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+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**G.1029**
+
+(02/2014)
+
+SERIES G: TRANSMISSION SYSTEMS AND MEDIA,  
+DIGITAL SYSTEMS AND NETWORKS
+
+Multimedia Quality of Service and performance – Generic  
+and user-related aspects
+
+# --- Voice service diagnosis framework
+
+Recommendation ITU-T G.1029
+
+## 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.1029
+
+# Voice service diagnosis framework
+
+## Summary
+
+Recommendation ITU-T G.1029 provides a framework and guidelines that describe how ITU-T speech quality assessment models can be used to identify common voice quality problems in live networks and how these can aid in diagnosing the cause of such problems once detected.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T G.1029   | 2014-02-13 | 12          | <a href="http://handle.itu.int/11.1002/1000/12121">11.1002/1000/12121</a> |
+
+## Keywords
+
+Cause analysis, ITU-T objective model, problem diagnosis, voice service.
+
+---
+
+\* 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 .....                                                      | 2    |
+| 3.1 Terms defined elsewhere .....                                        | 2    |
+| 3.2 Terms defined in this Recommendation.....                            | 2    |
+| 4 Abbreviations and acronyms .....                                       | 2    |
+| 5 Conventions .....                                                      | 3    |
+| 6 Framework concept and architecture.....                                | 3    |
+| 7 Introduction to speech quality measurement and assessment models ..... | 3    |
+| 7.1 Subjective and objective testing .....                               | 3    |
+| 7.2 Classes of objective models.....                                     | 5    |
+| 7.3 Measurement configurations .....                                     | 7    |
+| 8 Measurement data sources .....                                         | 8    |
+| 8.1 Intrusive test probes.....                                           | 8    |
+| 8.2 Non-intrusive test probes.....                                       | 8    |
+| 8.3 Embedded probes .....                                                | 8    |
+| 8.4 Additional metrics .....                                             | 8    |
+| 8.5 Multi-point measurements.....                                        | 9    |
+| 8.6 Signalling related measurements .....                                | 9    |
+| 9 Decision process .....                                                 | 9    |
+| 9.1 Thresholds .....                                                     | 9    |
+| 9.2 Analysing metrics derived from live signals .....                    | 9    |
+| 9.3 Mapping basic diagnostic parameters into root cause analysis .....   | 10   |
+| Appendix I – Example based on call clarity index .....                   | 11   |
+| Bibliography.....                                                        | 13   |
+
+
+
+# Voice service diagnosis framework
+
+# 1 Scope
+
+This Recommendation provides a framework and guidelines that describe how ITU-T speech quality assessment models can be used to identify common voice quality problems in live networks and how these can aid in diagnosing the cause of such problems once detected. The scope of this Recommendation is limited to voice service only.
+
+The Recommendation is intended to help non voice experts tasked with managing voice service and diagnosing voice quality problems, especially when voice is regarded as "just another IP application" on the network.
+
+The scope of this Recommendation relates to the perceived quality of the media stream; it does not include factors such as billing, availability, customer service, etc. The primary focus is point-to-point voice services; however, the methods and approaches described can also be applied to the individual legs of multi-party voice applications such as audio-conferencing.
+
+# 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 P.561] Recommendation ITU-T P.561 (2002), *In-service non-intrusive measurement device – Voice service measurements*.
+- [ITU-T P.562] Recommendation ITU-T P.562 (2004), *Analysis and interpretation of INMD voice-service measurements*.
+- [ITU-T P.563] Recommendation ITU-T P.563 (2004), *Single-ended method for objective speech quality assessment in narrow-band telephony applications*.
+- [ITU-T P.564] Recommendation ITU-T P.564 (2007), *Conformance testing for voice over IP transmission quality assessment models*.
+- [ITU-T P.800] Recommendation ITU-T P.800 (1996), *Methods for subjective determination of transmission quality*.
+- [ITU-T P.800.1] Recommendation ITU-T P.800.1 (2006), *Mean Opinion Score (MOS) terminology*.
+- [ITU-T P.800.2] Recommendation ITU-T P.800.2 (2013), *Mean opinion score interpretation and reporting*.
+- [ITU-T P.862] Recommendation ITU-T P.862 (2001), *Perceptual evaluation of speech quality (PESQ): An objective method for end-to-end speech quality assessment of narrow-band telephone networks and speech codecs*.
+- [ITU-T P.862.1] Recommendation ITU-T P.862.1 (2003), *Mapping function for transforming P.862 raw result scores to MOS-LQO*.
+
+- [ITU-T P.862.2] Recommendation ITU-T P.862.2 (2007), *Wideband extension to Recommendation P.862 for the assessment of wideband telephone networks and speech codecs.*
+- [ITU-T P.863] Recommendation ITU-T P.863 (2011), *Perceptual objective listening quality assessment.*
+- [ITU-T Y.1540] Recommendation ITU-T Y.1540 (2011), *Internet protocol data communication service – IP packet transfer and availability performance parameters.*
+- [IETF RFC 3550] IETF RFC 3550 (2003), *RTP: A Transport Protocol for Real-Time Applications.*
+
+# 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:
+
+|                    |                                            |
+|--------------------|--------------------------------------------|
+| CCI                | Call Clarity Index                         |
+| CQO                | Conversational Quality Objective           |
+| ERL                | Echo Return Loss                           |
+| INMD               | In-line Non-intrusive Measurement Device   |
+| IP                 | Internet Protocol                          |
+| LQO                | Listening Quality Objective                |
+| LQO <sub>N</sub>   | Listening Quality Objective narrowband     |
+| LQO <sub>W</sub>   | Listening Quality Objective wideband       |
+| LQO <sub>SWB</sub> | Listening Quality Objective super-wideband |
+| LQS                | Listening Quality Subjective               |
+| MOS                | Mean Opinion Score                         |
+| PCM                | Pulse Code Modulation                      |
+| PLC                | Packet Loss Concealment                    |
+| PSTN               | Public Switched Telephone Network          |
+| RMON               | Remote network Monitoring                  |
+| RTCP               | Real Time Control Protocol                 |
+| RTCP XR            | RTP Control Protocol extended Reports      |
+| RTP                | Real time Transport Protocol               |
+| SIP                | Session Initiation Protocol                |
+| UDP                | User Datagram Protocol                     |
+| VOIP               | Voice Over IP                              |
+
+# 5 Conventions
+
+None.
+
+# 6 Framework concept and architecture
+
+This Recommendation provides a set of high level guidelines. It provides an introduction to speech quality measurement and assessment models, measurement data sources and general considerations relating to defining decision thresholds and mapping diagnostic values to the root cause of voice service problems.
+
+Appendix I is provided as an example and is used to illustrate some of the concepts described in this Recommendation.
+
+The ITU-T intends to provide two more Recommendations addressing, in detail, a framework for invoking diagnostic functions and a framework for mapping diagnostic parameters to root cause parameters, as follows:
+
+- Framework for invoking diagnostic functions: Identification of decision parameters that can be used to detect the presence of a media quality problem in a network so that a diagnostic function can be invoked.
+- Framework for mapping diagnostic parameters to root cause parameters: This work item is concerned with mapping basic diagnostic parameters into root cause analysis parameters.
+
+Figure 1 shows the roadmap for the development of these two Recommendations.
+
+![Figure 1: Roadmap for further development of framework Recommendations. The diagram shows a flow from Terminals and Network through two framework boxes to QoE/QoS root-cause analysis parameters, with a Remedial action loop.](a234352dfaccdc24745c88eef7724cc6_img.jpg)
+
+The diagram illustrates the roadmap for the development of framework Recommendations. It shows a flow starting from 'Terminals' and 'Network' (represented by a cloud icon). The 'Terminals' and 'Network' feed into two main framework boxes. The top box, 'Framework for invoking diagnostic functions (Work Item 1)', contains 'QoE/QoS decision parameters' and 'Decision process'. The bottom box, 'Framework for mapping diagnostic parameters to root-cause parameters (Work Item 2)', contains 'QoE/QoS diagnostic parameters' and 'Diagnostic parameter to root-cause mapping'. An 'Invocation' arrow points from the 'Decision process' in the top box to the 'Diagnostic parameter to root-cause mapping' in the bottom box. The output of the bottom box is 'QoE/QoS root-cause analysis parameters'. A 'Remedial action' arrow points from the 'QoE/QoS root-cause analysis parameters' back to the 'Terminals' and 'Network'. The diagram is labeled G.1029(14)\_F01.
+
+Figure 1: Roadmap for further development of framework Recommendations. The diagram shows a flow from Terminals and Network through two framework boxes to QoE/QoS root-cause analysis parameters, with a Remedial action loop.
+
+Figure 1 – Roadmap for further development of framework Recommendations
+
+# 7 Introduction to speech quality measurement and assessment models
+
+## 7.1 Subjective and objective testing
+
+The perceived quality of a voice call is a subjective quantity. This means that the baseline for voice and audio quality is the subjective opinion of human listeners. One person's impression of "good" may be quite different to another person's impression, but neither is incorrect. Communications systems are therefore designed and tested against an "average" person's perception of voice quality. This is often summarized by the term mean opinion score (MOS). There are essentially two complementary approaches to measuring the quality of a voice signal as it will be perceived by the end user. These are:
+
+- Subjective testing
+- Objective testing
+
+These two approaches are described in the following clauses.
+
+### 7.1.1 Subjective testing
+
+Subjective tests aim to find the average user's perception of the voice quality delivered by a communications system. This is done by asking a panel of users a directed question and providing them with a limited response choice. For example, to determine the listening quality of a voice signal, users are asked to rate "the quality of the speech" on a five-point discrete scale from bad to excellent as described in [ITU-T P.800].
+
+The mean opinion score (MOS) for a particular test condition is calculated by averaging the votes of all subjects for that particular condition. A subjective test will typically contain many different conditions. Therefore, such tests take a long time to perform and the results are influenced by a wide range of factors.
+
+### 7.1.2 Objective testing
+
+Objective testing techniques measure physical properties of a system. Objective perceptual models map these physical properties to a predicted subjective score. In comparison with subjective testing, objective measurements are fast, inexpensive and repeatable. Significant work has led to objective prediction techniques that can be used in situations where it is impractical to perform formal subjective testing.
+
+### 7.1.3 MOS notation
+
+Voice subjective experiments are generally designed to either measure conversational quality or listening (one-way) quality. Conversational experiments investigate how effects such as delay, echo and level affect the ability of two people to carry out a conversation. Listening-only experiments are concerned with the perceived quality delivered by one side of a link and take into account factors such as distortion due to voice compression and packet loss. This distinction is also true for objective speech quality models and they can be designed to predict either listening quality or conversational quality.
+
+The ITU-T has defined terms to denote the difference between conversational and listening quality MOS values and the difference between MOS values from subjective experiments and MOS predictions made by objective models. The ITU-T notation defined in [ITU-T P.800.1] is shown in Table 1. The suffixes N (narrowband), W (wideband) and SWB (super-wideband)<sup>1</sup> are also sometimes added to the notation to denote whether the subjective experiment, or predicted experiment, was conducted in a narrowband (300-3 400 Hz), wideband (50-7 000 Hz) or super-wideband (50-14 000 Hz) context respectively. For example, listening quality assessed in a narrowband context subjective experiment would be denoted as MOS-LQSN.
+
+The reader is also directed to [ITU-T P.800.2], which introduces some of the more common types of mean opinion score (MOS) and describes the minimum information that should accompany MOS values to enable them to be correctly interpreted.
+
+---
+
+<sup>1</sup> The SWB suffix is not explicitly mentioned in [ITU-T P.800.1], but the use of such extensions is encouraged where appropriate.
+
+**Table 1 – ITU-T MOS notation**
+
+| <b>Description</b>                                     | <b>Notation</b> |
+|--------------------------------------------------------|-----------------|
+| Subjectively assessed listening quality                | MOS-LQS         |
+| Subjectively assessed conversational listening quality | MOS-CQS         |
+| Objectively assessed listening quality                 | MOS-LQO         |
+| Objectively assessed conversational listening quality  | MOS-CQO         |
+
+## 7.2 Classes of objective models
+
+In general, objective voice quality models fall into one of four classes: full-reference, reduced-reference, no-reference or parametric. The following clauses introduce the main classes of models and introduce some of the relevant ITU-T Recommendations. Table 2 provides an overview of these Recommendations.
+
+**Table 2 – Summary of ITU-T objective voice quality model standards**
+
+| <b>Model</b>                                                             | <b>Scope / brief definition</b> | <b>Input</b>                                                               | <b>Output</b>                                    |
+|--------------------------------------------------------------------------|---------------------------------|----------------------------------------------------------------------------|--------------------------------------------------|
+| <b>[ITU-T P.863]</b>                                                     | Full-reference model (LQO)      | Reference and degraded 16-bit PCM signals, 8 and 48 kHz                    | MOS-LQO <sub>N</sub> ,<br>MOS-LQO <sub>SWB</sub> |
+| <b>[ITU-T P.862]</b><br><b>[ITU-T P.862.1]</b><br><b>[ITU-T P.862.2]</b> | Full-reference model (LQO)      | Reference and degraded 16-bit PCM signals, 8 and 16 kHz                    | MOS-LQO <sub>N</sub> ,<br>MOS-LQO <sub>W</sub>   |
+| <b>[ITU-T P.561]</b>                                                     | No-reference model (CQO)        | PCM signals (for INMD classes A, B and C)<br>IP packets (for INMD class D) | Speech, noise and echo characterization          |
+| <b>Annex A of [ITU-T P.562]</b>                                          | No-reference model (CQO)        | ITU-T P.561 output                                                         | MOS-CQO <sub>N</sub>                             |
+| <b>[ITU-T P.563]</b>                                                     | No-reference (LQO)              | 8 kHz 16-bit PCM signal                                                    | MOS-LQO <sub>N</sub>                             |
+| <b>[ITU-T P.564]</b>                                                     | Parametric (LQO)                | RTP, UDP and IP headers                                                    | MOS-LQO <sub>N</sub> ,<br>MOS-LQO <sub>W</sub>   |
+
+NOTE – This table lists only what is currently available and it is envisioned that this table will be updated.
+
+### 7.2.1 Full-reference models
+
+Full-reference objective models measure the impact on perceived voice quality of one or more network elements by comparing two versions of a test signal. As shown in Figure 2, the first signal is a copy of the original signal that was injected into the system under test; the second is the received signal, which has typically been degraded. Full-reference models can be used to measure the quality of a single network element, such as a codec, or an entire link, such as a mobile radio link. [ITU-T P.863] is an example of a full-reference objective voice model that predicts a listening quality MOS or MOS-LQO [ITU-T P.863].
+
+![Figure 2: Diagram of an intrusive measurement configuration and a full-reference model. The diagram shows a 'Test signal injection' entering a 'Network element', which then enters another 'Network element'. 'Signal capture' points are shown after each network element. The first captured signal is labeled 'Captured signal (degraded input)' and the second is 'Copy of test signal (reference input)'. Both are inputs to a 'Full-reference model' block, which outputs a 'MOS prediction'. The diagram is labeled G.1029(14)_F02.](d4af765160d04ecef538e5066006dc77_img.jpg)
+
+```
+
+graph LR
+    A[Test signal injection] --> B[Network element]
+    B --> C[Network element]
+    B --> D[Signal capture]
+    C --> E[Signal capture]
+    D --> F[Full-reference model]
+    E --> F
+    F --> G[MOS prediction]
+    style F fill:none,stroke:none
+    style G fill:none,stroke:none
+  
+```
+
+Figure 2: Diagram of an intrusive measurement configuration and a full-reference model. The diagram shows a 'Test signal injection' entering a 'Network element', which then enters another 'Network element'. 'Signal capture' points are shown after each network element. The first captured signal is labeled 'Captured signal (degraded input)' and the second is 'Copy of test signal (reference input)'. Both are inputs to a 'Full-reference model' block, which outputs a 'MOS prediction'. The diagram is labeled G.1029(14)\_F02.
+
+**Figure 2 – Diagram of an intrusive measurement configuration and a full-reference model**
+
+### 7.2.2 Reduced-reference models
+
+Reduced-reference models are similar to full-reference models, but use a reduced set of information about the original test signal rather than an exact copy. Reduced-reference models are typically used in applications where the reference signal is live traffic rather than a predetermined test signal, as shown in Figure 3. This means that information about the reference signal must be transmitted to the point of assessment if a comparison is to be made between the two.
+
+![Figure 3: Diagram of a non-intrusive measurement configuration and a reduced-reference model. The diagram shows 'Live traffic' entering a 'Network element', which then enters another 'Network element'. A dashed line labeled 'Information about traffic' is shown from the first network element. 'Signal capture' points are shown after each network element. The first captured signal is 'Captured signal (degraded input)' and the 'Information about traffic' is 'Information about traffic (reduced reference input)'. Both are inputs to a 'Reduced-reference model' block, which outputs a 'MOS prediction'. The diagram is labeled G.1029(14)_F03.](1439cb942d9e363bbb3161b5540dd8c6_img.jpg)
+
+```
+
+graph LR
+    A[Live traffic] --> B[Network element]
+    B --> C[Network element]
+    B -.-> D[Information about traffic]
+    B --> E[Signal capture]
+    C --> F[Signal capture]
+    F --> G[Reduced-reference model]
+    D -.-> G
+    G --> H[MOS prediction]
+    style G fill:none,stroke:none
+    style H fill:none,stroke:none
+  
+```
+
+Figure 3: Diagram of a non-intrusive measurement configuration and a reduced-reference model. The diagram shows 'Live traffic' entering a 'Network element', which then enters another 'Network element'. A dashed line labeled 'Information about traffic' is shown from the first network element. 'Signal capture' points are shown after each network element. The first captured signal is 'Captured signal (degraded input)' and the 'Information about traffic' is 'Information about traffic (reduced reference input)'. Both are inputs to a 'Reduced-reference model' block, which outputs a 'MOS prediction'. The diagram is labeled G.1029(14)\_F03.
+
+**Figure 3 – Diagram of a non-intrusive measurement configuration and a reduced-reference model**
+
+### 7.2.3 No-reference models
+
+No-reference, or single-ended, models base their assessment on a single input signal and are typically used to monitor the quality of live traffic as shown in Figure 4. [ITU-T P.563] is an example of a no-reference objective speech model that predicts a listening quality MOS, or MOS-LQO [ITU-T P.563]; [ITU-T P.562] includes an example of a no-reference model that predicts conversational quality MOS, or MOS-CQO [ITU-T P.562].
+
+![Figure 4: Diagram of a non-intrusive measurement configuration and a no-reference model. The diagram shows 'Live traffic' entering a 'Network element', which then enters another 'Network element'. 'Signal capture' points are shown after each network element. The first captured signal is 'Captured signal' and is input to a 'No-reference model' block, which outputs a 'MOS prediction'. The diagram is labeled G.1029(14)_F04.](78ffccd66df9bafd96e3e081110d09dd_img.jpg)
+
+```
+
+graph LR
+    A[Live traffic] --> B[Network element]
+    B --> C[Network element]
+    B --> D[Signal capture]
+    C --> E[Signal capture]
+    E --> F[No-reference model]
+    F --> G[MOS prediction]
+    style F fill:none,stroke:none
+    style G fill:none,stroke:none
+  
+```
+
+Figure 4: Diagram of a non-intrusive measurement configuration and a no-reference model. The diagram shows 'Live traffic' entering a 'Network element', which then enters another 'Network element'. 'Signal capture' points are shown after each network element. The first captured signal is 'Captured signal' and is input to a 'No-reference model' block, which outputs a 'MOS prediction'. The diagram is labeled G.1029(14)\_F04.
+
+**Figure 4 – Diagram of a non-intrusive measurement configuration and a no-reference model**
+
+### 7.2.4 Parametric models
+
+Parametric models are designed to predict the impact of transmission impairments on the voice quality perceived by the end user of a system. Parametric models are no-reference models, but analyze parameters related to the underlying transmission system rather than the actual voice signal itself. For example, in the case of a voice over IP (VoIP) system, the main parameters will be derived from the packet loss and jitter characteristics of the link. Parametric voice quality models base their predictions on the assumption that the payload contains a typical, well-conditioned voice signal.
+
+Parametric models are useful in VoIP applications because simple measurements such as packet loss and jitter often correlate poorly with the quality perceived by the end-user. For example, 1% bursty packet loss may produce a number of mutes that will substantially degrade the voice quality perceived by the end-user; whereas 1% uniform packet loss may be largely concealed if the end-point includes an effective packet loss concealment (PLC) algorithm.
+
+An example of a parametric model is provided in [ITU-T P.564], which is concerned with a class of MOS-LQO prediction models that only analyse the IP/UDP/RTP header portion of the VoIP packets [ITU-T P.564]. This approach has several benefits including low-operational complexity and resilience to payload encryption. Note that [ITU-T P.564] does not specify a unique parametric model; it specifies minimum performance criteria that must be met by a model to achieve conformance with the Recommendation.
+
+## 7.3 Measurement configurations
+
+Objective measurement techniques can be categorized as either intrusive (active) or non-intrusive (passive). The distinction between classes of model and measurement configuration is often unclear because full-reference models are generally used in an intrusive configuration whilst no-reference and parametric models are used in a non-intrusive configuration. However, there can be exceptions to this rule, and so it is worth retaining the distinction.
+
+### 7.3.1 Intrusive (active) measurement
+
+In an intrusive measurement configuration a test signal is injected into the system under test and then captured and assessed at a later point as shown in Figure 2.
+
+Intrusive measurement is generally performed using a full-reference model because the test signal is known *a priori* and a copy can be stored at the assessment point. However, there is no reason in principal why a reduced-reference or no-reference model could not be used to measure the quality of the signal at the assessment point.
+
+Intrusive measurement is sometimes referred to as "active" measurement and can be used during the development, commissioning and routine monitoring of a communications service. Intrusive measurement configurations are also highly suitable for laboratory based testing because it is easy to isolate network components and inject and capture test signals.
+
+### 7.3.2 Non-intrusive (passive) measurement
+
+Non-intrusive measurement configurations are generally used to monitor live traffic, as shown in Figure 4.
+
+Non-intrusive measurement is typically performed using a no-reference or parametric model, although a reduced-reference model can also be used as described above. It is important that no-reference models can operate reliably over a very wide range of input signals because the input signal is not restricted to a carefully controlled test signal as it is with intrusive measurement. Parametric models avoid this issue because they do not use the voice signal in the quality calculation, but use an assumed voice signal instead.
+
+In VoIP testing, non-intrusive probes have visibility of all traffic at the monitoring point, including non-voice services. This can be useful in situations where the traffic profile is causing quality problems. For example, if VoIP traffic is transmitted with the wrong class-of-service marking, it may suffer from excessive jitter or packet loss due to the presence of other, non-voice traffic with the same marking.
+
+Non-intrusive measurement is sometimes referred to as "passive" measurement.
+
+# **8 Measurement data sources**
+
+## **8.1 Intrusive test probes**
+
+Intrusive test systems typically inject and capture at the edges of the network being tested, although it is possible to make multiple measurements from the same test signal as shown in Figure 2.
+
+Drive test systems are typically used to measure the voice quality of mobile systems as a function of geographical location. They comprise one or more central servers and a number of special mobile test devices. During each test call, a known test signal is sent in each direction and the received signal is processed by a full-reference model such as [ITU-T P.862] or [ITU-T P.863] to produce MOS-LQO values for each direction. Multiple MOS-LQO measurements may be made during each test call to improve measurement accuracy.
+
+VoIP test units are typically located at different points around the network and are configured to make scheduled test calls to each other. Such testing allows the ability of an IP network to carry VoIP traffic to be tested prior to the deployment of the actual VoIP system or at times when the system would otherwise be inactive. Such test arrangements can also be used to monitor live systems, although measurements are limited to the test traffic and not the customer traffic.
+
+## **8.2 Non-intrusive test probes**
+
+Non-intrusive, or passive, probes are generally used to monitor live network traffic.
+
+In a VoIP system, copies of packets may be taken at monitoring locations by means of a network tap or a mirror port configured on a switch or a router. VoIP streams can then be analysed using no-reference and/or parametric models to produce MOS-LQO and/or MOS-CQO values in addition to other voice diagnostic parameters, such as voice level, noise level, echo etc.
+
+Non-intrusive VoIP probes are typically located at key demarcation points in the network, such as public switched telephone network (PSTN) gateways, session initiation protocol (SIP) peering points, customer edge locations and conference bridges. Some vendors make signal quality measurements within the VoIP end-point. The methods by which such measurements are made available vary from vendor to vendor, but the aim is generally to send the measurements to a central point where the data can be analysed. The RTP control protocol extended reports (RTCP XR) mechanism defined in [b-IETF RFC 3611] describes a mechanism whereby measurements made at VoIP end-points are transported along the path taken by the voice packets and can thus be collected by monitoring probes at mid-network locations [b-IETF RFC 3611].
+
+## **8.3 Embedded probes**
+
+In addition to statistics collected at the monitoring locations, many network elements are capable of making transmission measurements and reporting them to a central data collector. A number of vendors support the collection of IP flow based metrics, and some have been standardized by the IETF in the form of the remote network monitoring (RMON) family of RFCs.
+
+## 8.4 Additional metrics
+
+Quality problems caused by transmission impairments represent an important class of diagnostic information, and it is recommended that signal related metrics, such as MOS, voice level, noise level, echo, etc. are accompanied by associated transmission statistics.
+
+For example, in a VoIP system statistics relating to packet loss, jitter, out-of-sequence packets, round-trip delay and class-of-service markings all provide useful information when diagnosing problems that are the result of IP transmission problems. Such metrics are outside the scope of this Recommendation, but the reader is directed to the measurements defined in [ITU-T Y.1540] and the real-time control protocol (RTCP) measurements defined in [IETF RFC 3550].
+
+## 8.5 Multi-point measurements
+
+The location of transmission problems that affect voice quality can be isolated by collecting and comparing measurements from multiple monitoring locations in the network. However, when performing such analysis, it is important to ensure that values such as MOS-LQO scores have been calculated using the same method or their comparison may be misleading.
+
+## 8.6 Signalling related measurements
+
+Signalling monitoring forms an important part of monitoring a VoIP deployment, but is outside the scope of this Recommendation. The ITU-T E-Series of Recommendations specify metrics that relate to signalling performance.
+
+# 9 Decision process
+
+Designing the optimum strategy for launching diagnostic processes will depend on the specific application, however the following points should be considered.
+
+## 9.1 Thresholds
+
+Detailed diagnostic or troubleshooting activities will generally be launched when one or more thresholds have been violated. Such thresholds may have absolute values or relative values, for example to detect deviations from normal operation.
+
+Many underlying problems will often only affect a subset of all calls. Hence applying thresholds to global averages across all calls may mean that decision thresholds are not violated because the problem traffic is too diluted.
+
+Invoking diagnostic analysis for every call that violates a threshold runs the risk of overwhelming the diagnostic function and generating "false-positive" alarms. This is especially true in the case of objective MOS values and other signal metrics derived from no-reference analysis of live calls (see clause 9.2). Thresholding the output of a parametric model might be appropriate in situations where there is little or no tolerance for transmission related quality problems.
+
+One means of achieving a balance is to define a threshold in terms of the proportion of calls that have violated an underlying threshold. For example, an alarm might be triggered if more than 10% of traffic in a given analysis period had a MOS-LQO value lower than 3.5. Such an approach can highlight problems that affect only a subset of calls, whilst still providing a degree of aggregation and protection from false-positive events.
+
+## 9.2 Analysing metrics derived from live signals
+
+Non-intrusive measurements provide an effective method of identifying systemic or underlying problems from live traffic measurements, i.e., problems that are consistently present, but it is important to ensure that a sufficient number of calls are analyzed before drawing any conclusions and invoking further diagnostic processes. Many factors relating to the quality of live customer calls
+
+naturally vary from call to call, for example the talker's speech characteristics, their acoustic environment, etc. This means that objective MOS values produced by a no-reference model will also naturally vary from call to call. The same is also true of other signal metrics calculated from live traffic, such as voice level, noise level and echo return loss.
+
+This inherent variability in signal related metrics means that inferences about system performance drawn from them for a single call are likely to be unreliable, and a suitable sample of calls should be used instead. However, it should be emphasized that since the main purpose of this type of analysis is to identify systemic issues, it is not necessary to analyse all calls – merely to ensure that a sufficient number of calls have been analysed. If a problem is systemic, analysis of a sub-sample of calls will be sufficient to identify the problem.
+
+The minimum sample size used in a decision process will depend on the decision mechanism and the natural variability of the metric being considered. Analysis of the standard deviation of a sample should provide an indication of how many samples are required to gain reliable results. The use of sampling can be applied both in the monitoring process that is used to invoke diagnostic functions, and in the diagnostic process itself.
+
+For example, if a contact centre were to change their headsets to models that were incorrectly matched to the agents' terminals, the conversational voice quality would be reduced due to sub-optimal voice levels. Such a systemic problem could be rapidly detected by analyzing a few hundred calls made to the contact centre, despite the fact that many thousands of calls could have been made in the same time interval. Further diagnostics, for example analysis of factors that contribute to conversational quality such as delay, echo, noise level and voice level, could also be based on a sub-sample of calls.
+
+## **9.3 Mapping basic diagnostic parameters into root cause analysis**
+
+The following factors should be considered when mapping between basic diagnostic parameters and the possible root cause of a problem:
+
+- What problems have been seen before and the likelihood of them occurring in the system being monitored
+- Which diagnostic values are sensitive to a given underlying problem, and which are not
+- The direction of problem voice flows and whether the equipment at the source of the flow is likely to generate a particular problem
+- What proportion of flows are likely to be affected
+- Equipment or configuration that is common to flows that have violated a particular threshold
+
+Table I.2 in Appendix I illustrates how [ITU-T P.561] and [ITU-T P.562] diagnostic parameters can be associated with common voice quality problems. For example, incorrectly set pads at interconnect points or handsets incorrectly matched to terminal devices are both common causes of very high or very low voice levels. For a given set of flows with an abnormal voice level, the likelihood of these two candidate root causes can be further separated by determining whether the source of the traffic is a gateway or a particular group of phones.
+
+The ability to group sets of measurements by common attributes can greatly assist in identifying the underlying root cause of a problem. This could be the type of equipment, source of configuration or physical location, depending on the particular root cause. For example, the ability to isolate all traffic flowing to and from a PSTN gateway or session border controller will greatly assist in detecting the root cause of common problems associated with these devices.
+
+Finally, it is important to recognize that the exact relationship between diagnostic parameters and possible root causes will often depend on the exact design and configuration of the voice service being monitored.
+
+
+
+# Appendix I
+
+## Example based on call clarity index
+
+(This appendix does not form an integral part of this Recommendation.)
+
+### Introduction to call clarity index
+
+The call clarity index (CCI) specified in Annex A of [ITU-T P.562] produces a MOS-CQO estimate of the conversational quality experienced at each end of a voice connection. The CCI output values are based on measurements of the voice level and the noise level in each direction, the echo return loss (ERL) at both ends of the connection and the roundtrip delay between the two ends. The inputs to CCI are taken from an in-line non-intrusive measurement device (INMD) conforming to [ITU-T P.561].
+
+### Decision metric
+
+The percentage of calls with a CCI of  $Y_C^A$  and  $Y_C^B$  exceeding a MOS-CQO threshold.
+
+NOTE 1 –  $Y_C^A$  denotes conversational speech quality as perceived from end A.
+
+NOTE 2 –  $Y_C^B$  denotes conversational speech quality as perceived from end B.
+
+### Thresholds and alerting strategies
+
+In common with any alerting strategy involving live traffic, alerting based on a threshold violation by a single call is not recommended when monitoring traffic using CCI [ITU-T P.562]. Instead, it is generally more appropriate to raise an alert when a certain proportion of calls have violated a MOS-CQO threshold.
+
+Some factors that reduce conversational quality are outside the control of the service provider, for example if a user makes a call from a noisy location; however, such events are unlikely to affect all calls, whereas systematic problems will, by definition, impact a large proportion of calls handled by the problematic equipment or link.
+
+### Diagnostic parameters
+
+The [ITU-T P.561] inputs to the CCI algorithm are all useful diagnostic parameters and are listed in Table I.1.
+
+**Table I.1 – Diagnostic parameters associated with ITU-T P.562 call clarity index**
+
+| Name            | Description                                               | Units |
+|-----------------|-----------------------------------------------------------|-------|
+| SL <sup>A</sup> | INMD measured active speech level in direction A → B      | dBm0  |
+| SL <sup>B</sup> | INMD measured active speech level in direction B → A      | dBm0  |
+| NL <sup>A</sup> | INMD measured psophometric noise level in direction A → B | dBm0p |
+| NL <sup>B</sup> | INMD measured psophometric noise level in direction B → A | dBm0p |
+| EL <sup>A</sup> | INMD measured echo path loss for echo path A → B → A      | dB    |
+| EL <sup>B</sup> | INMD measured echo path loss for echo path B → A → B      | dB    |
+| ED <sup>A</sup> | INMD measured echo path delay for echo path A → B → A     | ms    |
+| ED <sup>B</sup> | INMD measured echo path delay for echo path B → A → B     | ms    |
+
+### Interpretation and possible root causes
+
+A key factor in isolating the root cause of voice quality problems is the ability to analyse calls based on their source and destination. In particular, information about the route a call has taken before arriving at monitoring point that has raised an alert can be essential in diagnosing the root cause of the alert.
+
+If a particular route displays a large proportion of calls with a low CCI score, then further analysis is recommended by looking at the [ITU-T P.561] values associated with each CCI score. Note that low CCI scores will often be caused by a combination of factors, e.g., the presence of both echo and delay, or the combination of low voice levels and high noise levels.
+
+Some common causes of low a CCI score and the associated diagnostic parameters are listed in Table I.2.
+
+**Table I.2 – Diagnosing low call clarity index values**
+
+| Diagnostic                                                              | Example values                          | Possible causes                                                                                                                                                                                                                                                    |
+|-------------------------------------------------------------------------|-----------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Presence of echo with a delay exceeding a few tens of milliseconds.     | EL < 40 dB and<br>$ED^A + ED^B > 40$ ms | <ul style="list-style-type: none"><li>Absence of echo cancellation or suppression equipment.</li><li>Echo control equipment erroneously disabled.</li><li>Echo tail length in echo canceller too short to echo path.</li><li>Acoustic echo from devices.</li></ul> |
+| Large round-trip delay.                                                 | $ED^A + ED^B > 500$ ms                  | <ul style="list-style-type: none"><li>Excessive jitter on VoIP networks.</li><li>Unexpected call routing.</li></ul>                                                                                                                                                |
+| Very high or very low voice level.                                      | SL < -32 dBm0 or<br>SL > -8 dBm0        | <ul style="list-style-type: none"><li>Incorrectly set pads at interconnect points or gateways.</li><li>Handsets incorrectly matched to terminal devices.</li></ul>                                                                                                 |
+| Low signal-to-noise ratio due to low voice levels or high noise levels. | SL < -32 dBm0 or<br>NL > -50 dBm0p      | <ul style="list-style-type: none"><li>Large proportion of calls made from a noisy environment.</li><li>Also see low voice level.</li></ul>                                                                                                                         |
+
+# Bibliography
+
+- [b-IETF RFC 3577] IETF RFC 3577 (2003), *Introduction to the Remote Monitoring (RMON) Family of MIB Modules.*
+- [b-IETF RFC 3611] IETF RFC 3611 (2003), *RTP Control Protocol Extended Reports (RTCP XR).*
+- [b-IETF RFC 3919] IETF RFC 3919 (2004), *Remote Network Monitoring (RMON) Protocol Identifiers for IPv6 and Multi Protocol Label Switching (MPLS).*
+- [b-IETF RFC 5101] IETF RFC 5101 (2008), *Specification of the IP Flow Information Export (IPFIX) Protocol for the Exchange of IP Traffic Flow Information.*
+
+
+
+## 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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+
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**G.107**
+
+(06/2015)
+
+SERIES G: TRANSMISSION SYSTEMS AND MEDIA,  
+DIGITAL SYSTEMS AND NETWORKS
+
+International telephone connections and circuits –  
+Transmission planning and the E-model
+
+# --- **The E-model: a computational model for use in transmission planning**
+
+Recommendation ITU-T G.107
+
+## ITU-T G-SERIES RECOMMENDATIONS
+
+## TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS
+
+|                                                                                                                                              |                    |
+|----------------------------------------------------------------------------------------------------------------------------------------------|--------------------|
+| INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS                                                                                             | G.100–G.199        |
+| <b>Transmission planning and the E-model</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        |
+| 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        |
+| MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE – GENERIC AND USER-RELATED ASPECTS                                                             | G.1000–G.1999      |
+| TRANSMISSION MEDIA CHARACTERISTICS                                                                                                           | G.6000–G.6999      |
+| DATA OVER TRANSPORT – GENERIC ASPECTS                                                                                                        | G.7000–G.7999      |
+| PACKET OVER TRANSPORT ASPECTS                                                                                                                | G.8000–G.8999      |
+| ACCESS NETWORKS                                                                                                                              | G.9000–G.9999      |
+
+For further details, please refer to the list of ITU-T Recommendations.
+
+### Recommendation ITU-T G.107
+
+# The E-model: a computational model for use in transmission planning
+
+## Summary
+
+Recommendation ITU-T G.107 gives the algorithm for the so-called E-model as the common ITU-T transmission rating model. This computational model can be useful to transmission planners, to help ensure that users will be satisfied with end-to-end transmission performance. The primary output of the model is a scalar rating of transmission quality. A major feature of this model is the use of transmission impairment factors that reflect the effects of modern signal processing devices.
+
+In the 2000 version of this Recommendation, an enhanced version of the E-model was provided in order to better take into account the effects of room noise at the send side and quantizing distortion. With the 2002 version, the impairment due to random packet loss was included in a parametric way for different codecs. Since the 2003 version, an enhanced modelling of quality in the case of low talker sidetone levels is provided. The 2005 version enabled more accurate quality predictions for codecs under (short-term) dependent packet loss. The 2009 version included an Appendix II describing a provisional impairment factor framework for wideband speech transmission. In 2011, this appendix was updated in favour of a new Recommendation ITU-T G.107.1. In the current version, the model has been extended to provide an assessment of delay impairments that is also better tailored to less delay-sensitive use cases. Carrier-grade or enterprise-grade telephony systems must be assessed with the default delay sensitivity parameters, while communication systems with low or very low interactivity requirements can be assessed with different parameters. A reference implementation is given in Appendix III.
+
+## History
+
+| Edition | Recommendation            | Approval   | Study Group | Unique ID*                                                                |
+|---------|---------------------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T G.107               | 1998-12-03 | 12          | <a href="http://handle.itu.int/11.1002/1000/4541">11.1002/1000/4541</a>   |
+| 2.0     | ITU-T G.107               | 2000-05-18 | 12          | <a href="http://handle.itu.int/11.1002/1000/5074">11.1002/1000/5074</a>   |
+| 3.0     | ITU-T G.107               | 2002-07-14 | 12          | <a href="http://handle.itu.int/11.1002/1000/6080">11.1002/1000/6080</a>   |
+| 4.0     | ITU-T G.107               | 2003-03-16 | 12          | <a href="http://handle.itu.int/11.1002/1000/6253">11.1002/1000/6253</a>   |
+| 5.0     | ITU-T G.107               | 2005-03-01 | 12          | <a href="http://handle.itu.int/11.1002/1000/7822">11.1002/1000/7822</a>   |
+| 5.1     | ITU-T G.107 (2005) Amd. 1 | 2006-06-13 | 12          | <a href="http://handle.itu.int/11.1002/1000/8864">11.1002/1000/8864</a>   |
+| 6.0     | ITU-T G.107               | 2008-08-29 | 12          | <a href="http://handle.itu.int/11.1002/1000/9538">11.1002/1000/9538</a>   |
+| 7.0     | ITU-T G.107               | 2009-04-29 | 12          | <a href="http://handle.itu.int/11.1002/1000/9730">11.1002/1000/9730</a>   |
+| 8.0     | ITU-T G.107               | 2011-12-14 | 12          | <a href="http://handle.itu.int/11.1002/1000/11460">11.1002/1000/11460</a> |
+| 8.1     | ITU-T G.107 (2011) Amd. 1 | 2012-06-07 | 12          | <a href="http://handle.itu.int/11.1002/1000/11707">11.1002/1000/11707</a> |
+| 9.0     | ITU-T G.107               | 2014-02-13 | 12          | <a href="http://handle.itu.int/11.1002/1000/12120">11.1002/1000/12120</a> |
+| 10.0    | ITU-T G.107               | 2015-06-29 | 12          | <a href="http://handle.itu.int/11.1002/1000/12505">11.1002/1000/12505</a> |
+
+---
+
+\* 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 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 2015
+
+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 .....                                                                                                                 | 2    |
+| 3.1          | Terms defined elsewhere .....                                                                                                     | 2    |
+| 3.2          | Terms defined in this Recommendation.....                                                                                         | 2    |
+| 4            | Abbreviations and acronyms .....                                                                                                  | 2    |
+| 5            | Conventions .....                                                                                                                 | 2    |
+| 6            | The E-model, a computational model for use in transmission planning .....                                                         | 2    |
+| 6.1          | Introduction .....                                                                                                                | 2    |
+| 7            | Structure and basic algorithms of the E-model.....                                                                                | 3    |
+| 7.1          | Calculation of the transmission rating factor, R.....                                                                             | 4    |
+| 7.2          | Basic signal-to-noise ratio, Ro .....                                                                                             | 4    |
+| 7.3          | Simultaneous impairment factor, Is.....                                                                                           | 5    |
+| 7.4          | Delay impairment factor, Id .....                                                                                                 | 5    |
+| 7.5          | Equipment impairment factor, Ie.....                                                                                              | 7    |
+| 7.6          | Advantage factor, A.....                                                                                                          | 8    |
+| 7.7          | Default values.....                                                                                                               | 9    |
+| Annex A      | Conditions for using the E-model.....                                                                                             | 11   |
+| A.1          | Examples of conditions where caution must be exercised when using the E-model .....                                               | 11   |
+| A.2          | Conditions for which the performance of the E-model has been improved by updating from the earlier version .....                  | 12   |
+| Annex B      | – Quality measures derived from the transmission rating factor R .....                                                            | 15   |
+| Appendix I   | – Calculation of <i>R</i> from MOS <sub>CQE</sub> values .....                                                                    | 17   |
+| Appendix II  | – Provisional impairment factor framework for wideband speech transmission .....                                                  | 18   |
+| Appendix III | – Reference implementation of the E-model in ITU-T G.107 .....                                                                    | 19   |
+| Appendix IV  | – Use of the E-model in conjunction with noise reduction or echo canceller systems in the network or the terminal equipment ..... | 20   |
+| Bibliography | .....                                                                                                                             | 22   |
+
+
+
+# The E-model: a computational model for use in transmission planning
+
+# 1 Scope
+
+This Recommendation describes a computational model, known as the E-model, that has proven useful as a transmission planning tool for assessing the combined effects of variations in several transmission parameters that affect the conversational<sup>1</sup> quality of 3.1 kHz handset telephony. This computational model can be used, for example, by transmission planners to help ensure that users will be satisfied with end-to-end transmission performance whilst avoiding over-engineering of networks. It must be emphasized that the primary output from the model is the "rating factor"  $R$  but this can be transformed to give estimates of customer opinion. Such estimates are only made for transmission planning purposes and not for actual customer opinion prediction (for which there is no agreed-upon model recommended by the ITU-T).
+
+The E-model can be used with confidence for many combinations of high importance to transmission planners, but for some parameter combinations of high importance, E-model predictions have been questioned and are currently under study. Annex A provides further information in this regard.
+
+# 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.107.1] Recommendation ITU-T G.107.1 (2015), *Wideband E-model*.  
+<<http://www.itu.int/rec/T-REC-G.107.1>>
+- [ITU-T G.108] Recommendation ITU-T G.108 (1999), *Application of the E-model: A planning guide*.  
+<<http://www.itu.int/rec/T-REC-G.108>>
+- [ITU-T G.109] Recommendation ITU-T G.109 (1999), *Definition of categories of speech transmission quality*.  
+<<http://www.itu.int/rec/T-REC-G.109>>
+- [ITU-T G.113] Recommendation ITU-T G.113 (2007), *Transmission impairments due to speech processing*.  
+<<http://www.itu.int/rec/T-REC-G.113>>
+- [ITU-T P.833] Recommendation ITU-T P.833 (2001), *Methodology for derivation of equipment impairment factors from subjective listening-only tests*.  
+<<http://www.itu.int/rec/T-REC-P.833>>
+
+---
+
+<sup>1</sup> Conversational quality in this context refers to transmission characteristics, e.g., long transmission times, effects of talker echoes, etc. However, the E-model, as described in this Recommendation, is not intended to model transmission impairments during double talk situations.
+
+- [ITU-T P.834] Recommendation ITU-T P.834 (2015), *Methodology for the derivation of equipment impairment factors from instrumental models*.  
+<<http://www.itu.int/rec/T-REC-P.834>>
+- [ITU-T P.863] Recommendation ITU-T P.863 (2014), *Perceptual objective listening quality assessment*.  
+<<http://www.itu.int/rec/T-REC-P.863>>
+
+# **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:
+
+|        |                                                        |
+|--------|--------------------------------------------------------|
+| BurstR | Burst Ratio                                            |
+| GoB    | Good or Better                                         |
+| LSTR   | Listener Sidetone Rating                               |
+| MOS    | Mean Opinion Score                                     |
+| MNRU   | Modulated Noise Reference Unit                         |
+| OLR    | Overall Loudness Rating                                |
+| OPINE  | Overall Performance Index model for Network Evaluation |
+| PLC    | Packet Loss Concealment                                |
+| PoW    | Poor or Worse                                          |
+| qdu    | quantization distortion unit                           |
+| RLR    | Receive Loudness Rating                                |
+| SLR    | Send Loudness Rating                                   |
+| STMR   | Sidetone Masking Rating                                |
+| TELR   | Talker Echo Loudness Rating                            |
+| WEPL   | Weighted Echo Path Loss                                |
+
+# **5 Conventions**
+
+None.
+
+# **6 The E-model, a computational model for use in transmission planning**
+
+## **6.1 Introduction**
+
+The complexity of modern networks requires not only that, for transmission planning, each of the many transmission parameters be considered individually but also that their combined effects be taken into account. This can be done by "expert, informed guessing", but a more systematic approach is desirable, such as by using a computational model. The output from the model described here is a
+
+scalar quality rating value,  $R$ , which varies directly with the overall conversational quality. [ITU-T G.113] gives guidance about specific impairments, including combined effects based upon a simplification of the model. However, the output can also give nominal estimates of the user reactions, for instance in the form of percentages finding the modelled connection good or better (GoB) or poor or worse (PoW), as described in Annex B. Furthermore, detailed guidance on the proper application of the E-model, as described in this Recommendation, is provided in [ITU-T G.108]. In addition, the definition of categories of speech transmission quality can be found in [ITU-T G.109].
+
+# 7 Structure and basic algorithms of the E-model
+
+The E-model is based on the equipment impairment factor method, following previous transmission rating models. It was developed by an ETSI ad hoc group called "Voice Transmission Quality from Mouth to Ear".
+
+The reference connection, as shown in Figure 1, is split into a send side and a receive side. The model estimates the conversational quality from mouth to ear as perceived by the user at the receive side, both as listener and talker.
+
+![Figure 1 – Reference connection of the E-model. The diagram shows a 'Send side' on the left and a 'Receive side' on the right, connected by a central network block. On the send side, a user icon is connected to a 'Ds-factor' block, which is also influenced by 'Room noise Ps'. The signal then enters the network block. The network block contains a 'Weighted echo path loss WEPL' and 'Round-trip delay Tr' loop, a 'Coding/decoding' block, and is influenced by 'Circuit noise Nc referred to 0 dBr', 'Equipment impairment factor Ie', 'Packet-loss probability Ppl', and 'Packet-loss robustness factor Bpl'. The signal exits the network block to the receive side, passing through a 'Dr-factor' block influenced by 'Room noise Pr'. The receive side also includes 'Sidetone masking rating STMR', 'Listener sidetone rating LSTR (LSTR = STMR + Dr)', and 'Talker echo loudness rating TELR'. Horizontal double-headed arrows at the top indicate 'OLR' (Overall Loudness Rating) as the sum of 'SLR' (Send Loudness Rating) and 'RLR' (Receive Loudness Rating). Other horizontal arrows indicate 'Mean one-way delay T', 'Absolute delay Ta', 'Quantizing distortion qdu', and 'Expectation factor A'. A '0 dBr point' is marked at the network interface. The diagram is labeled 'G.107(08)_F01' at the bottom right.](7a0db9703b68b3d06cdaeefc084c0006_img.jpg)
+
+Figure 1 – Reference connection of the E-model. The diagram shows a 'Send side' on the left and a 'Receive side' on the right, connected by a central network block. On the send side, a user icon is connected to a 'Ds-factor' block, which is also influenced by 'Room noise Ps'. The signal then enters the network block. The network block contains a 'Weighted echo path loss WEPL' and 'Round-trip delay Tr' loop, a 'Coding/decoding' block, and is influenced by 'Circuit noise Nc referred to 0 dBr', 'Equipment impairment factor Ie', 'Packet-loss probability Ppl', and 'Packet-loss robustness factor Bpl'. The signal exits the network block to the receive side, passing through a 'Dr-factor' block influenced by 'Room noise Pr'. The receive side also includes 'Sidetone masking rating STMR', 'Listener sidetone rating LSTR (LSTR = STMR + Dr)', and 'Talker echo loudness rating TELR'. Horizontal double-headed arrows at the top indicate 'OLR' (Overall Loudness Rating) as the sum of 'SLR' (Send Loudness Rating) and 'RLR' (Receive Loudness Rating). Other horizontal arrows indicate 'Mean one-way delay T', 'Absolute delay Ta', 'Quantizing distortion qdu', and 'Expectation factor A'. A '0 dBr point' is marked at the network interface. The diagram is labeled 'G.107(08)\_F01' at the bottom right.
+
+Figure 1 – Reference connection of the E-model
+
+The transmission parameters used as an input to the computation model are shown in Figure 1. Values for room noise and for the  $D$ -factors are handled separately in the algorithm for the send side and receive side and may be of different amounts. The parameters send loudness rating (SLR), receive loudness rating (RLR) and circuit noise  $N_c$  are referred to a defined 0 dBr point. All other input parameters are either considered as values for the overall connection, such as overall loudness rating (OLR), i.e., the sum of SLR and RLR, number of qdu, equipment impairment factors  $I_e$  and advantage factor  $A$ , or referred to only for the receive side, such as sidetone masking rating (STMR), listener sidetone rating (LSTR), weighted echo path loss (WEPL) used for the calculation of listener echo and talker echo loudness rating (TELR).
+
+There are three different parameters associated with transmission time. The absolute delay  $T_a$  represents the total one-way delay between the send side and receive side and is used to estimate the
+
+impairment due to excessive delay. The parameter mean one-way delay  $T$  represents the delay between the receive side (in talking state) and the point in a connection where a signal coupling occurs as a source of echo. The round-trip delay  $Tr$  only represents the delay in a 4-wire loop, where the "double reflected" signal will cause impairments due to listener echo.
+
+## 7.1 Calculation of the transmission rating factor, $R$
+
+According to the equipment impairment factor method, the fundamental principle of the E-model is based on a concept given in the description of the OPINE model, see [b-ITU-T P-Sup.3].
+
+Psychological factors on the psychological scale are additive.
+
+The result of any calculation with the E-model in a first step is a transmission rating factor  $R$ , which combines all transmission parameters relevant for the considered connection. This rating factor  $R$  is composed of:
+
+$$R = Ro - Is - Id - Ie\text{-eff} + A \quad (7-1)$$
+
+$Ro$  represents in principle the basic signal-to-noise ratio, including noise sources such as circuit noise and room noise. Factor  $Is$  is a combination of all impairments which occur more or less simultaneously with the voice signal. Factor  $Id$  represents the impairments caused by delay and the effective equipment impairment factor  $Ie\text{-eff}$  represents impairments caused by low bit-rate codecs. It also includes impairment due to randomly distributed packet losses. The advantage factor  $A$  allows for compensation of impairment factors when the user benefits from other types of access to the user. The term  $Ro$  and the  $Is$  and  $Id$  values are subdivided into further specific impairment values. The following clauses give the equations used in the E-model.
+
+## 7.2 Basic signal-to-noise ratio, $Ro$
+
+The basic signal-to-noise ratio  $Ro$  is defined by:
+
+$$Ro = 15 - 1.5(SLR + No) \quad (7-2)$$
+
+The term  $No$  (in [dBm0p]) is the power addition of different noise sources:
+
+$$No = 10 \log \left[ 10^{\frac{Nc}{10}} + 10^{\frac{Nos}{10}} + 10^{\frac{Nor}{10}} + 10^{\frac{Nfo}{10}} \right] \quad (7-3)$$
+
+$Nc$  (in [dBm0p]) is the sum of all circuit noise powers, all referred to the 0 dBr point.
+
+$Nos$  (in [dBm0p]) is the equivalent circuit noise at the 0 dBr point, caused by the room noise  $Ps$  at the send side:
+
+$$Nos = Ps - SLR - Ds - 100 + 0.004(Ps - OLR - Ds - 14)^2 \quad (7-4)$$
+
+where  $OLR = SLR + RLR$ . In the same way, the room noise  $Pr$  at the receive side is transferred into an equivalent circuit noise  $Nor$  (in [dBm0p]) at the 0 dBr point.
+
+$$Nor = RLR - 121 + Pre + 0.008(Pre - 35)^2 \quad (7-5)$$
+
+The term  $Pre$  (in [dBm0p]) is the "effective room noise" caused by the enhancement of  $Pr$  by the listener's sidetone path:
+
+$$Pre = Pr + 10 \log \left[ 1 + 10^{\frac{(10 - LSTR)}{10}} \right] \quad (7-6)$$
+
+$Nfo$  (in [dBm0p]) represents the "noise floor" at the receive side,
+
+$$Nfo = Nfor + RLR \quad (7-7)$$
+
+with  $N_{for}$  usually set to  $-64$  dBmp.
+
+## 7.3 Simultaneous impairment factor, $I_s$
+
+The factor  $I_s$  is the sum of all impairments which may occur more or less simultaneously with the voice transmission. The factor  $I_s$  is divided into three further specific impairment factors:
+
+$$I_s = I_{olr} + I_{st} + I_q \quad (7-8)$$
+
+$I_{olr}$  represents the decrease in quality caused by too-low values of OLR and is given by:
+
+$$I_{olr} = 20 \left[ \left\{ 1 + \left( \frac{X_{olr}}{8} \right)^8 \right\}^{\frac{1}{8}} - \frac{X_{olr}}{8} \right] \quad (7-9)$$
+
+where:
+
+$$X_{olr} = OLR + 0.2(64 + N_o - RLR) \quad (7-10)$$
+
+The factor  $I_{st}$  represents the impairment caused by non-optimum sidetone:
+
+$$I_{st} = 12 \left[ 1 + \left( \frac{STMRO - 13}{6} \right)^8 \right]^{\frac{1}{8}} - 28 \left[ 1 + \left( \frac{STMRO + 1}{19.4} \right)^{35} \right]^{\frac{1}{35}} - 13 \left[ 1 + \left( \frac{STMRO - 3}{33} \right)^{13} \right]^{\frac{1}{13}} + 29 \quad (7-11)$$
+
+where:
+
+$$STMRO = -10 \log \left[ 10^{-\frac{STM R}{10}} + e^{-\frac{T}{4}} 10^{-\frac{TELR}{10}} \right] \quad (7-12)$$
+
+The impairment factor  $I_q$  represents impairment caused by quantizing distortion:
+
+$$I_q = 15 \log [1 + 10^Y + 10^Z] \quad (7-13)$$
+
+where:
+
+$$Y = \frac{R_o - 100}{15} + \frac{46}{8.4} - \frac{G}{9} \quad (7-14)$$
+
+$$Z = \frac{46}{30} - \frac{G}{40} \quad (7-15)$$
+
+and:
+
+$$G = 1.07 + 0.258Q + 0.0602Q^2 \quad (7-16)$$
+
+$$Q = 37 - 15 \log(qdu) \quad (7-17)$$
+
+In this equation, qdu means the number of qdu for the whole connection between the send side and the receive side.
+
+NOTE – If an impairment factor  $I_e$  is used for a piece of equipment, then the qdu value for that same piece of equipment must not be used.
+
+## 7.4 Delay impairment factor, $I_d$
+
+The impairment factor  $I_d$  representing all impairments due to delay of voice signals is also further divided into three factors:  $I_{dte}$ ,  $I_{dle}$  and  $I_{dd}$ , where
+
+$$I_d = I_{dte} + I_{dle} + I_{dd} \quad (7-18)$$
+
+The factor *Idte* gives an estimate for the impairments due to the talker echo:
+
+$$Idte = \left[ \frac{Roe - Re}{2} + \sqrt{\frac{(Roe - Re)^2}{4} + 100} - 1 \right] (1 - e^{-T}) \quad (7-19)$$
+
+where:
+
+$$Roe = -1.5(No - RLR) \quad (7-20)$$
+
+$$Re = 80 + 2.5(TERV - 14) \quad (7-21)$$
+
+$$TERV = TELR - 40 \log \frac{1 + \frac{T}{10}}{1 + \frac{T}{150}} + 6e^{-0.3T^2} \quad (7-22)$$
+
+For values of  $T < 1$  ms, the talker echo should be considered as sidetone, i.e.,  $Idte = 0$ . The computation algorithm furthermore combines the influence of STMR to talker echo. Taking into account that low values of STMR may have some masking effects on the talker echo and, for very high values of STMR, the talker echo may become more noticeable, the terms *TERV* and *Idte* are adjusted as follows:
+
+For STMR < 9 dB:
+
+In Equation 7-21, *TERV* is replaced by *TERVs*, where:
+
+$$TERVs = TERV + \frac{Ist}{2} \quad (7-23)$$
+
+For  $9 \text{ dB} \leq \text{STMR} \leq 20 \text{ dB}$ :
+
+Equations 7-19 to 7-22 apply.
+
+For STMR > 20 dB:
+
+In Equation 7-18, *Idte* is replaced by *Idtes*, where:
+
+$$Idtes = \sqrt{Idte^2 + Ist^2} \quad (7-24)$$
+
+The factor *Idle* represents impairments due to listener echo. The equations are:
+
+$$Idle = \frac{Ro - Rle}{2} + \sqrt{\frac{(Ro - Rle)^2}{4} + 169} \quad (7-25)$$
+
+where:
+
+$$Rle = 10.5(WEPL + 7)(Tr + 1)^{-0.25} \quad (7-26)$$
+
+The factor *Idd* represents the impairment caused by too-long absolute delay *Ta*, which occurs even with perfect echo cancelling. Only when the effect due to pure delay is attributed to the service, is the effect, to some extent, reflected in the respective speech quality evaluation by the user. It is noted that the effect due to pure delay may instead be attributed to the other conversation partner, or may be attributed to a conversational difficulty; for example if the conversation partners do not know each other, or delay may simply reduce the efficiency of the communication. In the current version of the E-model, different types of conversations and/or users are considered, in terms of their interactivity and delay-sensitivity. As a consequence, the predictions can be tailored to the delay sensitivity requirements of the user group.
+
+For  $Ta \leq mT$ :
+
+$$I_{dd} = 0$$
+
+For  $T_a > mT$ :
+
+$$I_{dd} = 25 \left\{ \left( 1 + X^{6 \cdot sT} \right)^{\frac{1}{6 \cdot sT}} - 3 \left( 1 + \left[ \frac{X}{3} \right]^{6 \cdot sT} \right)^{\frac{1}{6 \cdot sT}} + 2 \right\} \quad (7-27)$$
+
+with:
+
+$$X = \frac{\log \left( \frac{T_a}{mT} \right)}{\log 2} \quad (7-28)$$
+
+The following fixed settings of delay sensitivity,  $sT$  and minimum perceivable delay,  $mT$ , are recommended, reflecting different use cases and user groups. Two aspects are addressed by these settings:
+
+- The interactivity of the conversation and the sensitivity of the users to the delay-effect.
+- The application scenario, that is, whether a given call is being made in a business context or in an everyday situation. Even if users may not notice the delay, it may be very critical for the efficiency or even effectiveness of a given call, for example in a business context.
+
+As a consequence, in the case where it is uncertain what user group or what application scenario is being addressed with the planned service, it is recommended that the default class is used. Any case of non-default value usage should be explicitly mentioned when reporting results.
+
+Based on these considerations, the following settings, shown in Table 1, are recommended for  $sT$  and  $mT$ :
+
+**Table 1 – Delay-sensitivity classes for different use cases**
+
+| Class of delay-sensitivity | $sT$ | $mT$ (ms) | Use case                                                                                                                                                                                                                                                                                                                                                                        |
+|----------------------------|------|-----------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Default                    | 1    | 100       | <ul style="list-style-type: none"> <li>– Applicable to all types of telephone conversations.</li> <li>– Must be used for:               <ul style="list-style-type: none"> <li>• Carrier-grade fixed or mobile telephony;</li> <li>• Enterprise-grade fixed or mobile telephony;</li> <li>• When targeted user group and delay requirements are unknown.</li> </ul> </li> </ul> |
+| Low                        | 0.55 | 120       | <ul style="list-style-type: none"> <li>– Applicable only in cases where it is known that users have low sensitivity to delay, e.g., non time-sensitive conversation scenarios.</li> </ul>                                                                                                                                                                                       |
+| Very low                   | 0.4  | 150       | <ul style="list-style-type: none"> <li>– Applicable only in cases where it is known that users have very low sensitivity to delay, e.g., in primarily non-interactive cases, such as mainly listening to a conversation or to a lecture.</li> </ul>                                                                                                                             |
+
+## 7.5 Equipment impairment factor, $I_e$
+
+The values for the equipment impairment factor  $I_e$  of elements using low bit-rate codecs are not related to other input parameters. They depend on subjective mean opinion score (MOS) test results as well as on network experience. Refer to Appendix I of [ITU-T G.113] for the currently recommended values of  $I_e$ .
+
+Specific impairment factor values for codec operation under random<sup>2</sup> packet-loss have formerly been treated using tabulated, packet-loss dependent *Ie*-values. Now, the packet-loss robustness factor *Bpl* is defined as a codec-specific value. The packet-loss dependent effective equipment impairment factor *Ie-eff* is derived using the codec-specific value for the equipment impairment factor at zero packet-loss *Ie* and the packet-loss robustness factor *Bpl*, both listed in Appendix I of [ITU-T G.113] for several codecs. With the packet-loss probability *Ppl*, *Ie-eff* is calculated using the equation:
+
+$$Ie-eff = Ie + (95 - Ie) \cdot \frac{Ppl}{\frac{Ppl}{BurstR} + Bpl} \quad (7-29)$$
+
+*BurstR* is the so-called burst ratio, which is defined as:
+
+$$BurstR = \frac{\text{Average length of observed bursts in an arrival sequence}}{\text{Average length of bursts expected for the network under "random" loss}}$$
+
+When packet loss is random (i.e., independent) *BurstR* = 1; and
+
+when packet loss is bursty (i.e., dependent) *BurstR* > 1.
+
+For example, for packet loss distributions corresponding to a 2-state Markov model with transition probabilities *p* between a "found" and a "loss" state, and *q* between the "loss" and the "found" state, the burst ratio can be calculated as:
+
+$$BurstR = \frac{1}{p + q} = \frac{Ppl / 100}{p} = \frac{1 - Ppl / 100}{q} \quad (7-30)$$
+
+As can be seen from Equation 7-29, the effective equipment impairment factor in the case of *Ppl* = 0 (no packet-loss) is equal to the *Ie* value defined in Appendix I of [ITU-T G.113].
+
+Please refer to Annex A for the range of parameter values the algorithm has been validated for.
+
+*Ie-eff* should be derived by using the *Ie* and *Bpl* values if they are provided in [ITU-T G.113] and the packet-loss burstiness can be defined by observing packet-loss characteristics. If, for practical reasons, it is difficult to observe the packet-loss rate (*Ppl*) and/or packet-loss characteristics to derive the burstiness parameter (*BurstR*), the [ITU-T P.834] approach can be used to directly derive *Ie-eff*.
+
+If *Ie* is derived directly by using the instrumental method recommended in [ITU-T P.834], it already reflects the effect of packet loss introduced in the preparation of speech materials under test. Therefore, Equation 7-29 should not be used. Rather, the *Ie* value derived by [ITU-T P.834] in *Ie-eff* in Equation 7-1 should be used.
+
+## 7.6 Advantage factor, A
+
+Due to the specific meaning of the advantage factor *A*, there is consequently no relation to any of the other transmission parameters. Some provisional values are given in Table 2.
+
+<sup>2</sup> The probability of losing a packet is regarded as independent of the reception state (received/lost) of the previous packet.
+
+**Table 2 – Provisional examples for the advantage factor *A***
+
+| Communication system example                                                 | Maximum value of <i>A</i> |
+|------------------------------------------------------------------------------|---------------------------|
+| Conventional (wirebound)                                                     | 0                         |
+| Mobility by cellular networks in a building                                  | 5                         |
+| Mobility in a geographical area or moving in a vehicle                       | 10                        |
+| Access to hard-to-reach locations, e.g., via multi-hop satellite connections | 20                        |
+
+It should be noted that the values in Table 2 are only provisional. The use of factor *A* and its selected value in a specific application is the planner's decision. However, the values in Table 2 should be considered as absolute upper limits for *A*. Additional background information on the advantage factor *A* can be found in Appendix II to [ITU-T G.113].
+
+## 7.7 Default values
+
+The default values for all input parameters used in the algorithm of the E-model, are listed in Table 3. It is strongly recommended to use these default values for all parameters that do not vary during planning calculation. If all parameters are set to the default values, the calculation results in a very high quality with a rating factor of *R* = 93.2.
+
+**Table 3 – Default values and permitted ranges for the parameters**
+
+| Parameter                               | Abbr.  | Unit  | Default value | Permitted range | Remark       |
+|-----------------------------------------|--------|-------|---------------|-----------------|--------------|
+| Send loudness rating                    | SLR    | dB    | +8            | 0 ... +18       | (Note 1)     |
+| Receive loudness rating                 | RLR    | dB    | +2            | –5 ... +14      | (Note 1)     |
+| Sidetone masking rating                 | STMR   | dB    | 15            | 10 ... 20       | (Notes 2, 4) |
+| Listener sidetone rating                | LSTR   | dB    | 18            | 13 ... 23       | (Note 2)     |
+| D-Value of telephone, send side         | Ds     | –     | 3             | –3 ... +3       | (Note 2)     |
+| D-Value of telephone, receive side      | Dr     | –     | 3             | –3 ... +3       | (Note 2)     |
+| Talker echo loudness rating             | TELR   | dB    | 65            | 5 ... 65        |              |
+| Weighted echo path loss                 | WEPL   | dB    | 110           | 5 ... 110       |              |
+| Mean one-way delay of the echo path     | T      | ms    | 0             | 0 ... 500       |              |
+| Round-trip delay in a 4-wire loop       | Tr     | ms    | 0             | 0 ... 1000      |              |
+| Absolute delay in echo-free connections | Ta     | ms    | 0             | 0 ... 500       |              |
+| Delay sensitivity                       | sT     | –     | 1             | 0.4 ... 1       | (Note 7)     |
+| Minimum perceivable delay               | mT     | ms    | 100           | 20 ... 150      | (Note 7)     |
+| Number of quantization distortion units | qdu    | –     | 1             | 1 ... 14        |              |
+| Equipment impairment factor             | Ie     | –     | 0             | 0 ... 40        | (Note 5)     |
+| Packet-loss robustness factor           | Bpl    | –     | 4.3           | 4.3 ... 40      | (Notes 3, 5) |
+| Random packet-loss probability          | Ppl    | %     | 0             | 0 ... 20        | (Notes 3, 5) |
+| Burst ratio                             | BurstR | –     | 1             | 1 ... 8         | (Notes 3, 6) |
+| Circuit noise referred to 0 dBr-point   | Nc     | dBm0p | –70           | –80 ... –40     |              |
+| Noise floor at the receive side         | Nfor   | dBmp  | –64           | –               | (Note 3)     |
+| Room noise at the send side             | Ps     | dB(A) | 35            | 35 ... 85       |              |
+
+**Table 3 – Default values and permitted ranges for the parameters**
+
+| Parameter                      | Abbr. | Unit  | Default value | Permitted range | Remark |
+|--------------------------------|-------|-------|---------------|-----------------|--------|
+| Room noise at the receive side | Pr    | dB(A) | 35            | 35 ... 85       |        |
+| Advantage factor               | A     | –     | 0             | 0 ... 20        |        |
+
+NOTE 1 – Total values between microphone or receiver and 0 dBr-point.  
+NOTE 2 – Fixed relation:  $LSTR = STMR + D$ .  
+NOTE 3 – Currently under study.  
+NOTE 4 – Equation 7-24 provides also predictions for  $STMR > 20$  dB. However, such values can hardly be measured in a reliable way because the measurement device will mainly cover the acoustic coupling, and not the electrical one.  
+NOTE 5 – If  $Ppl > 0\%$ , then the Bpl must match the codec, packet size and packet loss concealment (PLC) assumed.  
+NOTE 6 – E-model predictions for values of  $BurstR > 2$  are only valid if the packet loss percentage is  $Ppl < 2\%$ .  
+NOTE 7 – Only predefined settings are allowed for sT and mT, reflecting specific use cases, see main body of the Recommendation.
+
+The 2000 version of this Recommendation provided an enhanced version of the E-model algorithm (see Annex A).
+
+Due to the changes made in the 2000 version of this Recommendation, the resulting rating  $R$  with all parameter values set to default has slightly changed (from  $R = 94.2$  to  $R = 93.2$ ). For practical planning purposes, however, this slight deviation should be considered insignificant.
+
+## Annex A
+
+### Conditions for using the E-model
+
+(This annex forms an integral part of this Recommendation.)
+
+NOTE – The assessment and enhancement of the E-model algorithm are for further study. New results will be included as soon as they become available.
+
+### A.1 Examples of conditions where caution must be exercised when using the E-model
+
+- *The overall level of equipment impairment factors*
+
+Some experimental investigations suggest that the general tendency of the equipment impairment factors is too pessimistic, so that a hidden security margin may be incorporated.
+
+- *The overall additivity property of the model*
+
+The E-model assumes that different kinds of impairments are additive on the scale of the transmission rating factor  $R$ . This feature has not been checked to a satisfactory extent. More specifically, very few investigations are available regarding the interaction of low bit-rate codecs with other kinds of impairments, e.g., with room noise. Additionally, the order effects when tandeming several low bit-rate codecs remain uncertain.
+
+- *The coverage of talker sidetone*
+
+Some experiments show that the E-model disregards some masking effects occurring for talker sidetone, namely in conjunction with circuit noise, room noise at receive side and low delay talker echo ( $< 10$  ms).
+
+- *The advantage factor  $A$*
+
+Up to now it has not been clarified under which conditions the given values for the advantage factor should be applied. It is expected that these values may depend for example on the user group, and that the absolute values will change in the long term.
+
+- *Derivation methodology for new equipment impairment factors*
+
+A new methodology for deriving equipment impairment factors from subjective listening quality tests has been adopted as [ITU-T P.833]. A new methodology for deriving equipment impairment factors from instrumental models such as [ITU-T P.863] has been adopted as [ITU-T P.834].
+
+- *Predictions for different types of room noise and different frequency shapes in the communication channel, in the sidetone path and in the echo path*
+
+The E-model regards the effect of room noise only by means of an A-weighted level. The actual opinion on the speech communication quality may depend even on the type and disturbance of the environmental noise. The frequency characteristics of the communication channel, of the sidetone and of the echo path are not explicitly regarded by the E-model, but only implicitly by means of loudness ratings. However, they may affect the perceived transmission quality.
+
+### A.2 Conditions for which the performance of the E-model has been improved by updating from the earlier version
+
+#### – *The effect of room noise at send side*
+
+With the present enhanced E-model algorithm (2000 version), the Lombard effect (the fact that the speaker adapts his/her pronunciation and speaking level according to the noise environment) is no longer disregarded. This had, in the 1998 version, led to too pessimistic E-model predictions for high room noise levels  $P_r$ .
+
+#### – *Predictions for quantizing distortion*
+
+In case of the 1998 version of the E-model, subjective test results for modulated noise reference unit (MNRU) reference conditions were very often more pessimistic than E-model predictions. The graphs in Figure A.1 have been derived from the 1998 version and the 2000 version of the E-model with all other parameters at their default values.
+
+![Figure A.1: Relation between the number of qdu and E-model rating R. The graph shows two curves: a dashed line for the 1998 version and a solid line for the 2000 version. The x-axis is 'Number of qdus' (1 to 15) and the y-axis is 'E-model rating R' (50 to 100). Both curves start at R ≈ 95 for 1 qdu. The 1998 curve (dashed) decreases to R ≈ 75 at 15 qdus. The 2000 curve (solid) decreases more sharply to R ≈ 65 at 15 qdus.](df7cb4ea9bd6c3f445f3e264773b125f_img.jpg)
+
+| Number of qdus | E-model rating $R$ (1998) | E-model rating $R$ (2000) |
+|----------------|---------------------------|---------------------------|
+| 1              | 95                        | 95                        |
+| 3              | 94                        | 90                        |
+| 5              | 92                        | 85                        |
+| 7              | 88                        | 78                        |
+| 9              | 83                        | 72                        |
+| 11             | 78                        | 67                        |
+| 13             | 74                        | 63                        |
+| 15             | 70                        | 59                        |
+
+Figure A.1: Relation between the number of qdu and E-model rating R. The graph shows two curves: a dashed line for the 1998 version and a solid line for the 2000 version. The x-axis is 'Number of qdus' (1 to 15) and the y-axis is 'E-model rating R' (50 to 100). Both curves start at R ≈ 95 for 1 qdu. The 1998 curve (dashed) decreases to R ≈ 75 at 15 qdus. The 2000 curve (solid) decreases more sharply to R ≈ 65 at 15 qdus.
+
+**Figure A.1 �� Relation between the number of qdu and E-model rating  $R$**
+
+With respect to the slightly enhanced algorithm of the E-model, as given in this Recommendation, the relation between the parameter qdu and the E-model rating  $R$  has been changed in order to align the algorithm better with the available subjective test results.
+
+#### – *Predictions for codec performance under random packet loss*
+
+Impairments due to codecs under packet-loss conditions were formerly handled by using codec-dependent tabulated equipment impairment factors for different packet-loss rates (in former versions of Appendix I of [ITU-T G.113]). As the aim is to reduce the amount of tabulated data for usage with the E-model, the possibilities of replacing tabulated  $I_{es}$  for packet loss with corresponding equations were investigated. The approach selected leads to results very similar to those previously defined as  $I_e$  for all codecs covered in the 2001 version of Appendix I of [ITU-T G.113].
+
+#### – *Predictions for codec performance under dependent packet loss*
+
+With this version of the algorithm, loss distributions characterized by medium (short-term) loss dependencies (as opposed to long-term loss dependencies) have been integrated in the E-model. Up to now, the included approach has been evaluated only for the ITU-T G.729(A) codec, but is assumed to be applicable also to the ITU-T G.723.1 codec, and supposedly other codecs. Pending further verification, the algorithm should not be used with burst ratios higher than  $BurstR = 2.0$ . The model can also be applied to burst ratios higher than 2.0, if the packet loss percentages  $Ppl$  are lower than 2%.
+
+#### – *The effect of talker sidetone*
+
+Estimates of voice quality as a function of STMR for values  $> 15$  dB, as provided by the 2002 version of this Recommendation, were too pessimistic and did not accurately match the results obtained in auditory tests. This proved to be especially important for telephones in North America that are typically specified to have nominal values of STMR from 16 to 18 dB.
+
+In the current revised version of the E-model algorithm, this observation is reflected by modifying the corresponding equation for  $Ist$  as a function of sidetone ( $STMR$ ), see Equation 7-11.
+
+As mentioned in the main body of this Recommendation, talker echo may become more noticeable for quiet values of STMR. This is addressed by switching from *Idte* to *Idtes*, see Equation 7-24. To remain consistent, the talker echo threshold from  $STMR > 15$  dB (2002 version of this Recommendation) was extended to  $STMR > 20$  dB (the current version of this Recommendation). The modifications have no impact for values of  $STMR < 15$  dB. Consequently, the quality prediction for the transmission rating factor  $R$  for the default settings ( $STMR = 15$  dB) does not differ from that predicted by the previous model version (2002). The default value of  $R$  is 93.2 for both the previous and the current versions. The situation is depicted in Figure A.2.
+
+![Figure A.2: Comparison of R versus STMR for the current and the previous versions of the E-model algorithm. The graph shows two curves: a solid blue line for the 2002 version and a dashed green line for the current version. The x-axis is STMR (dB) from 0 to 40, and the y-axis is R from 70 to 95. Both curves start at R ≈ 79 at 0 dB, rise to a peak of R ≈ 93.2 at 15 dB, and then diverge. The 2002 version drops sharply to R ≈ 70 at 30 dB, while the current version drops more gradually to R ≈ 75 at 40 dB.](3e0c2bf6c51c575d096c7fc95c1e8454_img.jpg)
+
+| STMR (dB) | 2002 version (R) | Current version (R) |
+|-----------|------------------|---------------------|
+| 0         | 79               | 79                  |
+| 5         | 88               | 88                  |
+| 10        | 93               | 93                  |
+| 15        | 93.2             | 93.2                |
+| 20        | 85               | 93                  |
+| 25        | 75               | 88                  |
+| 30        | 70               | 83                  |
+| 35        | -                | 78                  |
+| 40        | -                | 75                  |
+
+Figure A.2: Comparison of R versus STMR for the current and the previous versions of the E-model algorithm. The graph shows two curves: a solid blue line for the 2002 version and a dashed green line for the current version. The x-axis is STMR (dB) from 0 to 40, and the y-axis is R from 70 to 95. Both curves start at R ≈ 79 at 0 dB, rise to a peak of R ≈ 93.2 at 15 dB, and then diverge. The 2002 version drops sharply to R ≈ 70 at 30 dB, while the current version drops more gradually to R ≈ 75 at 40 dB.
+
+**Figure A.2 – Comparison of  $R$  versus STMR for the current and the previous versions of the E-model algorithm**
+
+#### – *The effect of pure delay*
+
+Based on several conversation tests, it has been shown that even long delay values may not affect the perceived speech quality, that is, in terms of the attribution of the delay effect to the system. In such cases, the predictions by previous versions of the E-model may be more pessimistic than actual user opinion. As a consequence, in specific cases speech quality predictions may be sought that are better tailored to some less stringent delay requirements.
+
+As a consequence, in the current revised version of the E-model, the delay sensitivity  $sT$  and minimum perceivable delay  $mT$  have been introduced. With an appropriate choice of these two parameters, both default and less delay-sensitive calls can be addressed. It is advisable to use these new parameters carefully according to the expected delay class according to Table 1.
+
+## Annex B
+
+### Quality measures derived from the transmission rating factor $R$
+
+(This annex forms an integral part of this Recommendation.)
+
+The transmission rating factor  $R$  can lie in the range from 0 to 100, where  $R = 0$  represents an extremely bad quality and  $R = 100$  represents a very high quality. The E-model provides a statistical estimation of quality measures. The percentages for a judgement of good or better (GoB) or poor or worse (PoW) are obtained from the  $R$ -factor by means of the Gaussian error function:
+
+$$E(x) = \frac{1}{\sqrt{2\pi}} \int_{-\infty}^x e^{-\frac{t^2}{2}} dt \quad (B-1)$$
+
+The equations are:
+
+$$GoB = 100E\left(\frac{R - 60}{16}\right)\% \quad (B-2)$$
+
+$$PoW = 100E\left(\frac{45 - R}{16}\right)\% \quad (B-3)$$
+
+An estimated mean opinion score ( $MOS_{CQE}$ ) for the conversational situation in the scale 1-5 can be obtained from the  $R$ -factor using the equations:
+
+$$\text{For } R < 0: \quad MOS_{CQE} = 1 \quad (B-4)$$
+
+$$\text{For } 0 < R < 100: \quad MOS_{CQE} = 1 + 0.035R + R(R - 60)(100 - R)7 \cdot 10^{-6}$$
+
+$$\text{For } R > 100: \quad MOS_{CQE} = 4.5$$
+
+This equation can be inverted in the range  $6.5 \leq R \leq 100$  to calculate  $R$  from  $MOS_{CQE}$ , see Appendix I. GoB, PoW and  $MOS_{CQE}$  as functions of  $R$  are depicted in Figures B.1 and B.2, respectively.
+
+![Figure B.1: A line graph showing Good or better (GoB) and poor or worse (PoW) as functions of rating factor R. The x-axis is R (0 to 100) and the y-axis is percentage (1 to 99). The PoW curve decreases from 100% at R=0 to 0% at R=100. The GoB curve increases from 0% at R=0 to 100% at R=100. The curves intersect at R=60, where both are approximately 50%.](1577abe02184da5a60ec8d469ddb439e_img.jpg)
+
+| R   | PoW (%) | GoB (%) |
+|-----|---------|---------|
+| 0   | 100     | 0       |
+| 20  | ~90     | ~10     |
+| 40  | ~75     | ~25     |
+| 60  | ~50     | ~50     |
+| 80  | ~25     | ~75     |
+| 100 | 0       | 100     |
+
+Figure B.1: A line graph showing Good or better (GoB) and poor or worse (PoW) as functions of rating factor R. The x-axis is R (0 to 100) and the y-axis is percentage (1 to 99). The PoW curve decreases from 100% at R=0 to 0% at R=100. The GoB curve increases from 0% at R=0 to 100% at R=100. The curves intersect at R=60, where both are approximately 50%.
+
+Figure B.1 – Good or better (GoB) and poor or worse (PoW) as functions of rating factor  $R$
+
+![Figure B.2: MOSCQE as function of rating factor R. The graph shows a curve on a grid where the x-axis is R (0 to 100) and the y-axis is MOS (1 to 5). The curve starts at (0, 1) and rises to approximately (100, 4.5).](60e9207be66a64332619bb4b667fe67b_img.jpg)
+
+The figure is a line graph showing the relationship between the rating factor  $R$  and the Mean Opinion Score (MOS). The x-axis represents  $R$  from 0 to 100 in increments of 20. The y-axis represents MOS from 1 to 5, with labels 'Bad 1', 'Poor 2', 'Fair 3', 'Good 4', and 'Excellent 5'. A smooth curve starts at the point (0, 1) and increases monotonically, ending at approximately (100, 4.5). The curve is concave down, indicating that the rate of increase in MOS decreases as  $R$  increases.
+
+Figure B.2: MOSCQE as function of rating factor R. The graph shows a curve on a grid where the x-axis is R (0 to 100) and the y-axis is MOS (1 to 5). The curve starts at (0, 1) and rises to approximately (100, 4.5).
+
+**Figure B.2 – MOS<sub>CQE</sub> as function of rating factor  $R$**
+
+In some cases, transmission planners may not be familiar with the use of quality measures such as the  $R$  rating factor obtained from planning calculations, and thus provisional guidance for interpreting calculated  $R$  factors for planning purposes is given in Table B.1<sup>3</sup>. This table also contains equivalent transformed values of  $R$  into estimated conversational MOS<sub>CQE</sub>, GoB and PoW.
+
+**Table B.1 – Provisional guide for the relation between  $R$ -value and user satisfaction**
+
+| <b><math>R</math>-value<br/>(lower limit)</b> | <b>MOS<sub>CQE</sub><br/>(lower limit)</b> | <b>GoB (%)<br/>(lower limit)</b> | <b>PoW (%)<br/>(upper limit)</b> | <b>User satisfaction</b>      |
+|-----------------------------------------------|--------------------------------------------|----------------------------------|----------------------------------|-------------------------------|
+| 90                                            | 4.34                                       | 97                               | ~0                               | Very satisfied                |
+| 80                                            | 4.03                                       | 89                               | ~0                               | Satisfied                     |
+| 70                                            | 3.60                                       | 73                               | 6                                | Some users dissatisfied       |
+| 60                                            | 3.10                                       | 50                               | 17                               | Many users dissatisfied       |
+| 50                                            | 2.58                                       | 27                               | 38                               | Nearly all users dissatisfied |
+
+<sup>3</sup> The source of Table B.1 is Table 1 of [ITU-T G.109].
+
+## Appendix I
+
+### Calculation of $R$ from $MOS_{CQE}$ values
+
+(This appendix does not form an integral part of this Recommendation.)
+
+In the range  $6.5 \leq R \leq 100$ ,  $R$  can be calculated from  $MOS_{CQE}$  using the formula:
+
+$$R = \frac{20}{3} \left( 8 - \sqrt{226} \cos \left( h + \frac{\pi}{3} \right) \right) \quad (I-1)$$
+
+with:
+
+$$h = \frac{1}{3} \arctan2 \left( 18566 - 6750 MOS_{CQE}, 15 \sqrt{-903522 + 1113960 MOS_{CQE} - 202500 MOS_{CQE}^2} \right) \quad (I-2)$$
+
+and:
+
+$$\arctan2(x, y) = \begin{cases} \arctan\left(\frac{y}{x}\right) & \text{for } x \geq 0 \\ \pi - \arctan\left(\frac{y}{-x}\right) & \text{for } x < 0 \end{cases} \quad (I-3)$$
+
+The function  $\arctan2(x, y)$  is implemented in ANSI C as the function  $\text{atan2}(y, x)$ . Users should note that the order of the two parameters differs in this case.
+
+## **Appendix II**
+
+### **Provisional impairment factor framework for wideband speech transmission**
+
+(This appendix does not form an integral part of this Recommendation.)
+
+The contents of this appendix have been moved to [ITU-T G.107.1].
+
+## Appendix III
+
+### Reference implementation of the E-model in ITU-T G.107
+
+(This appendix does not form an integral part of this Recommendation.)
+
+The reference implementation of the E-model is no longer provided in the traditional qbasic listing (which was provided in previous versions of this Recommendation), since it was no longer found to be appropriate. Therefore, the ITU-T provides a new implementation of the E-model in PHP4 scripting language.
+
+The associated electronic attachment (which is available free of charge on the ITU publications website at <http://www.itu.int/rec/T-REC-G.107-201112-S/en>) contains the following files in the Software folder:
+
+- General instructions: readme.txt
+- PHP4 script: calc.php
+- 3 required Java scripts:
+  - wz\_tooltip.js
+  - tip\_centerwindow.js
+  - tip\_followscroll.js
+- Copyright notice
+
+In order to run this software on any server outside ITU, a licence must be obtained from the organization indicated in the software Copyright notice.
+
+However, the very same PHP4 script has been implemented on the ITU website, where everyone has the right to use that software from that web server, under their own responsibility and at their own risk, without limitation, subject to no particular conditions, no royalties are due, etc. No software copyright licence agreements are required for such usage. That tool is available here: <http://www.itu.int/ITU-T/studygroups/com12/emodelv1/>
+
+## Appendix IV
+
+### Use of the E-model in conjunction with noise reduction or echo canceller systems in the network or the terminal equipment
+
+(This appendix does not form an integral part of this Recommendation.)
+
+Modern networks or terminals frequently contain devices for echo cancellation and/or noise reduction. Echo cancellers are expected to significantly reduce the echo and the amount of residual echo may be considered in the same way the standard E-model does, i.e., via the residual talker echo loudness rating *TELR* and the mean one-way delay *T* of the residual echo path. However, the echo attenuation may also vary over time (so-called "echo pumping"), and the cancellation process may lead to degradations of the transmitted speech signal. Degradations of the transmitted speech signal may also result from imperfect noise reduction, e.g., when parts of the speech spectrum are subtracted by the noise reduction algorithm. Such a degradation due to imperfect noise reduction is also not covered by the current version of the E-model.
+
+In order to assess these effects in a more elaborated way, it is proposed to go through all the steps of the following provisional procedure which apply to the given scenario (i.e., noise reduction, echo cancellation, or both), see also [b-Möller]:
+
+- 1) The residual noise resulting from imperfect background noise reduction may occur either during speech intervals or during pauses; parameters describing these two situations are defined in [b-ITU-T G.160], namely *SNRI* (the SNR improvement during speech in dB) and *TNLR* (the total noise level reduction in dB). It is proposed to use a weighting of half and half (corresponding to roughly 50% speech activity) for the speech and silence parts and change Equation 7-4 as follows:
+
+$$\begin{aligned} Nos &= Ps - SLR - Ds - 0.5(SNRI + TNLR) - 100 \\ &\quad + 0.004(Ps - OLR - Ds - 14)^2 \end{aligned} \quad (IV-1)$$
+
+This amendment is meant to capture the effect of residual noise of the noise reduction mechanism.
+
+In the case that a non-white background noise is assumed, the factor *Ds* of Equation IV-1 might depend on the noise type used for its measurement; see the ITU-T Handbook on Telephonometry [b-ITU-T HB Teleph]. In that case, it is suggested to use noise of the same type as it is assumed to occur in the background.
+
+- 2) The effects of speech degradation from imperfect noise reduction can be captured by estimating via an additional equipment impairment factor *Ie,nr* reflecting the noise reduction equipment. Such an additional equipment impairment factor should ideally be derived with the help of auditory listening-only tests carried out in accordance with [b-ITU-T P.835]. As an alternative, the S-MOS scores might also be estimated with the objective model of [b-ETSI EG 202]. Provided that such S-MOS scores are available for (1) the connection of the noise-reduced case and (2) for a noise-free connection without the noise-reduction system applied, *Ie,nr* can be calculated as:
+
+$$Ie,nr = \min(R(S-MOS2) - R(S-MOS1), 0) \quad (IV-2)$$
+
+In this equation, the transformation from S-MOS to *R* is performed using the relationship between MOS and *R* given in the E-model. The resulting *Ie,nr* scores are preferably normalized following the procedure of [ITU-T P.834].
+
+- 3) The effects of residual echo are taken into account in the standard way of the E-model, i.e., via the talker-echo impairment factor *Idte*; the frequency-dependent attenuation of the residual echo path has to be used for the calculation of *TELR* at this stage.
+
+- 4) The effects of speech degradation from imperfect echo cancellation can be estimated via an additional equipment impairment factor  $I_{e,ec}$  which is calculated with the help of the procedure of [ITU-T P.834], using the instrumental model of [ITU-T P.863]. The calculation is performed as in step 2 and it is also preferable to normalize the obtained raw  $I_{e,ec}$  score with the help of the procedure of [ITU-T P.834].
+
+Please note that [ITU-T P.863] is not intended to be used with talker echo as a test factor, so applying it to derive impairment factors for echo cancellers should be exercised with care.
+
+- 5) Both  $I_{e,nr}$  and  $I_{e,ec}$  are added to the effective equipment impairment factor  $I_{e,eff}$  before calculating the overall transmission rating  $R$ .
+- 6) The effects of delay are captured in the usual way via  $I_{dd}$ .
+
+The proposed methodology is only provisional, as it has not been thoroughly validated. However, it is assumed that it results in better estimations than by not considering the mentioned effects of noise reduction and echo canceller equipment. The following effects are not yet covered by the methodology and are thus for further study in ITU-T:
+
+- The effect of time-varying echo paths.
+- The effects of variable background noise transmission due to the echo canceller.
+- The reduction of the double-talk capability due to the echo canceller.
+- The degradation resulting from the acoustic characteristics of the terminal to which noise reduction and/or echo cancellers might be integrated.
+
+# Bibliography
+
+- [b-ITU-T G.160] Recommendation ITU-T G.160 (2012), *Voice enhancement devices*.
+- [b-ITU-T G.711] Recommendation ITU-T G.711 (1988), *Pulse code modulation (PCM) of voice frequencies*.  
+<<http://www.itu.int/rec/T-REC-G.711>>
+- [b-ITU-T G.712] Recommendation ITU-T G.712 (2001), *Transmission performance characteristics of pulse code modulation channels*.  
+<<http://www.itu.int/rec/T-REC-G.712>>
+- [b-ITU-T G.722] Recommendation ITU-T G.722 (2012), *7 kHz audio-coding within 64 kbit/s*.  
+<<http://www.itu.int/rec/T-REC-G.722>>
+- [b-ITU-T G.723.1] Recommendation ITU-T G.723.1 (2006), *Dual rate speech coder for multimedia communications transmitting at 5.3 and 6.3 kbit/s*.  
+<<http://www.itu.int/rec/T-REC-G.723.1>>
+- [b-ITU-T G.729] Recommendation ITU-T G.729 (2012), *Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear prediction (CS-ACELP)*.  
+<<http://www.itu.int/rec/T-REC-G.729>>
+- [b-ITU-T P.10] Recommendation ITU-T P.10/G.100 (2006), *Vocabulary for performance and quality of service*.  
+<<http://www.itu.int/rec/T-REC-P.10/G.100>>
+- [b-ITU-T P.48] Recommendation ITU-T P.48 (1988), *Specification for an intermediate reference system*.  
+<<http://www.itu.int/rec/T-REC-P.48>>
+- [b-ITU-T P.800] Recommendation ITU-T P.800 (1996), *Methods for subjective determination of transmission quality*.  
+<<http://www.itu.int/rec/T-REC-P.800>>
+- [b-ITU-T P.835] Recommendation ITU-T P.835 (2003), *Subjective test methodology for evaluating speech communication systems that include noise suppression algorithm*.  
+<<http://www.itu.int/rec/T-REC-P.835>>
+- [b-ITU-T P-Sup.3] ITU-T P-series Recommendations – Supplement 3 (1993), *Models for predicting transmission quality from objective measurements*.  
+<<http://www.itu.int/rec/T-REC-P.Sup3>>
+- [b-ETSI EG 202] ETSI EG 202 396-3 (2007), *Speech Quality Performance in the Presence of Background Noise – Part 3: Background Noise Transmission – Objective Test Methods*, European Telecommunications Standards Institute, Sophia Antipolis.  
+<[http://www.etsi.org/deliver/etsi\\_eg/202300\\_202399/20239603/01.03.01\\_60/eg\\_20239603v010301p.pdf](http://www.etsi.org/deliver/etsi_eg/202300_202399/20239603/01.03.01_60/eg_20239603v010301p.pdf)>
+- [b-Möller] Möller, S., Kettler, F., Gierlich, H.-W., Poschen, S., Côté, N., Raake, A., Wältermann, M. (2011), *Extending the E-Model For Capturing Noise Reduction and Echo Canceller Impairments*, Journal of the Audio Engineering Society.
+
+
+
+## **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        | 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        | Terminals and subjective and objective assessment methods                                                                                                 |
+| Series Q        | Switching and signalling                                                                                                                                  |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects and next-generation networks                                                                 |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |

marked/G/T-REC-G.212-198811-I_PDF-E/raw.md

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+
+
+![ITU logo](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features a globe with a lightning bolt superimposed on it, and the letters 'ITU' in a bold, sans-serif font.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**G.212**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**INTERNATIONAL ANALOGUE CARRIER SYSTEMS  
+GENERAL CHARACTERISTICS COMMON TO ALL  
+ANALOGUE CARRIER-TRANSMISSION SYSTEMS**
+
+---
+
+**HYPOTHETICAL REFERENCE CIRCUITS FOR  
+ANALOGUE SYSTEMS**
+
+**ITU-T Recommendation G.212**
+
+(Extract from the *Blue Book*)
+
+---
+
+# NOTES
+
+1 ITU-T Recommendation G.212 was published in Fascicle III.2 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## **HYPOTHETICAL REFERENCE CIRCUITS FOR ANALOGUE SYSTEMS**
+
+## **GENERAL DEFINITIONS**
+
+### **1 hypothetical reference circuit**
+
+*F: circuit fictif de référence*
+
+*S: circuito ficticio de referencia*
+
+This is a hypothetical circuit of defined length and with a specified number of terminal and intermediate equipments, this number being sufficient but not excessive. It forms a basis for the study of certain characteristics of long-distance circuits (noise, for example).
+
+### **2 hypothetical reference circuit for telephony**
+
+*F: circuit fictif de référence pour la téléphonie*
+
+*S: circuito ficticio de referencia para la telefonía*
+
+This is a complete telephone circuit (between audio-frequency terminals) established on a hypothetical international telephone carrier system and having a specified length and a specified number of modulations and demodulations of channels, groups, supergroups, these numbers being reasonably great but not having their maximum possible values. The hypothetical reference circuit has to reflect what is generally expected to be the practical application of the system.
+
+Various hypothetical reference circuits for telephony have been defined to allow the coordination of the different specifications concerning the constituent parts of the multichannel carrier telephone systems, so that the complete telephone circuits set up on these systems can meet CCITT standards.
+
+In order to take account of the variety of operating conditions and in particular the differences there may be in the size of the countries to be served, the CCITT has defined two categories of hypothetical reference circuits for telephony:
+
+- a set of hypothetical reference circuits with a length of 2500 km,
+- a hypothetical reference circuit with a length of 5000 km (see Recommendation G.215).
+
+The former includes the following hypothetical reference circuits for telephony:
+
+- on open-wire lines (see Recommendation G.311),
+- on symmetric pair cable (see Recommendation G.322),
+- on coaxial pair cable (see Recommendations G.332 to G.346 of sections 3.3 and 3.4).
+
+The 5000 km hypothetical reference circuit is used in various types of carrier systems on coaxial cable and on radio relay systems.
+
+The CCIR also has defined the following hypothetical-reference circuits for telephony:
+
+- 1) In line-of-sight radio-relay systems using frequency-division multiplex, with a capacity of 12 to 60 telephone channels or of more than 60 telephone channels (see Recommendation G.431 or CCIR Recommendations 391 [2] and 392 [3]);
+- 2) On tropospheric-scatter radio-relay systems (see CCIR Recommendation 396 [4]);
+- 3) For satellite systems (see CCIR Recommendation 352 [5]).
+
+Each of these various hypothetical reference circuits has the same total length<sup>1)</sup> and they are all used in the same way. They are only a guide for planning carrier systems.
+
+These hypothetical reference circuits allow designers to study through connection between different carrier systems at basic groups, supergroups, etc., as discussed in Recommendation G.211. Moreover, when they contain more than one pair of channel modulators and demodulators, they also allow the designers to study an international switched connection having the same total length.
+
+### 3 homogeneous section
+
+*F: section homogène*
+
+*S: sección homogénea*
+
+A section without diversion or modulation of any channel groups, supergroups, etc., established on the system which is being considered except for those modulations or demodulations defined at the ends of the section.
+
+All the hypothetical reference circuits defined above consist of homogeneous sections of equal length [6, 9 or 12 sections<sup>2)</sup> as the case may be].
+
+It is assumed that at the end of each homogeneous section, the channels, groups, supergroups, etc., are connected through at random.
+
+### 4 psophometric power
+
+*F: puissance psophométrique*
+
+*S: potencia sofométrica*
+
+Where square law addition (power addition) of noise can be assumed, it has been found convenient for calculations and design of international circuits to use the idea of psophometric power as defined below:
+
+$$\text{psophometric power} = \frac{(\text{psophometric voltage})^2}{600}$$
+
+or
+
+$$\text{psophometric power} = \frac{(\text{psophometric e.m.f.})^2}{4 \times 600}$$
+
+A convenient unit is the micro-microwatt or picowatt (pW), and this equation can then be given as follows:
+
+$$\text{psophometric power} = \frac{(\text{psophometric e.m.f. in mV})^2}{0.0024} \text{ (pW)}.$$
+
+1) With the exception of the hypothetical reference circuits for satellite systems and for circuits of 5000 km.
+
+2) The number is not specified for the tropospheric-scatter radio-relay systems.
+
+## References
+
+- [1] CCITT Recommendation *4-MHz valve-type systems on standardized 2.6/9.5-mm coaxial cable pairs*, Orange Book, Vol. III-I, Rec. G.338, ITU, Geneva, 1977.
+- [2] CCIR Recommendation *Hypothetical reference circuit for radio-relay systems for telephony using frequency-division multiplex with a capacity of 12 to 60 telephone channels*, Vol. IX, Rec. 391, Dubrovnik, 1986.
+- [3] CCIR Recommendation *Hypothetical reference circuit for radio-relay systems for telephony using frequency-division multiplex with a capacity of more than 60 telephone channels*, Vol. IX, Rec. 392, Dubrovnik, 1986.
+- [4] CCIR Recommendation *Hypothetical reference circuit for trans-horizon radio-relay systems for telephony using frequency-division multiplex*, Vol. IX, Rec. 396, Dubrovnik, 1986.
+- [5] CCIR Recommendation *Hypothetical reference circuits for telephony and television in the fixed satellite service*, Vol. IV, Rec. 352, Dubrovnik, 1986.

marked/G/T-REC-G.226-198811-I_PDF-E/raw.md

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+
+
+![ITU logo](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features the letters 'ITU' in a bold, sans-serif font, superimposed on a stylized globe with latitude and longitude lines.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**G.226**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+# **INTERNATIONAL ANALOGUE CARRIER SYSTEMS GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS** ---
+
+### **NOISE ON A REAL LINK**
+
+**ITU-T Recommendation G.226**
+
+(Extract from the *Blue Book*)
+
+---
+
+### NOTES
+
+- 1 ITU-T Recommendation G.226 was published in Fascicle III.2 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+- 2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+### **NOISE ON A REAL LINK**
+
+#### **1 Cable systems**
+
+It should be appreciated that designers are usually concerned, not with particular circuits or links, but with plant that will be used for the establishment of many links. It is not practicable for the CCITT to specify the performance of every real link that may be established, or for the designer to contemplate changing his design to suit the various lengths or other conditions on different real links. The CCITT has therefore defined hypothetical reference circuits, so that designers can be sure that, if their particular design of plant is used throughout a real circuit made up in the same way as a hypothetical reference circuit, the performance specified by the CCITT for the hypothetical reference circuit will be realized on that real circuit.
+
+A real international link usually has a different make-up from that of the hypothetical reference circuit, and often includes equipments of different design. For each of these two reasons the performance to be expected from real links cannot be deduced uniquely from the Recommendations relative to hypothetical reference circuits.
+
+However, on a real homogeneous section it must be expected that the noise power measured at the time of commissioning, and with a conventional load as defined in § 2 of Recommendation G.223, will be about the same as that calculated taking into account the particular composition of the real homogeneous section and the real parameters as well as the implications of Recommendation G.222, § 2.6. There should be no cause for anxiety unless the measured noise power exceeds the calculated power by an appreciable amount, which might indicate a fault somewhere in the equipment. In such a case, every effort should be made to reduce the measured noise power to a value of the same order as that calculated.
+
+#### **2 Radio links**
+
+See CCIR Recommendation 395 [1].
+
+## **Reference**
+
+- [1] CCIR Recommendation *Noise in the radio portion of circuits to be established over real radio-relay links for FDM telephony*, Vol. IX, Rec. 395, Dubrovnik, 1986.

marked/G/T-REC-G.233-198811-I_PDF-E/raw.md

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+
+
+![ITU logo](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features the letters 'ITU' in a bold, sans-serif font, superimposed on a stylized globe with latitude and longitude lines.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**G.233**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+# **INTERNATIONAL ANALOGUE CARRIER SYSTEMS GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER - TRANSMISSION SYSTEMS** ---
+
+## **RECOMMENDATIONS CONCERNING TRANSLATING EQUIPMENTS**
+
+**ITU-T Recommendation G.233**
+
+(Extract from the *Blue Book*)
+
+---
+
+## NOTES
+
+- 1 ITU-T Recommendation G.233 was published in Fascicle III.2 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+- 2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## RECOMMENDATIONS CONCERNING TRANSLATING EQUIPMENTS
+
+(amended at Geneva, 1964; further amended)
+
+This Recommendation concerns translating equipments with the exception of:
+
+- channel-translating equipment, in respect of which Recommendations G.232, G.234 [1] and G.235 should be consulted;
+- equipment for translation into the line-frequency band; the Recommendations relating to the various line systems should be consulted.
+
+### 1 Translating procedure
+
+The procedures whereby the translating equipments defined in Recommendation G.211 translate basic groups, supergroups and mastergroups or a basic 15-supermastergroup assembly (No. 1) are represented by the following figures:
+
+- 1) Figure 1/G.233 for group-translating equipments (procedures 1 and 2);
+- 2) Figure 2/G.233 for supergroup-translating equipments (procedure 1);
+- 3) Figure 3/G.233 for mastergroup-translating equipments (procedure 1);
+- 4) Figure 4/G.233 for supergroup-translating equipments (procedure 2);
+- 5) Figure 5/G.233 for translating equipments for basic 15-supergroup assembly (No. 1) (procedure 2).
+
+*Note* - Equipments 4 and 5 above are peculiar to procedure 2 described in Recommendation G.211. The conditions in which this procedure is used are described in that Recommendation.
+
+![Diagram showing the constitution of the basic supergroup. It illustrates five groups (Group No. 1 to 5) with their respective frequency bands and carrier frequencies. The x-axis represents frequency in kHz, ranging from 60 to 552. The y-axis shows the hierarchy of groups. Group 1 is the base group. Groups 2, 3, 4, and 5 are supergroups built on top of the base group. Carrier frequencies are indicated on the right: 420, 468, 516, 564, and 612 kHz. A note on the left refers to Recommendation G.241 for group pilot(s). A note on the right refers to Note in Figure 5/G.233 for carrier frequencies. The diagram is labeled CCITT - 45240.](9ccd03fe518c562a3fe2d3119f50935e_img.jpg)
+
+Diagram showing the constitution of the basic supergroup. It illustrates five groups (Group No. 1 to 5) with their respective frequency bands and carrier frequencies. The x-axis represents frequency in kHz, ranging from 60 to 552. The y-axis shows the hierarchy of groups. Group 1 is the base group. Groups 2, 3, 4, and 5 are supergroups built on top of the base group. Carrier frequencies are indicated on the right: 420, 468, 516, 564, and 612 kHz. A note on the left refers to Recommendation G.241 for group pilot(s). A note on the right refers to Note in Figure 5/G.233 for carrier frequencies. The diagram is labeled CCITT - 45240.
+
+FIGURE 1/G.233  
+Constitution of the basic supergroup
+
+![Diagram of the basic mastergroup (FIGURE 2/G.233) showing 5 supergroups. The x-axis represents frequency in kHz with markers at 312, 552, 812, 1052.8, 1300.8, 1556.8, 1796.8, 2044. Carrier frequencies are indicated by arrows pointing to specific points on the frequency axis: 1364, 1612, 1860, 2108, and 2356 kHz. Supergroup No. 4 is shown with its baseband from 812 to 1052.8 kHz. The diagram is labeled CCITT - 45250.](5d92d5c9cc01a262b0389d138caa9aea_img.jpg)
+
+Supergroup pilot(s)  
+(see Recommendation G.241)
+
+Carrier frequencies  
+(see Note in Figure 5/G.233)
+
+Supergroup No. 4
+
+CCITT - 45250
+
+Diagram of the basic mastergroup (FIGURE 2/G.233) showing 5 supergroups. The x-axis represents frequency in kHz with markers at 312, 552, 812, 1052.8, 1300.8, 1556.8, 1796.8, 2044. Carrier frequencies are indicated by arrows pointing to specific points on the frequency axis: 1364, 1612, 1860, 2108, and 2356 kHz. Supergroup No. 4 is shown with its baseband from 812 to 1052.8 kHz. The diagram is labeled CCITT - 45250.
+
+FIGURE 2/G.233
+
+#### **Constitution of the basic mastergroup**
+
+![Diagram of the basic supermastergroup (FIGURE 3/G.233) showing 3 mastergroups (7, 8, 9). The x-axis represents frequency in kHz with markers at 812, 2044, 8516, 9748.8, 11068.8, 12388. Carrier frequencies are indicated by arrows pointing to specific points on the frequency axis: 10560, 11096, 11880, and 13200 kHz. Mastergroup No. 7 is shown with its baseband from 8516 to 9748.8 kHz. The diagram is labeled CCITT - 45260.](f961cbef0f8217e216b553bed270315b_img.jpg)
+
+Carrier frequencies  
+(see Note in Figure 5/G.233)
+
+Mastergroup No. 7
+
+CCITT - 45260
+
+Diagram of the basic supermastergroup (FIGURE 3/G.233) showing 3 mastergroups (7, 8, 9). The x-axis represents frequency in kHz with markers at 812, 2044, 8516, 9748.8, 11068.8, 12388. Carrier frequencies are indicated by arrows pointing to specific points on the frequency axis: 10560, 11096, 11880, and 13200 kHz. Mastergroup No. 7 is shown with its baseband from 8516 to 9748.8 kHz. The diagram is labeled CCITT - 45260.
+
+FIGURE 3/G.233
+
+#### **Constitution of the basic supermastergroup**
+
+![Diagram showing the constitution of the basic 15-supergroup assembly. It plots 15 supergroups (numbered 2 to 16) against frequency in kHz. Each supergroup is represented by a horizontal line with a pilot symbol at its start. The carrier frequencies for each supergroup are indicated by arrows pointing to the right end of each line. The frequencies range from 312 kHz to 4,340 kHz.](de6e8b740c69dac308cce9edfec3eff4_img.jpg)
+
+Carrier frequencies  
+(see Note in Figure 5/G.233)
+
+Supergroup pilot(s)  
+(see Recommendation G.241)
+
+| Supergroup No. | Carrier Frequency (kHz) |
+|----------------|-------------------------|
+| 2              | 312                     |
+| 3              | 552                     |
+| 4              | 804                     |
+| 5              | 1052                    |
+| 6              | 1300                    |
+| 7              | 1552                    |
+| 8              | 1804                    |
+| 9              | 2052                    |
+| 10             | 2300                    |
+| 11             | 2548                    |
+| 12             | 2796                    |
+| 13             | 3036                    |
+| 14             | 3284                    |
+| 15             | 3532                    |
+| 16             | 3780                    |
+|                | 4,028                   |
+|                | 4,340                   |
+
+CCITT - 45270
+
+Diagram showing the constitution of the basic 15-supergroup assembly. It plots 15 supergroups (numbered 2 to 16) against frequency in kHz. Each supergroup is represented by a horizontal line with a pilot symbol at its start. The carrier frequencies for each supergroup are indicated by arrows pointing to the right end of each line. The frequencies range from 312 kHz to 4,340 kHz.
+
+FIGURE 4/G.233
+
+#### Constitution of the basic 15-supergroup assembly
+
+![Diagram showing the frequency mapping between Basic 15-supergroup assembly (No. 1) and 15-supergroup assembly (No. 3).](431b8889a0e7f676f0eef40859590349_img.jpg)
+
+The diagram illustrates the frequency mapping between two 15-supergroup assemblies. On the left, 'Basic 15-supergroup assembly (No. 1)' is shown with supergroup numbers 2 through 16, with a frequency range from 312 kHz to 4028 kHz. A specific frequency of 1552 kHz is marked. On the right, '15-supergroup assembly (No. 3)' is shown with supergroup numbers 16 down to 2, with a frequency range from 8620 kHz to 12336 kHz. A specific frequency of 11096 kHz is marked. Arrows indicate the mapping of supergroups: supergroup 2 in assembly No. 1 maps to supergroup 16 in assembly No. 3, and supergroup 16 in assembly No. 1 maps to supergroup 2 in assembly No. 3. A dashed line at the top right points to a frequency of 12648 kHz, labeled 'Carrier frequency (see Note)'. The text 'CCITT - 45281' is at the bottom right.
+
+Diagram showing the frequency mapping between Basic 15-supergroup assembly (No. 1) and 15-supergroup assembly (No. 3).
+
+FIGURE 5/G.233
+
+#### Constitution of 15-supergroup assembly No. 3
+
+*Note to Figures 1/G.233 to 5/G.233* - The virtual carrier frequencies shown in Figures 1/G.233 to 5/G.233 will normally be the frequencies actually used. However, they are all shown as virtual frequencies to allow for the possibility of using cheaper ways of constituting basic groups, supergroups, etc., in the future.
+
+### 2 Adjustment of level at basic group-frequency points
+
+When a group passes through different carrier systems, it is necessary to provide for an adjustment of level: for example, between the limits of about  $\pm 4$  dB, wherever the group passes through the basic frequency range.
+
+### 3 Relative power levels at group distribution frames and supergroup distribution frames
+
+Although the standardization of the relative power levels at group distribution frames and supergroup distribution frames would be desirable to facilitate the setting-up and maintenance of international carrier systems and routing changes of groups or supergroups from one system to another, it was not possible before the Plenary Assembly of 1972 to recommend such a standardization internationally, because of the diversity of carrier systems already in service. Table 1/G.233 shows, for information, the level used by different Administrations.
+
+The CCITT concerned itself solely with recommending preferred values for countries which have not yet fixed these values for their national networks. Accordingly:
+
+- a relative sending level of -36 dBr is recommended at group and supergroup distribution frames;
+- for reception, it is recommended that a choice be made between -23 dBr and -30 dBr;
+- the following values are recommended for the impedance:
+  - 150 ohms balanced for group distribution frames,
+  - 75 ohms unbalanced for supergroup distribution frames.
+
+TABLE 1/G.233
+
+#### **Relative power levels at the basic group and supergroup distribution frames in the carrier systems of various Administrations**
+
+| Country                                                   |          | Relative power level at group distribution frame |               | Impedance at group distribution frame    | Relative power level at supergroup distribution frame |               | Impedance at supergroup distribution frame |
+|-----------------------------------------------------------|----------|--------------------------------------------------|---------------|------------------------------------------|-------------------------------------------------------|---------------|--------------------------------------------|
+|                                                           |          | Transmit (dBr)                                   | Receive (dBr) |                                          | Transmit (dBr)                                        | Receive (dBr) |                                            |
+| Federal Republic of Germany                               |          | -36                                              | -30           | 150 ohms, balanced                       | -35                                                   | -30           | 75 ohms, unbalanced                        |
+| Australia<br>Denmark <sup>a)</sup>                        | System 1 | -36.5                                            | -30.5         | 150 ohms, symetrique                     | -35                                                   | -30.5         | id.                                        |
+|                                                           | System 2 | -42                                              | -5            | 135 ohms, balanced                       | -35                                                   | -30           | id.                                        |
+| Austria                                                   |          | -37<br>-36                                       | -8<br>-30     | 75 ohms, unbalanced<br>150 ohms balanced | -35                                                   | -30           | id.                                        |
+| Belgium                                                   |          | -37                                              | -8            | 150 ohms, balanced                       | -35                                                   | -30           | id.                                        |
+| People's Republic of Bulgaria                             |          | -36                                              | -23           | 150 ohms, balanced                       | -36                                                   | -23           | id.                                        |
+| Spain, Ireland, New Zealand, Norway, United Kingdom       |          | -37                                              | -8            | 150 ohms, unbalanced                     | -35                                                   | -30           | id.                                        |
+| USA<br>(American Telephone and Telegraph Company)         |          | -42                                              | -5            | 135 ohms, balanced                       | -25                                                   | -28           | id.                                        |
+| France                                                    |          | -33                                              | -15           | 150 ohms, balanced                       | -45                                                   | -35           | id.                                        |
+| Hungary, Italy, Netherlands                               |          | -37                                              | -30           | 150 ohms, balanced                       | -35                                                   | -30           | id.                                        |
+| India                                                     |          | -36.5                                            | -30.4         | 150 ohms, balanced                       | -34.8                                                 | -30.4         | id.                                        |
+| Japan (Nippon Telegraph and Telephone Public Corporation) |          | -36                                              | -18           | 75 ohms, balanced                        | -29                                                   | -29           | id.                                        |
+| Mexico<br>(Teléfonos de México)                           |          | -47                                              | -10           | 150 ohms, balanced                       | -47                                                   | -24           | id.                                        |
+
+TABLE 1/G.233 (continued)
+
+|                             |       |       |                     |     |     |     |
+|-----------------------------|-------|-------|---------------------|-----|-----|-----|
+| People's Republic of Poland | -36   | -23   | 150 ohms, balanced  | -36 | -23 | id. |
+| German Democratic Republic  | -36   | -23   | 150 ohms, balanced  | -36 | -23 | id. |
+| Sweden                      |       |       |                     | -35 | -30 | id. |
+| Switzerland                 | -36.5 | -30.5 | 75 ohms, unbalanced | -35 | -26 | id. |
+| USSR                        | -36   | -23   | 150 ohms, balanced  | -36 | -23 | id. |
+
+a) System 1 only.
+
+### 4 Relative power levels at mastergroup distribution frames
+
+The relative power levels at mastergroup distribution frames (see Figure 6/G.233) should be adjusted to the following values:
+
+- transmit: -36 dBr,
+- receive: -23 dBr,
+
+across a 75-ohm impedance, unbalanced to earth.
+
+![Diagram of relative levels at mastergroup distribution frame showing transmit and receive paths with power levels and equipment labels.](07b17a620c75522d53916a11e12d1bff_img.jpg)
+
+The diagram illustrates the signal flow and power levels at a mastergroup distribution frame. It is divided into two main horizontal sections: the transmit path (top) and the receive path (bottom).
+
+- Transmit Path:** On the left, a box labeled "Supergroup distribution frame" contains a symbol for a transmitter (triangle and sine wave). An arrow points from this symbol to a point on a dashed line labeled "Relative level -36 dBr". This dashed line connects to another transmitter symbol on the right, which then points to an output labeled "Line".
+- Receive Path:** On the right, a box labeled "Mastergroup translating equipment" contains a symbol for a receiver (sine wave and triangle). An arrow points from this symbol to a point on a dashed line labeled "Relative level -23 dBr". This dashed line connects back to the "Supergroup distribution frame" on the left.
+- Filter:** In the center, between the two dashed lines, is a box labeled "Through-master-group filter" containing a symbol for a filter (three squiggly lines). A label "Maximum attenuation 13 dB" is next to it.
+- Labels:** The top horizontal line is labeled "Mastergroup distribution frame". The left vertical section is bracketed and labeled "Supergroup distribution frame". The bottom left box is labeled "Supergroup translating equipment (supergroups 4 to 8)". The bottom right box is labeled "Mastergroup translating equipment" and "CCITT - 45291".
+
+Diagram of relative levels at mastergroup distribution frame showing transmit and receive paths with power levels and equipment labels.
+
+FIGURE 6/G.233
+
+#### Relative levels at mastergroup distribution frame
+
+### 5 Relative levels at supermastergroup distribution frames
+
+Relative power levels at supermastergroup distribution frames should be adjusted to the following values:
+
+- transmit: -33 dBr,
+- receive: -25 dBr,
+
+across a 75-ohm impedance, unbalanced to earth.
+
+### 6 Relative levels at the distribution frame of 15-supergroup assembly (No. 1)
+
+The relative power levels at the 15-supergroup assembly distribution frame should be adjusted to the following values:
+
+- send: -33 dBr,
+- receive: -25 or -33 dBr,
+
+across a 75-ohm impedance, unbalanced to earth.
+
+### 7 Return loss
+
+In relation to the nominal impedance, the return loss at the input and output of the translating equipment of supergroups, mastergroups, supermastergroups and 15-supergroup assemblies should not be lower than 20 dB in the wanted frequency band for both directions (send and receive) of transmission.
+
+With respect to the group translating equipment, the same limit applies at the high-frequency side; at the low-frequency side, it is also valid except in those areas in the vicinity of the group and supergroup pilots such as:
+
+- the band 103.7-104.6 kHz of group 3 when there is a stop filter for the 411.920 kHz pilot;
+- the band 63.7-64.6 kHz of group 5 when there is a stop filter for the 547.920 kHz pilot.
+
+The above limits relate to the intrinsic return loss, i.e., that obtained when the cords connecting the measuring apparatus to the equipment are as short as possible. In view of the station cabling encountered in practice, the return loss recorded at the distribution frame of groups, supergroups, etc., may differ from the intrinsic return loss. This factor should be taken into account in designing and establishing the links.
+
+### 8 Noise
+
+Recommendation G.222, § 4 gives information on the noise produced by group, supergroup, mastergroup and 15-supergroup assembly translating equipment.
+
+### 9 Interference related to supergroup reference pilot
+
+Interference from, or with, supergroup reference pilots may be avoided by taking suitable precautions in channel terminal equipments or group-translating equipment (see Recommendation G.232, § 13.2 and the Recommendation cited in [2]).
+
+#### 9.1 Pilots at 411.860 and 411.920 kHz
+
+9.1.1 For the protection of pilots at a through-connection point (see Recommendation G.243), group 3 should at the receive end of a supergroup link be through-connected without demodulation, for example to another supergroup link; the modulating equipment for group 3 should present an attenuation of at least 20 dB at the frequency of the supergroup pilot.
+
+9.1.2 Moreover, when an Administration wishes to route 8- or 12-channel groups free between one supergroup link and another with no restrictions on routing of group 3, then the group 3 modulating and group 3 demodulating equipment should each provide in all cases at least 20 dB suppression at the frequency of the supergroup reference pilot.
+
+#### 9.2 *Pilot at 547.920 kHz*
+
+If this pilot is used in a supergroup transmitting five groups (regardless of the use made of these groups) and not a wideband signal (for data, etc.) occupying most of the frequency band, the arrangements mentioned in § 9.1 above for the group 3 equipment should be adopted in the modulating and demodulating equipment of group 5.
+
+### **10 Accuracy of carrier frequencies**
+
+See Recommendation G.225, § 1).
+
+### **11 Carrier leaks**
+
+11.1 The carrier leak at the transmit side of a modulation stage should not exceed:
+
+-47 dBm0 for group modulation,
+
+-50 dBm0 for supergroup modulation,
+
+-45 dBm0 for mastergroup modulation,
+
+-50 dBm0 for supermastergroup modulation and 15-supergroup assembly modulation,
+
+-30 dBm0 for 15-supergroup assemblies Nos. 2 and 3 on 12-MHz and 60-MHz systems, and for the first modulation stage of 15-supergroup modulation on 60-MHz systems, since in this case the carrier leaks fall into bands of frequencies not used for traffic.
+
+11.2 Higher levels of carrier leaks can be tolerated at the output of a modulation stage at the receive side, provided no interference with adjacent groups, etc. occurs (e.g. by way of backward carrier leak, etc.)
+
+11.3 In the case of sound-programme transmission according to the Recommendation cited in [3] certain channel carrier leaks, pregroup carrier leaks etc. falling in adjacent groups may cause excessive interference. In order to meet Recommendation cited in [4] the level of such leaks, measured at the supergroup distribution frame or an equivalent point, should not be higher than the values indicated below:
+
+-75 dBm0 in the frequency ranges 73-82 kHz and 86-95 kHz,
+
+-55 dBm0 at 67 kHz and 101 kHz.
+
+In the frequency bands 67-73 kHz and 95-101 kHz the requirements are based on straight lines (linear frequency and dB scales) connecting the limits indicated above.
+
+*Note 1* - It is recognized that there are several possibilities of meeting this recommended limit, such as allocating the necessary attenuation wholly or partly to the channel or group translating equipment respectively, to insert special filters at the group distribution frame, or by selection of groups.
+
+*Note 2* - The above limit is applicable to the transmit side only.
+
+*Note 3* - The 7 dB margin between the Recommendation cited in [4] and § 11.3 above allows for cumulation on the group links involved.
+
+11.4 In the case of 3-kHz spaced channels, the following recommendations apply:
+
+When a baseband carries 3-kHz or a mixture of 3- and 4-kHz channels, the level of each carrier leak should not exceed the value given in Table 2/G.233 (limits apply to transmit path only).
+
+TABLE 2/G.233
+
+| Carrier leak of:                      | Group and supergroup carrying 3 kHz channels                                           | Recommended limit, dBm0 |
+|---------------------------------------|----------------------------------------------------------------------------------------|-------------------------|
+| Groups 1, 2, and 3 of any supergroup  | Same supergroup                                                                        | —60 <sup>a)</sup>       |
+| Groups 4 and 5 of supergroups 4 to 16 | Groups 1 and 2 respectively of the adjacent lower supergroup (i.e. supergroup 3 to 15) | —73 <sup>a),b)</sup>    |
+| Supergroup 1                          | Supergroup 3                                                                           | —60 <sup>a),b)</sup>    |
+| Supergroups 3 to 14                   | Group 4 of supergroups 5 to 16 respectively                                            | —73 <sup>a)</sup>       |
+
+a) Based on Recommendation G.235 relating to subgroup carrier leaks.
+
+b) Based on the assumption that the interference limit per single frequency is -73 dBm0p.
+
+The filters of the supergroup translating equipment may contribute to the suppression of the group 4 and 5 carrier leaks.
+
+Special attention is also necessary to avoid backward carrier leaks in the demodulation stage that may result in a product falling into a 3-kHz channel in either the group or supergroup demodulation stage.
+
+*Note* - No allowance has been given for cumulation. The effects of cumulation are offset at least in part by the noise masking effect of long interconnected sections that commonly accompany the use of 3-kHz channel equipments.
+
+### 12 Go-to-return crosstalk
+
+The following limits are recommended for crosstalk ratios (single frequency measurements) for group and higher order translating equipments; they will apply to both the low and high frequency sides:
+
+- group translation: 80 dB;
+- higher order translation stages: 85 dB.
+
+*Note* - On the basis of telephony considerations alone, a limit of 80 dB would have been proposed for all translation stages; this would also have sufficed to meet the recommended limit for intelligible crosstalk between programme circuits (74 dB in Recommendation J.21 [5]) in networks where programme circuits are systematically equipped with compandors. However, importance was attached to adopting a single requirement for each translation stage which would suffice for the most demanding network conditions to be encountered.
+
+### 13 Group-delay distortion
+
+#### 13.1 Group translating equipment
+
+It is recommended that the limits in Figure 7/G.233 for the group-delay distortion (relative to the value at 84 kHz) should not be exceeded by a group translating equipment consisting of a pair of group transmitting and receiving equipments. The given values are applicable to groups 2, 3 and 4 (without additional pilot stop filters). Groups 1 and 5 are excluded due to additional distortions caused by various sources (pilot stop filters, position at the end of the supergroup band, etc.); group 3 may be excluded, when the supergroup pilot 411.92 kHz or 411.86 kHz is used.
+
+*Note* - The range of measured values on modern equipments is indicated in Supplement 17 at the end of this fascicle.
+
+![Figure 7/G.233: A graph showing the group-delay distortion (ΔT) in microseconds (μs) versus frequency in kHz. The y-axis ranges from -5 to 25 μs, with major ticks at -5, 0, 10, 15, and 25. The x-axis ranges from 60 to 108 kHz, with major ticks at 60, 64, 68, 72, 84, 96, 100, 104, and 108. The graph shows a shaded region representing the allowed distortion limits. The upper limit is 25 μs from 64 to 68 kHz, then drops to 15 μs from 68 to 72 kHz, then to 10 μs from 72 to 96 kHz, then to 15 μs from 96 to 100 kHz, and finally to 25 μs from 100 to 104 kHz. The lower limit is -5 μs from 64 to 104 kHz. A small circle is marked on the x-axis at 84 kHz. The text 'CCITT - 32840' is in the bottom right corner.](252ea48d02dce93965b91746fb376f35_img.jpg)
+
+| Frequency (kHz) | Group-delay distortion (ΔT) (μs) |
+|-----------------|----------------------------------|
+| 60 - 64         | 0                                |
+| 64 - 68         | 25                               |
+| 68 - 72         | 15                               |
+| 72 - 96         | 10                               |
+| 96 - 100        | 15                               |
+| 100 - 104       | 25                               |
+| 104 - 108       | 0                                |
+
+Figure 7/G.233: A graph showing the group-delay distortion (ΔT) in microseconds (μs) versus frequency in kHz. The y-axis ranges from -5 to 25 μs, with major ticks at -5, 0, 10, 15, and 25. The x-axis ranges from 60 to 108 kHz, with major ticks at 60, 64, 68, 72, 84, 96, 100, 104, and 108. The graph shows a shaded region representing the allowed distortion limits. The upper limit is 25 μs from 64 to 68 kHz, then drops to 15 μs from 68 to 72 kHz, then to 10 μs from 72 to 96 kHz, then to 15 μs from 96 to 100 kHz, and finally to 25 μs from 100 to 104 kHz. The lower limit is -5 μs from 64 to 104 kHz. A small circle is marked on the x-axis at 84 kHz. The text 'CCITT - 32840' is in the bottom right corner.
+
+FIGURE 7/G.233
+
+#### 13.2 Supergroup translating equipment
+
+It is recommended that the limits in Figure 8/G.233 for the group-delay distortion (relative to the value at 412 kHz) should not be exceeded by a supergroup translating equipment consisting of a pair of supergroup transmitting and receiving equipments. The given values are not applicable to supergroups 1 and 3. Depending on the design of supergroup translating equipment this restriction may also apply to supergroups 6 and 7 (due to pilot protection filter).
+
+*Note* - The range of measured values on modern equipments is indicated in Supplement 17 at the end of this fascicle.
+
+![Graph of Group-delay distortion (Δτ) in μs versus Frequency in kHz. The y-axis ranges from -2 to 4.5 μs, with a zero line. The x-axis ranges from 312 to 552 kHz, with markers at 312, 352, 364, 412, 500, 512, and 552. The graph shows a shaded region representing the allowed distortion limits. The upper limit is 4.5 μs from 312 to 352 kHz, then drops to 3.5 μs from 364 to 500 kHz, and rises back to 4.5 μs from 512 to 552 kHz. The lower limit is -2 μs from 352 to 512 kHz. A small circle is marked on the zero line at 412 kHz. The text 'CCITT - 32851' is in the bottom right corner.](dd0f5301a5a6dd7c319701302110de88_img.jpg)
+
+Graph of Group-delay distortion (Δτ) in μs versus Frequency in kHz. The y-axis ranges from -2 to 4.5 μs, with a zero line. The x-axis ranges from 312 to 552 kHz, with markers at 312, 352, 364, 412, 500, 512, and 552. The graph shows a shaded region representing the allowed distortion limits. The upper limit is 4.5 μs from 312 to 352 kHz, then drops to 3.5 μs from 364 to 500 kHz, and rises back to 4.5 μs from 512 to 552 kHz. The lower limit is -2 μs from 352 to 512 kHz. A small circle is marked on the zero line at 412 kHz. The text 'CCITT - 32851' is in the bottom right corner.
+
+FIGURE 8/G.233
+
+## References
+
+- [1] CCITT Recommendation *8-channel terminal equipments*, Orange Book, Vol. III-I, Rec. G.234, ITU, Geneva, 1977.
+- [2] *Ibid.*, § f) 2.
+- [3] CCITT Recommendation *Characteristics of equipment lines used for setting up 15-kHz type sound-programme circuits*, Vol. III, Rec. J.31, § 1.
+- [4] *Ibid.*, § 2.
+- [5] CCITT Recommendation *Performance characteristics of 15-kHz type sound-programme circuits*, Vol. III, Rec. J.21.

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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 latitude and longitude lines. A lightning bolt symbol is positioned to the right of the globe.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**G.422**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**INTERNATIONAL ANALOGUE CARRIER SYSTEMS  
+GENERAL CHARACTERISTICS OF INTERNATIONAL  
+CARRIER TELEPHONE SYSTEMS ON  
+RADIO - RELAY OR SATELLITE LINKS AND  
+INTERCONNECTION WITH METALLIC LINES**
+
+---
+
+**INTERCONNECTION AT AUDIO-FREQUENCIES**
+
+**ITU-T Recommendation G.422**
+
+(Extract from the *Blue Book*)
+
+---
+
+# NOTES
+
+- 1 ITU-T Recommendation G.422 was published in Fascicle III.2 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+- 2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## Recommendation G.422
+
+# INTERCONNECTION AT AUDIO-FREQUENCIES
+
+CCIR Recommendation 268 [1] states that, as far as is practicable, radio-relay systems for telephony providing circuits which may form part of an international connection should be such that these circuits conform with the relevant CCIR Recommendations for modern types of telephone circuit in the following respects:
+
+- 1) the transmission characteristics of the circuits between audio-frequency terminals (the relevant Recommendations are contained in Section 1 of this Part);
+- 2) the characteristics of the multiplex terminal equipment, where applicable (see Recommendations G.232 and G.412);
+- 3) the method of signalling over international circuits, the relevant Recommendations are contained in Volume VI; see also the following Note:
+
+*Note* - Since the CCITT Recommendations mentioned in 2) above envisage the use of well-defined audio signalling frequencies sent over the speech path, no signal repetition problems should arise.
+
+When different signalling methods are used on a cable system and a radio-relay system, equipment will be necessary at the interconnection point to convert the two types of signalling to a common type, preferably d.c. signalling.
+
+## Reference
+
+- [1] CCIR Recommendation *Interconnection at audio frequencies of radio-relay systems for telephony*, Vol. IX, Rec. 268, Dubrovnik, 1982.

marked/G/T-REC-G.613-198811-I_PDF-E/raw.md

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+
+
+![ITU logo](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features the letters 'ITU' in a bold, sans-serif font, superimposed on a stylized globe with intersecting lines.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**G.613**
+
+# **TRANSMISSION MEDIA CHARACTERISTICS**
+
+---
+
+**CHARACTERISTICS OF SYMMETRIC CABLE  
+PAIRS USABLE WHOLLY FOR THE  
+TRANSMISSION OF DIGITAL SYSTEMS WITH  
+A BIT RATE OF UP TO 2 Mbits**
+
+**ITU-T Recommendation G.613**
+
+(Extract from the *Blue Book*)
+
+---
+
+## NOTES
+
+- 1 ITU-T Recommendation G.613 was published in Fascicle III.3 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+- 2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## **CHARACTERISTICS OF SYMMETRIC CABLE PAIRS USABLE WHOLLY FOR THE TRANSMISSION OF DIGITAL SYSTEMS WITH A BIT RATE OF UP TO 2 Mbits**
+
+*(Malaga-Torremolinos, 1984)*
+
+## **1 Preamble**
+
+This Recommendation deals with cables designed for the transmission of standard digital systems (Recommendations of the G.900 series), although these cables can also be used to transmit digital signals with a lower bit rate and voice frequency signals. The cables described carry signals in both transmission directions simultaneously. The provisions of this Recommendation apply to cables designed to allow for digital operation of all the cable circuits. However, some of the provisions may be used to assess the possibility of (partial or full) digital operation of existing cables.
+
+## **2 Parameters to be measured**
+
+### **2.1 Direct current resistance**
+
+The following formula is used to correct the value  $R_t$  of direct current resistance measured at  $t^\circ\text{C}$  for  $20^\circ\text{C}$ :
+
+$$R_{20} = R_t / (1 + 0.004 (t - 20))$$
+
+### **2.2 Capacitance per unit length**
+
+This is measured at 800 Hz or 1000Hz.
+
+### **2.3 Attenuation coefficient**
+
+The value of the attenuation coefficient is obtained either by direct measurement of the attenuation or by calculation on the basis of the mutual capacitance and direct current resistance of the pair. The attenuation coefficient is measured at one frequency only,  $f_0$ , near the timing half-frequency.
+
+| System      | Recommendation | $f_0$   |
+|-------------|----------------|---------|
+| 1544 kbit/s | G.951          | 772 kHz |
+| 2048 kbit/s | G.952          | 1 MHz   |
+
+For cables with polyolefin insulation, the value of the attenuation coefficient at frequency  $f$  (for values of  $f$  above with a few hundred kHz) can be related to  $\alpha_0$  by the equation  $\alpha_f = \alpha_0 \sqrt{\frac{f}{f_0}}$ .
+
+The value of the attenuation coefficient measured at  $t^\circ\text{C}$  is corrected for  $20^\circ\text{C}$  by the equation:
+
+$$\alpha_{20} = \alpha_t / (1 + 0.002 (t - 20))$$
+
+### 2.4 Characteristic impedance
+
+#### 2.4.1 Echometric measurement
+
+When a pulse echometer is used, the impedance of the pair measured must be compensated by a calibrated balancing network which can be set in steps of about 0.5 Ω. Pulse duration will be equal to or less than 500 ns. With this method, which is both fast and simple, the value of the end impedance of the pair measured is read off directly on the scale of the balancing network.
+
+#### 2.4.2 Sinusoidal measurement
+
+In this case, the pair tested will be terminated across an impedance, which is constantly equal to that measured by the bridge, unless it is long enough for the result of the measurement to be independent of end impedance (as for elementary cable sections).
+
+### 2.5 Crosstalk
+
+Crosstalk can be measured sinusoidally or digitally. The assignment of pairs to the direction of transmission depends on the structure and type of manufacture of the cable.
+
+#### 2.5.1 Sinusoidal measurement
+
+##### 2.5.1.1 Far-end crosstalk
+
+The measurements are made between pairs assigned to the same direction of transmission, at frequency  $f_0$ . If the frequency at which measurement is carried out is not the timing half-frequency, the value is corrected using the  $20 \log_{10} f$  law. When the measurement is carried out on a pair of length,  $L$ , which is different from the specified reference length  $L_0$ , the measured value is corrected using  $\sqrt{L/L_0}$  when the value is expressed in mV or  $10 \log_{10} \frac{L}{L_0}$  when the value is expressed in dB.
+
+##### 2.5.1.2 Near-end crosstalk
+
+The measurements are made between pairs assigned to transmission in opposite directions at a frequency near the system's timing half-frequency.
+
+#### 2.5.2 Digital measurement
+
+By means of digital measurement, it is possible to estimate the total noise on an elementary section, taking account of both near-end and far-end crosstalk. This estimate can be made on the basis of separate near-end and far-end crosstalk measurements on either factory lengths or elementary sections.<sup>1)</sup> These measurements can be made either in factory conditions or on installed cables.
+
+##### 2.5.2.1 Far-end crosstalk
+
+The measurements are carried out between pairs assigned to the same direction of transmission. When the measurement is carried out on a pair of length,  $L$ , which is different from the specified reference length  $L_0$ , the measured value is corrected using  $\sqrt{L/L_0}$  when the value is expressed in mV or  $10 \log_{10} (L/L_0)$  when the value is expressed in dB.
+
+##### 2.5.2.2 Near-end crosstalk
+
+The measurements are made between pairs *assigned* to transmission in opposite directions.
+
+## 3 Circuit characteristics
+
+These are given in Table 1/G.613.
+
+---
+
+1) One advantage of digital measurements is that it is possible to make a direct overall measurement of the total noise on an elementary section if enough generators are available.
+
+## 4 Characteristics of connected cable sections
+
+These are given in Table 2/G.613.
+
+TABLE 1/G.613  
+Circuit characteristics \*
+
+| Characteristics                                                   |               | Type of cable |          |                       |                  |          |  |
+|-------------------------------------------------------------------|---------------|---------------|----------|-----------------------|------------------|----------|--|
+|                                                                   |               | Type I        | Type II  | Type II<br><i>bis</i> | Type III<br>**** | f)       |  |
+| Operational bit rate (kbit/s)                                     |               | 2048          | 2048     | 2048                  | 2048             |          |  |
+| Repeaters gain **                                                 |               | 34 dB         |          |                       |                  |          |  |
+| Elements constituting the cable                                   |               | star quad     | pairs    | pairs                 | pairs            |          |  |
+| Nominal conductor diameter (mm)                                   |               | 0.8           | 0.7      | 1                     | 0.6              |          |  |
+| Nominal impedance *** at $f_0$ MHz (Ω)                            | 1 MHz         | 100           | 130      | 130                   |                  |          |  |
+|                                                                   | 772 kHz       |               |          |                       |                  |          |  |
+| Nominal attenuation coefficient at $f_0$ and at 20° C *** (dB/km) | 1 MHz         | 16            | 11.5 b)  | 8.5 b)                | 15.5             |          |  |
+|                                                                   | 772 kHz       |               |          |                       |                  |          |  |
+| Crosstalk in digital operation                                    |               | a)            | c)       | -                     | -                | -        |  |
+| Total noise voltage (maximum value)                               |               | a)            |          |                       |                  |          |  |
+| Minimum near-end crosstalk (mV)                                   | a)            | -             | 60 d, g) | 60 d, g)              |                  |          |  |
+|                                                                   | a)            |               |          |                       |                  |          |  |
+| Minimum far-end crosstalk (mV)                                    | a)            | -             | 45 e, g) | 45 e, g)              |                  |          |  |
+|                                                                   | a)            |               |          |                       |                  |          |  |
+| Sinusoidal crosstalk                                              | Near-end (dB) | 1 MHz         |          |                       |                  | 78 ± 3h) |  |
+|                                                                   |               | 772 kHz       |          |                       |                  |          |  |
+|                                                                   | Far-end (dB)  | 1 MHz         |          |                       |                  | 64 ± 3h) |  |
+|                                                                   |               | 772 kHz       |          |                       |                  |          |  |
+| Nominal direct current resistance at 20°C (Ω/km)                  |               |               | 68.6     | 94.1 b)               | 46.1 b)          | 63       |  |
+| Nominal mutual capacitance (nF/km)                                |               |               | 50       | 39                    | 39               | 44       |  |
+
+### Notes of Table 1/G.613
+
+- \* At the present stage the values are given for information.
+  - \*\* Reference value for the numerical data of the cable in question.
+  - \*\*\* A standard deviation or margins will be given at a later stage.
+  - \*\*\*\* Cable with diametral screen separating the pairs assigned to the two directions of transmission.
+- a) To be specified.
+  - b) Maximum value.
+  - c) The specification value for factory controls is calculated to ensure compliance with the characteristics of connected cable.
+  - d) Between pairs of different groups.
+  - e) Between pairs belonging to one and the same group.
+  - f) Other columns will contain the data supplied by administrations.
+  - g) Values given in dB.
+  - h) The value given here depends on the content of the cable. It is the rounded-down mean of a standard deviation of the total production and is therefore not a specification for individual cable lengths.
+
+TABLE 2/G.613
+
+### **Characteristics of connected cable sections \***
+
+| Characteristics                                              |                     | Type of cable |         |             |          |    |
+|--------------------------------------------------------------|---------------------|---------------|---------|-------------|----------|----|
+|                                                              |                     | Type I        | Type II | Type II bis | Type III | a) |
+| Operational bit rate (kbit/s)                                |                     | 2048          | 2048    | 2048        |          |    |
+| Nominal impedance at $f_0$ MHz ( $\Omega$ )                  | 1 MHz               | 100           | 130     | 130         |          |    |
+|                                                              | 772 kHz             |               |         |             |          |    |
+| Nominal attenuation coefficient at $f_0$ and at 20°C (dB/km) | 1 MHz               | 16            | 11.5    | 8.5         |          |    |
+|                                                              | 772 KHz             |               |         |             |          |    |
+| Crosstalk in digital operation                               | b)                  | 40 mV         |         |             |          |    |
+| Total noise voltage (maximum value)                          | b)                  |               |         |             |          |    |
+| Minimum near-end crosstalk (mV)                              | b)                  |               |         |             |          |    |
+|                                                              | b)                  |               |         |             |          |    |
+| Minimum far-end crosstalk (mV)                               | b)                  |               |         |             |          |    |
+|                                                              | b)                  |               |         |             |          |    |
+| Sinusoidal crosstalk                                         | Near-end (dB) 1 MHz |               |         |             |          |    |
+|                                                              | 772 MHz             |               |         |             |          |    |
+|                                                              | Far-end (dB) 1 MHz  |               |         |             |          |    |
+|                                                              | 772 MHz             |               |         |             |          |    |
+
+- \* At the present stage the values are given for information.
+- a) Other columns will contain the data supplied by Administrations.
+- b) To be specified.