (PT5), 'STB' (PT5), and 'TV' (PT5).
+
+G.1082(09)\_F03
+
+Figure 3: Monitoring points (PT1 to PT6) diagram showing the IPTV service delivery path across five domains (A-E) with various monitoring points (PT1-PT5) and a monitoring platform at the bottom.
+
+Figure 3 – Monitoring points (PT1 to PT6)
+
+## 8.1 Reported measurement information
+
+The MMPAP collects the measurement data from the monitoring points. After MMPAP processing, a set of metrics will be sent to the measurement-based adaptive resource control function.
+
+In Figure 3, Domain A provides content-related information, which is outside of the scope of this Recommendation.
+
+Domain B, in Figure 3, provides media encoded parameters and service quality. The following information elements may be reported by MMPAP after processing the information extracted from this domain.
+
+| <b>Information</b>                   | <b>Description</b>                                                                                                                                               |
+|--------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Identifier of media flow             | One example is 5-tuple of IP packet. It is transmitted with measurement information.                                                                             |
+| General program attribute            |                                                                                                                                                                  |
+| – Service type.                      | Indicate the application, e.g., linear TV, VoD. The resource control policy and method is different for each application.                                        |
+| – Total bit rate.                    | For multimedia services, it is the sum of the bit rate of video, audio, embedded program information when present.                                               |
+| Video parameters                     |                                                                                                                                                                  |
+| – Bit rate of video.                 |                                                                                                                                                                  |
+| – Encoding format of video content.  |                                                                                                                                                                  |
+| – Resolution of video content.       |                                                                                                                                                                  |
+| – GOP parameters.                    | Include GOP size, e.g., 9, 12, etc., and GOP structure, e.g., I, P, B, IBP, IBBP, etc.                                                                           |
+| – Timestamp of I frames.             | In encoding processing, the timestamp that reflects the sampling instant of I frames is derived. It may be provided to NP for frame-related metrics calculation. |
+| Audio parameters                     |                                                                                                                                                                  |
+| – Number of audio channels.          |                                                                                                                                                                  |
+| – Bit rate of each audio channel.    |                                                                                                                                                                  |
+| – Encoding format of audio channels. |                                                                                                                                                                  |
+| Video quality.                       | The video quality (e.g., in terms of MOS) before being sent into the network.                                                                                    |
+| Audio quality.                       | The audio quality (e.g., in terms of MOS) before being sent into the network.                                                                                    |
+| Multimedia quality.                  | The multimedia quality (e.g., in terms of MOS) before being sent into the network.                                                                               |
+
+The monitoring points located in domains C and D collect network-related metrics for monitoring media flows, including packet loss, delay, jitter, etc. The MMPAP deployed in the network domain collects and processes these metrics. The following measurement information elements may be reported by the MMPAP:
+
+| <b>Information</b>               | <b>Description</b>                                                                                                                               |
+|----------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------|
+| Identifier of media flow.        | One example is 5-tuple of IP packet. It is transmitted with measurement information.                                                             |
+| IP network capacity information. | The metrics are defined in [b-IETF RFC 5136] and Appendix VIII of [ITU-T Y.1540], including available link capacity and available path capacity. |
+| IP network performance.          | Measurement points in mid-point get network performance parameters. The metrics are defined in [ITU-T Y.1540], including IPLR, IPTD and IPDV.    |
+
+| Information                               | Description                                                                                                                                                                                                                                                               |
+|-------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| One-way loss pattern related performance. | For real-time IPTV services, burst packet loss is essential and may be taken into account in performance analysis. The metrics are defined in [b-IETF RFC 3357], including loss distance, loss period, and in Appendix VII of [ITU-T Y.1540] for impaired interval ratio. |
+| Video quality.                            | Indicate the video quality (e.g., in terms of MOS) in the network domain.                                                                                                                                                                                                 |
+| Audio quality.                            | Indicate the audio quality (e.g., in terms of MOS) in the network domain.                                                                                                                                                                                                 |
+| Multimedia quality.                       | Indicate the multimedia quality (e.g., in terms of MOS) in the network domain.                                                                                                                                                                                            |
+
+The monitoring points located in domain E (home network) are capable of collecting more sophisticated metrics. The following measurement information elements may be presented by the MMPAP that manages this domain.
+
+| Information               | Description                                                                                    |
+|---------------------------|------------------------------------------------------------------------------------------------|
+| Identifier of media flow. | One example is a 5-tuple. It is transmitted with measurement information.                      |
+| Video quality.            | Indicate the experienced video quality (e.g., in terms of MOS) perceived by the end user.      |
+| Audio quality.            | Indicate the experienced audio quality (e.g., in terms of MOS) perceived by the end user.      |
+| Multimedia quality.       | Indicate the experienced multimedia quality (e.g., in terms of MOS) perceived by the end user. |
+
+Packet network measurements on the home network may require an additional monitoring point at the home gateway, and are for further study.
+
+## 8.2 Intra-domain interactions
+
+The MMPAP sends the measurement information to the measurement-based resource adaptive control function. The interaction mainly includes the following three mechanisms.
+
+### Request-response transactions
+
+When the adaptive resource control function needs current performance status, it may request the MMPAP to provide the information. For example, the adaptive network resource control function may request the latest network available resource to adjust the delivery path.
+
+### Notification
+
+The MMPAP may predefine the threshold of measurement information and report the metric which exceeds the threshold. For example, the QoE-related metric collected from end-points can be informed of the media resource adaptive control function in SP immediately, if it is below a predefined value.
+
+### Periodic reports
+
+The MMPAP may report the measurement information in a periodical manner.
+
+# 9 Information exchanged between providers
+
+In the end-to-end IPTV services delivery, service providers (SPs) and network providers (NPs) might be under different administrative domains and be responsible for head-end processing and media flow delivery, respectively. Since the SPs and the NPs have different capabilities to access the media-related information and network-related information, there is a need to exchange information between SPs and NPs. It is not mandatory that the information listed below be shared. Some information may be difficult to be obtained/exchanged in some scenarios. Conversely, there may be some other information that is essential.
+
+## 9.1 Information provided by SPs
+
+In general, the IPTV service providers deploy head-end and end-point (i.e., STB) systems. At the head-end, it is capable of providing the codec-related information such as codec type, bit rate, etc. At the end-point, it is capable of monitoring the end-to-end QoE-related performance experienced by the end user.
+
+## 9.2 Information provided by NPs
+
+As for the network providers, they provide the bearer network for IPTV services. They are capable of providing network-related information such as packet loss, delay, jitter, available bandwidth, etc.
+
+## 9.3 Information exchanged between SPs and NPs
+
+In clause 8, it has been described that MMPAPs of SPs and NPs collect and report different monitoring information. Performance metrics collected in different domains may be gathered for more comprehensive analysis.
+
+The NP needs 1) the information collected from the head-end system to analyse QoE related performance; 2) information about the detailed behaviour at the head-end system, the quality experienced at the end-user side and SLA information, while deciding how to control the network resources. The following information may be provided from SP to NP through their MMPAPs for the first purpose, and through their adaptive resource control functions for the second purpose. Some information can be used for both purposes.
+
+| Information                         | Description                                                                                                                                                                  |
+|-------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Identifier of media flow.           | It is transmitted with the exchanged data. According to the identifier, the NP can find the information of the same media flow, collected from the network domain.           |
+| General program attribute.          |                                                                                                                                                                              |
+| – Service type.                     | Based on service type, e.g., linear TV, VoD, the network resource is adjusted by different methods.                                                                          |
+| – Total bit rate.                   | It may be exchanged between MMPAPs when the NP needs to analyse QoE-related performance.                                                                                     |
+| Video parameters.                   | They are exchanged between MMPAPs if the NP needs to analyse QoE-related performance.                                                                                        |
+| – Bit rate of the video.            | Besides QoE-related performance analysis, the NP considers the encoded bit rate for encoded layer adjustment when a scalable encoding method is used at the head end system. |
+| – Encoding format of video content. |                                                                                                                                                                              |
+| – Resolution of video content.      |                                                                                                                                                                              |
+| – GOP parameters.                   | It may be used in frame-related metrics calculation.                                                                                                                         |
+| – Timestamp of I frames.            | It may be used in frame-related metrics calculation.                                                                                                                         |
+
+| Information                                                                                                               | Description                                                                                                                                                       |
+|---------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Audio parameters.                                                                                                         | They are exchanged between MMPAPs if the NP needs to analyse QoE-related performance.                                                                             |
+| – Bit rate of each audio channel.                                                                                         |                                                                                                                                                                   |
+| – Encoding format of the audio channels.                                                                                  |                                                                                                                                                                   |
+| Video/Audio/Multimedia quality from domain E.                                                                             | It triggers the NP to adjust the network resource.<br>If the NP has the ability to collect this value from the end user, the value does not need to be exchanged. |
+| SLA information.                                                                                                          | Help the NP take a reasonable resource control decision if quality degradation is detected.                                                                       |
+| – User's agreement on experienced quality of IPTV services.                                                               | It may be an exact value or a range of accepted values. It is used for encoded layer adjustment in the network domain.                                            |
+| Configuration of application-layer error correction and concealment (e.g., forward error correction type and block size). | May be adjusted for network conditions, and can be used to enhance measurement efficiency and applicability.                                                      |
+
+On the other hand, the head-end system needs to know the network conditions in order to manage media resources. For this purpose, the following information may be provided from NP to SP:
+
+| Information                      | Description                                                                                                                                                                    |
+|----------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Identifier of media flow.        | It is transmitted with the exchanged data. Using the identifier, the SP finds the information of the same media flow collected from the head end system.                       |
+| IP network capacity information. |                                                                                                                                                                                |
+| – Available path capacity.       | It indicates the capacity of an end-to-end delivery path or a path between two network nodes. The SP adjusts the media resource according to the network's available capacity. |
+
+## 9.4 Inter-domain interactions
+
+NPs and SPs may have inter-provider agreements, which determine the interaction mechanism between them. In the above clauses, information may be transmitted from one provider to another. Two kinds of mechanisms are used for sharing information.
+
+### Request-response transactions
+
+One provider may request the other one to provide measurement information. It may take place between MMPAP entities for performance analysis or between resource adaptive control functions to adjust media and network resources. For example, NP may request encoding information for QoE performance analysis, or SP may request network resource information for media resource adjustment.
+
+### Notifications
+
+One provider may inform the other one in an on-demand manner. For example, if the GOP parameters are adjusted in the encoder, the SP may notify the NP of the new GOP parameters. Another example is that, if the SP detects that the perceived quality of a broadcast service is below the agreed value, it may inform the perceived QoE and other necessary information to the NP to trigger the resource adjustment in network domains.
+
+# **10 Measurement-based adaptive resource control for IPTV services**
+
+Based on the measurement information collected in various domains, SPs and NPs can dynamically control the media resource and network resource. If the measurement value exceeds the predefined threshold, SP and NP may share some necessary information and choose a proper method to adjust the resource to maintain the QoE.
+
+Information on the performance of network and end-to-end quality is fundamental for resource control.
+
+In order to implement the QoE assessment at the network mid-point, the SP and NP will collaborate with each other. The media server provides codec parameters of a certain media flow. The SP shares it with the NP. After receiving the codec information, the NP either distributes it to the monitoring points for evaluating QoE separately, or evaluates the QoE in a centralized MMPAP. In each situation, monitoring points or the MMPAP first recognize the media flow according to the flow identifier which is transmitted with the codec information. Then, they extract the QoS metrics of such media flow monitored at a monitoring point. QoE is assessed based on the QoS and codec information. Appendix I gives an example about QoE evaluation at network mid-point.
+
+## **10.1 Media resource control**
+
+Media resource is associated with media processing, such as codec parameters, established media service connections, etc. The head-end system in the SP domain manages media resources in encoding processing. Besides it, the network device which is aware of media resource can also manage it by analysing measurement information. The following media resource control mechanisms may be enforced in the device.
+
+### **10.1.1 Encoded bit rate adjustment**
+
+If the QoE perceived by the end user is below a predefined threshold, a possible reason is that the network cannot provide sufficient resources for the service. Both the encoded bit rate and network available bandwidth resources have an impact on QoE. In order to solve the degradation problem and minimize the impact on other services, the encoding bit rate may be adjustable without interfering with network resource allocation decision. Appendix II provides an example in which the encoded bit rate adjustment mechanism is deployed by SPs for a VoD service.
+
+### **10.1.2 Encoded layer adjustment**
+
+The scalable encoding method separates a media flow into two or more encoded layers. The base layer provides a basic level of video quality. The enhancement layers provide a higher experienced quality of media flow. For broadcast services, the media server often encodes the media flow into multi-layers. The end user can receive a set of encoded layers based on its ability and the delivery path capacity. The encoded layer delivered from the network node to the end user is adjusted according to the network capacity and the user's expectation. SP and NP can both adjust the encoded layer with each other's assistance. Appendix III illustrates this mechanism used in the access node and in the STB, respectively.
+
+## **10.2 Network resource control**
+
+Network providers may have the ability to obtain network performance and adjust network resources to guarantee end-to-end quality. Transport network resources mainly include the network bandwidth. This clause describes the way the NP adjusts network resources to provide high quality service.
+
+### **10.2.1 Resource allocation adjustment**
+
+NP predefines a method to control network resources. For example, if the reported QoE of a critical service indicates degradation caused by insufficient network resources, NP may re-allocate the network resource, e.g., degrade/pause/stop less critical services. This adjustment method may be used to control the access network resource when linear TV, VoD and data services are transmitted to the home network simultaneously. When the access network is insufficient to support all the services, the adaptive network-resource control function will determine the amount of re-allocated resources from less crucial services in terms of transmission performance (e.g., data service, etc.) to highly critical services (e.g., VoD, etc.) based on access link capacity, for example.
+
+### **10.2.2 FEC adjustment**
+
+A FEC block encapsulated in RTP packets can be used to minimize the effects of packet loss. The media adaptive resource control function is capable of adjusting the FEC redundant block in the head-end system based on the network condition. If the perceived quality reported by the end user system (e.g., STB) is good enough, the packet loss ratio seems to be under a threshold. The adaptive media resource control function decreases the FEC redundancy. The released network resource is then allocated to other services, e.g., best effort service. Otherwise, the adaptive media resource control function increases the FEC redundant block to facilitate the reconstruction of lost information at the receiver side, i.e., more network resource is allocated to FEC blocks. SP may use this mechanism to control the redundancy in encoding of VoD media flow, for example.
+
+### **10.2.3 Delivery path adjustment**
+
+The quality report from the end user devices often indicates the trend of degradation. If it is caused by network congestion, a possible method to avoid the congestion area is to re-establish the delivery path. Network devices may decide a new delivery path to improve the quality. In this mechanism, NP collects topology and resource information under the administrative area. It decides all potential delivery paths between edge nodes and calculates the cost of each path in the network domain. NP may choose a path based on the cost to avoid the congestion area, e.g., the path with least cost is selected. In a manageable network, NP can use this mechanism to adjust the network resource for both linear TV and VoD service. Appendix IV illustrates an example for adjusting the delivery path in an MPLS backbone network.
+
+# **11 Security consideration**
+
+There are no specific security considerations in this Recommendation.
+
+# Appendix I
+
+## QoE evaluation in mid-point
+
+(This appendix does not form an integral part of this Recommendation)
+
+### I.1 Introduction
+
+The service monitoring server and network monitoring server are regarded as instances of MMPAP in SP and NP, respectively. The service monitoring server collects codec parameters from the media server. The network monitoring server manages the monitoring points and collects performance data from these. This appendix describes how to calculate QoE-related performance in mid-point.
+
+### I.2 Collaboration between SP and NP to evaluate QoE in mid-point
+
+The media server provides codec information, including general program attribute, video parameters and audio parameters of media flows (1a). The monitoring point in the network domain monitors QoS information, e.g., IP network performance, one-way loss pattern related performance, etc. (1b). SP and NP already have an agreement to share information for QoE performance analysis. The service monitoring server notifies the codec information to the network monitoring server (2). The QoE of a media flow can be evaluated separately in the monitoring points or centrally in the network monitoring server. Figure I.1 shows a distributive QoE assessment example.
+
+![Figure I.1: Example for QoE assessment in monitoring points. The diagram shows four entities: Media server, Service monitoring server, Network monitoring server, and Monitoring point. The flow of information is: (1a) Codec information from Media server to Service monitoring server; (2) Codec information from Service monitoring server to Network monitoring server; (3) Codec information from Network monitoring server to Monitoring point; (1b) monitor QoS information from Monitoring point to (4) QoE assessment block; and (4) QoE assessment block to Monitoring point.](77464a47f104d0d647b2414591137b64_img.jpg)
+
+```
+graph LR; MS[Media server] -- "(1a) Codec information" --> SMS[Service monitoring server]; SMS -- "(2) Codec information" --> NMS[Network monitoring server]; NMS -- "(3) Codec information" --> MP[Monitoring point]; MP -- "(1b) monitor QoS information" --> QA[QoE assessment]; QA -- "(4) QoE assessment" --> MP;
+```
+
+Figure I.1: Example for QoE assessment in monitoring points. The diagram shows four entities: Media server, Service monitoring server, Network monitoring server, and Monitoring point. The flow of information is: (1a) Codec information from Media server to Service monitoring server; (2) Codec information from Service monitoring server to Network monitoring server; (3) Codec information from Network monitoring server to Monitoring point; (1b) monitor QoS information from Monitoring point to (4) QoE assessment block; and (4) QoE assessment block to Monitoring point.
+
+Figure I.1 – Example for QoE assessment in monitoring points
+
+The network monitoring server sends the codec information of multiple media flows to monitoring points located in the network (3). The monitoring point monitors QoS metrics of the media flow transmitted through it. It correlates codec information and QoS metrics of the same media flow using the flow identifier. QoE performance of each monitored media flow is evaluated at monitoring points based on these two kinds of information.
+
+In a centralized scenario, the network monitoring server embeds a QoE assessment method. The network monitoring server sends a part of codec information to the monitoring points for QoS metrics calculation. Monitoring points report the QoS metrics of monitored media flow to the network monitoring server. The network monitoring server associates the codec information with QoS metrics using the flow identifier. QoE performance of media flow is evaluated by network monitoring server based on these two kinds of information.
+
+In both scenarios, monitoring points may calculate frame-related QoS metrics. The codec information includes GOP parameters and timestamp of I frames, which are sent from the service monitoring server to the network monitoring server. The network monitoring server distributes the
+
+information to monitoring points for frame type analysis of each RTP packet. The monitoring point extracts the timestamp from RTP packets, compares the timestamp of I frames with the RTP timestamp. If there is a match, the corresponding RTP packet is marked as I frame. According to the GOP parameters, the frame type of other RTP packets in the same GOP is estimated. Based on the frame type of each RTP packet, monitoring points will analyse frame-related QoS metrics.
+
+# Appendix II
+
+## Encoded bit rate adjustment in the head-end system
+
+(This appendix does not form an integral part of this Recommendation)
+
+This appendix provides an example in which the SP adjusts the media encoded bit rate of the VoD service.
+
+The media resource controller, located in the SP's administrative area, collects media resource information (1a) and the quality experienced by the end user (1b).
+
+The network resource controller, located in the NP's administrative area, collects the network performance information (1c).
+
+The media resource controller will decide on a new bit rate to maintain the experienced quality according to the network resource information. The media server is required to adjust the encoded bit rate. Figure II.1 illustrates the interaction between NP and SP and the process followed to adjust the encoded bit rate.
+
+![Sequence diagram illustrating the interaction for encoded bit rate adjustment between a Media server, MMPAP of SP, Media resource controller, Network resource controller, and MMPAP of NP.](e636d7ccca0ad14c6b95201404324823_img.jpg)
+
+```
+sequenceDiagram
+    participant MS as Media server
+    participant MSPAP as MMPAP of SP
+    participant MRC as Media resource controller
+    participant NRC as Network resource controller
+    participant NPPAP as MMPAP of NP
+
+    Note right of MRC: (1a) Media information  
+(1b) QoE perceived by end user
+    MSPAP->>MRC: (1a) Media information (1b) QoE perceived by end user
+    Note right of NRC: (1c) Network performance
+    NRC->>NPPAP: (1c) Network performance
+    MRC->>NRC: (2) Request network resource information
+    NRC->>MRC: (3) Reply with network resource information
+    Note right of MRC: (4) Calculate a new encoded bit rate
+    MRC->>MSPAP: (5) Request to adjust bit rate
+    MSPAP->>MS: (5) Request to adjust bit rate
+```
+
+Sequence diagram illustrating the interaction for encoded bit rate adjustment between a Media server, MMPAP of SP, Media resource controller, Network resource controller, and MMPAP of NP.
+
+Figure II.1 – Encoded bit rate adjustment
+
+If the QoE reported by the end user indicates that quality is below a predefined value for the VoD service, the SP is chosen to mitigate the degradation. In order to decide a new encoded bit rate, the media resource controller needs the following information:
+
+- 1) Available path capacity: the media resource controller requests the current network available capacity of the transport path for the affected VoD service, from network resource controller (2). The network resource controller finds out the transport path of this service and the corresponding available link capacity. The minimum available link capacity is chosen as the available capacity of an end-to-end delivery path. The network resource controller replies with the available path capacity (3).
+
+- 2) Expected QoE value: the quality a user expects to perceive. The media resource controller obtains the expected QoE value from the end user or from predefined agreement profile.
+- 3) Current media encoded bit rate: the media server encodes the media flow at this bit rate. The media resource controller obtains the current encoded bit rate from the media server.
+
+The media resource controller collects the above three kinds of information and sends it to the media resource management mechanism as inputs for analysis. The encoded bit rate adjustment method includes two aspects. The first one defines how to calculate a new encoded bit rate according to available path capacity, current media encoded bit rate and an expected QoE. A mapping table or formula is used. The second aspect defines the highest or lowest encoded bit rate to the end user.
+
+The adjusted bit rate should not exceed the limit. The expected bit rate is determined according to the predefined adjustment method (4).
+
+The media resource controller requests the media server to adjust the encoded bit rate to the expected value (5).
+
+# Appendix III
+
+## Encoded layer adjustment
+
+(This appendix does not form an integral part of this Recommendation)
+
+### III.1 Introduction
+
+The performance of the access network is variable. If the quality experienced by the end user is impaired by congestion occurring in the access network, the transmitted encoded layer may be adjusted to comply with network performance. This appendix illustrates two adjustment approaches implemented by NP or SP, respectively.
+
+### III.2 Network device adjusts the encoded layer
+
+In scenario 1, program 1 (P1) is a broadcast media flow and encoded in one base layer (P1-B) with two enhancement layers (P1-E1, P1-E2). The network resource requirements of the three encoded layers are different. Program 1 has a multicast IP address which is explicit to the end-point, e.g., STB. Encoded layers are transmitted in three separate multicast groups which are unknown to the end-point. The end-point sends a request to join the multicast group of P1 (e.g., IGMP) when choosing this program. The access node translates the multicast address of P1 into three encoded layers' multicast addresses and requests the resource access. The access decision will be made based on the access network's available capacity, e.g., three encoded layers are accepted. The access node receives and keeps the resource access decision. The media server sends three media flows of program 1. The access node enforces the access decision in two steps, replaces the multicast IP address of accepted encoded layers to the multicast IP address of program 1, and then forwards the accepted encoded layers to the end user.
+
+The accepted encoded layers may be adjusted according to the access network performance. Figure III.1 illustrates the adjustment of the encoded layers that are transmitted on the access network.
+
+![Sequence diagram illustrating encode layer adjustment by access node. Lifelines: Media server, MMPAP of SP, Media resource controller, Network resource controller, MMPAP of NP, Access node, STB. The process involves: (1a) QoE perceived by end user from MMPAP of SP to Media resource controller; (2) Notify resource requirement and quality agreement from Media resource controller to Network resource controller; (1b) Collect network performance from Network resource controller to MMPAP of NP; (3) Compare and make decision in Network resource controller; (4) Request to adjust encoded layer from Network resource controller to Access node; (5) Stop forwarding in Access node. The Access node notes that P1 contains the data of accepted layers, with sub-layers P1-B, P1-E1, and P1-E2.](c914f51f4427bc672dd0526cfc90ebe9_img.jpg)
+
+```
+
+sequenceDiagram
+    participant Media server
+    participant MMPAP of SP
+    participant Media resource controller
+    participant Network resource controller
+    participant MMPAP of NP
+    participant Access node
+    participant STB
+
+    Note right of MMPAP of SP: (1a) QoE perceived by end user
+    MMPAP of SP->>Media resource controller: (1a) QoE perceived by end user
+    Note right of Media resource controller: (2) Notify resource requirement and quality agreement
+    Media resource controller->>Network resource controller: (2) Notify resource requirement and quality agreement
+    Note right of Network resource controller: (1b) Collect network performance
+    Network resource controller->>MMPAP of NP: (1b) Collect network performance
+    Note right of Network resource controller: (3) Compare and make decision
+    Note right of MMPAP of NP: P1-B, P1-E1, P1-E2
+    Note right of Access node: P1 contains the data of accepted layers
+    Note right of Network resource controller: (4) Request to adjust encoded layer
+    Network resource controller->>Access node: (4) Request to adjust encoded layer
+    Note right of Access node: (5) Stop forwarding
+    Access node->>STB: (5) Stop forwarding
+  
+```
+
+Sequence diagram illustrating encode layer adjustment by access node. Lifelines: Media server, MMPAP of SP, Media resource controller, Network resource controller, MMPAP of NP, Access node, STB. The process involves: (1a) QoE perceived by end user from MMPAP of SP to Media resource controller; (2) Notify resource requirement and quality agreement from Media resource controller to Network resource controller; (1b) Collect network performance from Network resource controller to MMPAP of NP; (3) Compare and make decision in Network resource controller; (4) Request to adjust encoded layer from Network resource controller to Access node; (5) Stop forwarding in Access node. The Access node notes that P1 contains the data of accepted layers, with sub-layers P1-B, P1-E1, and P1-E2.
+
+**Figure III.1 – Encode layer adjustment by access node**
+
+SP and NP receive the perceived quality and network performance metrics from MMPAP respectively (1a, 1b). If congestion occurs in the access network and the user's quality reports indicate the trend of QoE degradation, the NP is chosen to adjust the resource. SP notifies NP of the required resource of codec layers and the user's agreement about the accepted range of encoded layers (2). The network resource controller compares access network capacity with the required resource (3). Since the QoE will be improved because of less impairment, the decision is to remove some enhancement layers to mitigate the congestion, e.g., the highest layer P1-E2. The adjustment should not exceed the user's agreement of accepted range of the encoded layers. The access node receives the decision (4) and stops forwarding the media flow of P1-E2 (5). When the access network has enough resources, the highest encoded layer is resumed.
+
+This mechanism requires the network resource controller to be aware of the relation between program and its encoded layers and the resource requirement of each encoded layer. The end user is not aware of the encoded layer adjustment because it joins the multicast group of the program and receives the media flow of the program.
+
+### III.3 STB adjusts the encoded layer
+
+In scenario 2, program 1 (P1) is a broadcast media flow and encoded in one base layer (P1-B) with two enhancement layers (P1-E1, P1-E2). STB is aware of the separate multicast IP addresses of the three encoded layers. STB sends three requests to join P1-B, P1-E1 and P1-E2 multicast groups (e.g., IGMP) when choosing P1. Compared with scenario 1, the network node need not keep the correlation between program and the encoded layers.
+
+STB is requested to join or leave multicast groups of a certain program according to network performance. Figure III.2 illustrates the adjustment procedure.
+
+![Sequence diagram illustrating the encode layer adjustment process by the STB. The diagram shows interactions between seven entities: Media server, MMPAP of SP, Media resource controller, Network resource controller, MMPAP of NP, Network node, and STB. The process involves QoE perception, path capacity requests, network performance responses, decision making, adjustment requests, and leaving requests for specific encoded layers (P1-B, P1-E1, P1-E2).](c5452f95f3b28f1bfe29e84fbc2e1267_img.jpg)
+
+```
+
+sequenceDiagram
+    participant Media server
+    participant MMPAP of SP
+    participant Media resource controller
+    participant Network resource controller
+    participant MMPAP of NP
+    participant Network node
+    participant STB
+
+    Note right of STB: P1-B
+    Note right of STB: P1-E1
+    Note right of STB: P1-E2
+
+    MMPAP of SP->>Media resource controller: (1a) QoE perceived by end user
+    Media resource controller->>Network resource controller: (2) Request available path capacity
+    Network resource controller-->>Media resource controller: (3) Response
+    Note left of Network resource controller: (4) Compare and make decision
+    Media resource controller->>STB: (5) Request to adjust encoded layer
+    STB->>Network node: (6) Request of leaving encoded layer
+  
+```
+
+Sequence diagram illustrating the encode layer adjustment process by the STB. The diagram shows interactions between seven entities: Media server, MMPAP of SP, Media resource controller, Network resource controller, MMPAP of NP, Network node, and STB. The process involves QoE perception, path capacity requests, network performance responses, decision making, adjustment requests, and leaving requests for specific encoded layers (P1-B, P1-E1, P1-E2).
+
+**Figure III.2 – Encode layer adjustment by STB**
+
+SP and NP receive the perceived quality and network performance metrics from MMPAP (1a) and (1b) respectively. If network performance results in quality degradation, the media resource controller requests the available path capacity of the end user from the network resource controller (2). The network resource controller replies with the measurement metrics (3). The response information is compared with the requirement of each encoded layer (4). For example, the highest encoded layer (P1-E2) needs to be removed to guarantee quality. The media resource controller sends the adjustment decision to STB (5). STB sends a request to leave the multicast group of P1-E2 (e.g., IGMP) to the network node (6), e.g., an access node. The network node receives the multicast group leaving request, and stops forwarding the media flow of P1-E2 to the end user.
+
+## Appendix IV
+
+## Delivery path adjustment
+
+(This appendix does not form an integral part of this Recommendation)
+
+The core network implements MPLS technology for DiffServ purposes. The network resource controller is deployed to collect the network measurement information from MMPAP in the core network. The network resource controller constructs a network resource information database of administrative area, uses the database to establish potential paths and calculates the cost of each path in the managed area. The delivery path of media flow is selected from potential paths based on the cost. Network resource is allocated to the media flow. If the current delivery path is congested and results in quality degradation, the network resource controller will select again a new path for the impacted media flow based on the cost. Network resource is reallocated. Figure IV.1 provides a detailed description.
+
+![Diagram illustrating delivery path adjustments in a sub-network. The diagram shows a Headend system connected to ER1, which is part of a core network containing CR1, CR2, CR3, ER1, ER2, and ER3. An End user is connected to ER2. A Media resource controller and a Network resource controller are shown. The process involves: (1) Network measurement information from the core network to the Network resource controller; (2) Congestion occurs on the path from CR3 to ER2; (3) QoS perceived by end user is communicated to the Network resource controller; (4) Impacted media flow is communicated from the Media resource controller to the Network resource controller; (5) Choose a new delivery path is communicated from the Network resource controller to the core network.](e354b57563dae469c00b412b2abdf765_img.jpg)
+
+The diagram illustrates the delivery path adjustment process in a sub-network. It features a Headend system connected to edge router ER1, and an End user connected to edge router ER2. The core network contains three core routers: CR1, CR2, and CR3. ER1 is connected to CR1 and CR3. CR1 is connected to CR2. CR2 and CR3 are both connected to ER2. ER3 is connected to CR3. A Media resource controller and a Network resource controller are shown. The process steps are: (1) Network measurement information is sent from the core network to the Network resource controller. (2) Congestion occurs on the path from CR3 to ER2. (3) QoS perceived by the end user is communicated to the Network resource controller. (4) The Media resource controller sends an impacted media flow notification to the Network resource controller. (5) The Network resource controller chooses a new delivery path and communicates this to the core network.
+
+Diagram illustrating delivery path adjustments in a sub-network. The diagram shows a Headend system connected to ER1, which is part of a core network containing CR1, CR2, CR3, ER1, ER2, and ER3. An End user is connected to ER2. A Media resource controller and a Network resource controller are shown. The process involves: (1) Network measurement information from the core network to the Network resource controller; (2) Congestion occurs on the path from CR3 to ER2; (3) QoS perceived by end user is communicated to the Network resource controller; (4) Impacted media flow is communicated from the Media resource controller to the Network resource controller; (5) Choose a new delivery path is communicated from the Network resource controller to the core network.
+
+Figure IV.1 – Delivery path adjustments in sub-network
+
+The network resource controller constructs a network resource information database based on the resource and topology information, which includes the network node, the label switched path (LSP) ID and the LSP cost, in the administrative area. LSP here indicates the logical connection between routers, e.g., edge router 1 (ER1) to core router 1 (CR1), CR1 to CR2, etc. LSP cost is estimated from a physical connection attribute, such as link available capacity between routers. In the preparation process, the network resource controller calculates all potential delivery paths according to the topology information. Each path connects a pair of ERs in the core network. For example, between ER1 and ER2, there are two potential paths (ER1-CR1-CR2-ER2, ER1-CR3-ER2); between ER1 and ER3, there is one potential path (ER1-CR3-ER3); between ER2 and ER3, there is one potential path (ER2-CR3-ER3). The path cost is calculated by aggregating the weighted cost of LSPs along this path. The network resource controller collects the LSP cost from MMPAP and updates the path cost in a real-time manner.
+
+When the end user requests a media service, the network resource controller finds the pair of ingress and egress nodes according to the identifier of media flow (e.g., the media flow will traverse the network from ER1 to ER2). The possible delivery path of the media flow is filtered (e.g., ER1-CR1-CR2-ER2 and ER1-CR3-ER2) from all potential paths. The path of the least cost, e.g., ER1-CR3-ER2 is selected. If congestion (e.g., CR3-ER2) occurs in the delivery path (2), the user's report indicates the trend of quality degradation (3). The SP notifies the NP of the impacted media flow for which network resource adjustment (4) has to be requested. Network resource controller updates the cost of paths between ER1 and ER2, and selects a new least cost path, e.g., ER1-CR1-CR2-ER2. The rerouting decision is implemented in the related network node, e.g., ER1 (5). The network resource along the new path is allocated to the media flow.
+
+## Bibliography
+
+[b-IETF RFC 3357] IETF RFC 3357 (2002), *One-way Loss Pattern Sample Metrics*.
+
+[b-IETF RFC 5136] IETF RFC 5136 (2008), *Defining Network Capacity*.
+
+
+
+
+
+## **SERIES OF ITU-T RECOMMENDATIONS**
+
+|                 |                                                                                             |
+|-----------------|---------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                           |
+| Series D        | General tariff principles                                                                   |
+| Series E        | Overall network operation, telephone service, service operation and human factors           |
+| Series F        | Non-telephone telecommunication services                                                    |
+| <b>Series G</b> | <b>Transmission systems and media, digital systems and networks</b>                         |
+| Series H        | Audiovisual and multimedia systems                                                          |
+| Series I        | Integrated services digital network                                                         |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals |
+| Series K        | Protection against interference                                                             |
+| Series L        | Construction, installation and protection of cables and other elements of outside plant     |
+| Series M        | Telecommunication management, including TMN and network maintenance                         |
+| Series N        | Maintenance: international sound programme and television transmission circuits             |
+| Series O        | Specifications of measuring equipment                                                       |
+| Series P        | Terminals and subjective and objective assessment methods                                   |
+| Series Q        | Switching and signalling                                                                    |
+| Series R        | Telegraph transmission                                                                      |
+| Series S        | Telegraph services terminal equipment                                                       |
+| Series T        | Terminals for telematic services                                                            |
+| Series U        | Telegraph switching                                                                         |
+| Series V        | Data communication over the telephone network                                               |
+| Series X        | Data networks, open system communications and security                                      |
+| Series Y        | Global information infrastructure, Internet protocol aspects and next-generation networks   |
+| Series Z        | Languages and general software aspects for telecommunication systems                        |

marked/G/T-REC-G.225-198811-I_PDF-E/raw.md

@@ -0,0 +1,95 @@
+
+
+![ITU logo](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features the letters 'ITU' in a bold, sans-serif font, superimposed on a stylized globe with latitude and longitude lines.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**G.225**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+# **INTERNATIONAL ANALOGUE CARRIER SYSTEMS GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS** ---
+
+## **RECOMMENDATIONS RELATING TO THE ACCURACY OF CARRIER FREQUENCIES**
+
+**ITU-T Recommendation G.225**
+
+(Extract from the *Blue Book*)
+
+---
+
+## NOTES
+
+- 1 ITU-T Recommendation G.225 as published in Fascicle III.2 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+- 2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## **RECOMMENDATIONS RELATING TO THE ACCURACY OF CARRIER FREQUENCIES**
+
+*(amended at Geneva, 1964, and Mar del Plata, 1968)*
+
+### **1 Accuracy of the virtual carrier frequencies on an international circuit or on a chain of circuits**
+
+As the channels of any international telephone circuit should be suitable for voice-frequency telegraphy, the accuracy of the virtual carrier frequencies should be such that the difference between an audio-frequency applied to one end of the circuit and the frequency received at the other end should not exceed 2 Hz, even when there are intermediate modulating and demodulating processes.
+
+To attain this objective, the CCITT recommends that the channel and group carrier frequencies of the various stages should have the following accuracies:
+
+|                                                       |                       |
+|-------------------------------------------------------|-----------------------|
+| Virtual channel carrier frequencies in group.....     | $\pm 10^{-6}$         |
+| Group and supergroup carrier frequencies.....         | $\pm 10^{-7}$         |
+| Mastergroup and supermastergroup carrier frequencies: |                       |
+| - for the 12-MHz system.....                          | $\pm 5 \cdot 10^{-8}$ |
+| - for the 60-MHz system (above 12 MHz).....           | $\pm 10^{-8}$         |
+
+Experience shows that, if a proper check is kept on the operation of oscillators designed to these specifications, the difference between the frequency applied at the origin of a telephone channel and the reconstituted frequency at the other end hardly ever exceeds 2 Hz if the channel has the same composition as the 2500-km hypothetical reference circuit for the system concerned.
+
+Calculations indicate that, if these recommendations are followed, in the 4-wire chain forming part of the hypothetical reference connection defined in Figure 1/G.103<sup>1)</sup>) there is about 1 % probability that the frequency difference between the beginning and the end of the connection will exceed 3 Hz and less than 0.1% probability that it will exceed 4 Hz.
+
+*Note 1* - In small stations, i.e. in stations which do not need supergroup carrier frequencies, the accuracy of the group carrier may be  $\pm 10^{-6}$ , which is the same as for channel carrier frequencies.
+
+*Note 2* - The modulating frequencies appropriate to  $(n + n)$  systems should have the accuracies recommended in the relevant Recommendations:
+
+- Recommendation G.311 for 12-channel open-wire systems;
+- Recommendation G.361 for 3-channel open-wire systems;
+- Recommendations G.326 and G.327 [3] for  $(12 + 12)$  cable systems.
+
+### **2 Measure of alignment of the master oscillators**
+
+The recommendation in § 1 above cannot be met without some measure of alignment of the master oscillators at the various stations in which modulation occurs.
+
+<sup>1)</sup> In fact, the chain considered for these calculations comprised 16 (instead of 12) modulator/demodulator pairs to allow for the possibility that submarine cables with equipments in conformity with Recommendation G.235 might form part of the chain. No allowance was made, however, for the effects of Doppler frequency-shift due to inclusion of a non-stationary satellite; values for this shift are given in CCIR Report 214 [2].
+
+Carrier-transmission systems are formed into "partial networks" extending over the whole or a part of a country. Synchronization of the master oscillators of a partial network is ordinarily based on national frequency comparisons; international comparisons may be made if necessary.
+
+#### 2.1 *National frequency comparisons*
+
+It is necessary that, within the same partial network of coaxial carrier systems, the master oscillators in stations where frequencies are generated should be "coordinated". This "coordination" can consist of a control of one oscillator with respect to another to give one of the following three conditions:
+
+- 1) synchronization, i.e. identical frequency and fixed phase relationship;
+- 2) isochronization, i.e. identical frequency only;
+- 3) differential control to correct differences between the frequencies at intervals.
+
+Also, automatic devices can be used to give an alarm if the difference in frequency between the checking pilot and a local oscillator exceeds a certain fixed value.
+
+The CCITT has not recommended any particular method of comparing or controlling the master oscillators at different stations, and "routine frequency comparison" of the master oscillators may be thought sufficient; this comparison being followed if necessary by automatic or manual regulation, the master oscillators in each partial network being compared periodically with a national frequency standard, if possible.
+
+The routine comparison of the frequencies generated by the master oscillators is made by means of a "frequency check pilot" transmitted to line for this purpose. It is not necessary to compare phases.
+
+#### 2.2 *International frequency comparisons*
+
+The case may arise, either of a country that has a national frequency standard with no facilities for distributing it throughout the country (particularly in an area in which a coaxial carrier system is to be set up), or of a country that has no national frequency standard. Recommendation M.540 [4], describes methods by which such countries may obtain a standard frequency by radio, or may have a controlled frequency sent over a telephone circuit.
+
+## **References**
+
+- [1] CCITT Recommendation *Hypothetical reference connections*, Vol. III, Rec. G.103, Figure 1/G.103.
+- [2] CCITT Report *The effects of doppler frequency-shifts and switching discontinuities in the fixed satellite service*, Vol. IV, Report 214, Dubrovnik, 1986.
+- [3] CCITT Recommendation *Valve-type systems offering 12 telephone carrier circuits on a symmetric cable [(12 + 12) systems]*, Orange Book, Vol. III-1, Rec. G.327, ITU, Geneva, 1977.
+- [4] CCITT Recommendation *Routine maintenance of carrier and pilot generating equipment*, Vol. IV, Rec. M.540.

marked/G/T-REC-G.230-198811-I_PDF-E/raw.md

@@ -0,0 +1,172 @@
+
+
+![ITU logo](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features the letters 'ITU' in a bold, sans-serif font, superimposed on a stylized globe with latitude and longitude lines.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**G.230**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+# **INTERNATIONAL ANALOGUE CARRIER SYSTEMS**
+
+## **GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER - TRANSMISSION SYSTEMS** ---
+
+# **MEASURING METHODS FOR NOISE PRODUCED BY MODULATING EQUIPMENT AND THROUGH-CONNECTION FILTERS**
+
+**ITU-T Recommendation G.230**
+
+(Extract from the *Blue Book*)
+
+---
+
+## NOTES
+
+1 ITU-T Recommendation G.230 was published in Fascicle III.2 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## Recommendation G.230
+
+# MEASURING METHODS FOR NOISE PRODUCED BY MODULATING EQUIPMENT AND THROUGH-CONNECTION FILTERS
+
+(Geneva, 1976 and 1980)
+
+Considering the provisions of Recommendation G.222, § 4 and the assumptions for the calculation of noise of Recommendation G.223, the following methods for measuring the noise produced by modulating equipments are recommended:
+
+### 1 12-channel translating equipments
+
+For the measurement of noise produced by 12-channel translating equipments, eleven incoherent noise random signals with a normal (Gaussian) level distribution and with a power distribution according to Recommendation G.227 should be used. As a provisional value, the peak/r.m.s. ratio of each of the noise signals should be about 12 dB. The allocation on the 12-channel inputs of the conventional load of 2140 µW0 (+3.3 dBm0) should be as follows:
+
+|                                                     |                 |
+|-----------------------------------------------------|-----------------|
+| 1 channel being measured.....                       | 0 µW0           |
+| 2 adjacent channels at 32 µW0 (-15 dBm0) each ..... | 64 µW0          |
+| 9 channels at 230 µW0 (-6.4 dBm0) each .....        | <u>2070 µW0</u> |
+|                                                     | 2134 µW0        |
+
+## 2 Higher order translating equipments
+
+### 2.1 Allocation of loading
+
+For the measurement of noise produced by higher order translating equipments (groups, supergroups, etc. translating equipment), the values for the allocation of the conventional load to the different translating equipments are given in Table 1/G.222.
+
+The number of incoherent band-limited white noise signals is assumed to be equal to the number of the input ports of the groups, supergroups, etc. translating equipment under measurement. In certain circumstances, however, the number of noise signals may be smaller than the number of group input ports.
+
+### 2.2 Measuring frequencies
+
+The measuring frequencies in Table 1/G.230 are recommended.
+
+TABLE 1/G.230
+
+| Basic group to be measured | Frequency range (kHz) | Measuring frequencies (kHz) |       |        |
+|----------------------------|-----------------------|-----------------------------|-------|--------|
+| Group                      | 60- 108               | 70                          |       | 98     |
+| Supergroup                 | 312- 552              | 331                         |       | 534    |
+| Mastergroup                | 812- 2 044            | 1 002                       | 1 248 | 1 730  |
+| 15 supergroup assembly     | 312- 4 028            | 534                         | 1 248 | 3 886  |
+| Supermastergroup           | 8 516- 12 388         | 9 073                       |       | 11 700 |
+
+### 2.3 Filter characteristics
+
+The following filter characteristics are recommended:
+
+- 2.3.1 bandpass filters (see Table 2/G.230);
+- 2.3.2 bandstop filters (see Table 3/G.230).
+
+*Note* - Measuring frequencies of Table 1/G.230 and filter characteristics of Tables 2/G.230 and 3/G.230 (with the exception of the 70-kHz filter) are the same as in CCIR Recommendations 399 [1] and 482 [2] and CCITT Recommendation G.228 used for line system arrangements. Annex B to Recommendation G.228 deals with the subject of corrections, if any, to be applied to measurements to allow for filter effects.
+
+TABLE 2/G.230
+
+#### Bandpass filters
+
+|                                                                     | Capacity<br>(channels) | Limit of band<br>occupied<br>by telephone<br>channels<br>(Khz) | Effective cut-off<br>frequencies of<br>bandpass filters (kHz) |                  | Frequency bands (kHz) inside<br>of which the discrimination<br>should exceed 75 dB              |                       |
+|---------------------------------------------------------------------|------------------------|----------------------------------------------------------------|---------------------------------------------------------------|------------------|-------------------------------------------------------------------------------------------------|-----------------------|
+|                                                                     |                        |                                                                | Highpass                                                      | Lowpass          | Below the<br>passband                                                                           | Above the<br>passband |
+| Basic Group B                                                       | 12                     | 60- 108                                                        | $61 \pm 2$                                                    | $107 \pm 2$      | 6- 52                                                                                           | 116- 1 200            |
+| Basic supergroup                                                    | 60                     | 312- 552                                                       | $320 \pm 8$                                                   | $546 \pm 10$     | 6- 288                                                                                          | 577- 8 500            |
+| Basic mastergroup                                                   | 300                    | 812- 2 044                                                     | $840 \pm 16$                                                  | $2 004 \pm 30$   | 6- 412                                                                                          | 2 318- 26 000         |
+| Basic 15<br>supergroup<br>assembly                                  | 900                    | 312- 4 028                                                     | $320 \pm 8$                                                   | $4 070 \pm 60$   | 6- 288                                                                                          | 4 544- 30 000         |
+| Basic<br>supermastergroup<br><br>(15 supergroups<br>assembly No. 3) | 900                    | 8 516- 12 388                                                  | } $8 560 \pm 200$                                             | $12 250 \pm 180$ | 6- 7 686                                                                                        | 13 085-135 000        |
+|                                                                     | 900                    | 8 620- 12 336                                                  |                                                               |                  |                                                                                                 |                       |
+|                                                                     |                        |                                                                |                                                               |                  | Above and below these bands,<br>the discrimination may decrease<br>with a slope of 6 dB/octave. |                       |
+
+TABLE 3/G.230
+
+#### **Bandstop filters**
+
+| Centre frequence $f_c$<br>(kHz) | Bandwidth (kHz)<br>in relation to $f_c$ over<br>which the discrimination<br>should be at least |            |            | Bandwidth (kHz),<br>in relation to $f_c$ outside of<br>which the discrimination<br>should not exceed |           | Notes |
+|---------------------------------|------------------------------------------------------------------------------------------------|------------|------------|------------------------------------------------------------------------------------------------------|-----------|-------|
+|                                 | 70 dB                                                                                          | 55 dB      | 30dB       | 3dB                                                                                                  | 0.5dB     |       |
+| 70                              | $\pm 1.5$                                                                                      | $\pm 1.7$  | $\pm 2.0$  | $\pm 5$                                                                                              | $\pm 10$  |       |
+| 98                              | $\pm 1.5$                                                                                      | $\pm 1.8$  | $\pm 2.1$  | $\pm 4$                                                                                              | $\pm 9$   | a)    |
+| 331                             | $\pm 1.5$                                                                                      | $\pm 2.7$  | $\pm 4.0$  | $\pm 17$                                                                                             | $\pm 30$  |       |
+| 534                             | $\pm 1.5$                                                                                      | $\pm 3.5$  | $\pm 7.0$  | $\pm 15$                                                                                             | $\pm 48$  | b)    |
+| 1 002                           | $\pm 1.5$                                                                                      | $\pm 4.0$  | $\pm 9.0$  | $\pm 27$                                                                                             | $\pm 90$  | a)    |
+| 1 248                           | $\pm 1.5$                                                                                      | $\pm 4.0$  | $\pm 11.0$ | $\pm 35$                                                                                             | $\pm 110$ | b)    |
+| 1 730                           | $\pm 1.5$                                                                                      | $\pm 4.0$  | $\pm 14.0$ | $\pm 48$                                                                                             | $\pm 155$ | a)    |
+| 3 886                           | $\pm 1.5$                                                                                      | $\pm 4.2$  | $\pm 14.0$ | $\pm 48$                                                                                             | $\pm 155$ | b)    |
+| 3 886                           | $\pm 1.5$                                                                                      | $\pm 1.8$  | $\pm 3.5$  | $\pm 12$                                                                                             | $\pm 100$ |       |
+| 9 073                           | —                                                                                              | $\pm 15.0$ | $\pm 30.0$ | $\pm 110$                                                                                            | $\pm 350$ |       |
+| 11 700                          | $\pm 1.5$                                                                                      | $\pm 2.7$  | $\pm 5.8$  | $\pm 18$                                                                                             | $\pm 250$ | b)    |
+|                                 | $\pm 1.5$                                                                                      | $\pm 3.0$  | $\pm 7.0$  | $\pm 20$                                                                                             | $\pm 300$ |       |
+
+a) CCIR Recommendation 482 [2].
+
+b) CCIR Recommendation 399 [1].
+
+### 2.4 *Measuring procedures*
+
+The measuring procedures should comply with Recommendation G.228. Measurements must be carried out with the regulators, if any, not included and with the levels at the nominal value.
+
+*Note* - Some Administrations have chosen for groups and supergroups not being tested in conformance with Table 1/G.230 higher values of the load, but only for testing equipments with some margin to take account of the application where higher than nominal activity is to be expected.
+
+As a consequence, in such cases, higher noise limits have to be admitted than those indicated in Recommendation G.222, § 4).
+
+## **3 Through-connection filters**
+
+### 3.1 *Allocation of loading*
+
+For the measurement of noise produced by through-connection filters the values for the allocation of the conventional load according to Table 2/G.223 to the different filters are given in Table 4/G.230.
+
+TABLE 4/G.230
+
+| Filter for the basic   | Band of the noise spectrum (kHz) | level of the noise power (dBm0)   |
+|------------------------|----------------------------------|-----------------------------------|
+| Group                  | 12 to 252                        | + 6.1 ( $\hat{=}$ 60 channels)    |
+|                        | 60 to 108                        | + 3.3 ( $\hat{=}$ 12 channels)    |
+| Supergroup             | 60 to 1 296                      | + 9.8 ( $\hat{=}$ 300 channels)   |
+|                        | 316 to 552                       | + 6.1 ( $\hat{=}$ 60 channels)    |
+| Mastergroup            | 316 to 2 600                     | + 12.3 ( $\hat{=}$ 530 channels)  |
+| Supermastergroup       | 4 370 to 17 300                  | + 17.6 ( $\hat{=}$ 1800 channels) |
+| 15 supergroup assembly | 316 to 8 160                     | + 17.6 ( $\hat{=}$ 1800 channels) |
+
+*Note 1* - Group and supergroup through-connection filters require two measurements. One with "broadband loading" with components outside the pass-band, and an additional one with loading in the passband only. Since in these cases the number of transmitted channels is smaller than 240 (the range where the power level of the conventional load is not proportional to  $10 \log_{10} n$ , see § 2.1 of Recommendation G.223) the proportional part of the broadband loading transmitted in the passband gives a loading which is lower than the conventional load for 12 or 60 channels respectively.
+
+*Note 2* - The choice of the correct load figure for the measurement of the noise produced by the through-supermastergroup filter requires careful consideration bearing in mind that band limiting filters for a bandwidth complying with actual load conditions are not available.
+
+### 3.2 Measuring frequencies
+
+See § 2.2.
+
+### 3.3 Filter characteristics
+
+Highpass and lowpass filters complying with Table 2/G.228 and [3] can be used to limit the frequency of the noise spectrum. For bandstop filters, see Table 3/G.230.
+
+### 3.4 Measuring procedures
+
+The measuring procedure should comply with Recommendation G.228. For through-group and through-supergroup filters, two measurements have to be carried out in the appropriate measuring slots in the passband.
+
+## References
+
+- [1] CCIR Recommendation *Measurement of noise using a continuous uniform spectrum signal on frequency-division multiplex telephony radio-relay systems*, Vol. IX, Rec. 399, Dubrovnik, 1986.
+- [2] CCIR Recommendation *Measurement of performance by means of a signal of a uniform spectrum for systems using frequency-division multiplex telephony in the fixed satellite service*, Vol. IV, Rec. 482, Dubrovnik, 1986.
+- [3] CCIR Recommendation *Measurement of performance by means of a signal of a uniform spectrum for systems using frequency-division multiplex telephony in the fixed satellite service*, Vol. IV, Rec. 482, Table I, Dubrovnik, 1986.

marked/G/T-REC-G.241-198811-I_PDF-E/raw.md

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+
+
+![ITU logo](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features the letters 'ITU' in a bold, sans-serif font, superimposed on a stylized globe with intersecting lines.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**G.241**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+# **INTERNATIONAL ANALOGUE CARRIER SYSTEMS GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER - TRANSMISSION SYSTEMS** ---
+
+**PILOTS ON GROUPS, SUPERGROUPS, ETC.**
+
+**ITU-T Recommendation G.241**
+
+(Extract from the *Blue Book*)
+
+---
+
+## NOTES
+
+1 ITU-T Recommendation G.241 was published in Fascicle III.2 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+### Recommendation G.241
+
+## PILOTS ON GROUPS, SUPERGROUPS, ETC.
+
+*(amended at Geneva, 1964; further amended)*
+
+### 1 Use of pilots
+
+Experience has shown that, without the use of a group pilot transmitted throughout a group link, adequate stability of the channels of individual group links cannot be guaranteed in spite of the care given to the maintenance of the carrier systems on which they are routed.
+
+It may be necessary, in the first place, to place an automatic regulator, controlled by the pilot, at the end of some of the group sections forming the group link to compensate for inevitable variations in attenuation on each of the sections. This regulator is not, of course, designed to correct automatically for faults.
+
+It is desirable for the regulator to have a range of at least  $\pm 4$  dB. While no maximum range is specified, note should be taken that too great a range can prove unsatisfactory, e.g. due to noise or the masking of faults. A maximum range of approximately  $\pm 7$  dB has been found satisfactory by some Administrations.
+
+An alarm should be given when the amplitude of the pilot at the input of the regulator departs from its nominal value by more than  $\pm 4$  dB. The conditions governing the use of these regulators are given in Recommendation M.160 [1].
+
+It is also necessary to provide for measuring the level of the group pilot at the ends of group sections where it is not planned to use a regulator. In these cases, too, an alarm should be given when the level of the pilot departs from its nominal value by more than  $\pm 4$  dB.
+
+Precisely similar considerations apply to the use of supergroup, mastergroup and supermastergroup pilots, and also to the use of basic 15-supergroup assembly pilots.
+
+*Note* - When a group is through-connected from a cable section (on coaxial or symmetric pairs) to an open-wire line, transmission of the group pilot over the open-wire line, which is an advantage as regards maintenance of the complete group can, to a certain extent, facilitate "tapping" of conversations by means of radio receivers of a particular type in the territory traversed by the open-wire line. However, this risk of "tapping" is less than the similar risk arising from inadequate suppression of the carrier, because the frequency of the group pilot is more remote from the nearby carrier frequency, so that the quality of the overheard conversation would be necessarily degraded.
+
+### 2 Nominal characteristics of pilots (group, supergroup, etc.)
+
+When group, supergroup, etc., pilots are considered necessary, they should be permanently transmitted.
+
+The frequency and the level of these pilots are shown in Table 1/G.241.
+
+TABLE 1/G.241
+
+#### **Frequency and level of pilots**
+
+| Pilot for                            | Frequency (kHz)                                                                 | Absolute power level at a zero relative level point (dBm0) |
+|--------------------------------------|---------------------------------------------------------------------------------|------------------------------------------------------------|
+| Basic group                          | 84.080 <sup>a)</sup><br>84.140 <sup>b)</sup><br>104.080 <sup>a), b), c)</sup>   | —20<br>—25<br>—20                                          |
+| Basic supergroup                     | 411.860 <sup>a)</sup><br>411.920 <sup>a), c)</sup><br>547.920 <sup>a), b)</sup> | —25<br>—20<br>—20                                          |
+| Basic mastergroup                    | 1 552                                                                           | —20                                                        |
+| Basic supermastergroup               | 11 096                                                                          | —20                                                        |
+| Basic 15-supergroup assembly (No. 1) | 1 552 <sup>d)</sup>                                                             | —20                                                        |
+
+a) The group pilots 84.080 and 84.140 kHz and the supergroup pilots 411.860 and 411.920 kHz are used over groups and supergroups transmitting telephone channels and, in some cases, wide spectrum signals (data, facsimile, etc.). For each group (or supergroup) the two pilots at 84.080 and 84.140 kHz (or 411.860 and 411.920 kHz) should be transmitted simultaneously. However, only one of these two pilots need be used if there is agreement between the Administrations concerned (including the Administrations of transit countries).
+
+It is now apparent that transmission of wide spectrum signals (data, facsimile, etc.) may demand use of the pilots 104.080 kHz and 547.920 kHz instead of those previously used. These latter pilots may also be used on groups and supergroups carrying only telephone channels. The choice of pilots to be used is a matter of agreement between the Administrations concerned (including the Administrations of transit countries).
+
+b) However, the use of the pilots at 104.080 and 547.920 kHz might lead to the following difficulties:
+
+- 1) The group pilot at 104.080 kHz is incompatible with the line pilots situated at 4 kHz from one end of a group, which are to be found in the following systems:
+  - open-wire systems using frequency allocation 1 as shown in Figure 1/G.311;
+  - symmetric-pair systems using variant B as shown in Figure 5/G.322, especially the transistorized system described in Recommendation G.323.
+- 2) If the frequency allocation in the supergroup comprises groups A-E in accordance with Figure 2c/G.322 and 3/G.322, a supergroup pilot at 547.92 kHz will appear at frequency 103.92 kHz in group A. This frequency is liable to cause difficulties when group A is used for telephony. To avoid any disturbance, it might be necessary to introduce new routing restrictions.
+- 3) Difficulties would arise if these pilots were used on groups having terminal equipment with carrier frequency spacing of 6 kHz in accordance with Recommendation G.234, unless one further channel is abandoned in some groups.
+
+*Note* - These difficulties have already arisen in some cases with the pilots recommended at present.
+
+- 4) The choice of these frequencies would make it very difficult to use signalling at the virtual carrier frequency of a telephone channel in conformity with Recommendation Q.21 [2]. However, this point (and the preceding one) can be considered to be of purely national interest.
+
+c) The supergroup pilot at 411.920 kHz may also be used when the supergroup contains one or more groups transmitting wideband signals. It is impossible to route a group equipped with a pilot at 104.080 kHz in the position of group 3 in a supergroup with a pilot at 411.920 kHz.
+
+d) This pilot, after modulation of the 15-supergroup assembly to position No. 3 (see procedure 2 of Recommendation G.211, § 1), appears at the frequency of 11 096 kHz; this is identical with the frequency of the basic supermastergroup pilot.
+
+### 3 Tolerances on the sent level of pilots
+
+The following values are recommended for the frequency accuracy of the various pilots:
+
+|                                                   |             |
+|---------------------------------------------------|-------------|
+| Pilot frequency 84.080 kHz and 411.920 kHz .....  | $\pm 1$ Hz  |
+| Pilot frequency 84.140 kHz and 411.860 kHz .....  | $\pm 3$ Hz  |
+| Pilot frequency 104.080 kHz and 547.920 kHz ..... | $\pm 1$ Hz  |
+| Pilot frequency 1552 kHz <sup>1)</sup> .....      | $\pm 2$ Hz  |
+| Pilot frequency 11 096 kHz .....                  | $\pm 10$ Hz |
+
+*Note* - These tolerances can be taken as a basis for the specifications of the associated pilot receiving filters and stop filters, allowance also being made for recommendations concerning the accuracy of master oscillators.
+
+The following recommendations are made concerning the tolerances for the sent pilot level:
+
+- 1) The design of equipment should be such as to allow the sum of errors in the level of any group, etc., pilot as transmitted, due to finite level adjustment steps, change in number of groups supplied, and lack of adjustment facilities in individual groups, to be kept within  $\pm 0.1$  dB.
+- 2) The change in output level of the pilot generator with time (which is a factor included in equipment specifications) must not exceed  $\pm 0.3$  dB during the interval between two maintenance adjustments, e.g. in one month.
+- 3) To reduce pilot level variations with time, it is advisable to have a device to give an alarm when the variation at the generator output exceeds  $\pm 0.5$  dB, the zero of the warning device being aligned as accurately as possible with the lining-up level of the transmitted pilot.
+
+The attention of Administrations is drawn to the difficulty which could result from an appreciable reduction in the absolute power level of the pilot sent to line; such a reduction is liable to cause "near singing", resulting from the operation of the automatic gain-control amplifiers. It would be desirable to make arrangements for overcoming this difficulty if it should arise.
+
+### 4 Harmonics of pilots
+
+4.1 It is recommended that the levels of harmonics of group and supergroup pilots should not exceed the values given in Table 2/G.241. The point where these limits should be met is the distribution frame (or equivalent point) at the output of the next higher stage of modulation, e.g. the supergroup distribution frame in the case of the group pilot. Account should be taken of the change of frequency.
+
+TABLE 2/G.241  
+**Maximum level of harmonics of pilots**
+
+| Pilot      | Nominal frequency of pilot (kHz) | Maximum level of harmonics |                        |                              |
+|------------|----------------------------------|----------------------------|------------------------|------------------------------|
+|            |                                  | Second harmonics (dBm0)    | Third harmonics (dBm0) | Each higher harmonics (dBm0) |
+| Group      | 84.080 or 84.140                 | —73                        | —67                    | —75                          |
+| Group      | 104.080                          | —67<br>(see note)          | —67                    | —75                          |
+| Supergroup | 411.920 or 411.860               | —75                        | —73                    | —75                          |
+| Supergroup | 547.920                          | —67                        | —67<br>(see note)      | —75                          |
+
+*Note* - If the system includes 3-kHz spaced channels a maximum level of -73 dBm0 is recommended.
+
+<sup>1)</sup> This pilot, after modulation of the 15-supergroup assembly to position No. 3 (see procedure 2 of Recommendation G.211, § 1) appears at the frequency 11 096 kHz; this is identical with the frequency of the basic supermastergroup pilot.
+
+4.2 In the case of the pilot (1552 kHz) for a mastergroup, it is recommended that the level of the second harmonic of the pilot should not exceed - 50 dBm0 and the level of each other higher harmonic should not exceed - 75 dBm0 measured at the output of the next higher stage of modulation.
+
+4.3 In the case of the pilot (11 096 kHz) for a supermastergroup, it is recommended that the level of any harmonic should not exceed -75 dBm0 measured at the output of the next higher stage of modulation.
+
+4.4 In the case of the pilot (1552 kHz) for 15-supergroup assemblies, it is recommended that the level of the second harmonic should not exceed -50 dBm0, measured at the output of the supergroup translating equipment.
+
+Where the 15-supergroup assembly is not combined with other assemblies, there is no particular requirement on the level of the third and higher harmonics.
+
+Where the 15-supergroup assembly is combined with other assemblies, the level of the third and higher order harmonics should not exceed -75 dBm0, measured at the combined output.
+
+### 5 Protection of group, supergroup, etc., pilots against interference by noise
+
+Automatic regulators operated by group, supergroup, etc., reference pilots should be so designed that the interfering effect of noise does not exceed 0.02 dB for any significant period. If, for example, the regulator operates on the mean signal voltage, this corresponds to a long-term interfering signal of -20 dB relative to the pilot level. When the interference is of short duration compared with the time constant of the regulator, high levels of interference may be experienced without causing an error in regulation exceeding 0.02 dB.
+
+#### 5.1 *Group and supergroup pilots*
+
+If the pilot pick-off filter has a bandwidth of 50 Hz (25 Hz on each side of the nominal pilot frequency) the ratio between pilot and noise will always be considerably greater than 20 dB in the case of carrier systems over land-lines. This ratio is still respected if the unweighted power of the noise in a telephone channel reaches  $10^6$  pW at zero relative level (level of -30 dBm0), which very rarely occurs on radio-relay links conforming to the conditions of Recommendation G.441.
+
+In the case of very long group or supergroup links on such radio-relay links, the pilot-to-noise ratio will be smaller than 20 dB only for a period of less than some ten-thousandths of any month. In that case the resultant error in regulation will be negligible, as the duration of the very high-level noise will be short compared with the necessarily long time-constant of the regulator. In any case, such high-level bursts are not expected to occur with any significant frequency and the chief factor limiting the interference caused to a pilot by noise is therefore the effective bandwidth of the pick-off filter.
+
+#### 5.2 *Other pilots*
+
+Similar consideration applies also to mastergroup, supermastergroup and basic 15-supergroup assembly pilots. However, the bandwidth of the pick-off filter will certainly be greater than 50 Hz and more reliance will have to be placed on the relatively long time-constant of the regulator to minimize the effect of short-duration high-level noise.
+
+*Note 1* - Recommendations concerning the protection and suppression of pilots at certain points appear in Recommendation G.243.
+
+*Note 2* - When use is made of procedure 1, described in Recommendation G.211, the spacing between the 11 096 kHz supermastergroup pilot and the audio-frequencies transposed in the adjacent channels is 28 kHz and 60 kHz.
+
+This same spacing is only 4 kHz with procedure 2, described in Recommendation G.211.
+
+In view of this, a supermastergroup regulator is not necessarily suitable for the transmission of a 15-supergroup assembly over a supermastergroup link.
+
+### 6 Protection of group or supergroup pilots against signals transmitted in telephone channels
+
+This protection is ensured in the channel and group translating equipment, in accordance with Recommendation G.232, § 12 and the Recommendation cited in [4].
+
+### 7 Protection of group or supergroup link pilots transmitting wide-spectrum signals
+
+7.1 To protect the group or supergroup link pilots (used to establish wideband circuits) against other wide-spectrum signals (data, facsimile, etc.), it is recommended that the power spectrum emitted about the pilot frequency be limited in the equipment which transmits these signals. This limitation is so calculated that the group or supergroup regulators installed on the link will not receive interference of more than 0.1 dB, and the values to be specified therefore depend on the characteristics of the regulators (passband of the pilot filters, regulation operating time constant).
+
+With regard to continuous spectrum signals, the spectrum density in the band  $f_0 \pm 25$  Hz must not exceed  $-70$  dBm0/Hz.
+
+The limits to be set for discrete components are fixed by the Figure 1/G.241 which allows for the existing characteristics of regulators activated by pilots at frequencies ( $f_0$ ) of 84.08 or 104.08 kHz in group links and of 411.92 or 547.92 kHz in supergroup links.
+
+Such a limitation of the transmitted spectrum, obtained by a suitable choice of modulation characteristics, dispenses with the need to insert a bandstop filter to protect the pilot (such a filter would introduce harmful distortion of the group delay). However, if it is not possible to impose such a limitation on the emitted spectrum by this method, or if no guarantee can be secured that this limitation will be respected, the Administrations operating the transmission networks should, in order to protect the group regulators against interference caused by the wideband signals, insert bandstop filters (which would produce the smallest possible distortion to the group delay) at the input of the group or supergroup links under consideration, producing the limitation indicated by Figure 1/G.241.
+
+*Note* - The general problem of protecting the reference pilots from interference when a group or supergroup is used for the transmission of wide-spectrum signals arises because the protection of these pilots is not always secured by means of a band-clearing filter connected immediately before injection of the pilot. In normal telephone use such protection may depend upon the existence of filters in telephony channel or group translating equipment; however, these may not be in circuit when a wideband transmission path is set up.
+
+![Figure 1/G.241: A graph showing the maximum permissible level of discrete frequency components of wide-spectrum signals in the vicinity of group and supergroup pilot frequencies. The y-axis is 'Level of frequency component' in dBm0, ranging from -60 to -10. The x-axis is 'Frequency difference from f0 (pilot frequency)' in Hz, ranging from -300 to 300. The graph shows a sharp dip to -60 dBm0 at f0, with levels rising to -10 dBm0 at ±250 Hz and remaining constant at -10 dBm0 from ±250 Hz to ±300 Hz. The curves are symmetric around f0. A label 'CCITT - 41160' is present in the bottom right corner of the graph area.](023b142f90e1253702ac88b18380d3ec_img.jpg)
+
+Figure 1/G.241: A graph showing the maximum permissible level of discrete frequency components of wide-spectrum signals in the vicinity of group and supergroup pilot frequencies. The y-axis is 'Level of frequency component' in dBm0, ranging from -60 to -10. The x-axis is 'Frequency difference from f0 (pilot frequency)' in Hz, ranging from -300 to 300. The graph shows a sharp dip to -60 dBm0 at f0, with levels rising to -10 dBm0 at ±250 Hz and remaining constant at -10 dBm0 from ±250 Hz to ±300 Hz. The curves are symmetric around f0. A label 'CCITT - 41160' is present in the bottom right corner of the graph area.
+
+FIGURE 1/G.241
+
+Maximum permissible level of discrete frequency components of wide-spectrum. (group and supergroup) signals in the vicinity of group and supergroup pilot frequencies
+
+The use of a group containing the supergroup pilot should always be avoided (see Recommendation H.14 [5]). This means that no special suppression of the wideband signal has to be provided in the group for the purpose of the supergroup pilot.
+
+#### 7.2      *"Delayed transfer"*
+
+It may be imagined that some data-processing devices record the wideband signal in the form in which it reaches them from the network, and then retransmit this recorded signal over the network on a group or supergroup link. On this assumption, the pilot will be recorded at the same time as the signal; it will therefore be retransmitted with it and will then interfere with the pilot injected on the new link. In this case, the recording or retransmitting device should be equipped with a frequency-stop filter providing an attenuation of at least 40 dB at the pilot frequency under consideration, and contributing as little distortion as possible to the group delay. However, if Administrations have inserted, at the input of wideband links, the cut-off filter for protection of the pilot as mentioned in § 7.1 above, the aim sought in the present paragraph will have been reached and the frequency-stop filter will be superfluous.
+
+#### 7.3      *Multipoint links*
+
+In the case of multipoint links on tree-shaped networks, the pilot should be blocked at each confluence point on all the confluent links except one, by means of a filter like the one mentioned in § 7.2 above, leaving only one pilot protected against interference from the other pilots. It is also possible to block the pilots on all the confluent links and to transmit a locally produced pilot beyond that point of the link.
+
+## **References**
+
+- [1]      CCITT Recommendation *Stability of transmission*, Vol. IV, Rec. M.160.
+- [2]      CCITT Recommendation *8-channel terminal equipments*, Orange Book, Vol. III-1, Rec. G.234, ITU, Geneva, 1977.
+- [3]      CCITT Recommendation *Systems recommended for out-band signalling*, Vol. VI, Rec. Q.21.
+- [4]      CCITT Recommendation *8-channel terminal equipments*, Orange Book, Vol. III-1, Rec. G.234, § f), ITU, Geneva, 1977.
+- [5]      CCITT Recommendation *Characteristics of group links for the transmission of wide-spectrum signals*, Vol. III, Rec. H.14.

marked/G/T-REC-G.333-198811-I_PDF-E/raw.md

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+
+
+![ITU logo](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features a globe with a lightning bolt superimposed on it, and the letters 'ITU' in a bold, sans-serif font.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**G.333**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+# **INTERNATIONAL ANALOGUE CARRIER SYSTEMS INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES** ---
+
+**60 MHz SYSTEMS ON STANDARDIZED  
+2.6/9.5 mm COAXIAL CABLE PAIRS**
+
+**ITU-T Recommendation G.333**
+
+(Extract from the *Blue Book*)
+
+---
+
+## NOTES
+
+1 ITU-T Recommendation G.333 was published in Fascicle III.2 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## 60 MHz SYSTEMS ON STANDARDIZED 2.6/9.5 mm COAXIAL CABLE PAIRS
+
+## Introduction
+
+This Recommendation defines a coaxial cable pair system providing 10 800 telephone channels in the frequency band of approximately 4 to 60 MHz. The system may be used for the transmission of six television signals without any telephone signal or for a mixed transmission of telephone and television signals. The nominal repeater spacing is approximately 1.5 km and can be obtained by dividing the repeater spacing of 12 MHz systems by three.
+
+## 1 Line frequencies
+
+The allocation of line frequencies for telephony should be in conformity with one of the two plans given below.
+
+### 1.1 Plan 1 - Line-frequency allocation and modulation stages for 60-MHz systems (Figure 1/G.333)
+
+![Figure 1/G.333: Line-frequency allocation recommended for 60 MHz systems on 2.6/9.5 mm coaxial cable pairs using Plan 1. The diagram shows a frequency spectrum from 0 to 70,000 kHz. It identifies the 'Basic supermastergroup' (8516 to 12388 kHz) and 13 'Supermastergroup No.' blocks. Above each block is a 'Carrier frequency' indicated by an arrow and a formula: 16720 (440 x 38), 25520 (440 x 58), 30360 (440 x 69), 35200 (2380 x 15), 39600 (2200 x 18), 44000 (2200 x 20), 48400 (2200 x 22), 55000 (2200 x 25), 59400 (2200 x 27), 63800 (2200 x 29), and 68200 (2200 x 31). The bottom axis is labeled 'Frequency' and 'CCITT - 45641'.](87658d45f2d2f009cbb9cd1079519cb5_img.jpg)
+
+Figure 1/G.333: Line-frequency allocation recommended for 60 MHz systems on 2.6/9.5 mm coaxial cable pairs using Plan 1. The diagram shows a frequency spectrum from 0 to 70,000 kHz. It identifies the 'Basic supermastergroup' (8516 to 12388 kHz) and 13 'Supermastergroup No.' blocks. Above each block is a 'Carrier frequency' indicated by an arrow and a formula: 16720 (440 x 38), 25520 (440 x 58), 30360 (440 x 69), 35200 (2380 x 15), 39600 (2200 x 18), 44000 (2200 x 20), 48400 (2200 x 22), 55000 (2200 x 25), 59400 (2200 x 27), 63800 (2200 x 29), and 68200 (2200 x 31). The bottom axis is labeled 'Frequency' and 'CCITT - 45641'.
+
+FIGURE 1/G.333
+
+#### Line-frequency allocation recommended for 60 MHz systems on 2.6/9.5 mm coaxial cable pairs using Plan 1
+
+In this plan, the basic block for interconnection is the supermastergroup of 8516 to 12 388 kHz recommended by the CCITT in Recommendation G.211. It thus contains the three mastergroups constituting the basic supermastergroup, but the same frequency band could contain a 15-supergroup assembly (see Plan 2).
+
+All modulation and demodulation between the basic supermastergroup and the line-frequency band is carried out in one modulation step. The carrier frequencies for this modulation are shown in Figure 1/G.333. They are all low multiples of 440 kHz, or multiples of 2200 kHz. These two fundamental frequencies are both closely related to frequencies normally used in the 12-MHz systems.
+
+The extraction of blocks directly from the line-frequency band can be carried out individually for the four lowest supermastergroups. Higher supermastergroups can only be extracted in the form of an assembly of four supermastergroups. This method is chosen to save frequency bandwidth.
+
+The two lowest supermastergroups are identical with supermastergroups Nos. 2 and 3 shown in Figure 1/G.332.
+
+![Diagram showing line-frequency allocation for 60 MHz systems. It displays 15-supergroup assemblies numbered 2 through 13, with their respective frequency bands and carrier frequencies. The x-axis represents frequency in kHz from 0 to 70,000. Assembly 2 is shown as a shaded block from 312 to 4028 kHz. Assemblies 3-13 are shown as triangles with specific frequency ranges. Carrier frequencies are indicated above the assemblies with their respective modulation parameters in parentheses.](e94f3bbb6f7501b9a1344dd0210e5dd8_img.jpg)
+
+| Assembly No. | Frequency Range (kHz) | Carrier Frequency (kHz) | Modulation Parameters |
+|--------------|-----------------------|-------------------------|-----------------------|
+| 2            | 312 - 4028            | 8432                    | (124 x 68)            |
+| 3            | 4404 - 8620           | 12648                   | (124 x 102)           |
+| 4            | 8120 - 12336          | 25520                   | (440 x 58)            |
+| 5            | 8620 - 13184          | 30360                   | (440 x 69)            |
+| 6            | 16900 - 21740         | 35200                   | (2200 x 16)           |
+| 7            | 18024 - 22864         | 39600                   | (2200 x 18)           |
+| 8            | 21740 - 26580         | 44000                   | (2200 x 20)           |
+| 9            | 22864 - 27264         | 48400                   | (2200 x 22)           |
+| 10           | 26580 - 31664         | 55000                   | (2200 x 25)           |
+| 11           | 30380 - 35064         | 59400                   | (2200 x 27)           |
+| 12           | 35064 - 39780         | 63800                   | (2200 x 29)           |
+| 13           | 39780 - 42664         | 68200                   | (2200 x 31)           |
+
+Diagram showing line-frequency allocation for 60 MHz systems. It displays 15-supergroup assemblies numbered 2 through 13, with their respective frequency bands and carrier frequencies. The x-axis represents frequency in kHz from 0 to 70,000. Assembly 2 is shown as a shaded block from 312 to 4028 kHz. Assemblies 3-13 are shown as triangles with specific frequency ranges. Carrier frequencies are indicated above the assemblies with their respective modulation parameters in parentheses.
+
+FIGURE 2/G.333
+
+#### **Line-frequency allocation recommended for 60 MHz systems on 2.6/9.5 mm coaxial cable pairs using Plan 2**
+
+According to Plan 2, eleven assemblies of 15 supergroups are translated into the frequency band 8620 to 12 336 kHz which lies within the frequency band of the basic supermastergroup.
+
+The 15-supergroup assemblies transmitted to line and numbered 3 to 13, are obtained in the same way as the corresponding supermastergroups of Plan 1 above. The assembly of 15 supergroups numbered 2 is obtained by modulation of a 15-supergroup assembly in the band 312-4028 kHz, the carrier frequency being 68 x 124 = 8432 kHz.
+
+The facilities for extracting blocks directly from the basic-frequency band are identical to those of Plan 1.
+
+The two lowest 15-supergroup assemblies are identical with the second and third 15-supergroup assemblies in Figure 4/G.332.
+
+*Note* - It is understood that Plan 1 would be chosen in those countries whose national networks are based upon the use of basic mastergroup and supermastergroups, whereas Plan 2 could be adopted in those countries whose national networks are based on the use of supergroup assemblies only.
+
+In international connections between countries using the same plan in their national networks, i.e. both using Plan 1 or both using Plan 2, the plan common to these two countries would naturally be used.
+
+However, in international connections between countries which use different plans in their national networks and in the absence of any special agreement, between the interested Administrations, including Administrations of transit countries, use of Plan 1 is recommended.
+
+## **2 Pilots and additional measuring frequencies**
+
+### **2.1 Line-regulating pilots**
+
+The CCITT recommends that 61 160 kHz should be used for the main line-regulating pilot on all regulated-line sections crossing a frontier. The main line-regulating pilot is used for automatic temperature correction of the cable attenuation.
+
+In any regulated-line section crossing a frontier, it is recommended that in both directions of transmission the Administration on the transmitting side should permanently transmit so as to provide, for example, for additional regulation, one or more auxiliary line-regulating pilots chosen by the Administration on the receiving side from the following list:
+
+4287 kHz, 12 435 kHz, 22 372 kHz and 40 920 kHz.
+
+The power level of these pilots should be regulated, at the output of the transmit amplifier, to a nominal value of -10 dBm0. The harmonics of the 4287, 12 435, 22 372 kHz pilots should each have a level not higher than -70 dBm0.
+
+The frequency stability recommended for pilots is better than  $\pm 1 \times 10^{-5}$ .
+
+The tolerances for this level are the same as those given in Recommendation G.332, § 2.1.
+
+### 2.2 *Frequency comparison pilots*
+
+Since international comparison of frequencies is rarely carried out, the CCITT recommends that Administrations choose one of the following two frequencies:
+
+- 4200 kHz, which is a multiple of 300 kHz and a neighbouring value of 4400 kHz,
+- 8316 kHz ( $27 \times 308$  kHz) which can easily be included in the free intervals of the two frequency arrangements proposed (Figures 1/G.333 and 2/G.333).
+
+It is recommended that this pilot be transmitted at a power level of -10 dBm0. The harmonics of the frequency comparison pilots should each have a level not higher than -70 dBm0.
+
+### 2.3 *Additional measuring frequencies*
+
+Frequencies that may be used as additional measuring frequencies are given in Table 1/G.333.
+
+The power level of these additional measuring pilots should be adjusted at the output of the transmit amplifier, to obtain a nominal value of the line pilot of -10 dBm0. The harmonics of additional measuring frequencies below 30 MHz should each have a level at this point not higher than -70 dBm0.
+
+The frequency stability recommended is better than **Error! Reference source not found.**  $1 \times 10^{-5}$ .
+
+The additional measuring pilots should not be permanently transmitted. They will be transmitted only for as long as is necessary for actual measurement purposes. This does not apply when the frequency is used as a line pilot.
+
+### 2.4 *Band reserved for monitoring and fault-tracing signals*
+
+These signals should be below the 4200 kHz frequencies comparison pilot.
+
+## 3 **Hypothetical reference circuit**
+
+### 3.1 *General considerations*
+
+The reference circuit has to reflect what is expected to be the practical application of the system. The spacing of main stations is the same as in earlier systems, e.g. the 12 MHz system. A length of 2500 km, divided into 9 sections each of 280 km with a total of 10 main stations, has therefore been adopted.
+
+### 3.2 *Modulation*
+
+With either of the line-frequency allocations recommended in § 1 above, five modulation stages are generally needed to place a particular channel in its position in the line-frequency band.
+
+On the above basis, the hypothetical reference circuits shown in Figures 3/G.333 and 4/G.333 are recommended by the CCITT.
+
+### 3.3 *Direct through-connection at line frequencies*
+
+It was agreed that direct through-connection was envisaged not for points intermediate between the main stations as defined above, but rather at these stations themselves so that demodulation would be avoided. While this would be an advantage from the point of view of the amount of modulation equipment, it would involve more severe requirements on line equipment.
+
+TABLE 1/G.333
+
+| Frequency (see Note 1)<br>kHz<br>(1) | Frequency (see Note 2)<br>kHz<br>(2)        |
+|--------------------------------------|---------------------------------------------|
+|                                      | 4 200 (see Note 3)<br>or 4 287 (see Note 4) |
+| 8 472                                | 8 316 (see Note 3)                          |
+| 12 678                               |                                             |
+| 17 488                               | 22 302 (see Note 5)                         |
+|                                      | 22 372 (see Note 4)                         |
+| 26 922                               |                                             |
+| 31 322                               |                                             |
+| 35 722                               |                                             |
+| 40 122 (see Note 6)                  | 40 920 (see Note 4)                         |
+| 42 322                               |                                             |
+| 46 722                               |                                             |
+| 51 122                               |                                             |
+| 55 522                               | 59 922                                      |
+
+*Note 1* - (Applies to all frequencies in column 1.) Use of these frequencies will ensure that interference is not caused to the following fine-regulated section. They can therefore be transmitted at any time.
+
+*Note 2* - (Applies to all frequencies in column 2.) These frequencies will be provided when the Administration at the receiving end so requests. They should not be sent without the agreement of the Administration at the receiving end.
+
+*Note 3* - These frequencies may also be used as frequency-comparison pilots.
+
+*Note 4* - In accordance with Recommendation M.500 [1], Administrations choosing to use these frequencies must ensure that interference is not caused to a following line-regulated section which may be using these frequencies as line pilots.
+
+*Note 5* - If the frequency 22 372 kHz is used as an auxiliary line regulating pilot it should be ensured that no disturbance is caused to this pilot.
+
+*Note 6* - It may be unnecessary to use this frequency if an adjacent auxiliary line-pilot is used for regulation.
+
+![Diagram of a hypothetical reference circuit for 60 MHz system on 2.6/9.5 mm coaxial cable pairs (Plan 1).](fc46871d72c65d3381d9201646d23439_img.jpg)
+
+The diagram shows a sequence of stations: Station 1, Station 2, Station 3, Station 4, and Station 10. Each station is represented by a set of rectangular blocks. Station 1 has 5 blocks, Station 2 has 2, Station 3 has 4, Station 4 has 8, and Station 10 has 5. The blocks are connected by lines. Some blocks have diagonal hatching. A dashed line connects Station 4 and Station 10. The text 'CCITT - 45660' is at the bottom right.
+
+Legend:
+
+- Channel translation to form a basic group.
+- ▨ Group translation to form a basic supergroup.
+- ▤ Supergroup translation to form a basic mastergroup.
+- ▦ Mastergroup translation to form a basic supermastergroup.
+- ▧ Supermastergroup translation to the line-frequency allocation (except for supermastergroup 3).
+
+Diagram of a hypothetical reference circuit for 60 MHz system on 2.6/9.5 mm coaxial cable pairs (Plan 1).
+
+*Note* – Stations 5 and 8 are identical with Station 2 – Stations 6 and 9 are identical with Station 3 – Station 7 is identical with Station 4.
+
+FIGURE 3/G.333
+
+**Diagram of a hypothetical reference circuit for 60 MHz system on 2.6/9.5 mm coaxial cable pairs (Plan 1)**
+
+![Diagram of a hypothetical reference circuit for 60 MHz system on 2.6/9.5 mm coaxial cable pairs (Plan 2).](49ee89a1d5852ab005dbbab6de09a8a6_img.jpg)
+
+The diagram shows a sequence of stations: Station 1, Station 2, Station 3, Station 4, and Station 10. Each station is represented by a set of rectangular blocks. Station 1 has 5 blocks, Station 2 has 2, Station 3 has 4, Station 4 has 8, and Station 10 has 5. The blocks are connected by lines. Some blocks have diagonal hatching, and some have a dot in the center. A dashed line connects Station 4 and Station 10. The text 'CCITT - 45661' is at the bottom right.
+
+Legend:
+
+- Channel translation to form a basic group.
+- ▨ Group translation to form a basic supergroup.
+- ▤ Supergroup translation to form a basic 15-supergroup assembly in the band 312-4028 kHz.
+- ⊙ Modulation of the basic 15-supergroup assembly to place it within the frequency band of the basic supermastergroup or, in the case of assembly No. 2, within the line-frequency band.
+- ▧ Modulation of the 15-supergroup assembly situated within the frequency band of the basic supermastergroup to obtain the line-frequency allocation.
+
+Diagram of a hypothetical reference circuit for 60 MHz system on 2.6/9.5 mm coaxial cable pairs (Plan 2).
+
+*Note* – Stations 5 and 8 are identical with Station 2 – Stations 6 and 9 are identical with Station 3 – Station 7 is identical with Station 4.
+
+FIGURE 4/G.333
+
+**Diagram of a hypothetical reference circuit for 60 MHz system on 2.6/9.5 mm coaxial cable pairs (Plan 2)**
+
+It has, however, been found possible to use restricted through-connection at main repeater stations with equipment designed to meet the normal noise objectives defined in connection with a hypothetical reference circuit for the 60-MHz system on coaxial pairs (see Figure 3/G.333) without incurring a noise penalty.
+
+The necessary restrictions are as follows:
+
+- 1) The frequency band containing supermastergroups 6 to 9 inclusive may be directly through-connected over a total length which must not exceed 830 km, but the adjacent frequency bands in the sections concerned must be homogeneous sections which are not abnormally long.
+- 2) It is in principle also possible to use direct through-connection for the frequency band containing supermastergroups 2-5 inclusive provided that the adjacent frequency bands containing supermastergroups 6-9 and 10-13 are transmitted on normal length homogeneous sections. In practice it may be necessary to restrict the through-connection to supermastergroups which have a sufficiently low impedance mismatch effect (§ 7) to permit the extension without excessive accumulation of attenuation roll effect.
+
+## 4 Circuit noise
+
+It is recommended that the system be designed on the basis of Recommendation G.222, i.e. in such a way as to obtain a mean psophometric power of about 3 pW per km of line, on the worst telephone channel having the same composition as the 2500-km hypothetical reference circuit.
+
+## 5 Matching of repeater impedances and line impedance
+
+A value of 65 dB is recommended for the magnitude  $N$  defined in Recommendation G.332, § 5.
+
+## 6 Interconnection
+
+*Levels in a main station* (see Recommendation G.213)
+
+When one part of the frequency band is transmitted without demodulation, the same value of -33 dBr is recommended at the output of the direct through-connection filter.
+
+The level at the repeater output on the highest channel should be  $-19 \pm 1$  dBr.
+
+*Note* - Values for pre-emphasis ranging from 7 to 10 dB are commonly used.
+
+## 7 Power-feeding and alarm systems
+
+### 7.1 *Power feeding across a frontier*
+
+In the absence of a special agreement between the Administrations concerned with a power-feeding section crossing a frontier, it is recommended that each Administration power-feed only those repeater stations in its own country. Many Administrations used looped power-feeding on the two sides of a power-feeding station, half of each of the sections between this station and the adjacent power stations being so fed; they can close the loop at their frontier stations. Agreements will be necessary if, for example, the frontier is very far from the mid-point between the two nearest feeding stations, or if the Administrations concerned use looped power-feeding on the entire section between two feeding stations.
+
+If repeater stations in a country are fed from another country, special precautions will be required to protect the staff working on the cables.
+
+### 7.2 *Remote power-feeding systems*
+
+Although CCITT does not recommend the use of a specific remote power-feeding system for the 60-MHz coaxial line system, in practice only the constant current d.c. feeding via the inner conductors of the two coaxial pairs of a system is used.
+
+The 60-MHz coaxial cable system may be subject to induced voltages and currents caused by lightning, power lines, railways, etc.
+
+Precautions must be taken to protect the staff from any possible danger arising from the normal operating voltages and remote power-feed currents as well as from the induced voltages and currents.
+
+Many national Administrations have issued detailed rules and regulations for the protection of persons. It is obligatory in most cases to meet these rules and regulations. In addition the CCITT Directives [2] give guidance on these problems.
+
+Precautions are also needed for the protection of the equipment against induced voltages and currents. The equipment should therefore be designed in such a way that it passes the tests specified in Recommendation K.17 [3].
+
+### 7.3 *Supervision and alarms in a frontier section*
+
+This should be governed by agreement between the Administrations concerned. In particular, it is necessary at the points of interconnection between two systems that if frequencies are used for monitoring or for locating faults, they be attenuated to a level of -50 dBm0 on the receiving sides to prevent any disturbance to similar frequencies used in the system farther down the line.
+
+*Note* - Frequencies sent only over a system already withdrawn from service because of a fault may be selected by each Administration on the national level.
+
+## 8 **Use of 60-MHz systems for television transmission**
+
+### 8.1 *General remarks*
+
+In § 8 all additional requirements are summarized which are recommended in the case of television transmission on the 60-MHz system. The characteristics of the television signal in the first intermediate frequency allocation (transmit side conditions) are dealt with in Recommendation J.77 [4].
+
+### 8.2 *Circuit noise*
+
+If the 60-MHz system is used for television transmission on the basis of a hypothetical reference circuit (HRC) of a length of 2500 km, the mean value of the thermal noise of the line should not exceed 1 pW0p/km. Experience has shown that a mean value of 1.5 pW0p/km total noise of the line is sufficient when measured according to normal telephone conditions. In making through-connections between homogeneous sections of an HRC, different transmission bands may be used. As different transmission bands give different distributions of basic noise and intermodulation noise, it seems justified to assign noise limits which are average values within the whole transmission band, i.e., among the five measuring channels recommended in Recommendation G.228.
+
+### 8.3 *Matching of repeater impedances and line impedance*
+
+For television programme transmission a value of at least 72 dB for the magnitude  $N$ , defined in Recommendation G.332, § 5, has been agreed to in the band occupied by television signals.
+
+### 8.4 *Number, nature and position of line television channels*
+
+Television signals may be transmitted without any other wanted signals or simultaneously with telephone channels. In the first case, there are six television channels. In the case of mixed transmission, the attention of Administrations is drawn to the fact that, if there are more than two television channels, harmful interference may occur between the two types of signal, especially interference to telephony from television. This clause is therefore limited to cases where the number of channels is less than or equal to two.
+
+Whether or not the 60 MHz system is allocated wholly or partially to television, television channels are capable of transmitting the signals of all television systems defined by the CCIR having a video bandwidth not exceeding 6 MHz.
+
+When a 60 MHz system is used entirely for television, it can provide six television channels, arranged in three pairs each of which extends over the bandwidth of four supermastergroups. The line-frequency allocation is shown in Figure 5/G.333.
+
+When transmission is mixed, a distinction should be made according to whether the number of television channels is two or one.
+
+If there are two, the use of channels 3 and 4 is recommended.
+
+In the case of a single television channel, there are two possibilities:
+
+- first alternative: channel 3 or channel 4, the choice being immaterial;
+- second alternative: channel 1.
+
+The first alternative has the advantage of low group delay distortion and is suitable for long links. The second allows the use of simple modulation equipment, if modulation method No. 2 is applied (see Note 1 below). On the other hand, it has the disadvantage of a higher group delay distortion, requiring the use of correctors whose complexity increases with the length of exceeds a certain limit.
+
+*Note 1* - Two recommended modulating methods are shown in Annex A.
+
+*Note 2* - A television channel-pair pilot can be provided at the mean of the carrier frequencies of each television channel pair, i.e. 12 760 kHz ( $4 \times 3190$  kHz), 31900 kHz ( $10 \times 3190$  kHz) and 51 040 kHz ( $16 \times 3190$  kHz). It is recommended that these pilots be transmitted at a power level of -10 dBm0. The harmonics of the pilot 12 760 kHz should have a level of not higher than -70 dBm0; the level of the harmonics of the other pilots should not exceed -50 dBm0.
+
+![Diagram showing the line-frequency allocation of six television channels on the 60 MHz system. The diagram illustrates the frequency bands for channels 1 through 6, with specific frequency markers in kHz. Channel 1 starts at 5287 kHz and ends at 11287 kHz. Channel 2 starts at 11287 kHz and ends at 20233 kHz. Channel 3 starts at 24427 kHz and ends at 30427 kHz. Channel 4 starts at 30427 kHz and ends at 39373 kHz. Channel 5 starts at 43567 kHz and ends at 49567 kHz. Channel 6 starts at 49567 kHz and ends at 58513 kHz. The diagram also includes a reference 'CCITT - 45670'.](8ee3b76dd49f31624d287885bc2c81ee_img.jpg)
+
+Diagram showing the line-frequency allocation of six television channels on the 60 MHz system. The diagram illustrates the frequency bands for channels 1 through 6, with specific frequency markers in kHz. Channel 1 starts at 5287 kHz and ends at 11287 kHz. Channel 2 starts at 11287 kHz and ends at 20233 kHz. Channel 3 starts at 24427 kHz and ends at 30427 kHz. Channel 4 starts at 30427 kHz and ends at 39373 kHz. Channel 5 starts at 43567 kHz and ends at 49567 kHz. Channel 6 starts at 49567 kHz and ends at 58513 kHz. The diagram also includes a reference 'CCITT - 45670'.
+
+FIGURE 5/G.333
+
+**Line-frequency allocation of six television channels on the 60 MHz system**
+
+### 8.5 *Pilots and additional measuring frequencies*
+
+Those pilots and additional measuring frequencies (mentioned in § 2), falling in gaps between TV channels, can be used.
+
+## ANNEX A
+
+(to Recommendation G.333)
+
+### **Modulation methods for television transmission on the 60-MHz system**
+
+Two recommended modulating methods are shown in Figure A-1/G.333 and Figure A-2/G.333 respectively. The modulation methods are compatible with those of the 18-MHz system (see Annex A to Recommendation G.334).
+
+![Diagram of modulation method 1 for the 60 MHz system. It shows six channels (1-6) with their respective frequency bands and sub-carrier frequencies. Channel 1: 5 287 - 11 287 kHz; Channel 2: 11 287 - 20 233 kHz; Channel 3: 24 427 - 30 427 kHz; Channel 4: 30 427 - 39 373 kHz; Channel 5: 43 567 - 49 567 kHz; Channel 6: 49 567 - 58 513 kHz. Above the channels, a series of trapezoidal shapes represent the modulation envelope, with vertical dashed lines indicating sub-carrier frequencies: 8 097, 11 043, 19 140 (6 x 3190), 41 470 (13 x 3190), 44 660 (14 x 3190), and 82 940 (26 x 3190). The label '60 MHz system' is on the left, and 'CCITT - 45 681' is on the right.](d48475a25698b1c0592e4cfe07138f2a_img.jpg)
+
+Diagram of modulation method 1 for the 60 MHz system. It shows six channels (1-6) with their respective frequency bands and sub-carrier frequencies. Channel 1: 5 287 - 11 287 kHz; Channel 2: 11 287 - 20 233 kHz; Channel 3: 24 427 - 30 427 kHz; Channel 4: 30 427 - 39 373 kHz; Channel 5: 43 567 - 49 567 kHz; Channel 6: 49 567 - 58 513 kHz. Above the channels, a series of trapezoidal shapes represent the modulation envelope, with vertical dashed lines indicating sub-carrier frequencies: 8 097, 11 043, 19 140 (6 x 3190), 41 470 (13 x 3190), 44 660 (14 x 3190), and 82 940 (26 x 3190). The label '60 MHz system' is on the left, and 'CCITT - 45 681' is on the right.
+
+FIGURE A-1 /G.333  
+**Modulation method for television transmission on the 60 MHz system  
+ Modulation method 1**
+
+![Diagram of modulation method 2 for the 60 MHz system. It shows six channels (1-6) with their respective frequency bands and sub-carrier frequencies. Channel 1: 5 287 - 11 287 kHz; Channel 2: 11 287 - 20 233 kHz; Channel 3: 24 427 - 30 427 kHz; Channel 4: 30 427 - 39 373 kHz; Channel 5: 43 567 - 49 567 kHz; Channel 6: 49 567 - 58 513 kHz. Above the channels, a series of trapezoidal shapes represent the modulation envelope, with vertical dashed lines indicating sub-carrier frequencies: 6 000, 25 520 (8 x 3190), 44 660 (14 x 3190), and 63 800 (20 x 3190). The label '60 MHz system' is on the left, and 'CCITT - 45 691' is on the right.](10c82dcc5f2c237961329dd29d65859c_img.jpg)
+
+Diagram of modulation method 2 for the 60 MHz system. It shows six channels (1-6) with their respective frequency bands and sub-carrier frequencies. Channel 1: 5 287 - 11 287 kHz; Channel 2: 11 287 - 20 233 kHz; Channel 3: 24 427 - 30 427 kHz; Channel 4: 30 427 - 39 373 kHz; Channel 5: 43 567 - 49 567 kHz; Channel 6: 49 567 - 58 513 kHz. Above the channels, a series of trapezoidal shapes represent the modulation envelope, with vertical dashed lines indicating sub-carrier frequencies: 6 000, 25 520 (8 x 3190), 44 660 (14 x 3190), and 63 800 (20 x 3190). The label '60 MHz system' is on the left, and 'CCITT - 45 691' is on the right.
+
+FIGURE A-2/G.333  
+**Modulation method for television transmission on the 60 MHz system  
+ Modulation method 2**
+
+## References
+
+- [1] CCITT Recommendation *Routine maintenance measurements to be made on regulated line sections*, Vol. IV, Rec. M.500.
+- [2] CCITT manual *Directives concerning the protection of telecommunication lines against harmful effects from electricity lines*, ITU, Geneva, 1963, 1965, 1974 and 1978.
+- [3] CCITT Recommendation *Tests on power-fed repeaters using solid state devices in order to check the arrangements for protection from external interference*, Vol. IX, Rec. K. 17.
+- [4] CCITT Recommendation *Characteristics of the television signals transmitted over 18-MHz and 60-MHz systems*, Vol. III, Rec. J.77.

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+
+
+![ITU logo](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features the letters 'ITU' in a bold, sans-serif font, superimposed on a stylized globe with intersecting lines.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**G.631**
+
+# **TRANSMISSION MEDIA CHARACTERISTICS** ---
+
+**TYPES OF SUBMARINE CABLE  
+TO BE USED FOR SYSTEMS  
+WITH LINE FREQUENCIES OF LESS  
+THAN ABOUT 45 MHz**
+
+**ITU-T Recommendation G.631**
+
+(Extract from the *Blue Book*)
+
+---
+
+## NOTES
+
+- 1 ITU-T Recommendation G.631 was published in Fascicle III.3 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+- 2 In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## Recommendation G.631
+
+## TYPES OF SUBMARINE CABLE TO BE USED FOR SYSTEMS WITH LINE FREQUENCIES OF LESS THAN ABOUT 45 MHz
+
+(Geneva, 1976)
+
+The CCITT,
+
+*recognizing*
+
+that the special complications of cable repair in the case of submarine cable systems laid in deep water (i.e. at depths where there is no need to use armoured cables) justify measures which would reduce the number of cable types with which repair ships have to deal;
+
+*appreciating*
+
+at the same time that system designers require flexibility in the choice of cables in order to optimize the overall cost per unit length of individual systems;
+
+*recognizing*
+
+that the most significant cable characteristics in determining whether any two cables may be joined together are:
+
+- the inner diameter of the outer conductor,
+- the characteristic impedance of the cable,
+
+*recommends*
+
+that for submarine systems handling line frequencies up to 45 MHz the cable used in the deep water sections of such systems should conform with the limits set out in Table 1/G.631.
+
+TABLE 1/G.631
+
+|                                   |              |                          |                                        |
+|-----------------------------------|--------------|--------------------------|----------------------------------------|
+| Inner diameter of outer conductor | 25.0-25.5 mm | 37.0-38.5 mm             | 43.2 mm                                |
+| Characteristic impedance          | 43-46 Ω      | a) 53-54 Ω<br>b) 60-62 Ω | a) 49-50 Ω<br>b) 53-54 Ω<br>c) 60-62 Ω |

marked/G/T-REC-G.694.1-202010-I_PDF-E/raw.md

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+
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**G.694.1**
+
+(10/2020)
+
+SERIES G: TRANSMISSION SYSTEMS AND MEDIA,  
+DIGITAL SYSTEMS AND NETWORKS
+
+Transmission media and optical systems characteristics –  
+Characteristics of optical systems
+
+---
+
+**Spectral grids for WDM applications: DWDM  
+frequency grid**
+
+Recommendation ITU-T G.694.1
+
+# ITU-T G-SERIES RECOMMENDATIONS **TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS**
+
+|                                                                                                                                              |                    |
+|----------------------------------------------------------------------------------------------------------------------------------------------|--------------------|
+| INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS                                                                                             | G.100–G.199        |
+| GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS                                                                  | G.200–G.299        |
+| INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES                                                      | G.300–G.399        |
+| GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES | G.400–G.449        |
+| COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY                                                                                            | G.450–G.499        |
+| TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS                                                                                       | G.600–G.699        |
+| General                                                                                                                                      | G.600–G.609        |
+| Symmetric cable pairs                                                                                                                        | G.610–G.619        |
+| Land coaxial cable pairs                                                                                                                     | G.620–G.629        |
+| Submarine cables                                                                                                                             | G.630–G.639        |
+| Free space optical systems                                                                                                                   | G.640–G.649        |
+| Optical fibre cables                                                                                                                         | G.650–G.659        |
+| Characteristics of optical components and subsystems                                                                                         | G.660–G.679        |
+| <b>Characteristics of optical systems</b>                                                                                                    | <b>G.680–G.699</b> |
+| DIGITAL TERMINAL EQUIPMENTS                                                                                                                  | G.700–G.799        |
+| DIGITAL NETWORKS                                                                                                                             | G.800–G.899        |
+| DIGITAL SECTIONS AND DIGITAL LINE SYSTEM                                                                                                     | G.900–G.999        |
+| MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE – GENERIC AND USER-RELATED ASPECTS                                                             | G.1000–G.1999      |
+| TRANSMISSION MEDIA CHARACTERISTICS                                                                                                           | G.6000–G.6999      |
+| DATA OVER TRANSPORT – GENERIC ASPECTS                                                                                                        | G.7000–G.7999      |
+| PACKET OVER TRANSPORT ASPECTS                                                                                                                | G.8000–G.8999      |
+| ACCESS NETWORKS                                                                                                                              | G.9000–G.9999      |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+## Recommendation ITU-T G.694.1
+
+## Spectral grids for WDM applications: DWDM frequency grid
+
+## Summary
+
+Recommendation ITU-T G.694.1 provides a frequency grid for dense wavelength division multiplexing (DWDM) applications.
+
+The frequency grid, anchored to 193.1 THz, supports a variety of channel spacings ranging from 12.5 GHz to 100 GHz and wider.
+
+Edition 3.0 of this Recommendation also includes a flexible DWDM grid and definitions for "frequency slot" and "slot width" that can be applied also in fixed grid applications.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T G.694.1  | 2002-06-13 | 15          | <a href="http://handle.itu.int/11.1002/1000/6051">11.1002/1000/6051</a>   |
+| 2.0     | ITU-T G.694.1  | 2012-02-13 | 15          | <a href="http://handle.itu.int/11.1002/1000/11482">11.1002/1000/11482</a> |
+| 3.0     | ITU-T G.694.1  | 2020-10-29 | 15          | <a href="http://handle.itu.int/11.1002/1000/14498">11.1002/1000/14498</a> |
+
+## Keywords
+
+DWDM, flexible grid, frequency slot, slot width.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2021
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|                                                                     | Page |
+|---------------------------------------------------------------------|------|
+| 1 Scope .....                                                       | 1    |
+| 2 References.....                                                   | 1    |
+| 3 Definitions .....                                                 | 1    |
+| 3.1 Terms defined elsewhere .....                                   | 1    |
+| 3.2 Terms defined in this Recommendation.....                       | 1    |
+| 4 Abbreviations and acronyms .....                                  | 1    |
+| 5 Conventions .....                                                 | 1    |
+| 6 Dense wavelength division multiplexing and its applications.....  | 2    |
+| 7 Fixed grid nominal central frequencies for dense WDM systems..... | 2    |
+| 8 Flexible DWDM grid definition .....                               | 5    |
+| Appendix I – Use of the flexible grid .....                         | 6    |
+| I.1 Flexible grid examples .....                                    | 6    |
+| I.2 Flexible grid compliance .....                                  | 7    |
+
+
+
+## Recommendation ITU-T G.694.1
+
+## Spectral grids for WDM applications: DWDM frequency grid
+
+## 1 Scope
+
+The purpose of this Recommendation is to provide the definition of a frequency grid to support dense wavelength division multiplexing (DWDM) applications.
+
+## 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+[ITU-T G.671] Recommendation ITU-T G.671 (2019), *Transmission characteristics of optical components and subsystems*.
+
+## 3 Definitions
+
+### 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms as described in [ITU-T G.671] in relation to CWDM devices and DWDM devices:
+
+- Coarse wavelength division multiplexing (CWDM).
+- Dense wavelength division multiplexing (DWDM).
+
+### 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following terms:
+
+**3.2.1 frequency grid:** A reference set of frequencies used to denote allowed nominal central frequencies that may be used for defining applications.
+
+**3.2.2 frequency slot:** A contiguous frequency range characterized by its nominal central frequency and slot width. The frequency range allocated to a frequency slot is unavailable to other frequency slots.
+
+**3.2.3 slot width:** The full width of the contiguous frequency range allocated to a frequency slot.
+
+## 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+CWDM Coarse Wavelength Division Multiplexing
+
+DWDM Dense Wavelength Division Multiplexing
+
+WDM Wavelength Division Multiplexing
+
+## 5 Conventions
+
+None.
+
+## 6 Dense wavelength division multiplexing and its applications
+
+As defined in [ITU-T G.671], dense wavelength division multiplexing (DWDM), a wavelength division multiplexing (WDM) technology, is characterized by narrower channel spacing than coarse WDM (CWDM). In general, the transmitters employed in DWDM applications require a control mechanism to enable them to meet the application's frequency stability requirements, in contrast to CWDM transmitters, which are generally uncontrolled in this respect.
+
+The frequency grid defined by this Recommendation supports a variety of fixed channel spacings ranging from 12.5 GHz to 100 GHz and wider (integer multiples of 100 GHz) as well as a flexible grid. Uneven channel spacings using the fixed grids are also allowed.
+
+The current steps in channel spacing for the fixed grids have historically evolved by sub-dividing the initial 100 GHz grid by successive factors of two.
+
+## 7 Fixed grid nominal central frequencies for dense WDM systems
+
+For channel spacings of 12.5 GHz on a fibre, the allowed channel frequencies (in THz) are defined by:
+
+$$193.1 + n \times 0.0125 \text{ where } n \text{ is a positive or negative integer including } 0$$
+
+For channel spacings of 25 GHz on a fibre, the allowed channel frequencies (in THz) are defined by:
+
+$$193.1 + n \times 0.025 \text{ where } n \text{ is a positive or negative integer including } 0$$
+
+For channel spacings of 50 GHz on a fibre, the allowed channel frequencies (in THz) are defined by:
+
+$$193.1 + n \times 0.05 \text{ where } n \text{ is a positive or negative integer including } 0$$
+
+For channel spacings of 100 GHz or more on a fibre, the allowed channel frequencies (in THz) are defined by:
+
+$$193.1 + n \times 0.1 \text{ where } n \text{ is a positive or negative integer including } 0$$
+
+Table 1 illustrates some nominal central frequencies within the C and L bands based on the 12.5 GHz minimum channel spacing anchored to the 193.1 THz reference. Table 1 also illustrates the 25, 50 and 100 GHz grid frequencies within the same region. The endpoints shown are illustrative, not normative.
+
+Note that the value of "c" (speed of light in vacuum) that should be used for converting between frequency and wavelength is  $2.99792458 \times 10^8$  m/s.
+
+**Table 1 – Example nominal central frequencies of the DWDM grid**
+
+| Nominal central frequencies (THz) for spacings of: |         |        |                   | Approximate nominal central wavelengths (nm) (Note) |
+|----------------------------------------------------|---------|--------|-------------------|-----------------------------------------------------|
+| 12.5 GHz                                           | 25 GHz  | 50 GHz | 100 GHz and above |                                                     |
+| •                                                  | •       | •      | •                 | •                                                   |
+| •                                                  | •       | •      | •                 | •                                                   |
+| •                                                  | •       | •      | •                 | •                                                   |
+| 195.9375                                           | –       | –      | –                 | 1530.0413                                           |
+| 195.9250                                           | 195.925 | –      | –                 | 1530.1389                                           |
+| 195.9125                                           | –       | –      | –                 | 1530.2365                                           |
+| 195.9000                                           | 195.900 | 195.90 | 195.9             | 1530.3341                                           |
+| 195.8875                                           | –       | –      | –                 | 1530.4318                                           |
+
+**Table 1 – Example nominal central frequencies of the DWDM grid**
+
+| Nominal central frequencies (THz) for spacings of: |         |        |                      | Approximate nominal<br>central wavelengths (nm)<br>(Note) |
+|----------------------------------------------------|---------|--------|----------------------|-----------------------------------------------------------|
+| 12.5 GHz                                           | 25 GHz  | 50 GHz | 100 GHz<br>and above |                                                           |
+| 195.8750                                           | 195.875 | –      | –                    | 1530.5295                                                 |
+| 195.8625                                           | –       | –      | –                    | 1530.6271                                                 |
+| 195.8500                                           | 195.850 | 195.85 | –                    | 1530.7248                                                 |
+| 195.8375                                           | –       | –      | –                    | 1530.8225                                                 |
+| 195.8250                                           | 195.825 | –      | –                    | 1530.9203                                                 |
+| 195.8125                                           | –       | –      | –                    | 1531.0180                                                 |
+| 195.8000                                           | 195.800 | 195.80 | 195.8                | 1531.1157                                                 |
+| 195.7875                                           | –       | –      | –                    | 1531.2135                                                 |
+| 195.7750                                           | 195.775 | –      | –                    | 1531.3112                                                 |
+| 195.7625                                           | –       | –      | –                    | 1531.4090                                                 |
+| 195.7500                                           | 195.750 | 195.75 | –                    | 1531.5068                                                 |
+| 195.7375                                           | –       | –      | –                    | 1531.6046                                                 |
+| 195.7250                                           | 195.725 | –      | –                    | 1531.7024                                                 |
+| 195.7125                                           | –       | –      | –                    | 1531.8003                                                 |
+| 195.7000                                           | 195.700 | 195.70 | 195.7                | 1531.8981                                                 |
+| 195.6875                                           | –       | –      | –                    | 1531.9960                                                 |
+| 195.6750                                           | 195.675 | –      | –                    | 1532.0938                                                 |
+| 195.6625                                           | –       | –      | –                    | 1532.1917                                                 |
+| •                                                  | •       | •      | •                    | •                                                         |
+| •                                                  | •       | •      | •                    | •                                                         |
+| •                                                  | •       | •      | •                    | •                                                         |
+| •                                                  | •       | •      | •                    | •                                                         |
+| •                                                  | •       | •      | •                    | •                                                         |
+| •                                                  | •       | •      | •                    | •                                                         |
+| 193.2375                                           | –       | –      | –                    | 1551.4197                                                 |
+| 193.2250                                           | 193.225 | –      | –                    | 1551.5200                                                 |
+| 193.2125                                           | –       | –      | –                    | 1551.6204                                                 |
+| 193.2000                                           | 193.200 | 193.20 | 193.2                | 1551.7208                                                 |
+| 193.1875                                           | –       | –      | –                    | 1551.8212                                                 |
+| 193.1750                                           | 193.175 | –      | –                    | 1551.9216                                                 |
+| 193.1625                                           | –       | –      | –                    | 1552.0220                                                 |
+| 193.1500                                           | 193.150 | 193.15 | –                    | 1552.1225                                                 |
+| 193.1375                                           | –       | –      | –                    | 1552.2229                                                 |
+| 193.1250                                           | 193.125 | –      | –                    | 1552.3234                                                 |
+| 193.1125                                           | –       | –      | –                    | 1552.4239                                                 |
+| 193.1000                                           | 193.100 | 193.10 | 193.1                | 1552.5244                                                 |
+
+**Table 1 – Example nominal central frequencies of the DWDM grid**
+
+| Nominal central frequencies (THz) for spacings of: |         |        |                      | Approximate nominal<br>central wavelengths (nm)<br>(Note) |
+|----------------------------------------------------|---------|--------|----------------------|-----------------------------------------------------------|
+| 12.5 GHz                                           | 25 GHz  | 50 GHz | 100 GHz<br>and above |                                                           |
+| 193.0875                                           | –       | –      | –                    | 1552.6249                                                 |
+| 193.0750                                           | 193.075 | –      | –                    | 1552.7254                                                 |
+| 193.0625                                           | –       | –      | –                    | 1552.8259                                                 |
+| 193.0500                                           | 193.050 | 193.05 | –                    | 1552.9265                                                 |
+| 193.0375                                           | –       | –      | –                    | 1553.0270                                                 |
+| 193.0250                                           | 193.025 | –      | –                    | 1553.1276                                                 |
+| 193.0125                                           | –       | –      | –                    | 1553.2282                                                 |
+| 193.0000                                           | 193.000 | 193.00 | 193.0                | 1553.3288                                                 |
+| 192.9875                                           | –       | –      | –                    | 1553.4294                                                 |
+| 192.9750                                           | 192.975 | –      | –                    | 1553.5300                                                 |
+| 192.9625                                           | –       | –      | –                    | 1553.6307                                                 |
+| •                                                  | •       | •      | •                    | •                                                         |
+| •                                                  | •       | •      | •                    | •                                                         |
+| •                                                  | •       | •      | •                    | •                                                         |
+| •                                                  | •       | •      | •                    | •                                                         |
+| •                                                  | •       | •      | •                    | •                                                         |
+| •                                                  | •       | •      | •                    | •                                                         |
+| 184.7750                                           | 184.775 | –      | –                    | 1622.4731                                                 |
+| 184.7625                                           | –       | –      | –                    | 1622.5828                                                 |
+| 184.7500                                           | 184.750 | 184.75 | –                    | 1622.6926                                                 |
+| 184.7375                                           | –       | –      | –                    | 1622.8024                                                 |
+| 184.7250                                           | 184.725 | –      | –                    | 1622.9122                                                 |
+| 184.7125                                           | –       | –      | –                    | 1623.0220                                                 |
+| 184.7000                                           | 184.700 | 184.70 | 184.7                | 1623.1319                                                 |
+| 184.6875                                           | –       | –      | –                    | 1623.2417                                                 |
+| 184.6750                                           | 184.675 | –      | –                    | 1623.3516                                                 |
+| 184.6625                                           | –       | –      | –                    | 1623.4615                                                 |
+| 184.6500                                           | 184.650 | 184.65 | –                    | 1623.5714                                                 |
+| 184.6375                                           | –       | –      | –                    | 1623.6813                                                 |
+| 184.6250                                           | 184.625 | –      | –                    | 1623.7912                                                 |
+| 184.6125                                           | –       | –      | –                    | 1623.9012                                                 |
+| 184.6000                                           | 184.600 | 184.60 | 184.6                | 1624.0111                                                 |
+| 184.5875                                           | –       | –      | –                    | 1624.1211                                                 |
+| 184.5750                                           | 184.575 | –      | –                    | 1624.2311                                                 |
+| 184.5625                                           | –       | –      | –                    | 1624.3411                                                 |
+| 184.5500                                           | 184.550 | 184.55 | –                    | 1624.4511                                                 |
+| 184.5375                                           | –       | –      | –                    | 1624.5612                                                 |
+
+**Table 1 – Example nominal central frequencies of the DWDM grid**
+
+| Nominal central frequencies (THz) for spacings of: |         |        |                   | Approximate nominal central wavelengths (nm) (Note) |
+|----------------------------------------------------|---------|--------|-------------------|-----------------------------------------------------|
+| 12.5 GHz                                           | 25 GHz  | 50 GHz | 100 GHz and above |                                                     |
+| 184.5250                                           | 184.525 | –      | –                 | 1624.6712                                           |
+| 184.5125                                           | –       | –      | –                 | 1624.7813                                           |
+| 184.5000                                           | 184.500 | 184.50 | 184.5             | 1624.8914                                           |
+| •                                                  | •       | •      | •                 | •                                                   |
+| •                                                  | •       | •      | •                 | •                                                   |
+| •                                                  | •       | •      | •                 | •                                                   |
+
+NOTE – The wavelengths given in this table are approximations only. The specifications applied to DWDM applications are defined with respect to the nominal central frequencies and not the approximate wavelengths.
+
+## **8 Flexible DWDM grid definition**
+
+For the flexible DWDM grid, the allowed frequency slots have a nominal central frequency (in THz) defined by:
+
+$$193.1 + n \times 0.00625 \text{ where } n \text{ is a positive or negative integer including } 0 \text{ and } 0.00625 \text{ is the nominal central frequency granularity in THz}$$
+
+and a slot width defined by:
+
+$$12.5 \times m \text{ where } m \text{ is a positive integer and } 12.5 \text{ is the slot width granularity in GHz.}$$
+
+Any combination of frequency slots is allowed as long as no two frequency slots overlap.
+
+Further information on the use of the flexible grid can be found in Appendix I.
+
+## Appendix I
+
+### Use of the flexible grid
+
+(This appendix does not form an integral part of this Recommendation.)
+
+### I.1 Flexible grid examples
+
+In addition to the fixed spacing dense wavelength division multiplexing (DWDM) grids defined in clause 7, a newer flexible DWDM grid has been introduced in clause 8. One of the motivations for the flexible grid is to allow a mixed bit rate or mixed modulation format transmission system to allocate frequency slots with different widths so that they can be optimized for the bandwidth requirements of the particular bit rate and modulation scheme of the individual channels. Because of the complexity of defining multi-vendor interoperable transmission systems containing mixed bit rates or modulation formats, there are currently no DWDM optical interface Recommendations that make use of this grid.
+
+An example use of the flexible DWDM grid is shown in Figure I.1, where two 50 GHz slots are shown together with two 75 GHz slots. For each slot in the figure, the values of  $n$  and  $m$  in the formulae defining the slot parameters in clause 8 are also given. The frequency range between 193.125 THz and 193.18125 THz is shown unallocated. This range could be left as a "guard band" between the two sets of channels or it could subsequently be allocated to an additional slot with a width of 50 GHz ( $n=8, m=4$ ), leaving 6.25 GHz unallocated, or other alternatives (e.g., two 25 GHz slots  $n=6, m=2$  and  $n=10, m=2$ ).
+
+![Figure I.1: An example of the use of the flexible grid. The diagram shows a frequency spectrum from 193.025 THz to 193.3125 THz. It features two 50 GHz slots on the left (n = -8, m = 4 and n = 0, m = 4) and two 75 GHz slots on the right (n = 19, m = 6 and n = 31, m = 6). A gap between 193.125 THz and 193.18125 THz is unallocated.](dd330f8b8f6c16eae20c3a676b4eb804_img.jpg)
+
+Figure I.1 illustrates the flexible grid with two 50 GHz slots and two 75 GHz slots. The frequency scale ranges from 193.025 THz to 193.3125 THz. The first 50 GHz slot is defined by  $n = -8, m = 4$  and spans from 193.025 THz to 193.075 THz. The second 50 GHz slot is defined by  $n = 0, m = 4$  and spans from 193.075 THz to 193.125 THz. There is an unallocated gap between 193.125 THz and 193.18125 THz. The first 75 GHz slot is defined by  $n = 19, m = 6$  and spans from 193.18125 THz to 193.25625 THz. The second 75 GHz slot is defined by  $n = 31, m = 6$  and spans from 193.25625 THz to 193.3125 THz. The diagram is labeled G.694.1(20)\_FI.1.
+
+Figure I.1: An example of the use of the flexible grid. The diagram shows a frequency spectrum from 193.025 THz to 193.3125 THz. It features two 50 GHz slots on the left (n = -8, m = 4 and n = 0, m = 4) and two 75 GHz slots on the right (n = 19, m = 6 and n = 31, m = 6). A gap between 193.125 THz and 193.18125 THz is unallocated.
+
+Figure I.1 – An example of the use of the flexible grid
+
+The granularity of the nominal central frequency and slot width parameters for the flexible DWDM grid have been chosen so that any of the fixed spacing DWDM grids defined in clause 7 can also be described via suitable choices of slots in the flexible DWDM grid. For example, the 50 GHz fixed spacing DWDM grid is shown in Figure I.2 represented using the DWDM flexible grid.
+
+![Figure I.2: The 50 GHz fixed spacing grid represented using the flexible grid. The diagram shows a frequency spectrum from 193.025 THz to 193.325 THz, divided into six consecutive 50 GHz slots. The slots are defined by n = -8, m = 4; n = 0, m = 4; n = 8, m = 4; n = 16, m = 4; n = 24, m = 4; and n = 32, m = 4.](83dedc2074a453d13ce74cc2e1ae4ff5_img.jpg)
+
+Figure I.2 shows the 50 GHz fixed spacing grid represented using the flexible grid. The frequency scale ranges from 193.025 THz to 193.325 THz. The grid consists of six consecutive 50 GHz slots. The slots are defined by the following parameters:  $n = -8, m = 4$  (193.025 THz to 193.075 THz),  $n = 0, m = 4$  (193.075 THz to 193.125 THz),  $n = 8, m = 4$  (193.125 THz to 193.175 THz),  $n = 16, m = 4$  (193.175 THz to 193.225 THz),  $n = 24, m = 4$  (193.225 THz to 193.275 THz), and  $n = 32, m = 4$  (193.275 THz to 193.325 THz). The diagram is labeled G.694.1(20)\_FI.2.
+
+Figure I.2: The 50 GHz fixed spacing grid represented using the flexible grid. The diagram shows a frequency spectrum from 193.025 THz to 193.325 THz, divided into six consecutive 50 GHz slots. The slots are defined by n = -8, m = 4; n = 0, m = 4; n = 8, m = 4; n = 16, m = 4; n = 24, m = 4; and n = 32, m = 4.
+
+Figure I.2 – The 50 GHz fixed spacing grid represented using the flexible grid
+
+Since the smallest spacing fixed grid is 12.5 GHz, the slot width granularity needs to be 12.5 GHz. In order to be able to place a slot that has a width that is an even multiple of 12.5 GHz next to one
+
+with a width that is an odd multiple of 12.5 GHz without a gap, the nominal central frequency granularity needs to be 6.25 GHz. An example of this is shown in Figure I.3.
+
+![Figure I.3: A frequency spectrum diagram showing four contiguous slots with widths of 87.5 GHz, 87.5 GHz, 50 GHz, and 50 GHz. The slots are labeled with n and m values: n = -1, m = 7; n = 13, m = 7; n = 24, m = 4; and n = 32, m = 4. The frequency axis ranges from 193.05 to 193.325 THz with tick marks every 6.25 GHz.](2236272d3b3db6e6363337f5a8db72f6_img.jpg)
+
+The diagram illustrates a frequency spectrum with four contiguous slots. The top of the diagram shows the width of each slot using double-headed arrows: 87.5 GHz, 87.5 GHz, 50 GHz, and 50 GHz. Below this, the slots are represented as rounded rectangles labeled with their respective  $n$  and  $m$  values:  $n = -1, m = 7$ ;  $n = 13, m = 7$ ;  $n = 24, m = 4$ ; and  $n = 32, m = 4$ . A horizontal axis below the slots has tick marks every 6.25 GHz. Specific frequency labels (in THz) are placed vertically below certain tick marks: 193.05, 193.09375, 193.1375, 193.18125, 193.225, 193.25, 193.275, 193.3, and 193.325. The label G.694.1(20)\_FI.3 is present in the bottom right corner.
+
+Figure I.3: A frequency spectrum diagram showing four contiguous slots with widths of 87.5 GHz, 87.5 GHz, 50 GHz, and 50 GHz. The slots are labeled with n and m values: n = -1, m = 7; n = 13, m = 7; n = 24, m = 4; and n = 32, m = 4. The frequency axis ranges from 193.05 to 193.325 THz with tick marks every 6.25 GHz.
+
+**Figure I.3 – Example showing the need for 6.25 GHz nominal central frequency granularity**
+
+### I.2 Flexible grid compliance
+
+The flexible DWDM grid defined in clause 8 has a nominal central frequency granularity of 6.25 GHz and a slot width granularity of 12.5 GHz. However, devices or applications that make use of the flexible grid may not have to be capable of supporting every possible slot width or position. In other words, applications may be defined where only a subset of the possible slot widths and positions are required to be supported.
+
+For example, an application could be defined where the nominal central frequency granularity is 12.5 GHz (by only requiring values of  $n$  that are even) and that only requires slot widths as a multiple of 25 GHz (by only requiring values of  $m$  that are even).
+
+
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                                           |
+|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                                                         |
+| Series D        | Tariff and accounting principles and international telecommunication/ICT economic and policy issues                                                       |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                                                         |
+| Series F        | Non-telephone telecommunication services                                                                                                                  |
+| <b>Series G</b> | <b>Transmission systems and media, digital systems and networks</b>                                                                                       |
+| Series H        | Audiovisual and multimedia systems                                                                                                                        |
+| Series I        | Integrated services digital network                                                                                                                       |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                                               |
+| Series K        | Protection against interference                                                                                                                           |
+| Series L        | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant |
+| Series M        | Telecommunication management, including TMN and network maintenance                                                                                       |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                                           |
+| Series O        | Specifications of measuring equipment                                                                                                                     |
+| Series P        | Telephone transmission quality, telephone installations, local line networks                                                                              |
+| Series Q        | Switching and signalling, and associated measurements and tests                                                                                           |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities                               |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |