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+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**G.1028.1**
+
+(02/2019)
+
+SERIES G: TRANSMISSION SYSTEMS AND MEDIA,  
+DIGITAL SYSTEMS AND NETWORKS
+
+Multimedia Quality of Service and performance – Generic  
+and user-related aspects
+
+---
+
+**End-to-end quality of service for video  
+telephony over 4G mobile networks**
+
+Recommendation ITU-T G.1028.1
+
+ITU-T
+
+![ITU logo: A globe with a red lightning bolt and the text 'ITU International Telecommunication Union'.](1d7527f4316cfe2d342b08d1653d1592_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue globe with a red lightning bolt striking across it. To the right of the globe, the text "ITU" is written in a bold, blue, sans-serif font. Below "ITU", the words "International Telecommunication Union" are written in a smaller, blue, sans-serif font.
+
+ITU logo: A globe with a red lightning bolt and the text 'ITU International Telecommunication Union'.
+
+## 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.1028.1
+
+## End-to-end quality of service for video telephony over 4G mobile networks
+
+## Summary
+
+Recommendation ITU-T G.1028.1 provides guidelines concerning key aspects impacting end-to-end performance of carrier-grade (in opposition to over-the-top (OTT) approaches, which are outside of the scope of this Recommendation) conversational video services over long-term evolution (LTE) networks, also known as video-telephony over LTE (ViLTE), as defined by Global System for Mobile communications Association (GSMA). It identifies the preconditions for an optimally operating ViLTE network and provides remedial measures that operators can leverage to address the associated impact of quality of service (QoS) degradations in the LTE network.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T G.1028.1 | 2019-02-06 | 12          | <a href="http://handle.itu.int/11.1002/1000/13831">11.1002/1000/13831</a> |
+
+## Keywords
+
+LTE, QoS, quality of service, video, video telephony, ViLTE, 4G.
+
+---
+
+\* 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 2019
+
+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 .....                                                               | 3    |
+| 3.1 Terms defined elsewhere .....                                                 | 3    |
+| 3.2 Terms defined in this Recommendation.....                                     | 3    |
+| 4 Abbreviations and acronyms .....                                                | 3    |
+| 5 Conventions .....                                                               | 6    |
+| 6 Brief introduction on video-telephony over LTE and assumptions.....             | 6    |
+| 7 ViLTE network architecture .....                                                | 7    |
+| 8 QoS requirements for ViLTE – Segmented approach .....                           | 8    |
+| 8.1 Overview of QoS issues experienced by end-users.....                          | 8    |
+| 8.2 User equipment (codec design and implementation) .....                        | 9    |
+| 8.3 E-UTRAN (Radio resource management) .....                                     | 10   |
+| 8.4 Evolved packet core (QCI allocation and mobility management procedures) ..... | 11   |
+| 8.5 IMS and IP transit core (call control and signalling) .....                   | 11   |
+| 9 Budget estimation and QoS parameterization .....                                | 11   |
+| 9.1 Relevant indicators .....                                                     | 11   |
+| 9.2 Impact assessment of relevant operating conditions on QoS parameters.....     | 13   |
+| 9.3 Quality targets .....                                                         | 15   |
+| 10 Diagnostic strategy for QoS degradations .....                                 | 16   |
+| 10.1 QoS problem source-linked to availability of service .....                   | 17   |
+| 10.2 QoS problem source-linked to network performance .....                       | 17   |
+| 10.3 Tools and models for measurement and prediction of video quality .....       | 19   |
+| Bibliography.....                                                                 | 21   |
+
+## Introduction
+
+Mobile broadband operators, facing a competitive broadband market, are obliged to redefine their business models to enhance revenue-generating streams. This has necessitated a deployment shift to converged IP-based technology platforms and high-throughput access network technologies that deliver high-quality triple-play services (telephony, internet and video streaming) to consumers whose expectation for improved user experience continues to remain insatiable. In this perspective, video-telephony services over 4G networks (i.e., long-term evolution (LTE)) present an opportunity for operators to offer new value-added services to their customers and convince them to remain faithful. There still exists ongoing research work by academics, systems developers and standards organizations; all attempting to help fill the knowledge gap for successful commercial video-telephony over LTE (ViLTE) deployment worldwide.
+
+## Recommendation ITU-T G.1028.1
+
+## End-to-end quality of service for video telephony over 4G mobile networks
+
+## 1 Scope
+
+This Recommendation covers end-to-end quality of service (QoS) requirements for video-telephony over long-term evolution (LTE) (ViLTE) network segments (see [b-GSMA IR.94]), budget allocation considerations for different service architecture scenarios, QoS parameterization for regulatory compliance, impact assessment of some relevant operating conditions on identified service parameters as well as a diagnostic strategy for QoS degradations in ViLTE. The intention of this Recommendation is to serve as a reference guide for LTE operators and regulators.
+
+This Recommendation is a complement to [ITU-T G.1028]. All voice-related aspects of ViLTE are exactly similar to those for voice over LTE (VoLTE), and therefore covered by [ITU-T G.1028], and thus, they are not repeated in this Recommendation.
+
+## 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.1011] Recommendation ITU-T G.1011 (2016), *Reference guide to quality of experience assessment methodologies*.
+- [ITU-T G.1028] Recommendation ITU-T G.1028 (2016), *End-to-end quality of service for voice over 4G mobile networks*.
+- [ITU-T G.1070] Recommendation ITU-T G.1070 (2018), *Opinion model for video-telephony applications*.
+- [ITU-T G.1071] Recommendation ITU-T G.1071 (2016), *Opinion model for network planning of video and audio streaming applications*.
+- [ITU-T H.264] Recommendation ITU-T H.264 (2017), *Advanced video coding for generic audiovisual services*.
+- [ITU-T H.265] Recommendation ITU-T H.265 (2018), *High efficiency video coding*.
+- [ITU-T J.144] Recommendation ITU-T J.144 (2004), *Objective perceptual video quality measurement techniques for digital cable television in the presence of a full reference*.
+- [ITU-T J.246] Recommendation ITU-T J.246 (2008), *Perceptual visual quality measurement techniques for multimedia services over digital cable television networks in the presence of a reduced bandwidth reference*.
+- [ITU-T J.247] Recommendation ITU-T J.247 (2008), *Objective perceptual multimedia video quality measurement in the presence of a full reference*.
+- [ITU-T J.249] Recommendation ITU-T J.249 (2010), *Perceptual video quality measurement techniques for digital cable television in the presence of a reduced reference*.
+
+- [ITU-T J.341] Recommendation ITU-T J.341 (2016), *Objective perceptual multimedia video quality measurement of HDTV for digital cable television in the presence of a full reference.*
+- [ITU-T J.342] Recommendation ITU-T J.342 (2011), *Objective multimedia video quality measurement of HDTV for digital cable television in the presence of a reduced reference signal.*
+- [ITU-T J.343.1] Recommendation ITU-T J.343.1 (2014), *Hybrid-NRe objective perceptual video quality measurement for HDTV and multimedia IP-based video services in the presence of encrypted bitstream data.*
+- [ITU-T J.343.2] Recommendation ITU-T J.343.2 (2014), *Hybrid-NR objective perceptual video quality measurement for HDTV and multimedia IP-based video services in the presence of non-encrypted bitstream data.*
+- [ITU-T J.343.3] Recommendation ITU-T J.343.3 (2014), *Hybrid-RRe objective perceptual video quality measurement for HDTV and multimedia IP-based video services in the presence of a reduced reference signal and encrypted bitstream data.*
+- [ITU-T J.343.4] Recommendation ITU-T J.343.4 (2014), *Hybrid-RR objective perceptual video quality measurement for HDTV and multimedia IP-based video services in the presence of a reduced reference signal and non-encrypted bitstream data.*
+- [ITU-T J.343.5] Recommendation ITU-T J.343.5 (2014), *Hybrid-FRe objective perceptual video quality measurement for HDTV and multimedia IP-based video services in the presence of a full reference signal and encrypted bitstream data.*
+- [ITU-T J.343.6] Recommendation ITU-T J.343.6 (2014), *Hybrid-FR objective perceptual video quality measurement for HDTV and multimedia IP-based video services in the presence of a full reference signal and non-encrypted bitstream data.*
+- [ITU-T P.863] Recommendation ITU-T P.863 (2018), *Perceptual objective listening quality prediction.*
+- [ITU-T P.1201] Recommendation ITU-T P.1201 (2012), *Parametric non-intrusive assessment of audiovisual media streaming quality.*
+- [ITU-T P.1201.1] Recommendation ITU-T P.1201.1 (2012), *Parametric non-intrusive assessment of audiovisual media streaming quality – Lower resolution application area.*
+- [ITU-T P.1201.2] Recommendation ITU-T P.1201.2 (2012), *Parametric non-intrusive assessment of audiovisual media streaming quality – Higher resolution application area.*
+- [ITU-T P.1202.1] Recommendation ITU-T P.1202.1 (2012), *Parametric non-intrusive bitstream assessment of video media streaming quality – Lower resolution application area.*
+- [ITU-T P.1202.2] Recommendation ITU-T P.1202.2 (2013), *Parametric non-intrusive bitstream assessment of video media streaming quality – Higher resolution application area.*
+- [ETSI TS 122 105] ETSI TS 122 105 v15.0.0 (2018-07), *Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); LTE; Services and service capabilities (3GPP TS 22.105 version 15.0.0 Release 15).*
+- [ETSI TS 123 203] ETSI TS 123 203 v15.4.0 (2018-09), *Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System*
+
+*(UMTS); LTE; Policy and charging control architecture (3GPP TS 23.203 version 15.4.0 Release 15).*
+
+[ETSI TS 126 114] ETSI TS 126 114 v15.4.0 (2018-10), *Universal Mobile Telecommunications System (UMTS); LTE; IP Multimedia Subsystem (IMS); Multimedia telephony; Media handling and interaction (3GPP TS 26.114 version 15.4.0 Release 15).*
+
+## **3 Definitions**
+
+### **3.1 Terms defined elsewhere**
+
+None.
+
+### **3.2 Terms defined in this Recommendation**
+
+None.
+
+## **4 Abbreviations and acronyms**
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|         |                                           |
+|---------|-------------------------------------------|
+| 3G      | Third Generation of radio access network  |
+| 4G      | Fourth Generation of radio access network |
+| AEC     | Acoustic Echo Control                     |
+| AGC     | Automatic Gain Control                    |
+| AMR-WB  | Adaptive Multi-Rate Wideband              |
+| AS      | Application Server                        |
+| ATCF    | Access Transfer Control Function          |
+| ATGW    | Access Transfer Gateway                   |
+| BE      | Best Effort                               |
+| BGCF    | Border Gateway Control Function           |
+| BSC     | Base Station Controller                   |
+| BTS     | Base Transceiver Station                  |
+| CIF     | Common Intermediate Format                |
+| CS      | Circuit Switched                          |
+| CSFB    | Circuit Switched Fallback                 |
+| DL      | Downlink                                  |
+| DRB     | Data Radio Bearer                         |
+| DRX     | Discontinuous Reception                   |
+| DSCP    | Differentiated Services Code Point        |
+| DTMF    | Dual-Tone Multi-Frequency                 |
+| EF      | Expedited Forwarding                      |
+| eMSC    | Enhanced MSC                              |
+| e-NodeB | Enhanced Node B                           |
+| EPC     | Evolved Packet Core                       |
+
+|         |                                               |
+|---------|-----------------------------------------------|
+| E-UTRAN | Evolved UMTS Terrestrial Radio Access Network |
+| GBR     | Guaranteed Bit Rate                           |
+| GERAN   | GSM/Edge Radio Access Network                 |
+| GPRS    | General Packet Radio Service                  |
+| GSM     | Global System for Mobile Communications       |
+| GSMA    | GSM Association                               |
+| GTP     | GPRS Tunnelling Protocol                      |
+| GW      | Gateway                                       |
+| HARQ    | Hybrid Automatic-Repeat-Request               |
+| HD      | High Definition                               |
+| HSS     | Home Subscriber Server                        |
+| HVGA    | Half Video Graphics Array                     |
+| IBCF    | Interconnection Border Control Function       |
+| I-CSCF  | Interrogating Call Session Control Function   |
+| IMS     | IP Multimedia Subsystem                       |
+| LTE     | Long-Term Evolution                           |
+| MBR     | Maximum Bit Rate                              |
+| MGCF    | Media Gateway Controller Function             |
+| MGW     | Media Gateway                                 |
+| M-LWDF  | Modified Largest Weighted Delay First         |
+| MME     | Mobility Management Entity                    |
+| MOS     | Mean Opinion Score                            |
+| MOS-LQ  | Mean Opinion Score – Listening Quality        |
+| MRFC    | Multimedia Resource Function Controller       |
+| MRFP    | Multimedia Resource Function Processor        |
+| MSC     | Mobile Switching Centre                       |
+| MSCS    | MSC Server                                    |
+| MTSI    | Multimedia Telephony Service for IMS          |
+| NB      | Narrowband                                    |
+| NGN     | Next Generation Network                       |
+| NR      | Noise Reduction                               |
+| OFDMA   | Orthogonal Frequency-Division Multiple Access |
+| OT      | Third Operator                                |
+| OTT     | Over-The-Top                                  |
+| PCC     | Policy and Charging Control                   |
+| PCEF    | Policy and Charging Enforcement Function      |
+| PCRF    | Policy and Charging Rule Function             |
+
+|        |                                           |
+|--------|-------------------------------------------|
+| P-CSCF | Proxy Call Session Control Function       |
+| PDA    | Personal Digital Assistant                |
+| PDCP   | Packet Data Convergence Protocol          |
+| PDD    | Post Dialling Delay                       |
+| PF     | Proportionality Fair                      |
+| P-GW   | Packet Data Network Gateway               |
+| PLF    | Packet Loss Fair                          |
+| PSTN   | Public Switched Telephone Network         |
+| QCI    | QoS Class Identifier                      |
+| QCIF   | Quarter Common Intermediate Format        |
+| QoS    | Quality of Service                        |
+| QVGA   | Quarter Video Graphics Array              |
+| RACH   | Random Access Channel                     |
+| RLC    | Radio Link Control                        |
+| RNC    | Radio Network Controller                  |
+| RoHC   | Robust Header Compression                 |
+| RRC    | Radio Resource Control                    |
+| RSRP   | Reference Signal Received Power           |
+| RTCP   | Real-time Transport Control Protocol      |
+| RTP    | Real-time Transport Protocol              |
+| S-CSCF | Serving Call Session Control Function     |
+| SD     | Standard Definition                       |
+| SDP    | Session Description Protocol              |
+| S-GW   | Serving Gateway                           |
+| SIP    | Session Initiation Protocol               |
+| SRB    | Signalling Radio Bearer                   |
+| SRVCC  | Single Radio Voice Call Continuity        |
+| TAS    | Telephony Application Server              |
+| TrGW   | Trunking Gateway                          |
+| TTI    | Transmission Time Interval                |
+| UDP    | User Datagram Protocol                    |
+| UE     | User Equipment                            |
+| UL     | Uplink                                    |
+| UMTS   | Universal Mobile Telecommunication System |
+| UTRAN  | UMTS Terrestrial Radio Access Network     |
+| ViLTE  | Video-telephony over LTE                  |
+| VGA    | Video Graphics Array                      |
+
+|       |                 |
+|-------|-----------------|
+| VoLTE | Voice over LTE  |
+| VT    | Video Telephony |
+| WB    | Wideband        |
+
+## 5 Conventions
+
+None.
+
+## 6 Brief introduction on video-telephony over LTE and assumptions
+
+This Recommendation considers some key assumptions in respect of the IP multimedia subsystem (IMS) profile for video as defined by the Global System for Mobile communications Association (GSMA) in [b-GSMA IR.94] and the multimedia telephony service for IMS (MTSI) media handling procedures (video part only) defined by 3GPP in [ETSI TS 126 114].
+
+- To deploy ViLTE, VoLTE is required as a prerequisite. Voice aspects and network service architecture of ViLTE are adequately addressed in [ITU-T G.1028];
+- To support a video call, the user equipment (UE) transmits its video capability to the LTE network. The video call request encapsulates the video media with real-time transport protocol (RTP) on user datagram protocol (UDP) (RTP/UDP);
+- RTP is the media protocol for the transmission of realtime audio or video streams. Different than VoLTE, packet data network gateway (P-GW) and serving gateway (S-GW) establish two bearers for a video call: one for voice and one for video;
+- ViLTE uses the mandatory ITU-T H.264 codecs or preferably the optional (ITU-T H.265 Main tier level 3.1 codecs) to encode and decode the video stream with trade-off consideration for the optimization of both the bit rate and video signal quality;
+- The ITU-T H.264/ITU-T H.265 codec delivers superior quality as compared to the low bit ITU-T H.263 codec that is used in third generation (3G) conversational video calls;
+- Video resolution and coding rate is likely to adapt, during a call, to network conditions such as a reduction in downlink bandwidth. The real-time transport control protocol (RTCP) is used for the communication of capacities between the UE and the IMS entities inside the network during a call, thus triggering adaptation;
+- ViLTE uses the same control plane protocol as VoLTE, namely session initiation protocol (SIP);
+- The IMS core network along with the applicable application server (AS) performs the call control;
+- ViLTE video calls are allocated appropriate quality of service (QoS) to differentiate and prioritize such delay and jitter sensitive conversational traffic from other streaming video traffic that is not as delay or jitter sensitive;
+- The mechanism used is called QoS class identifier (QCI). The ViLTE bearer traffic is typically allocated QCI-2, and the SIP-based IMS signalling QCI-5;
+- During ViLTE sessions, video capable devices often ensure lip-synchronization across audio and video components, a phenomenon that is characterized by the sending of timing information to each other;
+- Call handling in ViLTE provides communicating devices with options to turn off video at any time during the call and continue with voice only;
+- Conversational video calling services may be carried out in either simplex or duplex mode;
+
+- Video streams can be changed from one mode to another by the sending of a re-INVITE request with a session description protocol (SDP) offer using appropriate media descriptors (e.g., sendrecv, sendonly, recvonly).
+
+**Table 1 – Standardized QCI characteristics for use in ViLTE [ETSI TS 123 203]**
+
+| QCI | Resource type             | Priority level | Packet delay budget | Packet error rate | Service type                          |
+|-----|---------------------------|----------------|---------------------|-------------------|---------------------------------------|
+| 1   | Guaranteed bit rate (GBR) | 2              | 100 ms              | 1/100             | Conversational voice                  |
+| 2   |                           | 4              | 150 ms              | 1/1000            | Conversational video (live streaming) |
+| 5   | Non-GBR                   | 1              | 100 ms              | 1/1000000         | IMS signalling                        |
+
+## 7 ViLTE network architecture
+
+The network architecture for ViLTE is similar to the one for VoLTE (see [ITU-T G.1028]).
+
+Figure 1 (taken from [ITU-T G.1028]) shows the overall network architecture for ViLTE services.
+
+![Overall network architecture for ViLTE services diagram showing Device, Radio access, Mobile core, and Mobile IMS layers with various network elements like LTE-UU, eNodeB, S-GW, P-GW, MME, HSS, and IMS components.](ddc7460821484f1ae2835c67955c554c_img.jpg)
+
+The diagram illustrates the overall network architecture for ViLTE services, organized into four main layers: Device, Radio access, Mobile core, and Mobile IMS.
+
+- Device:** Contains the LTE-UU (User Equipment) with protocol stacks (RLC, UM, AM, PDCP, DRB, SRB2, SRB1, SRB0). It connects to the Radio access via RRC and SIP/SDP.
+- Radio access:** Includes eNodeB (connected to LTE-UU), NodeB (connected to RNC), and BTS (connected to BSC/RNC). It also shows GERAN (GPRS) and UTRAN (UMTS) access networks.
+- Mobile core:** Features the MME (Mobility Management Entity), S-GW (Serving Gateway), P-GW (PDN Gateway), HSS (Home Subscriber Server), and SPR (Service Profile Repository). It handles data bearers (Dedicated bearer, Default bearer) and signaling (S1-MME, S11, S5, S6a, S12).
+- Mobile IMS:** Contains the SRVCC (Single Radio Voice Call Continuity) and AT&T (AT&T) components, including ATCF, ATGW, SCC-AS, ASs, TAS, voicemail, MRFP, and MRFC. It also shows connections to the PSTN, Broadband IMS, and OT (Over The Top) services via IBCF, TrGW, MGCF, and MGW.
+
+Other network elements shown include the PCRF (PDN Gateway Control and Policy Function), AF (Application Function), and various interfaces like SGi, S12, and Sh.
+
+Overall network architecture for ViLTE services diagram showing Device, Radio access, Mobile core, and Mobile IMS layers with various network elements like LTE-UU, eNodeB, S-GW, P-GW, MME, HSS, and IMS components.
+
+G.1028.1(19)\_F01
+
+**Figure 1 – Overall network architecture for ViLTE services**
+
+## 8 QoS requirements for ViLTE – Segmented approach
+
+### 8.1 Overview of QoS issues experienced by end-users
+
+ViLTE is a relatively new service, and not enough data is available yet to understand global QoS perceived by customers and how big the weight of the different dimensions of QoS is. However, An analogy can be made with existing services for which consolidated data are available.
+
+The main families of QoS parameters for conversational services are known from telephony. These are service accessibility, audio/video quality (part of service integrity including audio quality, video quality, and relations between simultaneous audio/video signals such as lip synchronization) and service continuity. A detailed list of the most relevant metrics pertaining to each QoS family is provided in clause 9.1.
+
+Furthermore, ViLTE shares several characteristics with other services available over the same access technology, such as VoLTE [ITU-T G.1028] and video streaming over LTE (for video aspects). Concerning this last point:
+
+- The intrinsic quality of video rendering, highly correlated with video coding technology and bit rate, video size, resolution (and their adequation with screen size) and video frame rate;
+- The occurrence of network (core or access) congestion, resulting in several visible artefacts (depending on decoding and buffering strategies at receiving side) like image freezing (similarly to re-buffering events in video streaming), pixelation, blocks, ghosting, etc.;
+- A combination of the two last elements, bandwidth limitation or jitter buffer, that can be compensated by video coding bitrate adaptation, yielding potential visible quality degradations.
+
+However, ViLTE is also characterized by the differences of media handling applied to voice and video, since the service profile for ViLTE, as defined in [b-GSMA IR.94], is based on QCI (see Table 1).
+
+Thus, in case of network congestion or in the event a ViLTE terminal is at the edge of radio coverage, voice will be given a priority over video. A mechanism like transmission time interval (TTI) bundling, allowing retransmission of voice packets to ensure they are not lost, and thus limiting the bandwidth for other packets, amplifies this priority. TTI bundling actually defines the final threshold for ViLTE coverage beyond which only 64 kbit/s video can run with non-acceptable quality using ITU-T H.264 "Baseline". By reducing the video bit rate, coverage is improved but by only 4 dB gain with half the bit rate, as illustrated in Figure 2 below. In the most severe situations, depending on the strategy defined by service provider, end users will face either a communication reduced to its voice component or a call drop.
+
+![Figure 2: Video bit rate versus coverage. A diagram showing three rows of quality levels (Video 768 kbps, Video 384 kbps, Voice 24 kbps) across a pathloss range from 128 dB to 142 dB. The diagram is divided into three quality zones: 'Good video quality' (green), 'Degraded video quality' (yellow), and 'Not acceptable degraded video quality' (red). A 'Coverage gap' is indicated between 132 dB and 142 dB. The x-axis is labeled 'Pathloss (dB)' with markers at 128, 132, and 142. Vertical dashed lines at 128 dB and 132 dB separate the zones. For Video 768 kbps, the 'Not acceptable' zone starts at 132 dB. For Video 384 kbps, it starts at 132 dB. For Voice 24 kbps, the 'Not acceptable' zone starts at 142 dB.](71ab4df17511d75261da8d462d643b1a_img.jpg)
+
+Figure 2: Video bit rate versus coverage. A diagram showing three rows of quality levels (Video 768 kbps, Video 384 kbps, Voice 24 kbps) across a pathloss range from 128 dB to 142 dB. The diagram is divided into three quality zones: 'Good video quality' (green), 'Degraded video quality' (yellow), and 'Not acceptable degraded video quality' (red). A 'Coverage gap' is indicated between 132 dB and 142 dB. The x-axis is labeled 'Pathloss (dB)' with markers at 128, 132, and 142. Vertical dashed lines at 128 dB and 132 dB separate the zones. For Video 768 kbps, the 'Not acceptable' zone starts at 132 dB. For Video 384 kbps, it starts at 132 dB. For Voice 24 kbps, the 'Not acceptable' zone starts at 142 dB.
+
+G.1028.1(19)\_F02
+
+**Figure 2 – Video bit rate versus coverage**
+
+Another element of consideration is how different overall ViLTE service quality, as experienced by users, can be when issues are related to audio only or to video only. It is known from user tests that customers are more sensitive to voice impairments than to video impairments during audio-video conversations. This generally results in better overall judgments when impairments affect video signal and to a lesser degree voice signal.
+
+### **8.2 User equipment (codec design and implementation)**
+
+ITU-T H.264 constrained high profile level 1.2, as specified in clause 5.2.2 of [ETSI TS 126 114], is mandatory in UE. However, for backward compatibility, it is required that UE also supports constrained baseline profile level 3.1 of the same release. Support for ITU-T H.265 Main profile, Main tier, level 3.1 is also recommended.
+
+Also, as part of procedures, in clause 2.2.2 of [b-GSMA IR.94], the UE and the network must be able to establish a video call directly during session establishment or by adding video to a voice session by sending SIP (re-) INVITE request with an SDP offer that contains both voice and video media descriptors. To ensure optimum QoS delivery it is imperative to adjust the maximum bit rate (MBR) of the video signal to levels far below the configuration settings of level 3.1 of [ITU-T H.264] and fine-tuned to the transmission capabilities of the network.
+
+It is recommended to align codec implementations for ViLTE so that codecs can be used in use cases taken as assumptions for the development of relevant parametric models proposed in [ITU-T G.1070] and [ITU-T P.1202.1]. Suffice to indicate that ITU-T H.264/ITU-T H.265 codec resolution, frame rate and encoding bit rate constitute key dependencies as far as maximum user perceived quality of the ViLTE service is concerned. Manufacturers of terminal devices (mobile phones and personal digital assistants (PDAs)) that support video telephony over the LTE network can find interesting guidance in the Table 2 assumptions, whereas codec design requirements should consider the coefficient derivation functions cited in Appendix I of [ITU-T G.1070].
+
+**Table 2 – Assumptions about monitor characteristics**
+
+| Monitor specifications | Nominal values |
+|------------------------|----------------|
+| Diagonal length (Note) | 2-10 inches    |
+| Dot pitch              | < 0.30         |
+| Colour temperature     | 6500 K         |
+| Bit depth              | 8 bits/colour  |
+
+**Table 2 – Assumptions about monitor characteristics**
+
+| Monitor specifications                                  | Nominal values            |
+|---------------------------------------------------------|---------------------------|
+| Refresh rate                                            | $\geq 60$ Hz              |
+| Brightness                                              | 100-300 cd/m <sup>2</sup> |
+| NOTE – Diagonal length means the image size of monitor. |                           |
+
+The end-to-end delay that a ViLTE video packet experiences may fluctuate from packet to packet. This variation in end-to-end delay is referred to as delay jitter. Delay jitter is a crucial problem for ViLTE because the receiving terminal (UE) must receive/decode/display frames in realtime and at a constant rate, any late frames resulting from the delay jitter can produce annoying artefacts in the reconstructed video e.g., jerks in the video.
+
+This problem is typically addressed by including a playout buffer at the receiver. While the playout buffer can compensate for the delay jitter, it can potentially introduce additional delay. Video jitter buffer management for guaranteed QoS in video channels requires placing a cap on the jitter buffer latency (delay threshold), probing the jitter buffer state and doing away with excess video packets from the jitter buffer. In the case of an overflow a latency exceeded message is sent to notify the application that there may be enough delay in the jitter buffer to affect media synchronization and this is addressed by purging the jitter buffer.
+
+### 8.3 E-UTRAN (Radio resource management)
+
+Within the evolved-UMTS terrestrial radio access network (E-UTRAN) segment of the ViLTE architecture model, it is the responsibility of the enhanced Node B (e-NodeB) to ensure the provisioning of the necessary QoS conditions for a dedicated (video) bearer over the radio interface, taking into consideration such key determinants as the QCI and the priority levels.
+
+One very key requirement in QoS provisioning at the radio-interface level is the type of scheduling strategy that must be administered on the e-NodeB as part of the radio resource management functions for a multi-user orthogonal frequency-division multiple access (OFDMA)-based mobile system. A good and efficient scheduling algorithm is required to demonstrate the desired performance levels in accordance with tolerable limits specified in [ETSI TS 123 203] for video telephony traffic. The priority and packet delay budget, and to some extent the acceptable packet loss rate from the QCI label, is required to determine the radio link control (RLC) mode configuration and how the scheduler in the medium access control (MAC) handles packets sent over the bearer.
+
+It is thus recommended to RAN equipment vendors and systems operators a scheduling strategy that overcomes some of the limits of traditional benchmark scheduling algorithms (e.g., packet loss fair (PLF), modified largest weighted delay first (M-LWDF) or proportionality fair (PF)) in terms of throughput, packet loss and fairness among others. An LTE network operating a radio cell coverage, reference signal received power (RSRP) level, of less than -105 dBm is required to guarantee basic rule of thumb on admission controls based on the appropriate QCI from the user equipment.
+
+An IMS session request for a video call (originating or terminating) in E-UTRAN requires that one dedicated bearer resource for voice and another dedicated bearer resource for video as specified in [b-GSMA IR.94] is created by authorizing the flows utilizing dynamic policy and charging control (PCC). The network must initiate the creation of dedicated bearer resources to transport the voice and video media. The dedicated bearer for conversational video stream may be a GBR or a non-GBR bearer. If a GBR bearer is used it must utilize the standardized QCI value of two (2) and have the associated characteristics as provided in [ETSI TS 123 203]. In the case of IMS termination of a session using conversational media, dedicated bearer resources must be deleted by withdrawing the authorization of the flows. The network must initiate the deletion of the bearer resources.
+
+### 8.4 Evolved packet core (QCI allocation and mobility management procedures)
+
+Evolved packet core (EPC) provides support to the QoS classification (between the policy and charging enforcement function (PCEF) and the ViLTE client), as defined in clause 5 of [ETSI TS 122 105] and clause 6.1.7 of [ETSI TS 123 203]. The mobility management entity (MME) provides tracking area updates to mobile UEs.
+
+When a UE attaches with the network, a mutual authentication of the UE and the network is performed between the UE and the MME/home subscriber server (HSS). This authentication function also establishes security keys that are used for encryption of the bearers. Signalling overhead due to excessive tracking area (TA) updates must be managed in such a way as to guarantee reduced delays during the video calling session setup.
+
+The S-GW supports transport level QoS through marking IP packets with appropriate Diffserv code points based on the parameters associated with the corresponding bearer. The P-GW is the point of interconnect to external IP networks through the SGi interface. It also has a key role in supporting QoS for end-user IP services.
+
+A good hierarchical design is required to provide for seamless coordination of control-plane signalling during mobility with the two (2) major QoS preconditions being minimization of interruption in QoS during handover as well as improved support for interoperability among mobility protocols (IP/IPv6).
+
+### 8.5 IMS and IP transit core (call control and signalling)
+
+The IMS core supports ViLTE client registration and authentication. Video over IP (VoIP) session setup and release is enabled by the IMS and requires SIP signalling operating at an assigned QCI-5 as well as a realtime transfer of voice and video RTP flow as at QCI-1 and QCI-2, respectively (see Table 1).
+
+To fulfil these requirements, and in the context of a capacity-constrained network, the Diffserv (differentiated services code point (DSCP)) approach may be used to ensure efficient bandwidth allocation and scheduling among several traffic applications including video telephony.
+
+An LTE operator providing triple-play service offerings (voice, video, data) can adapt to the varying traffic requirements on their network by creating a traffic class group for each of the service types.
+
+## 9 Budget estimation and QoS parameterization
+
+### 9.1 Relevant indicators
+
+There are two categories of indicators to consider when assessing the quality of ViLTE services:
+
+- 1) Session setup and continuity;
+- 2) Integrity of the content.
+
+In the first category, the target is to assess which level of quality a user can access and use the service over an entire ViLTE session. The recommended metrics are given in Table 3 below.
+
+**Table 3 – QoS parameters for session setup and continuity**
+
+| Name                                      | Definition                                                                                                                                                                                                                                 |
+|-------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Video telephony (VT) service availability | End-to-end service availability in terms of capacity to establish a call, as well as its audio and video components, from, and to, a ViLTE customer.<br>An attempted ViLTE call resulting in a voice-only session is considered as failed. |
+
+**Table 3 – QoS parameters for session setup and continuity**
+
+| Name                                      | Definition                                                                                                                                                                                                                                                                                                                                                                                                    |
+|-------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Video component availability              | The availability of the video component if it is requested to be added to an existing VoLTE call.                                                                                                                                                                                                                                                                                                             |
+| VT setup time (post dialling delay (PDD)) | Time interval (in seconds) between the end of dialling by a caller and the reception back of the appropriate ringing tone, in case of a successful ViLTE call.                                                                                                                                                                                                                                                |
+| Components setup time                     | Time interval (in seconds) between the reception of a ringing tone and the beginning of the corresponding audio and video sessions, in case of a successful ViLTE call, or the time it takes to add the video component after request from a VoLTE call.<br>Narrowband (NB): this metric does not consider whether or not the relevant QCI has been assigned to each flow (QCI-1 for voice, QCI-2 for video). |
+| VT service interruption time              | Time interval (in seconds) during which the session is paused (at least one medium, audio or video, is missing) before the session starts again.                                                                                                                                                                                                                                                              |
+| VT cut-off ratio                          | The possibility to use the service and/or its audio and video components until the user requests to release the call.<br>A ViLTE call with an undesired release of the video component, but the audio component still working, is considered as dropped.                                                                                                                                                      |
+
+The second category concerns video quality (audio quality is considered in [ITU-T G.1028]), with two complementary points of view: global quality (expressed in terms of mean opinion score (MOS)) and detection and characterization of artefacts. The recommended metrics are given in Table 4 below.
+
+**Table 4 – QoS parameters video quality measurements**
+
+| Name                      | Definition                                                                                                                          |
+|---------------------------|-------------------------------------------------------------------------------------------------------------------------------------|
+| Video quality (MOS)       | Provides an objective view on the quality of the video signal as perceived by the VT customer                                       |
+| Detection of freezing     | <ul style="list-style-type: none"> <li>number and rate of detections</li> <li>cumulative duration of all detected events</li> </ul> |
+| Detection of blurriness   | <ul style="list-style-type: none"> <li>number and rate of detections</li> <li>cumulative duration of all detected events</li> </ul> |
+| Detection of pixelization | <ul style="list-style-type: none"> <li>number and rate of detections</li> <li>cumulative duration of all detected events</li> </ul> |
+
+Guidance is given in clause 10.3 on video quality measurement methods.
+
+- **Freezing:** for reliable transmission freezing is the only distortion caused by transmission problems, in ViLTE it is just one in between others (and a minor one). In principle, it happens only if the (short) buffer runs empty. Based on current knowledge, the player decodes and plays-out what it gets, regardless of how destroyed the packets are. But it is a question of time that players apply other strategies as error concealment or freezing until the next I-frame is received for full synchronization.
+- **Blurriness:** caused by low resolution along with compression. Depending on the markets, the native image resolution is usually limited at 240p or 360p (quite blurry on a high definition (HD) phone display). Even if standards allow higher resolutions and also adaptive bit rates. Detection of 'blocks' in case of a 240p I-frame is considered as blurriness.
+
+- **Pixelization:** what can be seen in case of transmission errors is the full set of image distortions caused by wrong updates (erroneous intra-frames). These are false-colour macro-blocks appearing and moving around, wrongly moved macro-blocks in general, freezing part of the image, luminance information that does not fit to the chrominance and more. The effect of 'error propagation' also needs to be considered: one erroneous intra-frame destroys an image, so that, even if all following intra-frames are received without error, the update information is applied to a destroyed image.
+
+### 9.2 Impact assessment of relevant operating conditions on QoS parameters
+
+Below are feedbacks provided from laboratory or field tests concerning the influence of operating conditions on the various dimensions of QoS for ViLTE. This clause is to be completed in further revisions.
+
+- Codec resolution vs. video quality
+
+![Line graph showing Note (Y-axis, 1.0 to 5.0) versus Resolution (X-axis, 176x144 to 1280x720) for different Framerates (10, 12, 15, 20, 25 fps). The graph shows that video quality increases with resolution and framerate. The background is shaded green for Note values above 4.0 and orange for values between 3.0 and 4.0.](3468bcffa38de23cef94bfb460ccb301_img.jpg)
+
+| Resolution | Framerate 10 fps | Framerate 12 fps | Framerate 15 fps | Framerate 20 fps | Framerate 25 fps |
+|------------|------------------|------------------|------------------|------------------|------------------|
+| 176x144    | ~1.9             | ~2.0             | ~2.1             | ~2.2             | ~2.3             |
+| 320x240    | ~2.8             | ~2.9             | ~3.0             | ~3.1             | ~3.2             |
+| 352x288    | ~2.9             | ~3.1             | ~3.3             | ~3.4             | ~3.5             |
+| 640x360    | ~3.0             | ~3.5             | ~3.8             | ~4.0             | ~4.2             |
+| 640x480    | ~3.2             | ~3.6             | ~3.9             | ~4.0             | ~4.1             |
+| 704x576    | ~3.2             | ~3.7             | ~3.8             | ~4.1             | ~4.2             |
+| 960x540    | ~3.5             | ~3.7             | ~4.0             | ~4.2             | ~4.5             |
+| 1280x720   | ~3.5             | ~3.8             | ~4.1             | ~4.3             | ~4.5             |
+
+Line graph showing Note (Y-axis, 1.0 to 5.0) versus Resolution (X-axis, 176x144 to 1280x720) for different Framerates (10, 12, 15, 20, 25 fps). The graph shows that video quality increases with resolution and framerate. The background is shaded green for Note values above 4.0 and orange for values between 3.0 and 4.0.
+
+G.1028.1(19)\_F03
+
+**Figure 3 – Codec resolution versus video quality**
+
+Results from subjective tests show that video graphics array (VGA) (320×240) at 15 fps can only provide a medium quality user experience (MOS ≈ 3.0). A good quality (MOS ≈ 4) requires a minimum resolution of (640×360) at 15 fps. VGA (640×480) is however, the widely-supported resolution for achieving this quality level.
+
+- Encoding bitrate vs. video quality
+
+![Figure 4: Bit rate versus video quality. The figure consists of three line graphs for resolutions 320x240, 640x480, and 1280x720. Each graph plots Mean Opinion Score (MOS) on the y-axis (1.0 to 5.0) against bit rate on the x-axis. Three data series are shown: 10 fps (blue solid line with circles), 15 fps (red dashed line with squares), and 25 fps (green dotted line with diamonds). Shaded regions indicate quality levels: green for MOS ≥ 4.0 and red for MOS < 4.0. The 25 fps series generally achieves higher MOS than the others at the same bit rate, while the 10 fps series achieves lower MOS.](3102c32204f998dba666e1e915d5babf_img.jpg)
+
+Figure 4: Bit rate versus video quality. The figure consists of three line graphs for resolutions 320x240, 640x480, and 1280x720. Each graph plots Mean Opinion Score (MOS) on the y-axis (1.0 to 5.0) against bit rate on the x-axis. Three data series are shown: 10 fps (blue solid line with circles), 15 fps (red dashed line with squares), and 25 fps (green dotted line with diamonds). Shaded regions indicate quality levels: green for MOS ≥ 4.0 and red for MOS < 4.0. The 25 fps series generally achieves higher MOS than the others at the same bit rate, while the 10 fps series achieves lower MOS.
+
+G.1028.1(19)\_F04
+
+**Figure 4 – Bit rate versus video quality**
+
+It can be inferred from subjective test results that the optimal operating range for good video MOS using ITU-T H.264 baseline level 3.1 is a VGA resolution with frame rate of 15 fps to 30 fps and a bit rate of 384 kbit/s to 768 kbit/s. Thus, 384 kbit/s is the minimum bit rate to ensure a quite good quality experience (approx. 3.5 MOS) whereas a very good video quality ( $\geq 4.0$  MOS) requires a bit rate up to 768 kbit/s. A better codec will, however, not solve all capacity/coverage issues – rate adaptation is needed. Devices must be capable to detect transmission conditions (at receiver and sender side) and adapt bit rate/frame rate and resolution accordingly.
+
+– Video bit rate vs. capacity
+
+Dedicated bearer for ViLTE (with QCI-2) provides a GBR. The radio scheduler gives more radio resources to this bearer to ensure the GBR at cell edge. With a GBR at 768 kbit/s, a single ViLTE call consumes 20% of the radio resources in uplink (UL) (10 MHz bandwidth); thus, the overall data performance in the cell is impacted.
+
+**Table 5 – Video bit rate versus capacity**
+
+| %rRadio resource allocation per ViLTE terminal |            | Cell-centre | Mid cell | ViLTE cell edge |
+|------------------------------------------------|------------|-------------|----------|-----------------|
+| 10 MHz                                         | 384 kbit/s | 2.0%        | 8.0%     | 12%             |
+|                                                | 768 kbit/s | 3.2%        | 2.0%     | 20.6%           |
+| 20 MHz                                         | 384 kbit/s | 1.0%        | 4.0%     | 6.0%            |
+|                                                | 768 kbit/s | 1.6%        | 5.5%     | 10.3%           |
+
+To ensure ViLTE quality of experience (QoE) without affecting other user's throughput, practical best-fit measures would have to be taken. The use of GBR = MBR is actually not suitable for operation with rate adaptation. The possible options for maximum video quality are:
+
+- Use of QCI-2 with GBR < MBR; or
+- Use of a non-GBR QCI (6 or 7) with scheduling priority + cell based min bit rate + ViWifi whenever possible.
+
+In summary, to ensure a more optimal ViLTE performance there is the need for efficient codecs to reduce the video bit rate, adapt the video bit rate to transmission condition with rate adaptation and possibly consider other QCI options than 2.
+
+- Jitter buffer performance vs. video quality;
+- RTP packet loss vs. setup time (PDD);
+- Tracking area update vs. setup time;
+- Coverage/interference vs. service availability and call cut-off ratio;
+- Handover vs. service interruption time.
+
+### 9.3 Quality targets
+
+This clause is for further study. Table 6 below will be completed once feedback from field deployments are available.
+
+**Table 6 – Quality budget allocation**
+
+| Network segment     | LTE-LTE<br>(intra) |             | LTE-LTE<br>(with interconnection) |             | LTE-LTE<br>(with roaming) |             |
+|---------------------|--------------------|-------------|-----------------------------------|-------------|---------------------------|-------------|
+|                     | Indicator A        | Indicator B | Indicator A                       | Indicator B | Indicator A               | Indicator B |
+| UE                  |                    |             |                                   |             |                           |             |
+| E-UTRAN             |                    |             |                                   |             |                           |             |
+| EPC                 |                    |             |                                   |             |                           |             |
+| IMS/AS              |                    |             |                                   |             |                           |             |
+| <b>Total budget</b> |                    |             |                                   |             |                           |             |
+|                     | Indicator C        | Indicator D | Indicator C                       | Indicator D | Indicator C               | Indicator D |
+| UE                  |                    |             |                                   |             |                           |             |
+| E-UTRAN             |                    |             |                                   |             |                           |             |
+| EPC                 |                    |             |                                   |             |                           |             |
+| IMS/AS              |                    |             |                                   |             |                           |             |
+| <b>Total budget</b> |                    |             |                                   |             |                           |             |
+|                     | Indicator E        | Indicator F | Indicator E                       | Indicator F | Indicator E               | Indicator F |
+| UE                  |                    |             |                                   |             |                           |             |
+| E-UTRAN             |                    |             |                                   |             |                           |             |
+| EPC                 |                    |             |                                   |             |                           |             |
+
+**Table 6 – Quality budget allocation**
+
+| Network segment     | LTE-LTE<br>(intra) |             | LTE-LTE<br>(with interconnection) |             | LTE-LTE<br>(with roaming) |             |
+|---------------------|--------------------|-------------|-----------------------------------|-------------|---------------------------|-------------|
+|                     | Indicator G        | Indicator H | Indicator G                       | Indicator H | Indicator G               | Indicator H |
+| IMS/AS              |                    |             |                                   |             |                           |             |
+| <b>Total budget</b> |                    |             |                                   |             |                           |             |
+|                     |                    |             |                                   |             |                           |             |
+| UE                  |                    |             |                                   |             |                           |             |
+| E-UTRAN             |                    |             |                                   |             |                           |             |
+| EPC                 |                    |             |                                   |             |                           |             |
+| IMS/AS              |                    |             |                                   |             |                           |             |
+| <b>Total budget</b> |                    |             |                                   |             |                           |             |
+
+## 10 Diagnostic strategy for QoS degradations
+
+This clause explains the various video-centric degradations that can be encountered on a mobile LTE network. Main elements of the mobile network are depicted to show the signalling and media elements as well as the connections with public switched telephone network (PSTN) or mobile platforms.
+
+![Diagram illustrating sources of potential audiovisual impairments in ViLTE. It shows a network architecture with UE, eNodeB, EPC (MME, SGW, PGW), HSS, IMS (AS/SCC-AS, P-CSCF, I/S-CSCF), and IP Core network. Various impairments are listed in boxes connected to these elements.](09955ff8214ffb6947951fc0f60eb6ab_img.jpg)
+
+The diagram illustrates the network architecture for ViLTE and identifies potential sources of audiovisual impairments. The architecture includes:
+
+- UE (User Equipment):** Two mobile devices connected to eNodeB via S1c. Impairments: Echo, Noise, Low/high audio level, Device acoustic, White call, Chopped conversation, Encoding/decoding issues.
+- eNodeB:** Two base stations connected to the EPC via S1u. Impairments: Call drop, Handover latency, Radio degradation (BER/FER).
+- EPC (Evolved Packet Core):** Contains MME, SGW, and PGW. Impairments: IP packet loss, Network delay variation (Jitter), IP desequencement, Link failure, Availability of basic call service and Supplementary services, Identification failure (Sim card, ...).
+- HSS (Home Subscriber Server):** Connected to MME via S6a. Impairments: Availability, DTMF not recognized, Encoding/decoding issues.
+- IMS (IP Multimedia Subsystem):** Contains AS/SCC-AS, P-CSCF, and I/S-CSCF. Impairments: Availability, DTMF not recognized, Encoding/decoding issues.
+- IP Core network:** Connected to PGW via SGi and to IMS via AGW/CBGF. Impairments: Availability, DTMF not recognized, Encoding/decoding issues.
+
+A central box indicates that frozen image, pixelization, blockiness, back to only voice, E2E delay, availability of calls, and PDD are generated by all elements. The diagram is labeled G.1028.1(18)\_F05.
+
+Diagram illustrating sources of potential audiovisual impairments in ViLTE. It shows a network architecture with UE, eNodeB, EPC (MME, SGW, PGW), HSS, IMS (AS/SCC-AS, P-CSCF, I/S-CSCF), and IP Core network. Various impairments are listed in boxes connected to these elements.
+
+**Figure 5 – Sources of potential audiovisual impairments in ViLTE**
+
+In order to have a point of comparison in terms of QoS delivered, a reference call is taken whose ideal characteristics are:
+
+- Fourth generation (4G)-4G call with end-to-end codecs (adaptive multi-rate wideband (AMR-WB) for audio, ITU-T H.264/ITU-T H.265 for video) and associated video features (frame rate, ITU-T H.264/ITU-T H.265 profile, video orientation) correctly negotiated;
+- No degradation on EPC (no IP loss, no load, etc.);
+- No degradation on E-UTRAN (no radio degradation, no congestion, etc.);
+- Wideband audio compliant devices, both on 4G, with excellent acoustic, voice quality enhancement algorithms (noise reduction (NR), acoustic echo control (AEC) and automatic gain control (AGC)), electronic;
+- Quiet environment on both ends;
+- All services are available (e.g., call transfer, dual-tone multi-frequency (DTMF)).
+
+Below are the main possible technical reasons, which generate the encountered degradations. Separation is done according to the impact assessment due to the customer.
+
+### 10.1 QoS problem source-linked to availability of service
+
+**Table 7 – Degradations related to availability of the service and their potential causes**
+
+| Kind of degradation               | Possible reasons                                                                                                                                                                                                                                                                                                                                                                          | Location     |
+|-----------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------|
+| UE identification failure         | <ul style="list-style-type: none"> <li>• problem with MME, HSS or policy and charging rule function (PCRF)</li> </ul>                                                                                                                                                                                                                                                                     | EPC          |
+| Unavailability of basic call      | <ul style="list-style-type: none"> <li>• error in scheduling</li> <li>• radio resource control (RRC) connection setup failure (reception of RRC connection reject, or expiry of timer T300, no RRC connection setup complete sent after reception of RRC connection setup)</li> </ul>                                                                                                     | EUTRAN       |
+|                                   | <ul style="list-style-type: none"> <li>• not available due to load (S-GW or P-GW)</li> <li>• failed negotiation (e.g., allocation of QCI, codec)</li> <li>• reception of several SIP error codes (e.g., 401 = Unauthorized, 405 = Method Not Allowed)</li> <li>• reception of SIP CANCEL from IMS</li> <li>• TD internal timer expired, causing a "SessionSetupFailureTimeout"</li> </ul> | EPC          |
+| Unavailability of video component | <ul style="list-style-type: none"> <li>• failed negotiation (e.g., allocation of QCI, codec, resolution)</li> </ul>                                                                                                                                                                                                                                                                       | EPC/Terminal |
+| PDD                               | <ul style="list-style-type: none"> <li>• load</li> <li>• interworking between systems</li> <li>• circuit switched (CS) fallback at call setup</li> </ul>                                                                                                                                                                                                                                  | All          |
+| Link failure                      | <ul style="list-style-type: none"> <li>• bad negotiation between two pieces of equipment of the network during call establishment (bad codec management)</li> </ul>                                                                                                                                                                                                                       | EUTRAN/EPC   |
+| White call                        | <ul style="list-style-type: none"> <li>• terminal is not able to code or decode speech while the signalling is OK for the communication</li> </ul>                                                                                                                                                                                                                                        | Terminal     |
+
+### 10.2 QoS problem source-linked to network performance
+
+In this sub-section, QoS degradations, which are linked to network performance, are depicted. In concrete terms, these degradations, specific to network mainly lead to video degradation from the customer's perspective.
+
+**Table 8 – Degradations related to network performance and their potential causes**
+
+| <b>Kind of degradation</b>                        | <b>Possible reasons</b>                                                                                                                                                                                                                                                                                                                                                                                                                                       | <b>Location</b>     |
+|---------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------|
+| Frozen image                                      | <ul style="list-style-type: none"> <li>no reception of video frame</li> <li>network congestion (several causes: traffic load, distance from cell center causing activation of TTI bundling, for instance)</li> <li>jitter buffers not adapted to actual jitter amount</li> </ul>                                                                                                                                                                              | All                 |
+| Blurriness                                        | <ul style="list-style-type: none"> <li>no reception of infra video frame</li> <li>recovery strategy of decoder in terminal</li> </ul>                                                                                                                                                                                                                                                                                                                         | All                 |
+| Blockiness / Pixelization                         | <ul style="list-style-type: none"> <li>no reception of infra video frame</li> <li>recovery strategy of decoder in terminal</li> </ul>                                                                                                                                                                                                                                                                                                                         | All                 |
+| Encoding/Decoding issues                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                               | Terminal/<br>eUTRAN |
+| E2E delay (latency)                               | <ul style="list-style-type: none"> <li>network load</li> <li>media handling (packet construction, jitter buffer management)</li> <li>speech processing in terminals</li> <li>random access channel (RACH) upon receiving handover command</li> <li>RACH/contention procedure</li> <li>additional RACH attempts</li> <li>dynamic scheduling, link adaptation</li> <li>radio link failure/re-establishment during handover (possibly different cell)</li> </ul> | All                 |
+| Bad (lip) synchronization between voice and video | <ul style="list-style-type: none"> <li>network congestion associated with differentiated QoS (QCI)</li> <li>different jitter buffer size and behavior</li> <li>decoding time</li> </ul>                                                                                                                                                                                                                                                                       | All                 |
+| RTCP/IP packet loss                               | <ul style="list-style-type: none"> <li>network congestion (several causes: traffic load, distance from cell center causing activation of TTI bundling, for instance)</li> <li>jitter buffers not adapted to actual jitter amount or packet size (can depend on use of robust header compression (RoHC) or not)</li> </ul>                                                                                                                                     | EPC /<br>Terminal   |
+| RTP/IP desequencing                               | <ul style="list-style-type: none"> <li>new route after a problem such as congestion</li> </ul>                                                                                                                                                                                                                                                                                                                                                                | EPC                 |
+| Network delay variation (Jitter)                  | <ul style="list-style-type: none"> <li>network congestion.</li> <li>jitter buffers not adapted</li> </ul>                                                                                                                                                                                                                                                                                                                                                     | EPC /<br>Terminal   |
+| Radio degradations                                | <ul style="list-style-type: none"> <li>limit of the cell coverage</li> <li>interference</li> <li>area not well covered (e.g., obstacle)</li> <li>bad radio optimization.</li> <li>radio loss profile</li> <li>bad radio scheduling</li> <li>no or bad use of hybrid automatic-repeat-request (HARQ)</li> <li>mechanisms</li> <li>etc.</li> </ul>                                                                                                              | eUTRAN              |
+
+**Table 8 – Degradations related to network performance and their potential causes**
+
+| Kind of degradation              | Possible reasons                                                                                                                                                                                                                                                                                                                                                                                                                                       | Location            |
+|----------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------|
+| Handover latency                 | <ul style="list-style-type: none"> <li>latency due to new route after handover or single radio voice call continuity (SRVCC)</li> </ul>                                                                                                                                                                                                                                                                                                                | EPC / CS network    |
+| Call drop                        | <ul style="list-style-type: none"> <li>terminal bug, bad covered area, handover/SRVCC failures due to cells neighborhood problem, etc.<br/>RRC connection drop (at reception of RRC connection Re-establishment reject, or expiry of timer T301 or in case RRC connection release is received before new RRC connection setup attempt)</li> </ul>                                                                                                      | Terminal/<br>eUTRAN |
+|                                  | <ul style="list-style-type: none"> <li>link failure: system failure, bad re-negotiation between two equipments of the network during call</li> <li>reception of SIP status code 500 (server internal error)</li> <li>no RTP packet received during a period longer than "<i>SessionDropTimeout</i>" TD internal timer</li> <li>no SIP 200 OK on BYE is received within the time measured by "<i>SessionHangupTimeout</i>" TD internal timer</li> </ul> | EPC                 |
+| Back to voice-only communication | <ul style="list-style-type: none"> <li>network congestion (several causes: traffic load, distance from cell center causing activation of TTI bundling)</li> <li>strategy of service provided and/or device maker</li> </ul>                                                                                                                                                                                                                            |                     |
+
+### 10.3 Tools and models for measurement and prediction of video quality
+
+This clause is a complement for video to clause 10.3.2 of [ITU-T G.1028] where an overview of tools and models for voice quality is provided.
+
+A global view of all standard quality assessment methods is given in Table 10.3 of [ITU-T G.1011] and shows a detailed application scope of each model in terms of supported resolutions and codecs.
+
+Following the taxonomy provided there, the potential methods are:
+
+- Media layer models: all models for video media streaming quality assessment:
+  - full reference: [ITU-T J.144] (standard definition (SD)), [ITU-T J.247] (quarter common intermediate format (QCIF), common intermediate format (CIF), VGA), [ITU-T J.341] (HD);
+  - reduced reference: [ITU-T J.249] (SD), [ITU-T J.246] (QCIF, CIF, VGA), [ITU-T J.342] (HD);
+  - no reference: none.
+- Packet layer models:
+  - models for planning purposes: [ITU-T G.1070] (dedicated tool for video telephony, including also an audio quality module), [ITU-T G.1071] (for video streaming, SD, HD);
+  - models for monitoring purposes (no reference) on UDP for video media streaming quality assessment: [ITU-T P.1201.1] (QCIF, quarter video graphics array (QVGA), half video graphics array (HVGA)), [ITU-T P.1201.2] (SD, HD), [ITU-T P.1201] Amd. 2, App. III (HVGA, HD (1080i50, 1080p24, 1080i60, 1080p30)).
+- Bitstream layer models (no reference) on UDP for audiovisual media streaming quality assessment:
+  - [ITU-T P.1202.1] (QCIF, QVGA, HVGA), [ITU-T P.1202.2] (SD, HD).
+- Hybrid models: all models for video media streaming quality assessment:
+
+- full reference: [ITU-T J.343.5] (HD, encrypted bitstream), [ITU-T J.343.6] (HD, not encrypted bitstream);
+- reduced reference: [ITU-T J.343.3] (HD, encrypted bitstream), [ITU-T J.343.4] (HD, not encrypted bitstream);
+- no reference: [ITU-T J.343.1] (HD, encrypted bitstream), [ITU-T J.343.2] (HD, not encrypted bitstream).
+
+With the exception of [ITU-T G.1070], all these methods have been developed for an application on video or audiovisual streaming services, not for video telephony. Because of the relatively good similarity between contents of both types of services, their application for the evaluation of quality of video telephony services may be envisaged, though it need to be understood that it would require some hard validation work.
+
+Indeed, implementation of these methods raises some important concerns:
+
+- Rating the impairments of video quality based on (encrypted) bitstreams is rather complicated. A bitstream method can give some metrics, how it would look like in a general statistical view under assumption of medium players and encoding strategies, but the accuracy and the relevance of the measurement results must be considered with highest caution;
+- Full reference methods require the possibility to inject a reference video or audiovisual content at the applicative level inside UEs instead of the content provided by the camera. This feature is currently not supported on almost all models of mobile devices;
+- The video player strategy of mobile devices to deal with errors and to minimize their visibility is varying between devices. Models must be calibrated before they can be applied on a given model of device.
+
+## Bibliography
+
+[b-GSMA IR.94] GSMA IR.94 v 11.0 (2016), *IMS Profile for Conversational Video Service*.
+
+
+
+
+
+## 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                                                                                      |

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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.103**
+
+(12/98)
+
+SERIES G: TRANSMISSION SYSTEMS AND MEDIA,  
+DIGITAL SYSTEMS AND NETWORKS
+
+International telephone connections and circuits – General  
+definitions
+
+---
+
+# **Hypothetical reference connections**
+
+ITU-T Recommendation G.103
+
+(Previously CCITT Recommendations)
+
+---
+
+## ITU-T G-SERIES RECOMMENDATIONS **TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS**
+
+|                                                                                                                                              |                    |
+|----------------------------------------------------------------------------------------------------------------------------------------------|--------------------|
+| INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS                                                                                             | G.100–G.199        |
+| <b>General definitions</b>                                                                                                                   | <b>G.100–G.109</b> |
+| General Recommendations on the transmission quality for an entire international telephone connection                                         | G.110–G.119        |
+| General characteristics of national systems forming part of international connections                                                        | G.120–G.129        |
+| General characteristics of the 4-wire chain formed by the international circuits and national extension circuits                             | G.130–G.139        |
+| General characteristics of the 4-wire chain of international circuits; international transit                                                 | G.140–G.149        |
+| General characteristics of international telephone circuits and national extension circuits                                                  | G.150–G.159        |
+| Apparatus associated with long-distance telephone circuits                                                                                   | G.160–G.169        |
+| Transmission plan aspects of special circuits and connections using the international telephone connection network                           | G.170–G.179        |
+| Protection and restoration of transmission systems                                                                                           | G.180–G.189        |
+| Software tools for transmission systems                                                                                                      | G.190–G.199        |
+| <b>INTERNATIONAL ANALOGUE CARRIER SYSTEM</b>                                                                                                 |                    |
+| 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        |
+| <b>TESTING EQUIPMENTS</b>                                                                                                                    |                    |
+| <b>TRANSMISSION MEDIA CHARACTERISTICS</b>                                                                                                    | G.600–G.699        |
+| <b>DIGITAL TRANSMISSION SYSTEMS</b>                                                                                                          |                    |
+| TERMINAL EQUIPMENTS                                                                                                                          | G.700–G.799        |
+| DIGITAL NETWORKS                                                                                                                             | G.800–G.899        |
+| DIGITAL SECTIONS AND DIGITAL LINE SYSTEM                                                                                                     | G.900–G.999        |
+
+*For further details, please refer to ITU-T List of Recommendations.*
+
+# **HYPOTHETICAL REFERENCE CONNECTIONS**
+
+## **Summary**
+
+This Recommendation was revised to introduce Integrated Services Digital Network and Integrated Digital Network Hypothetical Reference Connections, and also to allow for the introduction of ATM Technology into the PSTN. This Recommendation provides a number of Hypothetical Reference Connections that can be used to perform transmission impairment studies.
+
+## **Source**
+
+ITU-T Recommendation G.103 was revised by ITU-T Study Group 12 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 3<sup>rd</sup> of December 1998.
+
+## FOREWORD
+
+ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The 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 Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics.
+
+The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 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 term *recognized operating agency (ROA)* includes any individual, company, corporation or governmental organization that operates a public correspondence service. The terms *Administration*, *ROA* and *public correspondence* are defined in the *Constitution of the ITU (Geneva, 1992)*.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The 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, the ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database.
+
+© ITU 1999
+
+All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.
+
+## CONTENTS
+
+|                                                                                                                                      | Page |
+|--------------------------------------------------------------------------------------------------------------------------------------|------|
+| 1 Scope .....                                                                                                                        | 1    |
+| 2 Purpose .....                                                                                                                      | 1    |
+| 3 References .....                                                                                                                   | 1    |
+| 4 Composition of hypothetical reference connections .....                                                                            | 2    |
+| 5 Number of modulation and demodulation equipments .....                                                                             | 12   |
+| 6 Developments arising from the ongoing introduction of PCM digital processes .....                                                  | 12   |
+| Annex A – An explanation of how hypothetical reference connections can be drawn<br>assuming all send switching levels are 0 dBr..... | 13   |
+
+
+
+# **HYPOTHETICAL REFERENCE CONNECTIONS**
+
+*(Mar del Plata, 1968; amended at Geneva, 1972, 1976 and 1980;  
+at Malaga-Torremolinos, 1984; revised in 1998)*
+
+## **1 Scope**
+
+This Recommendation provides a number of Hypothetical Reference Connections. In particular, connections involving hybrid, i.e. analogue/digital networks, and wholly digital networks are addressed. The ongoing transitional problems associated with the conversion of hybrid networks to wholly digital networks are addressed in clause 6.
+
+## **2 Purpose**
+
+A hypothetical reference connection for transmission impairment studies is a model in which the impairments contributed by circuits and exchanges are described.
+
+Such a model may be used by an Administration:
+
+- to examine the effect on transmission quality of possible changes of routing structure, noise allocations, signal processing impairments and transmission losses in national networks; and
+- to test national planning rules for prima facie compliance with any statistical impairment criteria which may be recommended by the ITU-T for national systems.
+
+For these purposes, several models are desirable. In each model, the international circuits and exchanges are assumed to be digital. The one wholly digital hypothetical reference connection and the five hybrid reference connections described below should encompass most of the studies required to be undertaken.
+
+Hypothetical reference connections are *not* to be regarded as recommending particular values of loss or noise or other impairments, although the various values quoted are in many cases recommended values. Hypothetical reference connections are not intended to be used for the design of transmission systems.
+
+## **3 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; all 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.
+
+- [1] *Transmission planning of switched telephone networks*, ITU, Geneva, 1976.
+- [2] CCITT Recommendation E.171 (1988), *International telephone routing plan*.
+- [3] ITU-T Recommendation G.101 (1996), *The transmission plan*.
+- [4] ITU-T Recommendation G.111 (1993), *Loudness Ratings (LRs) in an international connection*.
+
+- [5] ITU-T Recommendation G.113 (1996), *Transmission impairments*.
+- [6] ITU-T Recommendation G.114 (1996), *One-way transmission time*.
+- [7] ITU-T Recommendation G.120 (1998), *Transmission characteristics of national networks*.
+- [8] ITU-T Recommendation G.121 (1993), *Loudness Ratings (LRs) of national systems*.
+- [9] CCITT Recommendation G.726 (1990), *40, 32, 24, 16 kbit/s Adaptive Differential Pulse Code Modulation (ADPCM)*.
+- [10] ITU-T Recommendation M.60 (1993), *Maintenance terminology and definitions*.
+- [11] ITU-T Recommendation P.310 (1996), *Transmission characteristics for telephone-band (300 – 3400 Hz) digital telephones*.
+
+## 4 Composition of hypothetical reference connections
+
+4.1 The composition of the various connections is defined in Figures 1, 2, 3, 4, 5 and 6.
+
+*Figure 1* – The longest wholly digital Integrated Services Digital Network (ISDN) international connection with the maximum number of international and national circuits expected to occur in practice.
+
+*Figure 2* – The longest Integrated Digital Network (IDN) international connection comprising the maximum number of international and national circuits expected to occur in practice.
+
+*Figure 3* – An integrated digital network international connection comprising the maximum number of international circuits and the least number of national circuits expected to occur in practice.
+
+*Figure 4* – An international connection comprising the maximum number of digital international circuits and the least number of analogue national circuits expected to occur in practice.
+
+*Figure 5* – An international connection of moderate length (i.e. not longer than 2000 km) comprising the most frequent number of international and analogue national circuits. In such a connection, the noise contribution of the national systems would be expected to predominate.
+
+*Figure 6* – The longest international connection with the maximum number of digital international and analogue national circuits expected to occur in practice. In such a connection, the noise contribution of the national systems would be expected to predominate. The attenuation distortion, group delay, and group-delay distortion would also be higher than for the IDN case. Such connections are expected to be extremely rare.
+
+4.2 *General remarks applicable to Figures 1, 2, 3, 4, 5 and 6.*
+
+4.2.1 The hypothetical reference connections show the international circuits connected together at 0 dBr and 0 dBr virtual switching points, as they are digital switching points interconnected by digital facilities, instead of –3.5 dBr and –4 dBr points, the values normally assigned to analogue ISC switches. This was felt to be more directly useful to those who might have to use the reference connections in their studies.
+
+It might be felt that it is somewhat inconsistent that the hypothetical reference connections do not use "conventional" analogue ISC –3.5/–4 dBr virtual switching points. However, if the reference connections are drawn using that convention, the noise power figures appearing on the diagram can no longer be the familiar ones that appear elsewhere in other Recommendations. Annex A gives further explanations.
+
+4.2.2 The nomenclature is based on the international routing plan recommended in Recommendation E.171, i.e. ISC = International Switching Centre.
+
+**4.2.3** In each case, only one direction of transmission is shown.
+
+**4.2.4** The design objectives for the mean noise powers are indicated according to current national recommendations. For long-distance national analogue carrier circuits they are proportional to length, the appropriate noise power rate, 4 pW/km or 1 pW/km, being used according to whether the basic hypothetical reference circuit is one 2500 km long or 7500 km long.
+
+**4.2.5** The abbreviation pW0p stands for picowatts psophometric referred to a point of zero relative level. In the case of analogue exchange noise, the point referred to is considered to be in the circuit immediately downstream, of the exchange. The noise powers for circuits are referred to points of zero relative level in the circuits themselves and not to some point on the connection.
+
+**4.2.6** This Recommendation was prepared using the assumption that Plesiochronous Digital Hierarchy/Synchronous Digital Hierarchy (PDH/SDH) technology and ATM digital technology may be used in the PSTN.
+
+**4.2.7** It is recommended that the E-Model be used to evaluate the transmission performance of specific configurations, especially when speech compression technology, e.g. G.726 compliant Digital Circuit Multiplication Equipment (DCME), is used.
+
+![Figure 1/G.103 - The longest ISDN international connection likely to occur in practice](a5ee5c23b6dc52ec1d724b76d5a5f58f_img.jpg)
+
+The diagram shows a symmetrical vertical path of a digital telephone connection. It starts at a 'Digital telephone' at the top, goes through a series of exchanges (LE, PC, SC, TC, QC, ISC), crosses an international boundary through multiple ISCs, and then descends through a mirrored set of exchanges (ISC, QC, TC, SC, PC, LE) to another 'Digital telephone' at the bottom.
+
+**Vertical Segments:**  
+ - Top National segment: 1750 km  
+ - International segment: 24 000 km  
+ - Bottom National segment: 1750 km
+
+**Technical Specifications (Top to Bottom):**  
+ - 8 dB (SLR)  
+ - 8 dB (Note 1)  
+ - 100 pWp (400 pW0p) (Note 2)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 0 pW0p (Note 4)  
+ - 0 dB, σ = 0 dB (Note 5)  
+ - 0 pW0p (Note 3)  
+ - 2 dB (Note 6)  
+ - 0 pW0p (Note 7)  
+ - 2 dB (RLR)
+
+Figure 1/G.103 - The longest ISDN international connection likely to occur in practice
+
+*Legend for Figures 1, 2, 3, 4, 5 and 6*
+
+|     |                           |     |                                |       |          |
+|-----|---------------------------|-----|--------------------------------|-------|----------|
+| SLR | Sending Loudness Rating   | SC  | Secondary Centre               | ——    | Analogue |
+| RLR | Receiving Loudness Rating | TC  | Tertiary Centre                | - - - | Digital  |
+| LE  | Local Exchange            | QC  | Quaternary Centre              |       |          |
+| PC  | Primary Centre            | ISC | International Switching Centre |       |          |
+
+**Figure 1/G.103 – The longest ISDN international connection likely to occur in practice**
+
+4 Recommendation G.103 (12/98)
+
+![Diagram of the longest IDN international connection likely to occur in practice. It shows a vertical chain of network elements between two analogue telephones. The chain includes line elements (LE), switching centres (SC), tandem centres (TC), quality centres (QC), and international switching centres (ISC). Various loss and noise parameters are specified for each element and section. On the left, three vertical arrows indicate distances: 1750 km for the top national section, 24 000 km for the international section, and 1750 km for the bottom national section. Loss parameters include 10.5 dB (SLR) at the top, -1 dB (RLR) at the bottom, and 10 dB at 1600 Hz for unloaded line plants at both ends. Noise parameters include 100 pWp (500 pWp), 0 dB (T Pad), 0 pW0p, and 0 dB, sigma = 0 dB for various components.](cfef993dcc8fb513de79eb1f93cf26ae_img.jpg)
+
+Analogue telephone
+
+10 dB at 1600 Hz. Root-f law for unloaded line plant
+
+10.5 dB (SLR)
+
+1750 km
+
+100 pWp (500 pWp), (Note 8)
+
+0 dB (T Pad) (Note 9)
+
+LE \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+SC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+TC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+QC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+ISC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+ISC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+ISC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+ISC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+ISC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+QC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+TC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+SC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+PC \*
+
+0 pW0p (Note 3)
+
+0 pW0p (Note 4)
+
+0 dB,  $\sigma = 0$  dB (Note 5)
+
+LE \*
+
+0 pW0p (Note 3)
+
+7 dB (R Pad) (Note 10)
+
+10 dB at 1600 Hz. Root-f law for unloaded line plant
+
+100 pWp (500 pWp) (Note 8)
+
+-1 dB (RLR)
+
+1750 km
+
+24 000 km
+
+International
+
+National
+
+T1208870-98
+
+Analogue telephone
+
+Diagram of the longest IDN international connection likely to occur in practice. It shows a vertical chain of network elements between two analogue telephones. The chain includes line elements (LE), switching centres (SC), tandem centres (TC), quality centres (QC), and international switching centres (ISC). Various loss and noise parameters are specified for each element and section. On the left, three vertical arrows indicate distances: 1750 km for the top national section, 24 000 km for the international section, and 1750 km for the bottom national section. Loss parameters include 10.5 dB (SLR) at the top, -1 dB (RLR) at the bottom, and 10 dB at 1600 Hz for unloaded line plants at both ends. Noise parameters include 100 pWp (500 pWp), 0 dB (T Pad), 0 pW0p, and 0 dB, sigma = 0 dB for various components.
+
+Figure 2/G.103 – The longest IDN international connection likely to occur in practice
+
+![Figure 3/G.103 – An example of an IDN international connection of 4 international circuits between subscribers situated near the terminal ISCs](d4af765160d04ecef538e5066006dc77_img.jpg)
+
+The diagram shows a vertical signal path between two analogue sets.   
+ Top section (National):   
+ - Analogue set   
+ - 3 dB at 1600 Hz. Root-f law for unloaded line plant   
+ - 4 dB (SLR)   
+ - 100 pWp (500 pWp) (Note 8)   
+ - 0 dB (T Pad) (Note 9)   
+ - LE (Local Exchange) with 0 pW0p (Note 3)   
+ Middle section (International):   
+ - A series of ISCs (International Switching Centers) connected by circuits.   
+ - Each ISC/circuit segment has annotations:   
+ - 0 pW0p (Note 4)   
+ - 0 dB, σ = 0 dB (Note 5)   
+ - 0 pW0p (Note 3)   
+ - This pattern repeats for 4 international circuits.   
+ Bottom section (National):   
+ - LE (Local Exchange) with 0 pW0p (Note 3)   
+ - 7 dB (R Pad) (Note 10)   
+ - 3 dB at 1600 Hz. Root-f law for unloaded line plant   
+ - -4.5 dB (RLR)   
+ - 100 pWp (500 pWp) (Note 8)   
+ - Analogue telephone   
+ - T1208880-98
+
+Figure 3/G.103 – An example of an IDN international connection of 4 international circuits between subscribers situated near the terminal ISCs
+
+**Figure 3/G.103 – An example of an IDN international connection of 4 international circuits  
+between subscribers situated near the terminal ISCs**
+
+6          **Recommendation G.103 (12/98)**
+
+![Diagram of a hybrid international connection showing signal levels and reference points between two analogue telephones across national and international segments.](af7916c89a458fdab6c3f443217388ae_img.jpg)
+
+The diagram illustrates a hybrid international connection between two analogue telephones, showing signal levels and reference points across different network segments.
+
+**Top Segment (National):**
+
+- Starts with an **Analogue telephone** connected to a line with a loss of **3 dB at 1600 Hz. Root-f law for unloaded line plant**.
+- A reference point **4 dB (SLR)** is indicated.
+- The signal passes through a series of components:
+  - A point marked with a dot (●) with a reference of **100 pWp (500 pWp) (Note 8)**.
+  - A line element **LE** marked with an 'X' with a reference of **100 pWp (200 pWp) (Note 11)**.
+  - A point marked with a dot (●) with a reference of **0 dB (Note 12)**.
+  - An **ISC** (Interchange Switching Centre) marked with an 'X' with a reference of **0 pW0p (Note 3)**.
+
+**International Segment:**
+
+- The signal continues through a series of components:
+  - A point marked with a dot (●) with a reference of **0 pW0p (Note 4)**.
+  - A point marked with a dot (●) with a reference of **0 dB,  $\sigma = 0$  dB (Note 5)**.
+  - An **ISC** marked with an 'X' with a reference of **0 pW0p (Note 3)**.
+  - A point marked with a dot (●) with a reference of **0 pW0p (Note 4)**.
+  - A point marked with a dot (●) with a reference of **0 dB,  $\sigma = 0$  dB (Note 5)**.
+  - An **ISC** marked with an 'X' with a reference of **0 pW0p (Note 3)**.
+  - A point marked with a dot (●) with a reference of **0 pW0p (Note 4)**.
+  - A point marked with a dot (●) with a reference of **0 dB,  $\sigma = 0$  dB (Note 5)**.
+  - An **ISC** marked with an 'X' with a reference of **0 pW0p (Note 3)**.
+  - A point marked with a dot (●) with a reference of **0 pW0p (Note 4)**.
+  - A point marked with a dot (●) with a reference of **0 dB,  $\sigma = 0$  dB (Note 5)**.
+  - An **ISC** marked with an 'X' with a reference of **0 pW0p (Note 3)**.
+  - A point marked with a dot (●) with a reference of **4 dB (Notes 12 and 13)**.
+  - A point marked with a dot (●) with a reference of **0 pW0p (Notes 3 and 14)**.
+  - A point marked with a dot (●) with a reference of **0 dB (Notes 12 and 14)**.
+  - A line element **LE** marked with an 'X' with a reference of **100 pWp (200 pWp) (Note 11)**.
+
+**Bottom Segment (National):**
+
+- The signal passes through a line with a loss of **3 dB at 1600 Hz. Root-f law for unloaded plant line**.
+- A reference point **- 4.5 dB (RLR)** is indicated.
+- The signal ends at another **Analogue telephone**.
+- A final reference point is marked with a dot (●) with a reference of **100 pWp (500 pWp) (Note 8)**.
+
+The diagram is labeled **T1208890-98** at the bottom.
+
+Diagram of a hybrid international connection showing signal levels and reference points between two analogue telephones across national and international segments.
+
+**Figure 4/G.103 – An example of a hybrid international connection of 4 international circuits between subscribers situated near the terminal ISCs**
+
+![Diagram of a hybrid international connection of moderate length with only one international circuit. The diagram shows a vertical line representing the connection path between two analogue telephones. The path is divided into three main segments: National (top), International (middle), and National (bottom). The top National segment is labeled 'National' and '≤ 500 km'. It includes a 4 dB (SLR) loss at the top, followed by an analogue telephone, a 3 dB at 1600 Hz. Root-f law for unloaded line plant, a 100 pWp (500 pWp) (Note 8) point, an LE X point with a 100 pWp (200 pWp) (Note 11) point, a Zero or 500 pW0p (Note 15); see Note 16 for maximum value and length point, a 5.5 dB, σ = 0 or 3 dB, σ = 1 (Note 17) point, and a PC X point with a 100 pW0p (200 pW0p) (Note 11) point. The International segment is labeled 'International' and '1000 km'. It includes a 500 pW0p (2000 pW0p) (Note 18) point, a 0.5 dB, σ = 1; length 2500 km (Note 13) point, an ISC X point with a 0 pW0p (Note 3) point, a 0 pW0p (Note 4) point, a 0 dB, σ = 0 dB (Note 5) point, another ISC X point with a 0 pW0p (Note 3) point, and a 500 pW0p (2000 pW0p) (Note 17) point. The bottom National segment is labeled 'National' and '≤ 500 km'. It includes a 0.5 dB, σ = 1 point, a 14 dB point, a PC X point with a 100 pW0p (2000 pW0p) (Note 11) point, a Zero or 500 pW0p (Note 18); for maximum value and length see Note 15 point, a 5.5 dB, σ = 0 or 3 dB, σ = 1 (Note 17) point, an LE X point with a 100 pWp (200 pW0p) (Note 11) point, a 3 dB at 1600 Hz. Root-f law for unloaded line plant point, a 100 pWp (500 pWp) (Note 8) point, and finally an analogue telephone at the bottom. A -4.5 dB (RLR) loss is indicated at the bottom. The diagram is labeled T1208900-98 at the bottom left.](4801720824e4b5e2361a5564f91cfb70_img.jpg)
+
+National  
+ ≤ 500 km  
+ 4 dB (SLR)  
+ Analogue telephone  
+ 3 dB at 1600 Hz. Root-f law for unloaded line plant  
+ 100 pWp (500 pWp) (Note 8)  
+ LE X 100 pWp (200 pWp) (Note 11)  
+ Zero or 500 pW0p (Note 15); see Note 16 for maximum value and length  
+ 5.5 dB,  $\sigma = 0$  or 3 dB,  $\sigma = 1$  (Note 17)  
+ PC X 100 pW0p (200 pW0p) (Note 11)  
+ 500 pW0p (2000 pW0p) (Note 18)  
+ 0.5 dB,  $\sigma = 1$ ; length 2500 km (Note 13)  
+ ISC X 0 pW0p (Note 3)  
+ 0 pW0p (Note 4)  
+ 0 dB,  $\sigma = 0$  dB (Note 5)  
+ ISC X 0 pW0p (Note 3)  
+ 500 pW0p (2000 pW0p) (Note 17)  
+ 0.5 dB,  $\sigma = 1$   
+ 14 dB (Note 13)  
+ PC X 100 pW0p (2000 pW0p) (Note 11)  
+ Zero or 500 pW0p (Note 18); for maximum value and length see Note 15  
+ 5.5 dB,  $\sigma = 0$  or 3 dB,  $\sigma = 1$  (Note 17)  
+ LE X 100 pWp (200 pW0p) (Note 11)  
+ 3 dB at 1600 Hz. Root-f law for unloaded line plant  
+ 100 pWp (500 pWp) (Note 8)  
+ Analogue telephone  
+ -4.5 dB (RLR)  
+ T1208900-98
+
+Diagram of a hybrid international connection of moderate length with only one international circuit. The diagram shows a vertical line representing the connection path between two analogue telephones. The path is divided into three main segments: National (top), International (middle), and National (bottom). The top National segment is labeled 'National' and '≤ 500 km'. It includes a 4 dB (SLR) loss at the top, followed by an analogue telephone, a 3 dB at 1600 Hz. Root-f law for unloaded line plant, a 100 pWp (500 pWp) (Note 8) point, an LE X point with a 100 pWp (200 pWp) (Note 11) point, a Zero or 500 pW0p (Note 15); see Note 16 for maximum value and length point, a 5.5 dB, σ = 0 or 3 dB, σ = 1 (Note 17) point, and a PC X point with a 100 pW0p (200 pW0p) (Note 11) point. The International segment is labeled 'International' and '1000 km'. It includes a 500 pW0p (2000 pW0p) (Note 18) point, a 0.5 dB, σ = 1; length 2500 km (Note 13) point, an ISC X point with a 0 pW0p (Note 3) point, a 0 pW0p (Note 4) point, a 0 dB, σ = 0 dB (Note 5) point, another ISC X point with a 0 pW0p (Note 3) point, and a 500 pW0p (2000 pW0p) (Note 17) point. The bottom National segment is labeled 'National' and '≤ 500 km'. It includes a 0.5 dB, σ = 1 point, a 14 dB point, a PC X point with a 100 pW0p (2000 pW0p) (Note 11) point, a Zero or 500 pW0p (Note 18); for maximum value and length see Note 15 point, a 5.5 dB, σ = 0 or 3 dB, σ = 1 (Note 17) point, an LE X point with a 100 pWp (200 pW0p) (Note 11) point, a 3 dB at 1600 Hz. Root-f law for unloaded line plant point, a 100 pWp (500 pWp) (Note 8) point, and finally an analogue telephone at the bottom. A -4.5 dB (RLR) loss is indicated at the bottom. The diagram is labeled T1208900-98 at the bottom left.
+
+**Figure 5/G.103 – An example of a hybrid international connection of moderate length with only one international circuit**
+
+![Diagram of the longest hybrid international connection likely to occur in practice, showing signal levels and noise limits across National and International segments.](33ed1f9b27c7c21c797aa928b0f06851_img.jpg)
+
+The diagram illustrates a hybrid international connection between two analogue telephones, divided into three main segments: National (top), International (middle), and National (bottom).
+
+- Top National Segment (1750 km):**
+  - Starts at an **Analogue telephone**.
+  - Signal level: **10.5 dB (SLR)**.
+  - Line plant: **10 dB at 1600 Hz. Root-f law for unloaded line plant**.
+  - Equipment and limits:
+    - LE**: 100 pWp (500 pWp) (Note 8); 100 pWp (200 pW0p) (Note 11); Zero or 500 pW0p (Note 1); see Note 16 for maximum value and length.
+    - PC**: 5.5 dB,  $\sigma = 0$  or 3 dB,  $\sigma = 1$  (Note 17); 100 pW0p (200 pW0p) (Note 11).
+    - SC**: 500 pW0p (2000 pW0p) (Note 16); 0 dB,  $\sigma = 1$  (Note 20); 100 pW0p (200 pW0p) (Note 11).
+    - TC**: (1000 pW0p); 0 dB,  $\sigma = 1$  (Note 21); length 250 km; 100 pW0p (200 pW0p) (Note 11); (1000 pW0p).
+    - QC**: 0 dB,  $\sigma = 1$  (Note 20); length 250 km; 100 pW0p (200 pW0p) (Note 11); (2000 pW0p) (Note 21).
+  - A bracket on the right indicates: **See Note 19 for an alternative arrangement**.
+- International Segment (24 000 km):**
+  - Starts at **ISC**.
+  - Signal level: **0 dB,  $\sigma = 1$  (Note 21); length 500 km**.
+  - Equipment and limits:
+    - ISC**: 0 pW0p (Note 3); 0 pW0p (Note 4); 0 dB,  $\sigma = 0$  dB; (Note 5); 0 pW0p (Note 3); 0 pW0p (Note 4); 0 dB,  $\sigma = 0$  dB; (Note 5); 0 pW0p (Note 3); 0 pW0p (Note 4).
+    - ISC**: 0 dB,  $\sigma = 0$  dB; (Note 5); 0 pW0p (Note 3); 0 pW0p (Note 4); 0 dB,  $\sigma = 0$  dB; (Note 5); 0 pW0p (Note 3); (2000 pW0p) (Note 20).
+    - QC**: 0.5 dB,  $\sigma = 1$  dB; length 4500 km; 100 pW0p (200 pW0p) (Note 11); (1000 pW0p).
+    - TC**: 0.5 dB,  $\sigma = 1$  (Note 20) length 250 km; 100 pW0p (200 pW0p) (Note 11); (1000 pW0p).
+    - SC**: 0 dB,  $\sigma = 1$ ; (Note 20); length 250 km; 100 pW0p (200 pW0p) (Note 11); 500 pW0p (2000 pW0p); (Note 18).
+    - ISC**: 0 dB,  $\sigma = 1$  (Note 20); 7 dB,  $\sigma = 0$  ; (Note 20).
+  - A bracket on the right indicates: **See Note 19 for an alternative arrangement**.
+- Bottom National Segment (1750 km):**
+  - Starts at **PC**.
+  - Equipment and limits:
+    - PC**: 100 pW0p (200 pW0p) (Note 11); Zero or 500 pW0p (Note 15); (Note 16) for maximum value and length.
+    - LE**: 5.5 dB,  $\sigma = 0$  or 3 dB,  $\sigma = 1$  (Note 17); 100 pW0p (200 pW0p) (Note 11).
+    - Line plant: **10 dB at 1600 Hz. Root-f law for unloaded line plant**.
+    - Ends at **Analogue telephone** with signal level: **100 pW0p (500 pW0p) (Note 8)**.
+    - Signal level: **- 1 dB (RLR)**.
+
+T1208910-98
+
+Diagram of the longest hybrid international connection likely to occur in practice, showing signal levels and noise limits across National and International segments.
+
+**Figure 6/G.103 – The longest hybrid international connection likely to occur in practice**
+
+## NOTES to Figures 1, 2, 3, 4, 5 and 6
+
+NOTE 1 – A value of 8 dB was selected for the SLR of the digital telephone set to be consistent with Recommendation P.310.
+
+NOTE 2 – A nominal value of noise of 100 pW0p (–70 dBm) was selected as a typical value for the noise generated by a digital telephone set. A value of 400 pW0p (–64 dBm0p) was selected as the maximum noise generated by the transmit section of a digital telephone set to be consistent with Recommendation P.310.
+
+NOTE 3 – The noise contribution of a digital switch is assumed to be 0 pW0p.
+
+NOTE 4 – The noise contribution of a digital trunk is assumed to be 0 pW0p.
+
+NOTE 5 – The loss associated with a digital circuit is assumed to be 0 dB,  $\sigma = 0$ .
+
+NOTE 6 – A value of 2 dB was selected for the RLR of the digital telephone set to be consistent with Recommendation P.310.
+
+NOTE 7 – The noise contribution of a digital access and a digital telephone set receiver is assumed to be 0 pW0p.
+
+NOTE 8 – The average value of 100 pWp for subscriber line noise is considered to be typical and is used by at least one Administration as an objective for maximum noise at the receiver. The maximum planning value should never exceed 500 pWp.
+
+NOTE 9 – This is the T pad and a value of 0 dB was arbitrarily selected. The value of the T pad will depend upon the national transmission plan. Table C.1/G.121 provides values of T and R pads for various countries.
+
+NOTE 10 – This is the R pad and a value of 7 dB was arbitrarily selected. The value of the R pad will depend upon the national transmission plan. Table C.1/G.121 provides values of T and R pads for various countries.
+
+NOTE 11 – The value of 200 pW0p as the design objective for the maximum noise power in a national 4-wire automatic exchange was taken from clause 3/G.123, which is no longer in force. The same value, i.e. an absolute noise power of 200 pWp, has been assumed for national 2-wire exchanges. No assumption has been made concerning the position of any national zero relative level point.
+
+NOTE 12 – The value of this pad will depend upon the national transmission plan.
+
+NOTE 13 – Both countries are assumed to have the  $2 + 0.5 + 0.5 + 0.5$  dB type of plan. The nominal value of the 4 dB pad in the receiving direction at the switching centre includes the loss of the terminating unit (see General Remark, 4.2.12).
+
+NOTE 14 – The local exchange and primary centre are assumed to be both co-sited with the ISC.
+
+NOTE 15 – The noise power level may be taken as negligible if the circuit is provided on physical line plant. A mean value of 500 pW0p is appropriate if the circuit is provided on a *FDM or TDM* short-distance carrier system.
+
+NOTE 16 – For FDM or TDM short-distance carrier circuits not exceeding about 250 km, the maximum value of noise power may be taken to be 1000 pW0p.
+
+NOTE 17 – For circuits on physical line plant, the LR may be taken to have a nominal maximum value of 6 dB with  $\sigma = 0$ . This value was arrived at in the following way: Recommendation G.121 gives a 97% limit on 20 dB Sending Loudness Rating (SLR) referred to a point of –3.5 dBr on the international circuit at the IC. Referring this to a zero relative level point at the input to the chain of national and international circuits (i.e. to the primary centre) gives 16.5 dB. Reference [1] indicates that a 10.5 dB Sending Loudness Rating (SLR) is typical for maximum local lines, thus leaving 6 dB for the circuit from the local exchange to the primary centre, switching losses being included (see General Remark, 4.2.12).
+
+For FDM or TDM short-distance carrier circuits which are 2-wire switched at the primary centre, the nominal value of the circuit loss may be taken as 3 dB with  $\sigma = 1$ . This circuit may for instance be provided on a PCM system using either 7-bit encoding ( $\mu = 100$  or  $A = 87.6$ ) or 8-bit encoding ( $\mu = 225$  or  $A = 87.6$ ). Only 8-bit coding is recommended by the ITU-T.
+
+NOTE 18 – The maximum planning value of 2000 pW0p provides for a circuit length of about 500 km with some margin.
+
+NOTE 19 – The following arrangements may be encountered if 4-wire switching (space-division or time-division) is used at the primary centre. Clearly in principle the terminating set may be at any point between the 2-wire switch and the 4-wire switch, although in practice it is ordinarily associated with one or the other.
+
+![Two diagrams, (a) and (b), showing network configurations. Diagram (a) shows a line with an LE (Local Exchange) pad on the left, a central node, and a PC (Primary Centre) pad on the right. Diagram (b) shows a similar line but with the LE pad on the left connected to a node that has a branch to the left. Both diagrams have a dashed line extending from the left and right. The label 'T1210900-99' is present in diagram (b).](2cde062fd82833415971a8bd1a2cafab_img.jpg)
+
+Two diagrams, (a) and (b), showing network configurations. Diagram (a) shows a line with an LE (Local Exchange) pad on the left, a central node, and a PC (Primary Centre) pad on the right. Diagram (b) shows a similar line but with the LE pad on the left connected to a node that has a branch to the left. Both diagrams have a dashed line extending from the left and right. The label 'T1210900-99' is present in diagram (b).
+
+If arrangement b) is adopted, then the minimum loss *a-t-b* (called for in accordance with Recommendation G.122) must still be assured, irrespective of whether the national transmission plan uses the  $3.5 + 0 + 0 + 0$  or  $2.5 + 0.5 + 0.5 + 0.5$  basis, since there could now be an extra circuit in the 4-wire chain. Where an additional 0.5 dB is needed, this could in principle either be introduced by changing the loss of the tertiary centre/ISC circuit from 0 to 0.5 dB, or by allocating it to the PC/LE circuits. Such arrangements may be encountered at either end of the connection.
+
+NOTE 20 – Both countries are assumed to have the  $3.5 + 0 + 0 + 0$  dB type of plan. The nominal value of the pad in the receiving direction at the primary centre includes the loss of the terminating unit (see General Remark, 4.2.12).
+
+NOTE 21 – The noise value corresponds to a design objective of 4 pW0p/km for the most adverse noise power during the busy hour.
+
+**4.2.8** The pad symbols represent the nominal loss of the particular channel or circuit and the relative position of the noise generator. The pad also indicates that if the noise is to be referred to the receiving end of a circuit, it must be modified by the power ratio corresponding to the loss of the pad.
+
+If it is required to refer the noise powers to some particular point on the connection (for example, the receiving local exchange or the point of zero relative level on the first international circuit), then the rule to be applied is as follows:
+
+If a noise power level at a point *A* is to be referred to a point *B* downstream of its position, it is obtained by augmenting the level at point *B* by the sum of the losses that is imagined to be traversed from *A* to *B*. If it is to be referred to a point *C* upstream of its position, it is obtained by diminishing the level at point *C* by the sum of all the losses that is imagined to be traversed from *A* to *C*.
+
+**4.2.9** The nominal terminal loss of the connection [i.e. the normal overall loss less the sum of the transit losses (via net losses) of the individual circuits] is shown as one pad associated with the extreme right-hand circuit in the 4-wire chain. This artifice enables the noise powers to be indicated as if they were injected at zero relative level points on the individual circuits as explained in Annex A.
+
+**4.2.10** Information concerning the distributions of attenuation distortion and group-delay distortion for analogue circuits and exchanges is to be found in Annex A/G.113.
+
+Recommendation G.114 gives information concerning group delay.
+
+**4.2.11** The standard deviation of transmission loss of circuits is in accord with the objectives of clause 10/G.120.
+
+**4.2.12** "Circuit" in these reference connections is defined in the sense of Recommendation M.60 as the whole of the line and the equipment proper to the line; it extends from the switches of one exchange to the switches of the next. In this way, switching and exchange cabling losses are included in the values of transmission loss assigned to the circuits, together with the loss (or gain) introduced by the transmission system. If it is required to separately distinguish exchange losses, an additional pad symbol of appropriate value may be used.
+
+It should also be noted that, according to this convention, the 3.5 dB loss ordinarily assigned to a terminating set does not figure explicitly in 2-wire/4-wire circuits; its value is also included in the loss assigned to the circuit.
+
+## **5 Number of modulation and demodulation equipments**
+
+For the study of transmission performance, the longest international connection expected to occur (see Figure 6) may be considered to have the following arrangement of modulator/demodulator pairs in the 4-wire chain. See Table 1.
+
+**Table 1/G.103 – Number of maximum modulator/demodulator pairs in a wholly analogue national 4-wire chain and wholly digital international 4-wire chain**
+
+|            | <b>Eight national circuits</b> | <b>Circuits between ISCs</b> | <b>Total</b> |
+|------------|--------------------------------|------------------------------|--------------|
+| Channel    | 8                              | 0                            | 8            |
+| Group      | 12                             | 0                            | 12           |
+| Supergroup | 16                             | 0                            | 16           |
+
+Of the 12 channel modulator/demodulator pairs, a maximum of three may be of the special type which provide more than 12 telephone circuits per group.
+
+## **6 Developments arising from the ongoing introduction of PCM digital processes**
+
+The worldwide telephone network is undergoing a transition from what is largely a hybrid network to a wholly digital network. Looking farther into the future, this transition is expected to continue and result in a network that would be predominantly wholly digital. Background on this transitional process is given in clause 4/G.101.
+
+With reference to the hypothetical reference connections of Figures 1, 2, 3, 4, 5 and 6, the configurations used concerning numbers of circuits and numbers of exchanges should also be appropriate for network conditions in the mixed analogue/digital period. However, for transmission studies pertaining to mixed analogue/digital and wholly digital connections, account must also be taken of all unintegrated digital processes that might be present. Such unintegrated digital processes could have an important effect on overall transmission performance particularly with regard to such parameters as quantizing distortion (Recommendation G.113) and transmission delay.
+
+Where the worldwide network becomes all-digital, many of the transmission impairments that were present in the mixed analogue/digital period, due to the incorporation of unintegrated digital processes, would be eliminated. However, certain processes might remain which could introduce transmission penalties. These are the processes which operate on the basis of recoding the bit stream as is done, for example, in the case of digital pads or speech compression. Although the accumulated transmission impairments introduced by such processes may be well within recommended limits, the
+
+resulting loss of bit integrity could be an important disadvantage. This is particularly true in the case of services requiring the preservation of bit integrity on an end-to-end basis. Consequently, processes of this type should be avoided where possible, or appropriate arrangements made to circumvent them, where services requiring bit integrity are to be carried over the affected connections.
+
+## ANNEX A
+
+### An explanation of how hypothetical reference connections can be drawn assuming all send switching levels are 0 dBr
+
+**A.1** Consider the connection shown in Figure A.1 in which 3 circuits with losses of 1 dB, 6 dB and 2 dB are connected together by exchanges with actual send switching levels of -2, +1 and -3 dBr.
+
+![Figure A.1/G.103 – Connection with various send switching levels. The diagram shows a horizontal line representing a connection path. From left to right: a source symbol (circle with a vertical line), a segment labeled '8 dB (SLR)', an exchange symbol 'E1' with an arrow pointing up labeled '-2', a loss symbol '1' (two vertical bars), an exchange symbol 'E2' with an arrow pointing up labeled '+1', a loss symbol '6', an exchange symbol 'E3' with an arrow pointing up labeled '-3', a loss symbol '2', an exchange symbol 'E4', and a destination symbol (square with a vertical line). The text 'T1210910-99' is at the bottom right.](10781f43062bf3e9601a1e086710556c_img.jpg)
+
+Figure A.1/G.103 – Connection with various send switching levels. The diagram shows a horizontal line representing a connection path. From left to right: a source symbol (circle with a vertical line), a segment labeled '8 dB (SLR)', an exchange symbol 'E1' with an arrow pointing up labeled '-2', a loss symbol '1' (two vertical bars), an exchange symbol 'E2' with an arrow pointing up labeled '+1', a loss symbol '6', an exchange symbol 'E3' with an arrow pointing up labeled '-3', a loss symbol '2', an exchange symbol 'E4', and a destination symbol (square with a vertical line). The text 'T1210910-99' is at the bottom right.
+
+Figure A.1/G.103 – Connection with various send switching levels
+
+**A.2** We assume that noise powers of these circuits are  $N_1$ ,  $N_2$  and  $N_3$  pW0p respectively. Figure A.2 shows these noise powers entering their circuits via appropriately valued pads chosen to take cognizance of the switching level concerned and dispense with the arrow symbols.
+
+![Figure A.2/G.103 – The noise powers added. This diagram is similar to Figure A.1 but replaces the switching level arrows with noise power inputs. At exchange E1, a vertical line labeled '2' points down to noise power N1. At exchange E2, a vertical line labeled '-1' points down to noise power N2. At exchange E3, a vertical line labeled '3' points down to noise power N3. The text 'pW0p' is at the bottom right. The text 'T1210920-99' is also present.](12de9b926df0384ec07702671827c9cd_img.jpg)
+
+Figure A.2/G.103 – The noise powers added. This diagram is similar to Figure A.1 but replaces the switching level arrows with noise power inputs. At exchange E1, a vertical line labeled '2' points down to noise power N1. At exchange E2, a vertical line labeled '-1' points down to noise power N2. At exchange E3, a vertical line labeled '3' points down to noise power N3. The text 'pW0p' is at the bottom right. The text 'T1210920-99' is also present.
+
+Figure A.2/G.103 – The noise powers added
+
+**A.3** We note that  $N_1$  traverses a total of 11 dB to reach  $E_4$ ,  $N_2$  a total of 7 dB, and  $N_3$  a total of 5 dB. Also the difference between the accumulated Sending Loudness Rating (SLR) at each exchange and the corresponding circuit noise level is 6 dB (for  $N_1$ ), 10 dB (for  $N_2$ ) and 12 dB (for  $N_3$ ). Hence, we may redraw the connection reallocating the losses as shown in Figure A.3 in which all send switching levels are 0 dBr and all the other conditions are met as well.
+
+![Diagram of a transmission line showing switching levels and noise components. A horizontal line represents the transmission path, starting with a circle on the left and ending with a rectangle on the right. A bracket at the top left indicates a '6 dB (SLR)' range. Along the line, there are three switch points marked with 'x' and solid dots. Upward arrows from below point to these dots, labeled E1 + N1, E2 + N2, and E3 + N3. Between the switch points are vertical tick marks with numbers: '4' between the first and second switch points, '2' between the second and third, and '5' after the third. The label 'pW0p' is near the end of the line. The text 'T1210930-99' is in the bottom right corner of the diagram area.](b6671cfafda3820aafe9a24fa7a4d8c7_img.jpg)
+
+Diagram of a transmission line showing switching levels and noise components. A horizontal line represents the transmission path, starting with a circle on the left and ending with a rectangle on the right. A bracket at the top left indicates a '6 dB (SLR)' range. Along the line, there are three switch points marked with 'x' and solid dots. Upward arrows from below point to these dots, labeled E1 + N1, E2 + N2, and E3 + N3. Between the switch points are vertical tick marks with numbers: '4' between the first and second switch points, '2' between the second and third, and '5' after the third. The label 'pW0p' is near the end of the line. The text 'T1210930-99' is in the bottom right corner of the diagram area.
+
+**Figure A.3/G.103 – All send switching levels are 0 dBr**
+
+**A.4** Since the relative level of the immediate downstream circuit at each switch point is now arranged to be 0 dBr, the exchange noise powers can be added as is done in the hypothetical reference connections in Recommendation G.103.
+
+## ITU-T RECOMMENDATIONS SERIES
+
+|                 |                                                                                                                                |
+|-----------------|--------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of the ITU-T                                                                                          |
+| Series B        | Means of expression: definitions, symbols, classification                                                                      |
+| Series C        | General telecommunication statistics                                                                                           |
+| 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        | 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        | TMN and network maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits |
+| 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                                                                                                       |
+| 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 and open system communications                                                                                   |
+| Series Y        | Global information infrastructure                                                                                              |
+| Series Z        | Programming languages                                                                                                          |

marked/G/T-REC-G.1031-201402-I_PDF-E/raw.md

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+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**G.1031**
+
+(02/2014)
+
+SERIES G: TRANSMISSION SYSTEMS AND MEDIA,  
+DIGITAL SYSTEMS AND NETWORKS
+
+Multimedia Quality of Service and performance – Generic  
+and user-related aspects
+
+---
+
+**QoE factors in web-browsing**
+
+Recommendation ITU-T G.1031
+
+**ITU-T**
+
+![ITU logo: A globe with a red lightning bolt and the text 'ITU International Telecommunication Union'.](1d7527f4316cfe2d342b08d1653d1592_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue globe with a red lightning bolt striking across it. To the right of the globe, the text "ITU" is written in a bold, blue, sans-serif font. Below "ITU", the words "International Telecommunication Union" are written in a smaller, blue, sans-serif font.
+
+ITU logo: A globe with a red lightning bolt and the text 'ITU International Telecommunication Union'.
+
+# 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.1031
+
+# QoE factors in web-browsing
+
+## Summary
+
+Recommendation ITU-T G.1031 describes the framework for an opinion model for web-browsing quality of experience (QoE). User perceived quality for web-browsing is dependent on various influence factors (IF) that are related to user, context and system. This Recommendation addresses the latter two influence factors (context and system) and provides an overview of them. At the perceptual level, it defines the relevant events that the user perceives while accessing a web page and contrasts them with the events taking place at the application level and at the network level.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T G.1031   | 2014-02-13 | 12          | <a href="http://handle.itu.int/11.1002/1000/12123">11.1002/1000/12123</a> |
+
+## Keywords
+
+Modeling, page-view cycle, perceptual events, web-browsing session, web-QoE.
+
+---
+
+\* 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 2014
+
+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 .....                           | 2    |
+| 6 Factors influencing web-QoE .....           | 2    |
+| 6.1 Context influence factors.....            | 2    |
+| 6.2 System influence factors.....             | 3    |
+| 7 Perceptual dimension.....                   | 4    |
+| 8 Use cases of a web-QoE opinion model .....  | 4    |
+| Bibliography.....                             | 6    |
+
+
+
+# Recommendation ITU-T G.1031
+
+## QoE factors in web-browsing
+
+# 1 Scope
+
+This Recommendation describes the framework for an opinion model for web-browsing QoE. This Recommendation aims to provide:
+
+- guidance in the development of an opinion model
+- an overview of key influence factors (IF)
+- a starting point for performance assessment and KPI definitions.
+
+This Recommendation introduces a taxonomy of influence factors and related model parameters, as well as a definition of QoE relevant perceptual events.
+
+# 2 References
+
+This Recommendation does not use any normative references.
+
+# 3 Definitions
+
+## 3.1 Terms defined elsewhere
+
+None.
+
+## 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following terms:
+
+**3.2.1 element:** Visual content of a webpage, which is displayed to the user on the rendered webpage, e.g., text, pictures, widgets, videos, etc.
+
+**3.2.2 first element:** A character or a picture for example.
+
+**3.2.3 object:** A HTTP object that is used for processing and rendering the webpage and is referenced by the page mark-up or script. An object however is not necessarily visible on the fully rendered page (see the definition for element).
+
+**3.2.4 visible portion:** The part of the requested web page that is visible to the user.
+
+**3.2.5 web-browsing session:** A web-browsing session is an interactive information exchange between a user and one or more websites over a limited period of time, mediated via a web-browsing application. The starting point of such a session is the first page request initiated by the user, which is followed by a number of request-response interactions between the user and the webhost(s), resulting in a series of page views [b-Egger1]. A web session is typically terminated when the user exits the browsing application or stops the browsing activity for a certain period of time.
+
+# 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+CPU Central Processing Unit
+
+HTML Hyper Text Mark-up Language
+
+IF Influence Factor
+
+OS Operating System
+
+|     |                       |
+|-----|-----------------------|
+| PLT | Page Load Time        |
+| QoE | Quality of Experience |
+| RTT | Round Trip Time       |
+
+# 5 Conventions
+
+This Recommendation uses the following notation:
+
+|                                     |                                                                                                                                                                                     |
+|-------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| <b>t<sub>0</sub>:</b>               | The moment in time when the user requests a new web page (typically by clicking or pressing enter "Enter" after having typed the URL of the web page in the browser's address bar). |
+| <b>t<sub>SB<sub>r</sub></sub>:</b>  | The moment in time when a change in the status bar happens (usually a progress bar becomes visible at this moment).                                                                 |
+| <b>t<sub>Sg<sub>B</sub></sub>:</b>  | The moment in time when the previously viewed web page vanishes and the content of the requested page has not yet started to render.                                                |
+| <b>t<sub>Pr<sub>s</sub></sub>:</b>  | The moment in time when the first element of the requested page appears on the screen, independent of the type of element.                                                          |
+| <b>t<sub>PPLT:</sub></b>            | The moment in time when from the point of view of the user the page is sufficiently rendered such that he can access the information he is looking for.                             |
+| <b>t<sub>V<sub>Src</sub></sub>:</b> | The moment of time when the visible portion of the web page (as determined by screen or browser windows size) is fully rendered <sup>1</sup> .                                      |
+| <b>t<sub>IHR<sub>s</sub></sub>:</b> | The moment in time when the initial HTTP request is sent by the browser.                                                                                                            |
+| <b>t<sub>BHP<sub>r</sub></sub>:</b> | The moment in time when the first HTML <head> element is received (see [b-W3schools]).                                                                                              |
+| <b>t<sub>HP:</sub></b>              | The moment in time when the HTML page is processed by the browser (can only be observed at application level).                                                                      |
+| <b>t<sub>PLT_1:</sub></b>           | The moment of time when all objects of the page are downloaded from the server at the browser's device.                                                                             |
+| <b>t<sub>PLT_2:</sub></b>           | The moment of time when the page is completely rendered and displayed by the browser.                                                                                               |
+
+# 6 Factors influencing web-QoE
+
+Typically, QoE influence factors (IFs) are grouped according to the following three main categories:
+
+- User influence factors
+- Context influence factors
+- System influence factors
+
+User influence factors are outside of the scope of this Recommendation. Context influence factors are discussed in clause 6.1. System influence factors are discussed in clause 6.2.
+
+## 6.1 Context influence factors
+
+The context in which a web page is accessed can have a critical influence on the user behaviour and his QoE. The range of context influence factors spans:
+
+- Location: Cafeteria, office, home
+
+---
+
+<sup>1</sup> It should be noted that there can be further rendering activity outside of the visible screen area.
+
+- Interactivity: High level interactivity vs. low level interactivity
+- Task type: business, entertainment, etc.
+- Task urgency: urgent vs. casual (without time constraints).
+
+## 6.2 System influence factors
+
+The range of system influence factors spans the following content, network and client related IFs:
+
+- Server-related influence factors (see clause 6.2.1)
+- Content-related influence factors (see clause 6.2.2)
+- Delivery network influence factors (see clause 6.2.3)
+- Client influence factors (see clause 6.2.4)
+
+In order to better understand the position of these IFs in the delivery chain, a typical Web-QoE delivery chain is depicted in Figure 1.
+
+![Figure 1 – Delivery chain for a typical webpage. The diagram shows a flow from left to right: 'Perceived quality' (User icon) connected to a 'Device' (laptop icon), which is connected to an 'Access network' box, then a 'Core network' box, then an 'Internet' cloud, and finally a 'Server + content' box (server icon) leading to 'Produced quality'. A small label 'G.1031(14)_F01' is at the bottom right.](367926125450c2bc3f4bdca9d59a62ba_img.jpg)
+
+```
+
+graph LR
+    User((User)) -- Perceived quality --> Device[laptop icon]
+    Device --> Access[Access network]
+    Access --> Core[Core network]
+    Core --> Internet((Internet))
+    Internet --> Server[Server + content]
+    Server -- Produced quality --> End[ ]
+    style End fill:none,stroke:none
+  
+```
+
+Figure 1 – Delivery chain for a typical webpage. The diagram shows a flow from left to right: 'Perceived quality' (User icon) connected to a 'Device' (laptop icon), which is connected to an 'Access network' box, then a 'Core network' box, then an 'Internet' cloud, and finally a 'Server + content' box (server icon) leading to 'Produced quality'. A small label 'G.1031(14)\_F01' is at the bottom right.
+
+**Figure 1 – Delivery chain for a typical webpage**
+
+### 6.2.1 Server-related influence factors
+
+- Response time (determined by CPU, OS, memory, software, etc.)
+- Capacity of the link(s) connecting the server(s) and the Internet.
+
+### 6.2.2 Content-related influence factors
+
+These factors go beyond the established notion of content as used in QoE. This is because in Web QoE, content is typically constituted by a mix of different element types such as text, pictures, audio files and videos. In addition, the HTML mark-up of the webpage (and related scripts) strongly determines the actual loading behaviour of the page according to its internal structure and the utilized objects such as:
+
+- Number of objects
+- Type of objects
+- Size of objects
+- Order of objects
+- Number of elements
+- Type of elements
+- Size of elements
+- Element appearance on the screen (determined by the order of the objects as well as by the rendering strategy of the browser, see [b-Strohmeier]).
+
+### 6.2.3 Delivery network influence factors
+
+- Network contribution to transaction time (see [b-ITU-T G.1040])
+- Available capacity (see [b-ITU-T Y.1540])
+- Caching along the delivery network: The caching elements lower perceived server response time as they shorten client-to-server requests and therefore lower the RTT.
+
+### 6.2.4 Client influence factors
+
+- Resource (webpage) loading procedure
+- Processing power and other processes demanding processing power
+- Browser implementation
+- TCP/IP stack and configuration
+- Operating system.
+
+All of these IF's impact the user perceived performance of the web page display when requested by the user.
+
+# 7 Perceptual dimension
+
+When the end user requests a page by means of entering a dedicated web address or clicking on a link on an already loaded web page, the download of content from a web server is initiated. This requested content (typically a base HTML page that references additional elements like images and scripts) is progressively fetched and rendered by the browser. During this process the user encounters several observable events as depicted in Figure 2.
+
+![Figure 2: Perceptual events in a web page view cycle from the end-user point of view. The diagram shows two horizontal timelines. The top timeline, labeled 'User perception', has a black line with an arrow pointing right, labeled 'Time'. It has tick marks at t0, tSBr, tSGB, tPRs, tPPLT, and tSVrc. The bottom timeline, labeled 'Application and network', has a blue line with tick marks at tIHRs, tBHPr, tHp, tTPLT_1, and tTPLT_2. The tick marks on the two timelines are vertically aligned. A small label 'G.1031(14)_F02' is at the bottom right of the diagram.](b8661c6c54f72ecc7ff6cb05e47b2891_img.jpg)
+
+G.1031(14)\_F02
+
+Figure 2: Perceptual events in a web page view cycle from the end-user point of view. The diagram shows two horizontal timelines. The top timeline, labeled 'User perception', has a black line with an arrow pointing right, labeled 'Time'. It has tick marks at t0, tSBr, tSGB, tPRs, tPPLT, and tSVrc. The bottom timeline, labeled 'Application and network', has a blue line with tick marks at tIHRs, tBHPr, tHp, tTPLT\_1, and tTPLT\_2. The tick marks on the two timelines are vertically aligned. A small label 'G.1031(14)\_F02' is at the bottom right of the diagram.
+
+**Figure 2 – Perceptual events in a web page view cycle from the end-user point of view**
+
+Note that in this figure the application and network timeline (in blue) displays related technical events at the application or network levels. Note also that in this figure the distance between the perceptual events is shown as being equal, but this is not necessarily the case in real-world browser implementations.
+
+This description differentiates between perceived page load time (PLT)  $t_{PPLT}$  and technical page load time  $t_{TPLT\_1}$  (or  $t_{TPLT\_2}$  depending on the actual measurement procedure). This differentiation is important since ultimately, for the user QoE, only the perceived PLT  $t_{PPLT}$  matters. This distinguishes this description from related work described in Annex A of [b-ITU-T G.1030], where only the technical PLT  $t_{TPLT}$  is used as a basis for QoE estimation. This difference is essential, since  $t_{PPLT}$  can be considerably shorter than  $t_{TPLT}$  and depends on several technical and non-technical influence factors such as user task, web page design, number of elements, etc. This is shown in [b- Egger2] where the presented empirical data from subjective tests quantifies the differences between these two points in time.
+
+NOTE – In a regular web-browsing session the end user encounters several sets of such page view event sequences.
+
+# 8 Use cases of a web-QoE opinion model
+
+A perceptual opinion model for Web-QoE can be used in the following use cases:
+
+- Network dimensioning, including:
+  - Network planning
+
+- Traffic management solutions design and optimization
+- Online/offline measurement of Web-QoE based on network and application logs or probes
+- Performance testing (of elements in the delivery chain).
+
+## Bibliography
+
+- [b-ITU-T G.1030] Recommendation ITU-T G.1030 (2014), *Estimating end-to-end performance in IP networks for data applications*.
+- [b-ITU-T G.1040] Recommendation ITU-T G.1040 (2006), *Network contribution to transaction time*.
+- [b-ITU-T Y.1540] Recommendation ITU-T Y.1540 (2011), *Internet protocol data communication service – IP packet transfer and availability performance parameters*.
+- [b-Egger1] Egger, *et al.*, "Waiting times in quality of experience for web based services," In Proc. of 2012 Fourth International Workshop on Quality of Multimedia Experience (QoMEX), pp. 86, 96, 5-7 July 2012.
+- [b-Egger2] Egger, *et al.*, "Time is bandwidth"? Narrowing the gap between subjective time perception and Quality of Experience, "In Proc. of 2012 IEEE International Conference on Communications (ICC), pp. 1325, 1330, 10-15 June 2012.
+- [b-W3schools] W3schools (2013, November 25). *HTML head elements*.  
+<[http://www.w3schools.com/html/html\\_head.asp](http://www.w3schools.com/html/html_head.asp)>
+- [b-Strohmeier] Strohmeier, *et al.*, (2012), *Toward task-dependent evaluation of Web-QoE: Free exploration vs. "Who Ate What?"*, In: Proc. QoEMC at GLOBECOM 2012, pp. 1309, 1313, 3-7 Dec. 2012.
+
+
+
+## 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                        |

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+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**G.1033**
+
+(10/2019)
+
+SERIES G: TRANSMISSION SYSTEMS AND MEDIA,  
+DIGITAL SYSTEMS AND NETWORKS
+
+Multimedia Quality of Service and performance – Generic  
+and user-related aspects
+
+---
+
+**Quality of service and quality of experience  
+aspects of digital financial services**
+
+Recommendation ITU-T G.1033
+
+ITU-T
+
+![ITU logo](1d7527f4316cfe2d342b08d1653d1592_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features a stylized globe with a red lightning bolt striking through it, symbolizing global connectivity and telecommunications. To the right of the globe, the text "International Telecommunication Union" is written in a blue, sans-serif font.
+
+ITU logo
+
+International  
+Telecommunication  
+Union
+
+# 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.1033
+
+# Quality of service and quality of experience aspects of digital financial services
+
+## Summary
+
+Recommendation ITU-T G.1033 highlights important aspects related to quality of service (QoS) and quality of experience (QoE) that require consideration in the context of digital financial services (DFSs).
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T G.1033   | 2019-10-14 | 12          | <a href="http://handle.itu.int/11.1002/1000/14065">11.1002/1000/14065</a> |
+
+## Keywords
+
+Digital financial service, QoE, QoS
+
+---
+
+\* 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 2019
+
+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 .....                                       | 2    |
+| 6            | Problem statements .....                                | 2    |
+| 6.1          | Different use cases.....                                | 3    |
+| 6.2          | Legal entities .....                                    | 3    |
+| 6.3          | Mobile network QoS affecting all services .....         | 4    |
+| 6.4          | Possible solutions .....                                | 5    |
+| 7            | Conclusions .....                                       | 5    |
+| 7.1          | Conclusions for service category 1 .....                | 5    |
+| 7.2          | Conclusions for service category 2.....                 | 6    |
+| 7.3          | Conclusions related to digital financial services ..... | 6    |
+| 8            | Future considerations: Top-level view .....             | 6    |
+| 8.1          | Use cases and related top-level KPI .....               | 7    |
+| 8.2          | Technological components of DFSs.....                   | 8    |
+| 8.3          | Stakeholders .....                                      | 9    |
+| 8.4          | QoS monitoring .....                                    | 10   |
+| Annex A      | – Underlying functionalities of DFS applications .....  | 12   |
+| A.1          | Service category 1 (feature phone).....                 | 12   |
+| A.2          | Service category 2 (smartphone).....                    | 14   |
+| Appendix I   | – Considerations related to the fitness for DFSs.....   | 16   |
+| Appendix II  | – Is DFS a "popular service"?.....                      | 19   |
+| II.1         | Relationship between QoS and QoE.....                   | 19   |
+| II.2         | Services, applications or "popular services" .....      | 21   |
+| II.3         | Is a DFS a "popular service"?.....                      | 21   |
+| Bibliography | .....                                                   | 23   |
+
+
+
+# Recommendation ITU-T G.1033
+
+## Quality of service and quality of experience aspects of digital financial services
+
+# 1 Scope
+
+This Recommendation highlights important aspects related to quality of service (QoS) and quality of experience (QoE) which shall be considered in the context of digital financial services (DFSs).
+
+NOTE – This Recommendation builds upon the discussions in the (now closed) DFS Focus Group and on [b-ITU-T DFS TR]. The continuation of work on QoS and QoE aspects is undertaken by the Financial Inclusion Global Initiative (FIGI) [b-FIGI 2019a], [b-FIGI 2019b], [b-FIGI 2019c].
+
+# 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 E.811] Recommendation ITU-T E.811 (2017), *Quality measurement in major events*.
+
+[ETSI TS 103 296] ETSI TS 103 296 V1.1.1 (2016), *Speech and multimedia transmission quality (STQ); Requirements for emotion detectors used for telecommunication measurement applications; Detectors for written text and spoken speech*.
+
+# 3 Definitions
+
+## 3.1 Terms defined elsewhere
+
+None.
+
+## 3.2 Terms defined in this Recommendation
+
+None.
+
+# 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|      |                                         |
+|------|-----------------------------------------|
+| 2G   | second Generation                       |
+| 3G   | third Generation                        |
+| CPU  | Central Processing Unit                 |
+| DFS  | Digital Financial Service               |
+| DTMF | Dual Tone Multi Frequency               |
+| E2E  | End-to-End                              |
+| FEC  | Forward Error Correction                |
+| GSM  | Global System for Mobile communications |
+| HLR  | Home Location Register                  |
+
+|       |                                            |
+|-------|--------------------------------------------|
+| HTML  | Hypertext Markup Language                  |
+| HTTP  | Hypertext Transfer Protocol                |
+| HTTPS | Hypertext Transfer Protocol Secure         |
+| IP    | Internet Protocol                          |
+| IPTV  | IP Television                              |
+| IVR   | Interactive Voice Response                 |
+| KPI   | Key Performance Indicator                  |
+| KQI   | Key Quality Indicator                      |
+| MMS   | Multimedia Messaging Service               |
+| MOS   | Mean Opinion Score                         |
+| OTT   | Over The Top                               |
+| P2P   | Person to Person                           |
+| QoE   | Quality of Experience                      |
+| QoS   | Quality of Service                         |
+| QoSE  | QoS Experienced                            |
+| QoSP  | QoS Perceived                              |
+| RTP   | Real-Time Protocol                         |
+| SIP   | Session Initiation Protocol                |
+| SLA   | Service Level Agreement                    |
+| SMS   | Short Message Service                      |
+| SMSC  | Short Message Service Centre               |
+| SSL   | Secure Sockets Layer                       |
+| TCP   | Transmission Control Protocol              |
+| TLS   | Transport Layer Security                   |
+| UMTS  | Universal Mobile Telecommunications System |
+| USSD  | Unstructured Supplementary Service Data    |
+| VoIP  | Voice over IP                              |
+| VoLTE | Voice over Long-Term Evolution             |
+| WAP   | Wireless Application Protocol              |
+| WML   | Wireless Markup Language                   |
+| XML   | extensible Markup Language                 |
+
+# 5 Conventions
+
+None.
+
+# 6 Problem statements
+
+QoS and QoE aspects depend in particular on the use case under consideration and related aspects like environment and detailed macro parameters.
+
+## 6.1 Different use cases
+
+Use cases of DFSs can be easily categorized and analysed when applying the hierarchy concept depicted in Figure 1.
+
+![Figure 1: Hierarchy of use cases, types, and macroscopic parameters. The diagram shows a three-level hierarchy. The top level, 'Main use case', contains 'P2P money transfer'. The second level, 'Type/environment', branches into 'National, same DFS operator', 'Interoperability: national; different DFS operators', and 'Interoperability, international'. The third level, 'Macro parameter', branches from 'National, same DFS operator' into 'Smartphone based' and 'Feature phone based'.](562f471e8153729557e6a4ee6343c32c_img.jpg)
+
+```
+graph TD; A[P2P money transfer] --> B[National, same DFS operator]; A --> C[Interoperability: national; different DFS operators]; A --> D[Interoperability, international]; B --> E[Smartphone based]; B --> F[Feature phone based];
+```
+
+G.1033(19)\_F01
+
+Figure 1: Hierarchy of use cases, types, and macroscopic parameters. The diagram shows a three-level hierarchy. The top level, 'Main use case', contains 'P2P money transfer'. The second level, 'Type/environment', branches into 'National, same DFS operator', 'Interoperability: national; different DFS operators', and 'Interoperability, international'. The third level, 'Macro parameter', branches from 'National, same DFS operator' into 'Smartphone based' and 'Feature phone based'.
+
+**Figure 1 – Hierarchy of use cases, types, and macroscopic parameters**
+
+Other main use cases are, for example, transfers between a mobile device and a bank account, or bulk transfers such as payment of wages by an employer. The hierarchy also allows the introduction of higher-level classifications (transfer types), e.g., one-to-one, one-to-many, many-to-one
+
+NOTE – The use case hierarchy shown in Figure 1 displays some variants that are for further study.
+
+QoS aspects of DFSs need to be assessed for two different service categories that are, with reference to Figure 1, macroscopic parameters of a main use case, namely person to person (P2P) money transfers.
+
+- 1) In service category 1, the targeted group of users is limited to the use of (cheap) basic feature phones. This excludes for example browser-based DFS solutions.
+- 2) In service category 2, the additional QoS aspects are assessed when the minimum requirements to the phones used for DFSs are raised and basic smartphone functionality can be assumed.
+
+## 6.2 Legal entities
+
+It is important to accept that in reality the provision of a service offer ("service") is – as a general rule – independent of the physical operation of a telecommunication network.
+
+Whereas for most service offers there is – beside the general legal framework – no specific regulation, DFS "services" are under the close control of banking sector regulators, whereas operators of telecommunication networks are under the control of telecom sector regulators.
+
+Therefore, legal aspects (from a QoS perspective) need to assess two different legal cases:
+
+- 1) in legal case A, the provider of a DFS "service" and the operator of a physical telecommunication network are two distinct and different legal entities;
+- 2) in legal case B, the provider of a DFS "service" and the operator of a physical telecommunication network are the same and identical legal entity.
+
+NOTE – This Recommendation is without prejudice regarding actual legal actions or situations or conclusions or any combination thereof.
+
+## 6.3 Mobile network QoS affecting all services
+
+Figure 2 (adapted from [b-ITU-T E.804] and [b-ETSI TS 102 250-2]) shows a model for QoS parameters. This model has four layers, each of which provides the necessary precondition for the next layer, i.e., that a property belonging to layer  $N$  needs the presence of the properties of layer  $N - 1$ .
+
+The first layer is network availability, which determines QoS from the viewpoint of the service provider than the service user. The second layer is network access. From the service user's point of view, this is the basic requirement for all the other QoS aspects and parameters. The third layer contains the other three QoS aspects: service access, service integrity and service retainability. The different services are located in the fourth layer; the performance of these services is characterized by service specific QoS key performance indicators (KPIs).
+
+The first three layers (with green highlights) are common to all mobile services or applications.
+
+They are characterized typically by the following parameters (KPIs):
+
+- network availability;
+- network accessibility;
+- service accessibility;
+- service integrity;
+- service retainability.
+
+In cases where the KPIs in layers 1, 2 and 3 are not maintained at a stable high level, it is useless to attempt to assess the QoS of any kind of service, because prerequisite conditions are not met and the relevance of QoS figures received will be close to zero.
+
+![Figure 2 – Model for quality of service parameters. A hierarchical diagram showing four layers of QoS parameters. Layer 1 (Network availability) is at the top. Layer 2 (Network accessibility) is below it, with sub-categories 'Circuit switched' and 'Packet switched'. Layer 3 (Service accessibility, Service integrity, Service retainability) is below Layer 2. Layer 4 (various services) is at the bottom, with sub-categories 'E-mail', 'File transfer', 'MMS', 'Mobile broadcast', 'Ping', 'PoC', 'SMS', 'Streaming', 'Telephony', 'Video telephony', 'Web browsing', and 'DFS'. The first three layers are highlighted in green, and the fourth layer is highlighted in yellow. The DFS box is highlighted in orange.](c2fc2621e8206d24427b56bcb2398fc0_img.jpg)
+
+The diagram illustrates a four-layer model for quality of service (QoS) parameters. Layer 1 (Network availability) is at the top. Layer 2 (Network accessibility) is below it, with sub-categories 'Circuit switched' and 'Packet switched'. Layer 3 (Service accessibility, Service integrity, Service retainability) is below Layer 2. Layer 4 (various services) is at the bottom, with sub-categories 'E-mail', 'File transfer', 'MMS', 'Mobile broadcast', 'Ping', 'PoC', 'SMS', 'Streaming', 'Telephony', 'Video telephony', 'Web browsing', and 'DFS'. The first three layers are highlighted in green, and the fourth layer is highlighted in yellow. The DFS box is highlighted in orange.
+
+G.1033(19)\_F02
+
+Figure 2 – Model for quality of service parameters. A hierarchical diagram showing four layers of QoS parameters. Layer 1 (Network availability) is at the top. Layer 2 (Network accessibility) is below it, with sub-categories 'Circuit switched' and 'Packet switched'. Layer 3 (Service accessibility, Service integrity, Service retainability) is below Layer 2. Layer 4 (various services) is at the bottom, with sub-categories 'E-mail', 'File transfer', 'MMS', 'Mobile broadcast', 'Ping', 'PoC', 'SMS', 'Streaming', 'Telephony', 'Video telephony', 'Web browsing', and 'DFS'. The first three layers are highlighted in green, and the fourth layer is highlighted in yellow. The DFS box is highlighted in orange.
+
+Figure 2 – Model for quality of service parameters
+
+Persisting problems with the KPIs for layers 1, 2 and 3 of a mobile network need to be resolved by the stakeholder in the interest of any mobile service and are therefore clearly out of scope of QoS-for-DFS-considerations.
+
+NOTE – Figure 2 requires an update. First of all, layers 1 to 3 describe actually a kind of "pyramid of needs", i.e., before starting to think about service integrity (e.g., call drop rate in telephony), the service needs to be accessible first. Also, the "service" picture needs an overhaul. The "circuit/packet switched" division is legacy from 2G or 3G. Some of the "services" in layer 4 actually depend on each other or belong to different groups. There are "carrier services" such as the basic Internet protocol (IP), and also combined services using one or more such carrier services, e.g., the multimedia messaging service (MMS) that relies on the short message service (SMS) (which is actually an end user-related service as well) for notification, and uses packet data to actually transfer data. A "service" with the same effect for end users, e.g., some kind of over the top (OTT) chat with attached files, uses only basic packet data. In any case, there is no longer any real "technology dependency". If an operator decides to suppress Skype, or prioritizes certain video streaming, this is not the result of some fundamental ability or inability, but just the effect of some "traffic shaping" elements.
+
+## 6.4 Possible solutions
+
+DFSs are realized through utilization of basic services provided by a network. Assuming that the reliability of DFSs has to be very high, there are two basic ways to ensure this reliability.
+
+- Network centric: The QoS level for basic services provided by the network is sufficiently high to create the required reliability.
+- User centric: Robust E2E protocols on UE- and DFS-related infrastructure ensure the reliability of the actual service, even in the presence of deficiencies in the underlying functionality.
+
+Such robustness can be described by key criteria for DFSs. Topmost is, for each transaction, a clear indication whether it was successful, which needs to be consistent for both sides. Assume a transaction is composed of a number of steps, each step being the exchange of a data token. If the transfer of a data token has no clear "lost" criterion, but can take, in principle, indefinite time, a time-out needs to create a defined situation. The essential property of robustness is that, if a data token now arrives after its time-out, the protocol needs to ensure that this token is not causing any action any more.
+
+With respect to practical aspects of DFS implementations, this poses some fundamental differences. When the main goal is to introduce DFSs in the near future, it needs to operate with the existing installed base of end user devices. This will automatically limit the spectrum of applicable methods to those which can be supported by those devices. A possible drawback of this approach is that if a technology has been deployed and is widely used, it will – as long as it is working without major problems – be difficult to replace, even if the new technology is superior. This may be less an issue with respect to end user devices as the penetration of smartphones continues to increase strongly due to their manifold advantages. It may be that these retaining factors are more on the side of infrastructure, as introduction of new technologies requires new investment that may, at least in the first years of usage, not be balanced by similar new opportunities to generate additional revenue.
+
+# 7 Conclusions
+
+The following conclusions are, with respect to clause 6, based on the assumption that necessary DFS performance is achieved by ensuring a sufficiently high performance of the basic services used to implement DFSs. The case of using a robust E2E protocol is not treated here.
+
+## 7.1 Conclusions for service category 1
+
+Four different techniques are discussed in Annex B, which might be used in conjunction with DFS offers for service category 1.
+
+- SMS is a store and forward service. Even if the share of short transfer times may be high in typical cases, it cannot – without modifications – be used reliably for real-time transactions.
+- Dual tone multi-frequency (DTMF) has limited transfer capabilities and will most probably only be used to complement one of the other techniques.
+- Interactive voice response (IVR) typically requires reasonably high listening quality, which might pose a problem with feature phones in environments with higher levels of background noise.
+- Unstructured supplementary service data (USSD) is a true real-time technique. However, the message transfers which could be used for DFSs are not standardized.
+
+## 7.2 Conclusions for service category 2
+
+Seven different techniques are discussed in Annex A, which might be used in conjunction with DFS offers for service category 2. As per availability on smartphones, solutions based on the hypertext transfer protocol secure (HTTPS) appear to be the optimal carrier technology for DFSs.
+
+## 7.3 Conclusions related to digital financial services
+
+It is of importance for any further work in the field of QoS/QoE for DFSs to get access to more detailed information, such as descriptions of the various DFS offers to see on a technical level, which underlying services in the network are used and which are the technical parameters associated with them, e.g., timer values, timeout events and number of interactions involved in a single financial transaction. Doing so carries potential for improving the quality of standards development and testing, which has been an on-going need.
+
+Therefore, it is suggested that telecom regulators collect such information prior to the issue of licenses in order to make their own judgement of the quality of the planned DFS offering.
+
+Such information should be submitted by regulators to ITU-T Study Group 12, where the experts could start categorizing the different approaches and provide comments and guidance on such implementations. If possible, the information on the DFSs should be summarized in a flowchart.
+
+There are even more issues remaining currently open, which will need further discussion.
+
+- Mobile operators have increasing problems with the huge amount of data traffic in their networks. Therefore, if high-speed fixed networks are available, there is a massive trend to use so-called "Wi-Fi offloading", where data traffic is redirected via Wi-Fi accesses to the internet backbone core. The consequences for DFSs seem to be quite unexplored, as yet.
+- The text displayed in the course of DFS interactions or the accentuation in spoken dialogue systems may be loaded with emotion, which could affect the user experience of the service (QoE). Emotion detectors could be used to minimize any negative impact from this text and speech material. Currently, requirements for emotion detectors in telecommunications have been published in [ETSI TS 103 296].
+- A serious problem (mostly for regulators) are effects that cannot easily be allocated to one of the stakeholders in the DFS process. A prominent example is so-called early timeouts in DFSs, which anyone outside the DFS provider would interpret as dropped- calls, i.e., blame the network or blame the terminal or blame the user – in reality it turns out just to be a badly designed flow-of-actions: users still reading instructions on their screens before initiating the next step of a transaction are hit by an invisible timer's timeout action.
+
+# 8 Future considerations: Top-level view
+
+This clause deals with an end-to-end (E2E) model of DFSs. It focuses on the essence for user-related functionality of DFSs by providing a top-level view of (selected) DFS use cases.
+
+The term "transaction" is used to describe a single instance of a complete use case from a customer point of view, in accordance with the usage of this term in other fields of QoS standardization. It is noted that in this case, the term is also part of the common expression "financial transaction".
+
+The use cases described serve as examples to explain the underlying framework. The underlying model can, however, be easily applied to other use cases that are identified to be relevant in the DFS context.
+
+From the use cases, quality metrics are derived. The key point of the model is that it is, on its topmost level, "technology agnostic". The actual implementation may be in manifold ways, with specific technical characteristics, strengths and weaknesses; these come in at lower levels of the model. The technology agnostic top level makes sure that no "technology-related" allowances are made (such as "discounts" for known technical weaknesses of particular implementations). Also, the model makes sure that new technical developments in realizing DFSs do not disrupt existing QoS metrics.
+
+The underlying general principle of the QoS metrics proposed is also to provide the smallest possible number of KPIs, with each KPI having a clearly defined relation to user perception. This shall avoid the situation, observed in some KPI sets, where individual KPIs overlap in meaning, which can lead to unclear or even contradictory results.
+
+An actual DFS implementation uses different network- related "services" or functionality. The relevant clause shows how the use case related top-level view – and its KPIs – can be mapped to this technological level of currently existing "carrier services" with appropriate (mostly already existing) KPIs.
+
+The principle of having a small number of strong KPIs does not exclude additional KPIs with diagnostic or administrative functions.
+
+It is recognized that there are several stakeholders with different interests. The relevant clause – which is also to be seen as an expandable illustration of the underlying concept – describes this view in more detail.
+
+The fact that different stakeholders have different interests also leads to the conclusion that not all KPIs are of equal importance to all stakeholders. This aspect can provide guidance when it comes to the provision of a legal or regulatory framework to enable or support emergence of DFSs.
+
+Clause 8.4 considers how practical monitoring of DFS service performance could be implemented. It differentiates between test and measurement in the introduction phase, and continuous quality monitoring in the operational phase of DFSs.
+
+## **8.1 Use cases and related top-level KPI**
+
+### **8.1.1 Transfer of money from A to B**
+
+Basic flow of activities:
+
+Party A decides to transfer amount  $X$  from its account to the account of B. Key interests of this transfers are:
+
+- 1) the transfer is made with a clear indication of success or failure on both sides within a reasonable time span;
+- 2) the success rate of a money transfer needs to be high;
+- 3) the duration of a transaction is reasonably short;
+- 4) if the transaction fails, the situation needs to be completely reversed within a reasonably short time span (i.e., no money "lost in limbo");
+- 5) the transaction leads to a stable and correct end state for all participants in a reasonably short time span (i.e., all accounts are "up to date" as fast as possible);
+
+- 6) there are no losses or duplications of money during the transaction (i.e., money not deducted from A's account but appearing in B's account).
+
+NOTE – Not all of these conditions are of equal importance to all stakeholders, e.g., the absence of "money duplications" may not be of interest to end users.
+
+A further differentiation of the use case may come from the question whether some kind of proof for the transaction is created, and if yes, in which way. This may be a crucial element if money is paid to clear debts, e.g., an electricity bill. This may involve data transmission to a possible third party to send such a proof, or access to appropriate services to produce this.
+
+From these requirements, the following E2E KPIs can be derived:
+
+- money transfer completion rate;
+- money transfer completion time;
+- money transfer false positive rate;
+- money transfer false negative rate;
+- money transfer failed transaction resolution rate;
+- money transfer account stabilization success rate;
+- money transfer account stabilization time;
+- money transfer loss rate;
+- money transfer duplication rate.
+
+NOTE – These KPIs and their technical basis are currently not standardized and therefore cannot be assessed in a comparative manner.
+
+This list clearly contains elements that are not primarily related to mobile network behaviour or performance; they also relate to the performance of underlying banking processes and implementations. So, the list can probably be reduced to elements that are assumed to be primarily linked to mobile networks.
+
+There is, however, a connection. If, for example, a connection loss occurs during a transaction consisting of a number of roundtrips estimated to complete a DFS transaction, this may have different results depending on a particular implementation of such banking processes. Therefore, it is assumed that the robustness and stability of such processes against failures which are typical to specific basic services of mobile networks will also have an effect on the overall QoS of DFSs.
+
+### 8.1.2 Other use cases
+
+This is for further study.
+
+## 8.2 Technological components of DFSs
+
+As outlined in other parts of this Recommendation, there are some services and functionalities within existing mobile networks that can be used – with a further selection by available features of mobile devices – to realize DFSs.
+
+From the concept of a "pyramid of needs" and assessment of the E2E KPIs for DFSs, a clear hierarchy of quality requirements can be derived.
+
+The topmost requirement will be the integrity of a transaction. Integrity in DFSs is the clear and reliable assessment, whether a transaction has been successful or not. This is seen as even more important than the overall success rate of an implementation. If a transaction is erroneously assessed as being successful or failed, the objective damage (e.g., to a person's financial condition) will be larger than a case where a transaction has to be repeated due to a detected failure. The same applies to a transaction that is erroneously assessed as unsuccessful, which would result in duplicate transfer due to a repetition of the process.
+
+From a QoE point of view, the situation can be more complex. Assuming there are two implementations: one of them being stable and robust in the sense of low (ideally zero) probability of false positives or negatives, but slow; the other one faster, but more sensitive to such errors. Unless the false-assessment error is quite large, it is likely that in the customer perception, the latter will appear as the "better" one. It follows that in this area, consideration beyond mere competition according to market rules is needed.
+
+An E2E approach needs to be taken because the overall robustness of a particular implementation depends on several factors.
+
+Assume that there are two alternatives, one of them requiring a number,  $N_1$ , of roundtrips, each having a time duration of  $T_1$ , and a success rate per roundtrip of  $S_1$ ; the other is characterized likewise by  $N_2$ ,  $T_2$  and  $S_2$ . Clearly, there are several interactions with typical network properties. For instance, if the transaction is performed while the actor is moving (e.g., in a public transport vehicle or as a passenger in a car), the change of network conditions during a transaction influences the overall success rate. This links the time scale of motion-related impairments to transaction characteristics. If the typical overall duration of a DFS transaction ( $T_1*N_1$  and  $T_2*N_2$ ) is above the typical time during which network properties show degradations, the probability of failure increases. In a more general view, the overall success rate of a DFS transaction can be expressed as  $S_1^{N_1}$  and  $S_2^{N_2}$ . So even if an individual success rate per roundtrip of a specific implementation (where the motion profile can be factored in) is lower, the resulting E2E success rate may be higher if the number of roundtrips in this implementation is sufficiently smaller.
+
+The same linkage between characteristics includes the times involved. For instance, if a transaction fails (in a "proper" way, i.e., with correct assessment of the result), the negative impact on QoE will presumably be smaller if this result is obtained in a shorter period of time, as a follow-up try can be started and completed faster.
+
+## 8.3 Stakeholders
+
+This clause is not meant to be a complete analysis of stakeholder structure and their requirements. The point is that different stakeholder types exist, and that their concerns and main interests differ. This will have an impact on the relative weighting of particular QoS metrics and therefore on definition of QoE.
+
+### *End customers*
+
+The main interest of end customers will be to have access to DFSs at low cost (which also means without the need to spend more on new mobile devices) and with a high degree of reliability, as financial losses due to service failures will be felt relatively strongly, in particular in low-income segments. It is assumed that transaction speed considerations are (as long as transaction times are within certain reasonable limits) of less importance.
+
+### *Businesses*
+
+Assuming the same basic need for reliable and affordable transactions, larger enterprises at least will have an interest in DFS technologies that allow for efficient processing of recurring or larger scale transfers. It is further assumed that there may be interest in technologies that can be deployed on fixed-network equipment (i.e., personal computers) without excessive cost. This will in turn affect market acceptance of solutions with different ways of interfacing. An example is access to certain gateways or other network-based functions like a short message service centre (SMSC).
+
+### *Network operators*
+
+As network operators are, usually, subject to regulation, relevant factors actually can be separated into two categories. The first category contains general technical and commercial requirements, such as cost of operation of a particular technology in relation to profits that can be generated. The second category may include cost of non-compliance with legal or regulatory requirements, in terms of
+
+service level agreements (SLAs), or linkages between, for example, licenses and obligations to provide certain services or service properties.
+
+### ***DFS operators***
+
+Although DFS operators are not identical to network operators, they will basically be subject to similar conditions to them, with perhaps other governmental entities responsible for setting and enforcing the rules under which they operate. Commercially, their market power will probably be large enough to impose quality standards (SLAs) or other market forces to service providers (network operators).
+
+### ***Governments/Regulators***
+
+Assuming that the main objective of governments is economic development, their task is to find a balance between carrot and stick, i.e., a level of rules and regulations that enables technical evolution, while leaving DFS operators enough room to run a profitable service, and making sure that costs of DFS services are in an affordable range. For this stakeholder group, it is assumed that the main objectives are stable, reliable services in combination with a technology that gives the target segment of the population a sufficiently barrier-free access to DFSs.
+
+Furthermore, there are different ways in which each of these stakeholder groups has influence on other stakeholders, for instance in rewarding or sanctioning market offerings or more general decisions. The crucial point to be made here is that beyond the directly visible first-order effects, second-order interactions exist that do not necessarily have to be weaker, but may work in a "cybernetic" way, i.e., with longer time constants, but with likewise or even stronger effects than first-order dependencies.
+
+## **8.4 QoS monitoring**
+
+In order to secure the necessary quality level of DFSs, appropriate regulatory guidance and comprehensive performance targets need to be established. Basically, it would be possible to refer to basic performance measurements of respective carrier services (such as SMS, telephony (for DTMF or IVR) or packet data. Due to the nature of services implementation this will, however, be a surrogate with considerable risk of predicting actual DFS performance incorrectly.
+
+It is therefore – owing to the importance of DFS – assumed that a better way of monitoring needs to be established. This monitoring should – while being fully aware of practical issues in definition and implementation – use actual use cases, i.e., actual money transfer.
+
+The monitoring is proposed to have multiple forms that cover all stages of the technical life cycle of any DFS implementation.
+
+### ***Assessment and roll-out phase:***
+
+E2E performance measurements as professionally done by dedicated systems, e.g., under control of regulatory authorities.
+
+### ***Operational phase:***
+
+Regular E2E performance measurements as professionally done by dedicated systems, e.g., under control of regulatory authorities.
+
+### ***"Test panel" performance measurements, integrated into selected end user devices/apps:***
+
+For this kind of measurement, a group of end users, selected to be representative for the general usership, would be recruited and equipped with specially designed DFS clients. This group would, along with doing their "real life" DFS usage, also file additional reports. These reports would then allow responsible entities to constantly assess the performance of DFSs in the field.
+
+### ***"Crowd-sourced" performance measurements, integrated into end user devices/apps:***
+
+This would be a simple and non-intrusive way to obtain information on DFS performance on a broad scale. Professional systems used would be equipped with functionality to not only measure E2E performance, but also collect diagnostic information allowing to track root causes for poor performance or malfunction of services.
+
+Using real use cases creates additional cost. This cost needs to be assessed against the benefits of obtaining real instead of surrogate data that only can estimate actual service performance. Moreover, it is possible, with a little additional effort in planning and implementation, to design processes that optimize additional cost, such as re-transferring money that has been moved by a DFS.
+
+It is therefore proposed to add appropriate concepts to a DFS implementation strategy. To increase the effectiveness of such concepts, it is recommended that a pilot phase be designed to give insight into practical aspects and provide information to optimize respective operations.
+
+# Annex A
+
+## Underlying functionalities of DFS applications
+
+(This annex forms an integral part of this Recommendation.)
+
+### A.1 Service category 1 (feature phone)
+
+This clause focuses on DFS applications that can be run using simple mobile feature phones (low-end mobile phones that are limited in capabilities in contrast to modern smartphones, see clause 6.1). Therefore it is assumed in the following that financial services requiring file transfer protocol, hypertext transfer protocol (HTTP) or browser-based transactions can be safely excluded from the discussion in this clause.
+
+**Table A.1 – Summary of technologies for service category 1**
+
+| Technique   | Main features                                                                    | Disadvantages                             | Advantages                               |
+|-------------|----------------------------------------------------------------------------------|-------------------------------------------|------------------------------------------|
+| <b>SMS</b>  | Store-and-forward alphanumerical messages                                        | Not real-time                             | Globally available<br>Interconnection ok |
+| <b>IVR</b>  | Interaction with user by artificial or recorded voice, voice recognition or DTMF | Requires good speech quality transmission | Real-time                                |
+| <b>DTMF</b> | Simple keypad operation                                                          | Limited character set                     | Real-time                                |
+| <b>USSD</b> | Alphanumerical messages                                                          | Requires USSD Gateways                    | Real-time                                |
+
+#### A.1.1 Short message service
+
+The SMS is used to send text messages to and from mobile phones, fax machines or IP addresses. The messages can typically be up to 160 characters in length, though some services use 5-bit mode, which supports 224 characters. SMS was originally created for phones that use the global system for mobile communications (GSM), but now all major mobile phone systems support it. Once a message is sent, it is received by an SMSC, which must then get it to the appropriate mobile device.
+
+To do this, the SMSC sends an SMS request to the home location register (HLR) to find the roaming customer. Once the HLR receives the request, it will respond to the SMSC with the subscriber's status:
+
+- 1) inactive or active;
+- 2) where subscriber is roaming.
+
+If the response is "inactive", then the SMSC will hold on to the message for a period of time. When the subscriber accesses his device, the HLR sends an SMS notification to the SMSC, and the SMSC will attempt delivery.
+
+The SMSC transfers the message in a short message delivery point to point format to the serving system. The system pages the device, and if it responds, the message gets delivered.
+
+The SMSC receives verification that the message was received by the end user, then categorizes the message as "sent" and will not attempt to send again.
+
+SMS falls into the group of the so-called store-and-forward services and is normally being transported in the background class according to [b-ETSI TS 123 107]. As a consequence, parameters like SMS delivery time or SMS response time depend very much on the traffic load of the mobile network and cannot be guaranteed.
+
+#### **A.1.2 Interactive voice response**
+
+IVR is a technology that allows a computer to interact with human users through the use of voice and DTMF tone input via a keypad.
+
+In telecommunications, IVR allows customers to interact with a company's host system via a telephone keypad or by speech recognition, after which they can service their own enquiries by following the IVR dialogue. IVR systems can respond with pre-recorded or dynamically generated audio to further direct users on how to proceed. IVR applications can be used to control almost any function where the interface can be broken down into a series of simple interactions.
+
+#### **A.1.3 Dual tone multi-frequency signalling**
+
+The DTMF system uses a set of eight audio frequencies transmitted in pairs to represent 16 signals, represented by the 10 digits, the letters A to D, and the symbols # and \* as described in [b-ITU-T Q.23]. Detailed requirements for DTMF are specified in [b-ETSI ES 201 235-1], [b-ETSI ES 201 235-2], [b-ETSI ES 201 235-3] and [b-ETSI ES 201 235-4]. As the signals are audible tones in the voice frequency range, they can be transmitted like speech signals. Originally used to dial the number of the remote terminal, it became a common method to transmit small amounts of data.
+
+In packet based networks, there are three common ways of sending DTMF:
+
+- session initiation protocol (SIP) INFO packets as described in [b-IETF RFC 2976];
+- as specially marked events in the real-time protocol (RTP) stream – as described in [b-IETF RFC 2833];
+- inband as normal audio tones in the RTP stream with no special coding or markers.
+
+For mobile networks [b-ETSI TS 123 014] describes how DTMF signals are supported. A message-based signalling system is used across the air interface. Inband transmission is not possible.
+
+That means that in mobile communication, the originating mobile terminal directly creates relevant messages when the keys are pressed by the user during a call.
+
+#### **A.1.4 Unstructured supplementary service data – both push and pull services**
+
+USSD is a protocol used by mobile terminals to communicate with the network of the mobile operator.
+
+USSD messages are up to 182 alphanumeric characters in length. USSD messages create a real-time connection during a USSD session. The connection remains open, allowing a two-way exchange of a sequence of data. This makes USSD more responsive than services that use SMS.
+
+Messages sent over USSD are not standardized:
+
+Normally, USSD is used in the format \*nnn# as part of configuring the phone on the network. In order to transfer text messages via USSD to another mobile network, a special USSD gateway is required, which mobile operators do not normally provide.
+
+USSD is sometimes used in conjunction with SMS. The user sends a request to the network via USSD, and the network replies within the same USSD session with an acknowledgement of receipt.
+
+Subsequently, one or more mobile terminated SMS messages communicate the status or results of the initial request. In such cases, SMS is used to "push" a reply or updates to the handset when the network is ready to send them. In contrast, USSD is used for command-and-control only.
+
+USSD is generally associated with real-time or instant messaging services. There is no store-and-forward capability, as is typical of other short-message protocols like SMS.
+
+USSD is specified in [b-ETSI TS 100 625], [b-ETSI TS 100 549] and in [b-ETSI EN 300 957]. USSD modes are:
+
+- mobile-initiated: USSD/ PULL or USSD/P2P.
+
+When the user dials a code from mobile terminal
+
+- network-initiated: USSD/ PUSH or USSD/A2P.
+
+When the user receives a push message from the network:
+
+USSD can be used, e.g., for prepaid call-back service, mobile-money services, location-based content services, menu-based information services and as part of configuring the phone on the network.
+
+### A.2 Service category 2 (smartphone)
+
+In addition to service category 1, the underlying techniques listed in Table A.2 can be taken into account. Even basic smart phones (see clause 6.1) will provide services based on these techniques.
+
+**Table A.2 – Summary of technologies for service category 2**
+
+| Technique    | Main features                                                                    | Disadvantages                             | Advantages                                                |
+|--------------|----------------------------------------------------------------------------------|-------------------------------------------|-----------------------------------------------------------|
+| <b>SMS</b>   | Store-and-forward alphanumerical messages                                        | Not real-time                             | Globally available<br>Interconnection ok                  |
+| <b>IVR</b>   | Interaction with user by artificial or recorded voice, voice recognition or DTMF | Requires good speech quality transmission | Real-time                                                 |
+| <b>DTMF</b>  | Simple keypad operation                                                          | Limited character set                     | Real-time                                                 |
+| <b>USSD</b>  | Alphanumerical messages                                                          | Requires USSD Gateways                    | Real-time                                                 |
+| <b>WAP</b>   | Simple web browser                                                               | Limited set of functions                  | Available on some phones even if they do not support HTTP |
+| <b>HTTP</b>  | Standard web browser                                                             | Unsecure                                  | Internet-like access                                      |
+| <b>HTTPS</b> | Safe web browser                                                                 | Complex                                   | Encrypted, not even subject to traffic shaping            |
+
+#### A.2.1 Wireless application protocol
+
+The WAP is a technical standard for accessing information over a mobile wireless network. A WAP browser is a web browser for mobile devices such as mobile phones that use the protocol.
+
+WAPs that use displays and access the Internet run what are called micro browsers – browsers with small file sizes that can accommodate the low memory constraints of hand-held devices and the low-bandwidth constraints of a wireless hand-held network.
+
+Although WAP supports hypertext markup language (HTML) and extensible markup language (XML), the wireless markup language (WML; an XML application) is specifically devised for small screens and one-hand navigation without a keyboard. WML is scalable from two- line text displays
+
+up through graphic screens found on items such as smart phones and communicators. WAP also supports WMLScript, which is similar to JavaScript, but makes minimal demands on memory and central processing unit (CPU) power, because it does not contain many of the functions found in other scripting languages that are unnecessary in this context.
+
+#### **A.2.2 Hypertext transfer protocol**
+
+The HTTP is an application protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the world wide web. Hypertext is structured text that uses logical links (hyperlinks) between nodes containing text. HTTP is the protocol to exchange or transfer hypertext.
+
+HTTP functions as a request-response protocol in the client-server computing model. A web browser, for example, may be the client and an application running on a computer hosting a web site may be the server. The client submits an HTTP request message to the server. The server, which provides resources such as HTML files and other content or performs other functions on behalf of the client returns a response message to the client. The response contains completion status information about the request and may also contain requested content in its message body.
+
+#### **A.2.3 Hypertext transfer protocol secure**
+
+HTTPS (also called HTTP over transport layer security (TLS), HTTP over a secure sockets layer (SSL), and HTTP Secure) is a protocol for secure communication over a computer network that is widely used on the Internet. HTTPS consists of communication over HTTP within a connection encrypted by TLS or its predecessor, SSL. The main motivation for HTTPS is authentication of websites visited and protection of the privacy and integrity of the exchanged data.
+
+In its popular deployment on the internet, HTTPS provides authentication of the website and associated web server with which the user is communicating, which protects against man-in-the-middle attacks. Additionally, it provides bidirectional encryption of communications between a client and server, which protects against eavesdropping and tampering with or forging the contents of the communication.
+
+# Appendix I
+
+## Considerations related to the fitness for DFSs
+
+(This appendix does not form an integral part of this Recommendation.)
+
+A successful introduction of DFSs via a mobile network requires fitness of the whole environment used, which is
+
+- fitness of the mobile network, to provide a minimum level of availability and accessibility;
+- fitness of the mobile network to provide the services required for realization of DFSs;
+- fitness of mobile devices used, to support the basic services used to realize DFSs;
+- fitness of the DFS service itself to provide useable interfaces;
+- fitness of users to successfully use DFSs – this may include the necessary skills to operate DFSs on phones as well as basic understanding of properties of DFSs in general, to protect users against exploitation of insufficient knowledge, see [b-FIGI 2019c];
+- fitness of the general society and the governmental institutions for DFSs.
+
+Figures I.1 to I.5 are decision diagrams meant to facilitate discussion between stakeholders in different regions or countries. Figures I.1 to I.5 do not contain any numbers or specific target values. This is by intention, because target values acceptable for all stakeholders will vary from region to region and from country to country.
+
+The term "major events" used in Figures I.1 to I.5 refers to [ITU-T E.811], aiming at QoS in mobile networks during major events, as for example, major sports events.
+
+![Decision diagram for fitness of a mobile network for DFSs](90ddf538ef276510e2b631f7b96654e6_img.jpg)
+
+The diagram illustrates four categories of network fitness for DFSs, each represented by a colored circle and a corresponding vertical bar:
+
+- INSUFFICIENT (Red Circle):** Unstable radio connections, Service interruptions, Handover problems.
+- CRITICAL (Purple Circle):** Stable radio conditions, Core network congestion, Coverage problems in some areas.
+- GOOD (Green Circle):** Radio network operation well, No congestions or dropouts, Fit for DFS (highlighted in a green box).
+- MAJOR EVENTS (Blue Circle):** Possible overload of radio network, Possible congestions, DFS may be affected.
+
+G.1033(19)\_FI.1
+
+Decision diagram for fitness of a mobile network for DFSs
+
+Figure I.1 – Decision diagram for fitness of a mobile network for DFSs
+
+![Decision diagram for fitness of mobile terminals for DFSs. It consists of four vertical bars: INSUFFICIENT (SMS), CRITICAL (USSD, HTTP), GOOD (HTTPS, Data protection, Fit for DFS), and MAJOR EVENTS (TBD).](c914f51f4427bc672dd0526cfc90ebe9_img.jpg)
+
+This diagram illustrates the fitness of mobile terminals for DFSs across four categories:
+
+- INSUFFICIENT:** SMS
+- CRITICAL:** USSD, HTTP
+- GOOD:** HTTPS, Data protection, Fit for DFS
+- MAJOR EVENTS:** TBD
+
+G.1033(19)\_FI.2
+
+Decision diagram for fitness of mobile terminals for DFSs. It consists of four vertical bars: INSUFFICIENT (SMS), CRITICAL (USSD, HTTP), GOOD (HTTPS, Data protection, Fit for DFS), and MAJOR EVENTS (TBD).
+
+Figure I.2 – Decision diagram for fitness of mobile terminals for DFSs
+
+![Decision diagram for fitness of mobile network services for DFSs. It consists of four vertical bars: INSUFFICIENT (No proof of concept), CRITICAL (High session drop rate, Large delay fluctuations, Process not under control), GOOD (Stable 24/7/365 provision, Low volatility of KPIs, Fit for DFS), and MAJOR EVENTS (Capable of increase in number of transactions?).](d734a6ea1b381280f043fcf70391b6db_img.jpg)
+
+This diagram illustrates the fitness of mobile network services for DFSs across four categories:
+
+- INSUFFICIENT:** No proof of concept
+- CRITICAL:** High session drop rate, Large delay fluctuations, Process not under control
+- GOOD:** Stable 24/7/365 provision, Low volatility of KPIs, Fit for DFS
+- MAJOR EVENTS:** Capable of increase in number of transactions?
+
+G.1033(19)\_FI.3
+
+Decision diagram for fitness of mobile network services for DFSs. It consists of four vertical bars: INSUFFICIENT (No proof of concept), CRITICAL (High session drop rate, Large delay fluctuations, Process not under control), GOOD (Stable 24/7/365 provision, Low volatility of KPIs, Fit for DFS), and MAJOR EVENTS (Capable of increase in number of transactions?).
+
+Figure I.3 – Decision diagram for fitness of mobile network services for DFSs
+
+![Decision diagram for fitness of mobile users for DFSs. It consists of four vertical bars: INSUFFICIENT (High illiteracy), CRITICAL (Low technical understanding), GOOD (Ability to access situations correctly w/respect to success/failure, Ability to report deficiencies in services, Fit for DFS), and MAJOR EVENTS (User may be distracted).](844077b3034f0030b404207db0ad76b4_img.jpg)
+
+This diagram illustrates the fitness of mobile users for DFSs across four categories:
+
+- INSUFFICIENT:** High illiteracy
+- CRITICAL:** Low technical understanding
+- GOOD:** Ability to access situations correctly w/respect to success/failure, Ability to report deficiencies in services, Fit for DFS
+- MAJOR EVENTS:** User may be distracted
+
+G.1033(19)\_FI.4
+
+Decision diagram for fitness of mobile users for DFSs. It consists of four vertical bars: INSUFFICIENT (High illiteracy), CRITICAL (Low technical understanding), GOOD (Ability to access situations correctly w/respect to success/failure, Ability to report deficiencies in services, Fit for DFS), and MAJOR EVENTS (User may be distracted).
+
+Figure I.4 – Decision diagram for fitness of mobile users for DFSs
+
+![Decision diagram for fitness of a society/government for DFSs. The diagram consists of four vertical bars representing different levels of fitness: INSUFFICIENT, CRITICAL, GOOD, and MAJOR EVENTS. The INSUFFICIENT bar shows 'No regulatory framework'. The CRITICAL bar shows 'Lack of effective sanctioning mechanisms', 'Lack of cost transparency', and 'Monopolistic structures'. The GOOD bar shows 'Functioning mechanisms to identity, report and sanction criminal misuse', 'Market mechanisms sanction exploitation or over pricing', and a green box labeled 'Fit for DFS'. The MAJOR EVENTS bar shows 'TBD'.](c5452f95f3b28f1bfe29e84fbc2e1267_img.jpg)
+
+| INSUFFICIENT            | CRITICAL                                                                                         | GOOD                                                                                                                                                     | MAJOR EVENTS |
+|-------------------------|--------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------|--------------|
+| No regulatory framework | Lack of effective sanctioning mechanisms<br>Lack of cost transparency<br>Monopolistic structures | Functioning mechanisms to identity, report and sanction criminal misuse<br>Market mechanisms sanction exploitation or over pricing<br><b>Fit for DFS</b> | TBD          |
+
+Decision diagram for fitness of a society/government for DFSs. The diagram consists of four vertical bars representing different levels of fitness: INSUFFICIENT, CRITICAL, GOOD, and MAJOR EVENTS. The INSUFFICIENT bar shows 'No regulatory framework'. The CRITICAL bar shows 'Lack of effective sanctioning mechanisms', 'Lack of cost transparency', and 'Monopolistic structures'. The GOOD bar shows 'Functioning mechanisms to identity, report and sanction criminal misuse', 'Market mechanisms sanction exploitation or over pricing', and a green box labeled 'Fit for DFS'. The MAJOR EVENTS bar shows 'TBD'.
+
+G.1033(19)\_FI.5
+
+**Figure I.5 – Decision diagram for fitness of a society/government for DFSs**
+
+It is important for any further work in the field of QoS/QoE for DFSs to get access to more detailed information, such as descriptions of the various DFS offers to see on a technical level, which underlying services in the network are used and which are the technical parameters associated with them, e.g., timer values, timeout events, number of interactions involved in a single financial transaction.
+
+Therefore, it is suggested that telecom regulators collect such information prior to the issue of licences in order to make their own judgement of the quality of the planned DFS offering.
+
+Such flowchart information should be submitted by regulators to ITU-T SG12, where the experts could start categorizing the different approaches, and provide comments and guidance on such implementations.
+
+There are even more issues remaining currently open, which will need further discussions:
+
+- Mobile operators have increasing problems with the huge amount of data traffic in their networks. Therefore, if high speed fixed networks are available, there is a massive trend to use so-called "WiFi offloading", where data traffic is redirected via Wi-Fi accesses to the internet backbone core. The consequences for DFS seem to be quite unexplored, as yet.
+- The text displayed in the course of DFS interactions or the accentuation in spoken dialogue systems may be loaded with emotions, which could affect the users' experience of the service (QoE). Emotion detectors could be used to minimize any negative impact from this text and speech material. Requirements for emotion detectors in telecommunications are provided in [ETSI TS 103 296].
+- A serious problem (mostly for regulators) are effects that cannot easily be allocated to one of the stakeholders in the DFS process. A prominent example is so-called early timeouts in DFSs, which anyone outside the DFS provider would interpret as dropped- calls, i.e., blame the network or blame the terminal or blame the user – in reality it turns out just to be a badly designed flow-of-actions: users still reading instructions on their screens before initiating the next step of a transaction are hit by an invisible timer's timeout action.
+
+Because the field of DFSs and its related QoS and QoE aspects is both of high importance and quite complex, capacity building is essential.
+
+# Appendix II
+
+## Is DFS a "popular service"?
+
+(This appendix does not form an integral part of this Recommendation.)
+
+## II.1 Relationship between QoS and QoE
+
+In addition to the term QoS, the term QoE is often used nowadays to stress the purely subjective nature of quality assessments in telecommunications and their focus on the user's perspective of the overall value of the service provided.
+
+The increased significance of the term QoE is related to the fact that in the past the term QoS was used mostly for only technical concepts focused on networks and network elements. The definition of QoS, however, does include the degree of satisfaction of a user with a service. Thus, non-technical aspects are included, like e.g., the user's environment, expectations, the nature of the content and its importance. However, most service providers used QoS only in relation to the actual user-service interaction to cross-check whether user requirements were met by the service implementation of a provider (as perceived by the user). Therefore, there was a strong focus on the actual network performance and its immediate influence on user perceivable aspects, while additional subjective and not directly related service aspects were omitted.
+
+QoE is defined in [b-ITU-T P.10] as the degree of delight or annoyance of the user of an application or service. It includes the complete E2E system effects (client, terminal, network, services infrastructure, etc.) and may be influenced by user expectations and context. Hence, QoE is measured subjectively by the end user and may differ from one user to another. However, it is often estimated by a combination of objective measurements and metrics describing subjective elements.
+
+NOTE – The definition of QoE and, in particular, the dividing line between QoS and QoE is, however, quite fuzzy, and up to today it does not appear that a globally accepted definition exists. For example, [b-ITU-T E.800] does not use the term QoE at all; instead, it uses a four-viewpoint model (similar to the one in [b-ITU-T G.1000]) with terminology, like QoS experienced (QoSE) or QoS perceived (QoSP).
+
+For working purposes, preferably the use of QoS can be limited to things that can be measured by machines or technical means (including, for example, speech quality metrics, like [b-ITU-T P.863], which already contain some perceptual considerations), and QoE should be used for items further down a "processing chain" where some kind of assessment has been applied. This assessment can be, for instance, some kind of usually nonlinear (clipping) function expressing limits where service quality is either "unacceptable" anyway, or so good that a further improvement will not have any practical consequences. It is important to note that such limits will be strongly dependent on previous experience, i.e., will vary between regions or countries, and will also vary with time as people get accustomed to improvements. Therefore, the issue of "typical values" or "threshold values" is characteristic for the QoE domain.
+
+Objective measurements deal with quantities that can usually be determined by technical measurements, such as information loss and delay. Subjective elements are components of human perception that may include emotions, linguistic background, attitude, motivation, etc., which determine the overall acceptability of the service by the end user. An important part of subjectivity is expectations that usually are formed by previous experience of users for the same or similar types of service.
+
+Figure II.1 shows factors contributing to QoE. These factors are organized as those related to QoS and those that can be classified as human components. QoE for voice and video is often measured via carefully controlled subjective tests, where voice or video samples are played to viewers who are asked to rate them on a scale. The ratings assigned to each case are averaged together to yield the mean opinion score (MOS).
+
+QoS is defined in [b-ITU-T E.800] as the totality of characteristics of a telecommunications service that bear on its ability to satisfy stated and implied needs of the user of the service.. In general, QoS is measured in an objective way.
+
+In telecommunications, QoS is usually a measure of performance of services delivered by networks. QoS mechanisms include any mechanism that contributes to improvement of the overall performance of the system and hence to improving the end user experience. QoS mechanisms can be implemented at different levels.
+
+Example – At the network level, QoS mechanisms include traffic management mechanisms, such as buffering and scheduling employed to differentiate between traffic belonging to different applications. Other QoS mechanisms at levels other than transport include loss concealment, application forward error correction (FEC), etc.
+
+QoS parameters are used to describe the QoS observed. Similar to the QoS mechanisms, QoS parameters can be defined at different layers. Figure II.1 shows the factors that have an influence on QoS and QoE.
+
+![A hierarchical diagram showing the factors influencing Quality of Experience (QoE). QoE is at the top, branching into 'Objective' and 'Subjective' categories. 'Objective' leads to 'Quality of service', which further branches into 'Service factors', 'Transport factors', and 'Application factors'. 'Subjective' leads to 'Human components', which branches into 'Emotions', 'Service billing', and 'Experience'. A dashed line connects 'Emotions' and 'Service billing'. The diagram is labeled G.1033(19)_FII.1 at the bottom right.](58f4167687de8d7339594e5f6fbe0bc6_img.jpg)
+
+```
+graph TD; QoE[QoE] -- Objective --> QoS[Quality of service]; QoE -- Subjective --> HC[Human components]; QoS --> SF[Service factors]; QoS --> TF[Transport factors]; QoS --> AF[Application factors]; HC --> E[Emotions]; HC --> SB[Service billing]; HC --> EX[Experience]; E -.-> SB;
+```
+
+A hierarchical diagram showing the factors influencing Quality of Experience (QoE). QoE is at the top, branching into 'Objective' and 'Subjective' categories. 'Objective' leads to 'Quality of service', which further branches into 'Service factors', 'Transport factors', and 'Application factors'. 'Subjective' leads to 'Human components', which branches into 'Emotions', 'Service billing', and 'Experience'. A dashed line connects 'Emotions' and 'Service billing'. The diagram is labeled G.1033(19)\_FII.1 at the bottom right.
+
+**Figure II.1 – Factors that have an influence on QoS and QoE**
+
+In general, there is a correlation between the subjective QoE as measured by the MOS and various objective parameters of QoS.
+
+Typically, there will be multiple service level performance (QoS) metrics that impact overall QoE.
+
+The relation between QoE and service performance (QoS) metrics is typically derived empirically.
+
+Having identified the QoE/QoS relationship, it can be used in two ways:
+
+- 1) given a QoS measurement, the expected QoE for a user can be predicted;
+- 2) given a target QoE, the net required service layer performance can be deduced.
+
+– These prediction and deduction steps are built on assumptions and approximations.
+
+Due to the complexity of services and the many factors that have an influence on QoS/QoE, there is no close one-to-one relationship that would allow statements like "If the bandwidth is increased by 200 kbit/s, then the rating by the user will rise by 0.5 points".
+
+To ensure that the appropriate service quality is delivered, QoE targets should be established for each service and be included early on in system design and engineering processes where they are translated into objective service level performance metrics.
+
+QoE is an important factor in services that are successful in the marketplace and is a key differentiator with respect to competing service offerings. Subscribers to network services do not care how service quality is achieved. What matters to them is how well a service meets their expectations (e.g., in terms of price, effectiveness, operability, availability, and ease of use).
+
+### II.2 Services, applications or "popular services"
+
+Within the formal standardization community, the term "service" was always understood as a functionality for which all aspects are standardized (i.e., standardized service); the concept behind this was that globally all networks would (be able and willing to) offer exactly the same – fully interoperable, harmonized service.
+
+However, over time the terminology got corrupted in a sense that service today stands for any application. For example, the Internet Engineering Task Force (IETF) refers to their standards which basically describe network functionalities as services.
+
+Under end user aspects, "service" is used for any application offered in the networks; this makes it very difficult to standardize assessment methods and target values or requirements for related KPIs.
+
+Therefore, if we speak about services, today, we can distinguish multiple dimensions:
+
+|    |                                 |     |    |                                |
+|----|---------------------------------|-----|----|--------------------------------|
+| a) | applications with global reach  | vs. | b) | locally limited applications   |
+| c) | specifically named applications | vs. | d) | application class denominators |
+
+Typical examples for each dimension are:
+
+- a) Netflix or YouTube;
+- b) eGovernment application in country xyz;
+- c) Netflix or YouTube;
+- d) video streaming, IP television (IPTV).
+
+Since services in all these dimensions are not standardized in their functionality *a priori*, the communities involved in assessing QoS and QoE for them have focused on what are called "popular services". The underlying concept is to provide assessment methods and targets for such services that are used frequently by a huge number of users.
+
+- Looking first at dimension a) with the examples given above, these are truly "popular services" – however, the underlying technical aspects, such as carrier services, may change from time to time.
+- For dimension b), the main obstacle is the limitation itself. It is highly probable that there will not be any international standard to measure the QoS or QoE of exactly one of those specific services.
+- Dimension c) requires close cooperation between the stakeholder providing these services and standardization experts.
+- Appropriate handling of dimension d) requires the standardization of new E2E mechanisms. Otherwise, existing carrier services will be confronted with more stringent targets for existing services.
+
+## II.3 Is a DFS a "popular service"?
+
+*A DFS is popular, yes – but DFS is only a class denominator.*
+
+NOTE 1 – At the time work on mobile QoS started (about 10 years ago), the experts considered "service" as something that has a direct impact on the customer's perception. Typical examples are telephony or web browsing. A "service" in this view is understood as something connected to an E2E use case. However, many E2E use cases relate to "carrier services", such as some types of packet data functionality having their own QoS metrics (KPIs).
+
+In this context, a DFS can be considered as a classical example of such a user-related service, which can be realized in several ways, using "carrier services" such as SMS or packet data functionality of networks.
+
+A DFS is not alone in this "top level service" view. Today's telephony is a prominent example. End users basically do not care if the function they are looking for (being able to orally communicate with another) is realized using legacy GSM or the universal mobile telecommunications system (UMTS), voice over long-term evolution (VoLTE) or some OTT voice over IP (VoIP) technology. Their quality assessment is based on universal metrics such as setup time, call drop rate or speech quality, which are exactly those metrics which are at the core of documents such as [b-ITU-T E.804] or [b-ETSI TS 102 250].
+
+The sometimes very detailed KPI definitions in these documents arise due to a "diagnostic" approach, but this is by no means "the golden rule". Future developments will attempt to reveal true "end customer" related key quality indicators (KQIs).
+
+An additional example for this may be web browsing using HTTPS instead of HTTP. For the user, nothing seems to have changed, so top-level QoS KPIs to assess user perception are the same – however, the networks are treating HTTPS and HTTP traffic in many cases differently, which will lead to a difference in usage of such KPIs for diagnostic purposes.
+
+If a technical assessment is desired of the expected top-level QoS of a particular DFS offering using a carrier service point of view, knowledge is needed of the technical flow of data and signalization. This information is not normally available from service providers' websites or brochures.
+
+NOTE 2 – Strictly speaking this is true for most other services offered by network operators. First of all, operators typically do not commit themselves (at least not towards end customers) to strict performance targets; in the case of mobile networks, this is perfectly understandable as the local conditions vary in a wide range (e.g., from rooftop to cellar of a house even in the same geographical spot). Then, with networks going even more towards "content sensitive" behaviour for the sake of resource optimization, the performance cannot safely be predicted from just some general "bit pipe" properties, measured using simple E2E services, such as web browsing. However, a DFS can be – as will be shown later – made subject to objective measurement quite easily.
+
+Ideally, this must be dealt with when licences are negotiated between regulators and potential DFS service providers.
+
+NOTE 3 – This is well known and understood for other services, e.g., video streaming:
+
+When YouTube first became popular, it was based on transmission control protocol (TCP) streaming; with this information KPIs could be defined in standards, QoS could be assessed and QoE could be predicted. Today, for good reasons, the same service by the same entity is rendered as adaptive streaming using HTTPS. Consequently, new standards have been written with new KPIs in order to assess QoS for the "same service".
+
+Strictly speaking, the KPIs with respect to video quality are still the same; only the methods have changed (or were forced to change). Most importantly, KPI definitions using "low level" technical events as those from the IP level no longer work if encrypted connections such as HTTPS are used.
+
+If it is possible to identify categories of different DFS offerings, it can be concluded, which of such categories constitute "popular services" (i.e., which are widespread and used by many customers) and a more selective look into KPI definitions could be initiated.
+
+# Bibliography
+
+- [b-ITU-T E.800] Recommendation ITU-T E.800 (2008), *Definitions of terms related to quality of service*.
+- [b-ITU-T E.804] Recommendation ITU-T E.804 (2014), *Quality of service aspects for popular services in mobile networks*.
+- [b-ITU-T G.1000] Recommendation ITU-T G.1000 (2001), *Communications quality of service: A framework and definitions*.
+- [b-ITU-T P.10] Recommendation ITU-T P.10/G.100 (11/2017), *Vocabulary for performance, quality of service and quality of experience*.
+- [b-ITU-T P.863] Recommendation ITU-T P.863 (2018), *Perceptual objective listening quality prediction*.
+- [b-ITU-T Q.23] Recommendation ITU-T Q.23 (1988), *Technical features of push-button telephone sets*.
+- [b-ITU-T DFS TR] ITU-T Focus Group Digital Financial Services: Technical Report (2016), *QoS and QoE aspects of digital financial services*. Available [viewed 2019-11-07] at: [https://www.itu.int/en/ITU-T/focusgroups/dfs/Documents/09\\_2016/FGDFSQoSReport.pdf](https://www.itu.int/en/ITU-T/focusgroups/dfs/Documents/09_2016/FGDFSQoSReport.pdf)
+- [b-ITU FIGI 2019a] ITU Financial Inclusion Global Initiative, Security, Infrastructure and Trust Working Group (SIT WG) (2019a), *Methodology for measurement of QoS KPIs for DFS*. Available [viewed 2019-11-07] at: [https://www.itu.int/en/ITU-T/extcoop/figisymposium/Documents/ITU\\_SIT\\_WG\\_Methodology%20for%20measurement%20of%20QoS%20KPIs%20for%20DFS.pdf](https://www.itu.int/en/ITU-T/extcoop/figisymposium/Documents/ITU_SIT_WG_Methodology%20for%20measurement%20of%20QoS%20KPIs%20for%20DFS.pdf)
+- [b- ITU FIGI 2019b] ITU Financial Inclusion Global Initiative, Security, Infrastructure and Trust Working Group (SIT WG) (2019b), *Report on the DFS pilot measurement campaign conducted in Ghana* Available [viewed 2019-11-07] at: [Pilot measurement of QoS KPIs for DFS in Ghana](#)
+- [b-ITU FIGI 2019c] ITU Financial Inclusion Global Initiative, Security, Infrastructure and Trust Working Group (SIT WG) (2019c), *DFS consumer competency framework*. Available [2019-11-15] at: <https://extranet.itu.int/sites/itu-t/initiatives/sitwg/Meeting/SIT-0060.docx>
+- [b-ETSI EN 300 957] ETSI EN 300 957 V7.0.1 (2000-01), *Digital cellular telecommunications system (Phase 2+); Unstructured Supplementary Service Data (USSD); Stage 3 (GSM 04.90 version 7.0.1 Release 1998)*.
+- [b-ETSI ES 201 235-1] ETSI ES 201 235-1 V1.1.1 (2000-09), *Specification of dual tone multi-frequency (DTMF) transmitters and receivers; Part 1: General*.
+- [b-ETSI ES 201 235-2] ETSI ES 201 235-2 V1.2.1 (2002-05), *Access and terminals (AT); Specification of dual-tone multi-frequency (DTMF) transmitters and receivers; Part 2: Transmitters*.
+- [b-ETSI ES 201 235-3] ETSI ES 201 235-3 V1.3.1 (2006-03), *Access and terminals (AT); Specification of dual-tone multi-frequency (DTMF) transmitters and receivers; Part 3: Receivers*.
+- [b-ETSI ES 201 235-4] ETSI ES 201 235-4 V1.3.1 (2006-03), *Access and terminals (AT); Specification of dual-tone multi-frequency (DTMF) transmitters and*
+
+*receivers; Part 4: Transmitters and receivers for use in terminal equipment for end-to-end signalling.*
+
+- [b-ETSI TS 100 549] ETSI TS 100 549 V7.0.0 (1999-08), *Digital cellular telecommunications system (Phase 2+); Unstructured supplementary service data (USSD) – Stage 2 (GSM 03.90 version 7.0.0 release 1998).*
+- [b-ETSI TS 100 625] ETSI TS 100 625 V7.0.0 (1999-08), *Digital cellular telecommunications system (Phase 2+); Unstructured supplementary service data (USSD) – Stage 1 (GSM 02.90 version 7.0.0 Release 1998).*
+- [b-ETSI TS 102 250] ETSI TS 102 250 series, *Speech and multimedia transmission quality (STQ); QoS aspects for popular services in mobile networks [8 parts].*
+- [b-ETSI TS 102 250-2] ETSI TS 102 250-2 V2.4.1 (2015-05), *Speech and multimedia transmission quality (STQ); QoS aspects for popular services in mobile networks; Part 2: Definition of quality of service parameters and their computation.*
+- [b-ETSI TS 123 014] ETSI TS 123 014 V15.0.0 (2018-06), *Digital cellular telecommunications system (Phase 2+) (GSM); Universal mobile telecommunications system (UMTS); Support of dual tone multi-frequency (DTMF) signalling (3GPP TS 23.014 version 15.0.0 Release 15).*
+- [b-ETSI TS 123 107] ETSI TS 123 107 V15.0.0 (2018-06), *Digital cellular telecommunications system (Phase 2+) (GSM); Universal mobile telecommunications system (UMTS); LTE; Quality of service (QoS) concept and architecture (3GPP TS 23.107 version 15.0.0 Release 15).*
+- [b-IETF RFC 2833] IETF RFC 2833 (2000), *RTP payload for DTMF digits, telephony tones and telephony signals.*
+- [b-IETF RFC 2976] IETF RFC 2976 (2000), *The SIP INFO method.*
+
+
+
+## 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                                                                                      |

marked/G/T-REC-G.1035-202111-I_PDF-E/raw.md

@@ -0,0 +1,638 @@
+
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**G.1035**
+
+(11/2021)
+
+SERIES G: TRANSMISSION SYSTEMS AND MEDIA,  
+DIGITAL SYSTEMS AND NETWORKS
+
+Multimedia Quality of Service and performance – Generic  
+and user-related aspects
+
+# --- **Influencing factors on quality of experience for virtual reality services**
+
+Recommendation ITU-T G.1035
+
+## 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.1035
+
+# Influencing factors on quality of experience for virtual reality services
+
+## Summary
+
+Recommendation ITU-T G.1035 classifies virtual reality (VR) services and identifies the key quality of experience (QoE) factors of VR.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T G.1035   | 2020-05-29 | 12          | <a href="http://handle.itu.int/11.1002/1000/14274">11.1002/1000/14274</a> |
+| 2.0     | ITU-T G.1035   | 2021-11-29 | 12          | <a href="http://handle.itu.int/11.1002/1000/14826">11.1002/1000/14826</a> |
+
+## Keywords
+
+Cybersickness, presence, quality of experience, QoE, simulator sickness, virtual reality, VR.
+
+---
+
+\* 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/software copyrights, 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 appropriate ITU-T databases available via the ITU-T website at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2022
+
+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.....         | 2    |
+| 4 Abbreviations and acronyms .....                    | 2    |
+| 5 Conventions .....                                   | 3    |
+| 6 Virtual reality overview .....                      | 3    |
+| 6.1 Devices .....                                     | 3    |
+| 6.2 Content .....                                     | 3    |
+| 6.3 Platform .....                                    | 3    |
+| 6.4 Services.....                                     | 4    |
+| 7 Virtual reality QoE influencing factors .....       | 4    |
+| 7.1 Human influencing factors .....                   | 5    |
+| 7.2 System influencing factors .....                  | 7    |
+| 7.3 Context influencing factors .....                 | 12   |
+| Appendix I – Virtual reality services use cases ..... | 14   |
+| I.1 Use scenario.....                                 | 14   |
+| Appendix II – Tile-based streaming.....               | 16   |
+| Bibliography.....                                     | 17   |
+
+
+
+# Influencing factors on quality of experience for virtual reality services
+
+# 1 Scope
+
+This Recommendation categorizes and summarizes the factors affecting the user-perceived experience of a virtual reality (VR) service, with the intention of helping to identify the methodologies for assessing VR quality. VR quality of experience (QoE) assessment methodologies are left for further study. Since VR technologies are still evolving, this Recommendation mainly addresses omnidirectional video services, while leaving others, e.g., point-cloud or volumetric video types, for further study.
+
+VR is a new type of media which is different from traditional video and audio. It generates realistic images, sounds and other sensations that replicate a real environment and simulate a user's physical presence in this environment by enabling the user to interact with this space and any objects depicted therein using specialized display screens or projectors and other devices. These multisensory experiences, which can include sight, hearing and, less commonly, touch and smell, are well coordinated and synchronized through the user's interaction and feedback. A person using VR equipment is typically able to "look around" the artificial world, move about within it and interact with features or items that are depicted on a screen or in goggles as in the real world.
+
+In order to understand whether QoE or user-perceived performance of the VR service is good enough or not, benchmarking is critical. Benchmarking aims to measure user-perceived performance or QoE in the VR environment. Compared with traditional video and audio, the multisensory experience in VR imposes a new set of requirements for QoE assessment. The challenge is to characterize VR's real-life immersive video, spatial audio and interactivity. Prior to being able to benchmark the QoE, it is important to address the requirements and basic factors that are relevant for assessing the VR quality for different VR services.
+
+# 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.
+
+None.
+
+# 3 Definitions
+
+## 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+**3.1.1 frame rate** [b-ITU-T H.262]: The rate at which frames are output from the decoding process.
+
+**3.1.2 quality of experience (QoE)** [b-ITU-T P.10]: The degree of delight or annoyance of the user of an application or service.
+
+**3.1.3 QoE influencing factors** [b-ITU-T P.10]: Include the type and characteristics of the application or service, context of use, the user's expectations with respect to the application or service
+
+and their fulfilment, the user's cultural background, socio-economic issues, psychological profiles, emotional state of the user, and other factors whose number will likely expand with further research.
+
+## 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following terms:
+
+**3.2.1 cybersickness or simulator sickness:** A physiological condition arising when exposed to a virtual reality environment.
+
+NOTE – Definition based on combined information in [b-Kennedy] and [b-Stanney].
+
+**3.2.2 degree of freedom (DoF):** Represents the ways an object can move within a space, which is a key element in helping create an immersive environment for a user.
+
+**3.2.3 immersion:** A psychological state characterized by perceiving oneself to be enveloped by, included in and interacting with an environment that provides a continuous stream of stimuli and experiences.
+
+NOTE – Definition based on [b-Witmer].
+
+**3.2.4 motion-to-photon latency:** The time it takes between the user moving their head and this motion being reflected on the screen of the head-mounted display (HMD).
+
+NOTE – Definition based on [b-Brandenburg].
+
+**3.2.5 presence:** The subjective experience of being in one place or environment, when one is physically situated in another place or environment.
+
+NOTE – Definition based on [b-Witmer].
+
+**3.2.6 refresh rate:** The frequency at which a display updates its image, expressed in hertz.
+
+# 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|      |                                  |
+|------|----------------------------------|
+| 2D   | Two Dimensional                  |
+| 3D   | Three Dimensional                |
+| AR   | Augmented Reality                |
+| DoF  | Degree of Freedom                |
+| FoV  | Field of View                    |
+| GPU  | Graphic Processing Unit          |
+| HD   | High Definition                  |
+| HMD  | Head-Mounted Display             |
+| HRTF | Head-Related Transfer Function   |
+| MPEG | Moving Picture Experts Group     |
+| MR   | Mixed Reality                    |
+| PPD  | Pixel Per Degree                 |
+| PPI  | Pixel Per Inch                   |
+| SSQ  | Simulator Sickness Questionnaire |
+| UHD  | Ultra High Definition            |
+| VR   | Virtual Reality                  |
+
+VoD Video on Demand
+
+VVC Versatile Video Coding
+
+# 5 Conventions
+
+Within the scope of this Recommendation, a person interacting with a VR head-mounted display (HMD) is referred to as a user, viewer or player, all with equivalent inference.
+
+# 6 Virtual reality overview
+
+Virtual reality (VR) is a technology that uses game engines (e.g., Unity) to create artificial environments that enable people to interact in six degrees of freedom (DoF). VR generates realistic images, sounds and other sensations that emulate a real environment or create a synthetic one. VR services aim to provide users with high levels of immersion and presence wherein users may feel detached from their physical, real-world surroundings. This is different from augmented reality (AR) or mixed reality (MR), which enhance user experiences by adding virtual components such as digital images, graphics or sensations as a new layer of interaction with the real world.
+
+## 6.1 Devices
+
+A VR display device is usually a typical head-mounted display (HMD) with two goggle-size miniature screens – one per eye. These displays focus and reshape the picture for each eye and can create a stereoscopic three-dimensional (3D) image by angling the two dimensional (2D) images to mimic how human eyes see the world.
+
+To achieve an immersive experience, head tracking or eye tracking are used in HMDs to create the correct camera angle and perspective so as to attain a natural viewing experience. In addition, tracking may include capturing of the movements of any other body parts.
+
+Depending on the VR service and DoF permitted for the users, audio hardware needs to take into account headphone or loudspeaker audio reproduction. The headphones may be standalone or integrated into the HMD, both of which allow open and closed acoustic design. When using standalone headphones, additional hardware such as a soundcard or wireless technology may also be involved.
+
+## 6.2 Content
+
+There are two types of content to consider when constructing a virtual environment for the VR experience.
+
+The first consideration is synthetic, which is completely invented from geometric primitives and simulated physics. This is common in VR games and VR social services. Synthetic representations of individuals, called avatars, enable users to interact and can provide a level of anonymity in some contexts.
+
+The second consideration is captured using 360° cameras. For example, 360°/omnidirectional images and videos are captured to allow users to explore the scene in  $360^\circ \times 180^\circ$  from a given viewpoint in a VR system, which could be seen as an extension of traditional video streaming applications.
+
+## 6.3 Platform
+
+When using online VR applications, VR contents are stored in servers, streamed by requests and rendered locally in user's devices. Local rendering requires high-performance terminal devices to provide an acceptable user experience.
+
+Cloud VR [b-GSMA AR/VR] is a new cloud computing technology, where VR content is stored and rendered in the server. Therefore, video and audio outputs are coded, compressed and transmitted to
+
+user terminals. Servers in cloud VR are required to be as close as possible to end-users to reduce the influence introduced on QoE by the additional network processing time.
+
+## 6.4 Services
+
+VR services can be classified into two types: weak-interaction VR and strong-interaction VR [b-Huawei VR].
+
+Weak-interaction VR services mainly comprise but are not limited to 360° video, VR theatre and VR live broadcast. In this kind of VR services, users can explore the scene by turning their head; however, they do not interact with the objects present in the scene. For example, touching the entities in the virtual world is not possible.
+
+Strong-interaction VR services include VR games, VR home fitness, VR social networking, etc. Users can interact with these virtual environments through interactive entities (e.g., controllers) in addition to HMD head tracking.
+
+Appendix I provides information for some typical VR services.
+
+# 7 Virtual reality QoE influencing factors
+
+QoE influencing factor categories are illustrated in Figure 1. (See also [b-Reiter].)
+
+![A hierarchical diagram showing 'Virtual reality influencing factors' at the top, branching into three categories: 'Human', 'System', and 'Context'. 'Human' includes Vision and hearing, Simulator sickness, Immersion, Expectations and expertise, Demographic background, and Emotions. 'System' includes Content, Media/coding, Network transmission, and Hardware. 'Context' includes Physical, Temporal, Social, and Task. The label G.1035(20)_F01 is at the bottom right.](54fabc351eda5228d2fa28cd9ba07971_img.jpg)
+
+```
+graph TD; A[Virtual reality influencing factors] --> B[Human]; A --> C[System]; A --> D[Context]; B --> B1[Vision and hearing]; B --> B2[Simulator sickness]; B --> B3[Immersion]; B --> B4[Expectations and expertise]; B --> B5[Demographic background]; B --> B6[Emotions]; C --> C1[Content]; C --> C2[Media/coding]; C --> C3[Network transmission]; C --> C4[Hardware]; D --> D1[Physical]; D --> D2[Temporal]; D --> D3[Social]; D --> D4[Task];
+```
+
+G.1035(20)\_F01
+
+A hierarchical diagram showing 'Virtual reality influencing factors' at the top, branching into three categories: 'Human', 'System', and 'Context'. 'Human' includes Vision and hearing, Simulator sickness, Immersion, Expectations and expertise, Demographic background, and Emotions. 'System' includes Content, Media/coding, Network transmission, and Hardware. 'Context' includes Physical, Temporal, Social, and Task. The label G.1035(20)\_F01 is at the bottom right.
+
+**Figure 1 – Virtual reality QoE influencing factor categories**
+
+Furthermore, influencing factors can occur on different levels of magnitude (micro vs. macro), behaviour (static vs. dynamic), and patterns of occurrence (rhythmic vs. random), either independently or as usual mixtures of all three levels [b-Reiter]. That is because this is not a binary state; all factors can be static or dynamic, but the time-frequency of changes can determine whether a factor is dynamic or static.
+
+## 7.1 Human influencing factors
+
+### 7.1.1 Vision and hearing
+
+Visual abnormalities such as longsightedness, shortsightedness, astigmatism and chromatic aberration may occur in the human eye. Each eye may also be affected differently. Such vision problems may negatively affect the user experience. When vision problems can be corrected by lenses, having the user wear their normal glasses may be a solution, although this may be uncomfortable for the user.
+
+Hearing impairments may result in attenuated hearing over the full audible frequency range or at specific frequencies. An impairment may also occur asymmetrically in only the left or the right ear, which has consequences on spatial hearing. Loss of sensitivity at high frequencies is a normal age-related hearing impairment, but different types of impairments are present in populations of all ages. Often, individuals are not aware of having a hearing impairment as they develop over time and the auditory system adapts to the lowered sensitivity.
+
+It is important to consider that each individual hears differently, and that audio reproduction has to take this into account in order to provide a good experience. Head-related transfer functions (HRTFs) describe the individual filtering process that occurs when sound travels from a point in space to the two ears. HRTFs depend on the shape of the pinna and ear canal, and the size and shape of the head and upper torso. They vary individually and to achieve perfect binaural reproduction the HRTFs should be individually measured and applied in the audio rendering process. In practice, generalized HRTFs are often used, resulting in possible degradation in sound localization.
+
+### 7.1.2 Simulator sickness
+
+Cybersickness is also known as simulator sickness, VR sickness or visually induced motion sickness and is triggered only by visual stimuli. This undesirable phenomenon is caused by the sensory conflict arising between the visual and vestibular system. While watching 360° videos in an HMD, a user may experience symptoms of simulator sickness such as fatigue, sweating, vertigo or nausea [b-Kennedy]. The most popular questionnaire for assessing simulator sickness is the simulator sickness questionnaire (SSQ), published in 1993.
+
+Simulator sickness is an important factor that affects QoE for 360°/VR videos [b-Singla-1]. There are different factors such as resolution, audio, time, field of view (FoV), the orientation of users, HMD, player, type of video sequences, etc., by which simulator sickness scores can be affected. (These and other factors are discussed in clause 7.2.) When considering QoE, the video sequences that are noted to lead to the highest simulator sickness scores also lead to the lowest QoE scores. Inversely, those video sequences that have the lowest simulator sickness scores also have the highest QoE scores. These observations indicate that simulator sickness interacts with QoE when 360° videos are watched in HMDs [b-Singla-1].
+
+Apart from technical factors, there are individual factors such as age, gender, postural stability, etc., contextual factors such as duration of task, orientation of users, etc. and co-variate constructs such as QoE, presence and exploration behaviour that can impact the severity of simulator sickness. The symptoms of simulator sickness can be reduced but cannot be eliminated for every user. If everything is performed correctly and the needs of the user are met, then the symptoms of simulator sickness will become motion sickness [b-Kopyt].
+
+Simulator sickness can also be caused by vergence-accommodation conflict. This symptom occurs when the brain receives mismatching information between a focusing distance and the distance to the virtual object [b-George]. Vergence-accommodation conflict can cause eye strain, fatigue, focusing problems, etc.
+
+### 7.1.3 Immersion
+
+The tendency to experience immersion and the level of expertise in using VR systems vary individually. People who tend to be more immersed in a virtual environment may not notice small impairments in reproduction. How immersion affects VR QoE is for further study. Relevant investigations are continuing in ITU-T.
+
+### 7.1.4 Expectations and expertise
+
+The attitude towards VR creates varying contexts for experiencing it. Some people may dislike a VR experience regardless of its technical quality based on their beliefs and fears of using such systems. The level of expertise in using VR systems may affect how capable the users are in using the systems to achieve a certain goal, which in turn affects the QoE. Some users may be awed by the novel experience, while more experienced users can focus on the task at hand.
+
+The influence of a subject's internal reference, provided by their interactions and experiences in the real world, will also influence the QoE of a VR service.
+
+### 7.1.5 Demographic background
+
+Demographic data is a statistical representation of variables such as age and gender, as well as socio-economic information such as employment, education, income, race, marital status and others. When it comes to VR services in general, depending on the demographic background, users could have different experiences and performances. Solutions for VR services in a number of areas (from gaming over telemeeting, e-learning and sports) have been researched in order to determine which user attributes have a considerable influence on the experience.
+
+Demographic factors such as age is a user factor that influences one's preference for VR technology. When it comes to how likely individuals are to interact with technology in general [b-Franke], younger participants had a higher affinity for technology, including a comparable inclination for VR services [b-Kojic-1]. Also, gender is another influencing factor where significant differences in technological affinity were reported [b-Franke], in particular for VR [b-Kojic-2]. Further on, there is a gender gap reported while exploring presence in VR services. Significant differences were identified on presence subscales (considering the binary gender scale) [b-Felnhofer], where men reported a different feeling presence than women for VR services.
+
+### 7.1.6 Emotions
+
+The increasing availability of VR equipment and advances in technology have inspired its use in a variety of research sectors, including human emotional states and responses to VR services. At the level of human emotional states, the effect of moods and emotions on QoE has been researched [b-Felnhofer]; although both have a relatively brief duration, moods typically last longer (varying from hours to days) than emotions (ranging from seconds to minutes) [b-Reiter]. Overall, emotions can have an impact on QoE in general including for VR services in the same way as a stimulus that triggers (among other things) an emotional response in the recipient; secondly, a stimulus may generate an emotional response in the recipient as a result of its meaning [b-Schleicher].
+
+Studies have shown that content and interaction possibilities with VR environments can change arousal and valence levels. Further on, for example, the possibility to interact with the virtual environment can impact various quality and emotion related parameter such as involvement and spatial presence [b-Voigt-Antons-2]. Furthermore, when implementing the most immersive presentation method (such as head-mounted display), 360° video stimuli might be used to evoke the intended emotional reactions in participants with a greater sense of presence [b-Voigt-Antons-1].
+
+## 7.2 System influencing factors
+
+### 7.2.1 Content related factors
+
+VR content is crucial for the user's experience and has additional requirements when compared with traditional multimedia content. In addition to the requirements for good quality of video and audio, VR content also requires stitching, special effects, stereoscopic 3D and composition. To ensure an immersive experience, it is important that the VR content is generated at a good quality and then delivered as perfectly as possible. This clause lists the aspects related to VR content which will influence the quality of a VR service.
+
+#### 7.2.1.1 Spatial audio
+
+Spatial audio involves the use of spatial audio reproduction techniques that are loudspeaker- or headphone-based such as multiloudspeaker stereophonic approaches, generalizations such as vector-base amplitude panning, sound-field synthesis (higher-order ambisonics, wave-field-synthesis), headphone-based binaural, or combinations thereof. By using spatial audio, virtual sound sources can be created at any point within the 3D space. Sound reproduction for VR is most often done via headphones, but loudspeaker setups are also possible especially in three DoF and six DoF scenarios. In addition to the direct sound, spatial audio can further include the auditory spatial impression of the room acoustics (e.g., early reflections and reverberation), perceptually plausible acoustic effects of sound sources being occluded by structures in the VR world (e.g., attenuation and diffraction), and sound radiation patterns of individual audio objects. Spatial audio is an important aspect for creating the illusion of immersion for VR services. QoE-related aspects are, in particular, the perceived coloration and spaciousness (including features such as source width, envelopment, locatedness) of the (virtual) sources, as well as additional artefacts due to coding or other types of processing.
+
+#### 7.2.1.2 Spatial depth (3D)
+
+It also is possible to playout stereoscopic video content, addressing human binocular vision, which is based on the depth-dependent disparity stemming from the two slightly different views presented to the two eyes. This allows humans to judge distance and have a perception of depth. To avoid crosstalk effects, the left view of the content has to be displayed only to the left eye and the right view of the content has to be displayed only to the right eye (see [b-Woods]). In the system design of most HMD systems, which are commonly used for playing out VR content, both views are already separated from each other.
+
+Encoding the stereoscopic representation with a low bitrate has to be avoided as it decreases the perceived quality even more than using non-stereoscopic content with the same bitrate. The quality advantage of the 3D over the 2D representation is only slightly visible for higher bitrates. Thus, a relatively high bitrate should be used for encoding to assure that the advantage of stereoscopic over non-stereoscopic omnidirectional video content becomes visible. It has to be mentioned that this is strongly dependent on the general stereoscopic quality of the video content. Simulator sickness scores and how a stereoscopic representation influences the VR QoE are for further study.
+
+Note that this factor is not mandatory in VR. Many VR services use 2D content while still allowing people to feel immersed due to the rendered omnidirectional scenes.
+
+#### 7.2.1.3 Spatiotemporal complexity
+
+Spatial perceptual information indicates the complexity of a video picture. With some high complexity content, the viewer may be distracted, while with less complexity content, the subject may be more focused on the main objects. Temporal perceptual information indicates the amount of changing of the video picture. Different spatial and temporal complexity video sequences require a different amount of bandwidth. For example, sequences with higher spatial and temporal information generally require higher bandwidth.
+
+Spatiotemporal complexity is a content feature which may affect VR QoE. For example, if the VR content has high temporal values, it may produce a high amount of simulator sickness which may affect QoE [b-Singla-1].
+
+### 7.2.2 Media/codec related factors
+
+#### 7.2.2.1 Compression
+
+Video/audio codecs are used to compress original scene data from raw format so that they can be saved offline or streamed via a network, saving bandwidth and resources. Various codecs have been developed in the industry and are widely used for traditional media coding and these codecs may be used for VR media. However, some codecs are unsuitable for certain scene representations.
+
+#### 7.2.2.2 Video
+
+Traditional video codecs (e.g., [b-ITU-T H.264], [b-ITU-T H.265], VP8, VP9) may also be used for VR content, but may not be suitable for certain spatial representations (e.g., point-clouds).
+
+These different codec technologies are based on different compression implementations, and each can cause different information loss when the encoder compresses the raw data, and the decoder renders it back for display. This results in different perceived quality of the experience and decoding speed.
+
+A common shortcoming for traditional video codecs being used in VR is that the compression rate is still too low. This means that the bandwidth consumption is still a big problem for streaming the VR content when dealing with full VR streaming. New video coding technologies in progress such as versatile video coding (VVC) will significantly improve the transport quality for VR content in the industry.
+
+In order to save bandwidth and network resources for 360°/VR videos, many streaming service providers propose to transmit only pixels in the users' FoV in high resolution, and the remaining pixels in minimal quality resolution. This technique is called viewport-adaptive or tile-based streaming of omnidirectional video. The tile-based adaptive streaming architecture is shown in Figure 2. The two main strategies of tile-based streaming are described in Appendix II.
+
+![Figure 2: Tile-based adaptive streaming – behaviour dependent. A block diagram showing the flow from a 360-degree video source with a highlighted 'View-port' rectangle, through 'Encoding', 'CDN', 'IP-network', and 'Player' blocks. The Player block connects to a 3D diagram of a human head with three rotational axes labeled: 'roll' (red circular arrow), 'pitch' (green circular arrow), and 'yaw' (blue circular arrow).](c036e2540a94b31357ceb0002f0cacab_img.jpg)
+
+```
+
+    graph LR
+    A[360 Video with View-port] --> B[Encoding]
+    B --> C[CDN]
+    C --. IP-network .--> D[Player]
+    D --> E[User Head: Roll, Pitch, Yaw]
+  
+```
+
+G.1035(20)\_F02
+
+Figure 2: Tile-based adaptive streaming – behaviour dependent. A block diagram showing the flow from a 360-degree video source with a highlighted 'View-port' rectangle, through 'Encoding', 'CDN', 'IP-network', and 'Player' blocks. The Player block connects to a 3D diagram of a human head with three rotational axes labeled: 'roll' (red circular arrow), 'pitch' (green circular arrow), and 'yaw' (blue circular arrow).
+
+**Figure 2 – Tile-based adaptive streaming – behaviour dependent**
+
+#### 7.2.2.3 Audio
+
+For non-interactive three DoF and six DoF VR scenes, requirements on audio metadata are typically consistent with current 3D audio content. Where a categorical number of static positions can be authored, additional data for user head rotation should be incorporated to render a spatial auditory scene consistent with listener movements. For interactive and six DoF VR services where an infinite number of source and listener positions are available, translating user movements and geometric data of the auditory environment is essential for setting the requirements for an audio codec. Direct sound, early reflections and late reverberation should be accounted for and be coherent with all sound sources and listener(s) movements as they may influence the QoE.
+
+The production of audio content for VR may also feature various approaches such as channel-based, object-based or ambisonics. These may be recorded via multichannel microphones or single microphones, with both techniques requiring various formatting in order to implement and deliver immersive audio. An audio codec would need to be adaptive in the input data stream of content, as seen in the current moving picture experts group (MPEG) H-series codec for three DoF scenes, along with a consistent input stream of user actions.
+
+#### **7.2.2.4 Storage and transport**
+
+In 2016, a new approach was released to encode 360° videos with a pyramid geometry, which saves almost 80% of the bitrate [b-Kuzyakov]. In pyramid projection, the base of the pyramid is always available in the full resolution and the sides of the pyramid decrease gradually in quality until all the sides meet at a point. When a user changes the viewing direction, it is decided which stream should be fetched based on the network condition and the orientation of the user.
+
+Besides that, other technologies (e.g., tile-based streaming) are also used in VR to reduce bandwidth and resource consumption. MPEG has now developed a standard called omnidirectional media format [b-ISO/IEC 23090-2] which intends to standardize the storage and transmission of VR content, mainly for 360° videos. There are multiple media profiles supported, one of which divides the entire 360° video into independently coded tiles that the HMD has to recompile into the image from the tiles required according to the user's viewing directions.
+
+#### **7.2.2.5 Bitrate**
+
+Bitrate is the number of audio or video bits that are conveyed or processed per unit of time. Bitrate serves as a more general indicator of quality. Higher resolution, higher frame rates and lower compression usually lead to an increased bitrate under the same encoding environment.
+
+#### **7.2.2.6 Resolution**
+
+Video resolution represents the number of distinct pixels contained in the video content that can be displayed in each dimension. Resolution of a video should be compatible with the resolution of the display device, otherwise the video resolution might have to be reduced or cannot even be displayed.
+
+Higher resolution for VR is required as compared with 2D video in order to have similar visual quality because pixels are spread in a 360° viewing sphere around the viewer. Depending upon the field of view of the HMD, a viewer sees around 25% of the total pixels. For example, if a 4K video is shown to a user in an HMD, it would appear as if the user were watching a 1K video. In order to provide a 4K experience to the viewers, 16K video should be displayed.
+
+#### **7.2.2.7 Frame rate**
+
+Frame rate indicates the frequency at which consecutive images, called frames, are displayed. For improving the QoE, the frame rate of the VR content should be exactly the same as the refresh rate of the HMD's display. Playing back the content in a frame rate not matching the panel's refresh rate leads to artefacts such as frame fluctuation, frame drops and frame manipulation using black frame insertion. These artefacts mostly lead to jerkiness, which leads to a lower QoE [b-Hofmeyer].
+
+The frame rate in VR services has higher requirements than normal 2D video services because jerkiness in the motion may lead to simulator sickness in the VR environment. Frame rate is even more demanding for VR gaming applications where scenes are rendered by a graphic processing unit (GPU) instead of those created by video cameras.
+
+In the area of 360° videos, applying motion interpolation to contents with a lower frame rate than the HMD's display refresh rate is a suitable method for increasing the QoE. This especially applies to videos with a higher amount of motion. (See [b-Hofmeyer] and [b-Fremerey].)
+
+#### **7.2.2.8 Audio sample rate**
+
+The sample rate is the number of samples of audio carried per second, measured in hertz (Hz). In VR services, this factor has no difference from the traditional streaming services.
+
+#### **7.2.2.9 Coding delay**
+
+As the codec standards only describe the algorithmic decoding procedure and profile features, there are still many options in selecting coding modes and parameters when designing a system. VR related applications typically require low and even extremely low delay. Therefore, how to effectively reduce the coding delay which contributes to the final end to end delay should be considered. Extremely low coding delays will also satisfy the need to synchronize audio and video presentation.
+
+Perceptual thresholds exist for television (TV) broadcasting (e.g., [b-ITU-T J.248]), but VR brings new challenges due to the immersive experience and sensorimotor coupling in six DoF where additionally synchronizing the rendered content with self-movement is essential. Perceptual thresholds in six DoF scenarios are topics for future study.
+
+### **7.2.3 Network/transmission related factors**
+
+Network/transmission related factors only exist in online VR services.
+
+#### **7.2.3.1 Delay**
+
+In VR environments, stringent latency requirements are of utmost importance for providing a pleasant immersive VR experience. Delay includes queuing delay, over-the-air delay and buffering delay. Delay is usually the main reason for high motion-to-photon latency leading to simulator sickness (see clause 7.1.2). It is also the cause of presentation quality degradation, e.g., long initial loading delay and stalling. Some VR services may offload computing tasks, such as rendering capability, to remote cloud servers to significantly relieve the computing burden from the user's HMDs, which is at the expense of incurring additional communication delay.
+
+The influence of resolution, bandwidth and network round-trip delay on QoE aspects of tile-based streaming of 360° videos was studied in [b-Singla-2]. These experimental results showed that lowering delay by up to 50 ms has a minimal effect on QoE ratings. The video quality degrades significantly for higher values (>100 ms) of delay. The effect of network delay on the simulator sickness scores cannot be seen. This may be explained by the fact that the background is always visible in the low resolution and always moves consistently with head motion [b-Singla-2].
+
+#### **7.2.3.2 Bandwidth**
+
+Immersive experience with VR streaming application requires a lot of data. If the required bandwidth is not guaranteed for specific VR applications, the quality of the content will be degraded during network transmission. That is, congestion can cause long delays and packet loss which can then degrade the perceived immersive QoE of the VR system.
+
+#### **7.2.3.3 Loss**
+
+The impact of packet loss on the VR experience depends on the method of transmission. In reliable transmission protocols, packet loss incurs packet retransmissions which increase the overall delay. With unreliable transmission, packet loss may result in the loss of parts of frames or entire frames and thus degrade audiovisual quality, which may be presented as phenomena such as video freezing and tiling artefacts.
+
+### **7.2.4 Hardware related**
+
+Hardware plays an important role in creating an immersive experience for users. VR hardware comprises HMDs, headphones, haptic feedback devices, input controllers and tracking systems with various possibilities to bring real-world objects into the VR domain.
+
+#### **7.2.4.1 Head-mounted display**
+
+Unlike traditional terminal devices, HMD wearing comfort may also greatly impact the final VR QoE. To improve this, it is important to consider device weight, size, heat dissipation, resolution, refresh rate, etc.
+
+#### **7.2.4.2 Headphones**
+
+The frequency response of headphones, when used, is a factor that affects QoE. Neutral headphones or headphones whose frequency response have been compensated may be able to better convey the spatial audio experience of the listener. Additionally, the ability to block outside noise may be of importance for VR, with closed headphones or in-ear headphones being best suited for this. However, the use of such headphones that entirely block outside noise may cause the user to feel disoriented in their real environment and may be a safety hazard.
+
+#### **7.2.4.3 Decoder performance**
+
+The decoder capability has an impact on the overall resolution of the video to be transmitted and decoded in the display device, whether high definition (HD) or ultra high definition (UHD), and thus decides the final resolution of the video that could be displayed to the user. In addition, codec support, e.g., [b-ITU-T H.264] or [b-ITU-T H.265], is also important since different codecs have different decoding performances.
+
+The codecs supported by the decoder should be compatible with the encoder; otherwise, the content may not be displayed correctly.
+
+The number of decoders determines the number of streams the device is capable of decoding, e.g., if streams are separately encoded when tiled streaming is applied.
+
+Compared with those implemented in software, decoders implemented in hardware have much faster performance when decoding the same content, which contribute less delay to VR media processing and lead to a better QoE.
+
+Some decoders may also have some error correction mechanisms that are capable of fixing errors that may occur during transport or encoding. This can also increase the QoE of the final VR experience.
+
+#### **7.2.4.4 Head tracking**
+
+To enable interaction between users and the environment, it is important to obtain the positions and motion information of users. This is usually done, for example, by the inertial measurement unit implemented inside the HMD. Typical devices use combinations of accelerometers, gyroscopes and sometimes magnetometers to track objects' motions.
+
+There are two tracking technologies that are used thus far: outside-in and inside-out. Outside-in tracking indicates that the headset and accessories rely on some external devices, e.g., a lighthouse sensor or computer display. It has more accuracy and better latency than an inside-out unit but is limited by the environment. Inside-out tracking does not rely on external devices. It uses the HMD sensor to determine how the position is changing in relation to the external environment.
+
+Low head-tracking latency and back tracking accuracy are certainly important attributes to provide a smooth change of view for the user, while long head-tracking latency induces discomfort and loss of immersive experience.
+
+#### **7.2.4.5 Field of view**
+
+FoV is the extent of the observable environment at any given time. With a wider FoV, a user is more likely to feel at-the-scene in the experience. FoV is the solid angle that is visible by a human through the HMD lenses. When it comes to VR FoV, the limiting factor is the lenses, not the pupils. To get a better FoV, the user can either move closer to the lenses, as is the case with VR HMD lenses, or increase the size of the lenses [b-VR Lens Lab].
+
+While a wide FoV can increase immersion, it can also more easily cause simulator sickness to certain individuals. This is mainly because some people are sensitive to the flickers or movements of images, and also because the large visual input brought from large FoV may cause conflicts with the vestibular and proprioceptive systems.
+
+Therefore, FoV is an important parameter that helps evaluate to what extent a VR device could create an immersive experience.
+
+#### **7.2.4.6 Display resolution**
+
+Display resolution is a basic attribute of the screen that indicates the pixels per inch that a screen supports. An appropriate screen resolution, relative to the resolution of viewpoint shown in the HMD, would provide the best and most comfortable experience.
+
+Pixel per degree (PPD) is a core technology specification that is better suited for measuring the pixel density of a VR near-eye display rather than the more traditional pixel per inch (PPI) value. Typically, the higher the PPD, the better of the image quality will be. A lower PPD may result in the screen-door effect.
+
+#### **7.2.4.7 Refresh rate**
+
+The refresh rate is the number of times per second that a display grabs a new image from the GPU. A lower refresh rate can contribute to increased processing latency and lead to VR sickness, i.e., viewing glitches on the screen.
+
+## **7.3 Context influencing factors**
+
+Context influencing factors are related to the setting or situational property which influences a user's environment in terms of direct influences on the signals presented to the user (audio, video, etc.), the goals connected to a certain system usage and the impact on the user's expectations.
+
+### **7.3.1 Physical context**
+
+Physical context factors are related to the environment where a user is experiencing the VR services. Background noises may affect the user's experience. In addition, the experience of the user may differ depending on whether the HMD device is wireless or connected to a stationary processing device, e.g., a PC, which could restrict movement and the possibilities to explore a VR scene. Room lighting may not affect users' experience as much when using HMDs as compared with traditional video environments since the devices are close to their eyes. The ambient temperature of the room in which the user is engaged with the VR service affects the QoE. Normally, the room temperature is set to a typical room temperature to which the user is accustomed, so that they will feel comfortable enough not to get distracted. However, in some cases, the room temperature can be modulated to approximate the virtual world in order to achieve the best immersive experience. For example, if a user is immersed in a VR skiing scene, they may have a better sense of 'being there' when the room temperature is cold enough to make them feel as if they are in the real world, as simulated in the VR scene.
+
+The amount of sunlight entering the environment can also affect VR QoE. Only a low amount or ideally no direct sunlight should enter the environment. The infrared light could influence the performance of the HMD's tracking system, which could lead to picture outages and other errors.
+
+Furthermore, the respective safety features of the provided HMD system (such as virtual walls or a pass-through mode using cameras) should be activated to avoid any collisions of the VR user with their physical environment. Ideally, a second person who is not participating in the VR services should pay attention to the physical actions of the user consuming the VR service.
+
+### **7.3.2 Temporal context**
+
+Temporal context factors include the frequency and duration of use. A VR device may not be able to support long usage periods. Over time, simulator sickness symptoms such as dizziness, loss of spatial
+
+awareness, nausea and eye soreness typically become worse as the duration of use increases. These effects will greatly reduce the QoE.
+
+### **7.3.3 Social context**
+
+Social context factors include considerations such as VR content popularity and how VR services are consumed (i.e., alone or in a group). A user may be affected by the interaction with a group of other people, e.g., their family, friends or even strangers. For example, co-located co-viewing or co-playing may increase a user's overall satisfaction with a program. This may also hold true for VR services, especially for social VR, in which people use a virtual reality platform to form synthetic societies which contain avatars connected to real people to simulate the physical world. To what extent this factor affects the overall QoE of VR services requires further investigation.
+
+### **7.3.4 Task context**
+
+VR experience depends on the goals of the user of the VR service. These factors are called task context factors. For example, if the task is formal, the participants may pay specific attention to some aspects of perceived influence, while they may ignore such experience when doing a relatively casual task. Additionally, the QoE for streaming-type VR, e.g., 360° VR, would be quite different from gaming VR or social VR. For the former, users may have less tolerance towards video impairments. For the latter, users may have less tolerance towards bad interaction experience.
+
+# Appendix I
+
+## Virtual reality services use cases
+
+(This appendix does not form an integral part of this Recommendation.)
+
+Generally, VR applications can be divided into two types, online and offline:
+
+- Online VR: VR applications of this type work either partially or primarily through the Internet or another computer network. In this case, VR content is streamed from a server at the time when the user is using it. Obviously, any network delay occurring in this type of VR application may affect the experience of users. However, it can save the local storage of VR terminal devices and expand the range of content that the user can experience.
+- Offline VR: VR applications of this type work offline. To do this, users need to download the VR content completely to their devices in advance. While running these applications there are usually no network delay issues and no requirement for network bandwidth. However, the content that the user can experience is limited by the capacity of a local storage device. Offline VR services are not in the study scope of this Recommendation.
+
+## I.1 Use scenario
+
+There are many different types of VR services. Five types are listed in this clause.
+
+### I.1.1 Live
+
+Live VR is broadcast in real time, as events happen, in the present. The difference between the traditional live program and live VR is that live VR is panoramic and interactive. Live VR can provide an immersive experience of attending the live event at the event venue. The live 360° VR described in [b-ITU-T H.430.3] is a service of this type, which constructs 360° panoramic view in real time via multiple cameras feeds from the site. Users can observe the live event with proper VR HMDs that constantly process and stitch multiple images to project the real world.
+
+Live VR services require extremely stringent delay so that users can smoothly change the viewpoints when watching it. Live VR services also require UHD resolutions to make users feel as if they are in the real venue. The bandwidth consumption issue is very challenging when a massive number of users consume the live VR service at the same time. Interaction is also an important issue, although in 360° VR, only a few actions can be taken, for example, turning your head around.
+
+### I.1.2 Video on demand
+
+Video on demand (VoD) VR services allow users to select and experience the content at any preferable time of their choice rather than a specific broadcast time. Live and VoD VR share the same experience. The only difference is that the content of VoD VR is prepared in advance rather than in real time. The typical usage could be that some applications offered by some major over the top (OTT) providers allow users to watch the entire environment in every scene.
+
+VoD VR services have the same requirements as live VR for delay issues and video resolutions. The bandwidth consumption is relatively smaller than live VR as viewers can consume the same content at different times.
+
+Many VR applications in different industries can be seen as VoD VR services. For example, some applications present a user with a cinematic experience with HMD at home and some applications use VR for education, but they are all basically VoD VR services.
+
+### I.1.3 Gaming
+
+VR gaming services allow a user to experience being in a 3D virtual entertainment environment through an avatar and interact with the environment during the game. VR gaming services may
+
+require more devices other than an HMD. One example is a data glove with small sensors that can capture the movements made by the user, which are then interpreted by computers and trigger a variety of responses within that space.
+
+VR game services require extremely sensitive interaction to reach the best experience. Also, the immersive experience of "being there" where "there" is not equivalent to the position of one's own body but the place the VR content suggests is what a VR game seeks. Other aspects of gaming discussed in [b-ITU-T G.1032] should also be considered.
+
+### **I.1.4 Social**
+
+VR social is a service that allows users of the VR platform to form synthetic societies which contain avatars connected to real people to simulate the physical world. A typical example would be the Facebook of VR which provides new social VR features for Oculus Rift. Users can create a custom avatar based on photos from their profile and spend time with other people in a virtual space.
+
+Like a VR game, VR social also requires extremely sensitive interaction so that users feel as if they are in a real world. Non-synchronized movement of these synthetic avatars with actual human motion will result in a very bad experience for users of the services.
+
+### **I.1.5 Shopping**
+
+In addition to the VR services listed in this clause, there are other applications which may be promising in the future when using VR devices. For example, VR shopping could allow users to purchase items through a VR headset by virtually transporting themselves to international retail outlets, enabling them to experience the entire shopping experience from finding products to payment. VR shopping is similar to VR VoD, which records the content in advance, but requires more interaction and less data consumption than VoD streaming VR.
+
+# Appendix II
+
+## Tile-based streaming
+
+(This appendix does not form an integral part of this Recommendation.)
+
+In tile-based streaming, only the field of view is transmitted in the highest quality and rest of the video is transmitted in lower quality. Based on the client, this can be divided mainly into two categories:
+
+- 1) Full delivery basic: In this method, the base layer is always available in the low resolution and high-resolution tiles are only available for the current field of view/viewport. When a user changes the viewing direction, the player software finds which of the tiles are in current viewport and fetch those tiles from the network [b-Brandenburg].
+- 2) Full delivery advanced: In this method, the tiles that belongs to the user's viewport are sent in higher quality. In addition, the user head motion is continuously predicted to find where the user's viewport will be in future. These corresponding tiles are requested in a higher quality at the time when it is expected that the user will move into a specific direction [b-Mario].
+
+# Bibliography
+
+- [b-ITU-T G.1032] Recommendation ITU-T G.1032 (2017), *Influence factors on gaming quality of experience*.
+- [b-ITU-T H.262] Recommendation ITU-T H.262 (2012), *Information technology – Generic coding of moving pictures and associated audio information: Video*.
+- [b-ITU-T H.264] Recommendation ITU-T H.264 (2019), *Advanced video coding for generic audiovisual services*.
+- [b-ITU-T H.265] Recommendation ITU-T H.265 (2021), *High efficiency video coding*.
+- [b-ITU-T H.430.3] Recommendation ITU-T H.430.3 (2018), *Service scenario of immersive live experience (ILE)*.
+- [b-ITU-T J.248] Recommendation ITU-T J.248 (2008), *Requirements for operational monitoring of video-to-audio delay in the distribution of television programs*.
+- [b-ITU-T P.10] Recommendation ITU-T P.10/G.100 (2017), *Vocabulary for performance, quality of service and quality of experience*.
+- [b-ISO/IEC 23090-2] ISO/IEC 23090-2 (2019), *Information technology – Coded representation of immersive media – Part 2: Omnidirectional media format*.
+- [b-Brandenburg] R. van Brandenburg, R. Koenen, and D. Szytkman (2017). *CDN optimization for VR streaming*.  
+<<https://www.ibc.org/cdn-optimisation-for-vr-streaming-/2457.article>>
+- [b-Felnhofer] Felnhofer, A., et al. (2012), *Is virtual reality made for men only? Exploring gender differences in the sense of presence*. Proceedings of the International Society on Presence Research, pp. 103–112.
+- [b-Franke] Franke, T., Attig, C., and Wessel, D. (2019), *A personal resource for technology interaction: development and validation of the affinity for technology interaction (ATI) scale*. International Journal of Human–Computer Interaction Vol. 35, No. 6, 456–467.  
+<<https://doi.org/10.1080/10447318.2018.1456150>>
+- [b-Fremerey] Fremerey, S., Hofmeyer, F., et al. (2019). *Impact of Various Motion Interpolation Algorithms on 360° Video QoE*. 11th International Conference on Quality of Multimedia Experience (QoMEX 2019), IEEE Signal Processing Society.
+- [b-George] Koulieris, G., Bui, B., et al. (2017). *Accommodation and comfort in head-mounted displays*. ACM Transactions on Graphics, Vol. 36, No. 4, Article 87, July.  
+<<https://doi.org/10.1145/3072959.3073622>>
+- [b-GSMA AR/VR] GSMA (2019). *Cloud AR/VR Streaming: Accelerate mass adoption and improve quality of experience of AR/VR using 5G and edge cloud*. GSMA Mobile World Congress, booklet.  
+<<https://www.gsma.com/futurenetworks/wp-content/uploads/2019/03/Cloud-ARVR-booklet-for-MWC19.pdf>>
+- [b-Hofmeyer] Hofmeyer, F., Fremerey, S., et al. (2019). *Impacts of internal HMD playback processing on subjective quality perception*. Society for Imaging Science and Technology, International Symposium on Electronic Imaging 2019, pp. 219-1-291-7.  
+<<https://doi.org/10.2352/ISSN.2470-1173.2019.12.HVEI-219>>
+
+- [b-Huawei VR] iLab (2019). *Cloud VR – Service Quality Monitoring White Paper*. Huawei iLab.  
+<[https://www.huawei.com/minisite/static/Cloud\\_VR\\_Service\\_QM\\_WhitePaper.pdf](https://www.huawei.com/minisite/static/Cloud_VR_Service_QM_WhitePaper.pdf)>
+- [b-Kennedy] Kennedy, R. S., Lane, N. E., et al. (1993). *Simulator sickness questionnaire: An enhanced method of quantifying simulator sickness*. The International Journal of Aviation Psychology, Vol. 3, No. 3, pp. 203–220.  
+<[https://www.tandfonline.com/doi/abs/10.1207/s15327108ijap0303\\_3](https://www.tandfonline.com/doi/abs/10.1207/s15327108ijap0303_3)>
+- [b-Kojic-1] Kojic, Tanja, et al (2010), *Influence of UI complexity and positioning on user experience during VR exergames*. Eleventh International Conference on Quality of Multimedia Experience (QoMEX). IEEE.  
+<<https://doi.org/10.1109/QoMEX.2019.8743273>>
+- [b-Kojic-2] Kojić, Tanja, et al (2020), *Exploring visualisations for financial statements in virtual reality*. IEEE International Conference on Artificial Intelligence and Virtual Reality (AIVR). IEEE.  
+<<https://doi.org/10.1109/AIVR50618.2020.00018>>
+- [b-Kopyt] Koyt, A., Narkiewicz, J. (2013). *Technical factors influencing simulator sickness*. Zeszyty Naukowe Politechniki Rzeszowskiej. Mechanika Vol. 85 [288], No. 4 (2013), pp. 455–467.
+- [b-Kuzyakov] Kuzyakov, E., Pio, D. (2016). *Next-generation video encoding techniques for 360 video and VR*. Blogpost, January.  
+<<https://engineering.fb.com/virtual-reality/next-generation-video-encoding-techniques-for-360-video-and-vr/>>
+- [b-Mario] Graf, M., Timmerer, C., Mueller, C. (2017). *Towards bandwidth efficient adaptive streaming of omnidirectional video over http: Design, implementation, and evaluation*. Proceedings of the 8th ACM on Multimedia Systems Conference. pp. 261–271.  
+<<https://dl.acm.org/doi/abs/10.1145/3083187.3084016>>
+- [b-Reiter] Reiter, U., et al. (2014). *Factors Influencing Quality of Experience*. Quality of Experience. T-Labs Series in Telecommunication Services. Springer, Cham, Switzerland. pp. 55–72.  
+<[https://doi.org/10.1007/978-3-319-02681-7\\_4](https://doi.org/10.1007/978-3-319-02681-7_4)>
+- [b-Schleicher] Schleicher, R., and Antons, J.-N. (2014) *Evoking emotions and evaluating emotional impact*. Quality of Experience. Springer, Cham, Switzerland. 121–132.  
+<[https://doi.org/10.1007/978-3-319-02681-7\\_9](https://doi.org/10.1007/978-3-319-02681-7_9)>
+- [b-Singla-1] Singla, A., Fremerey, S., et al. (2017). *Measuring and comparing QoE and simulator sickness of omnidirectional videos in different head mounted displays*. 9th International Conference on Quality of Multimedia Experience (QoMEX 2017). pp. 1–6.  
+<<https://doi.org/10.1109/QoMEX.2017.7965658>>
+- [b-Singla-2] Singla, A., Göring, S., et al. (2019). *Subjective quality evaluation of tile-based streaming for omnidirectional videos*. Proceedings of the 10th ACM Multimedia Systems Conference (MMSys '19). Association for Computing Machinery, New York, NY, USA. pp. 232–242.  
+<<https://doi.org/10.1145/3304109.3306218>>
+- [b-Stanney] Stanney, K. M., Kennedy, R. S., Drexler, J. M. (1997). *Cybersickness is Not Simulator Sickness*. Proceedings of the Human Factors and Ergonomics Society Annual Meeting. Vol. 41, No. 2. pp. 1138–1142.
+
+- [b-Voigt-Antons-1] Voigt-Antons, Jan-Niklas, et al. (2020), *Comparing emotional states induced by 360° videos via head-mounted display and computer screen*. Twelfth International Conference on Quality of Multimedia Experience (QoMEX). IEEE.  
+<<https://doi.org/10.1109/QoMEX48832.2020.9123125>>
+- [b-Voigt-Antons-2] Voigt-Antons, Jan-Niklas, et al (2021), *Don't Worry be Happy - Using virtual environments to induce emotional states measured by subjective scales and heart rate parameters*. IEEE Virtual Reality and 3D User Interfaces (VR). IEEE.  
+<<https://doi.org/10.1109/VR50410.2021.00094>>
+- [b-VR Lens Lab] VR Lens Lab (2016). *Field of View for Virtual Reality Headsets Explained*. Website.  
+<<https://vr-lens-lab.com/field-of-view-for-virtual-reality-headsets/>>
+- [b-Witmer] Witmer, B. G., Singer, M. J. (1998). *Measuring Presence in Virtual Environments: A Presence Questionnaire*.
+- [b-Woods] Woods, A. (2010). *Understanding crosstalk in stereoscopic displays*. Keynote Presentation at the Three-Dimensional Systems and Applications Conference, Tokyo, Japan.
+
+
+
+
+
+## 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                                                                                      |