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ITU-T RECOMMENDATION G107

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ITU-T RECOMMENDATION G107

INTERNATIONAL TELECOMMUNICATION UNION

ITU-T G.107

    (05/2000) TELECOMMUNICATION

    STANDARDIZATION SECTOR

    OF ITU

    SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS

    International telephone connections and circuits General definitions

     The E-model, a computational model for use in

    transmission planning

ITU-T Recommendation G.107

    (Formerly CCITT Recommendation)

    ITU-T G-SERIES RECOMMENDATIONS

    TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS

    INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 General definitions G.100G.109 General Recommendations on the transmission quality for an entire international telephone G.110G.119 connection

    General characteristics of national systems forming part of international connections G.120G.129 General characteristics of the 4-wire chain formed by the international circuits and national G.130G.139 extension circuits

    General characteristics of the 4-wire chain of international circuits; international transit G.140G.149 General characteristics of international telephone circuits and national extension circuits G.150G.159 Apparatus associated with long-distance telephone circuits G.160G.169 Transmission plan aspects of special circuits and connections using the international telephone G.170G.179 connection network

    Protection and restoration of transmission systems G.180G.189 Software tools for transmission systems G.190G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-G.200G.299 TRANSMISSION SYSTEMS

    INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE G.300G.399 SYSTEMS ON METALLIC LINES

    GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE G.400G.449 SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES

    COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999

For further details, please refer to the list of ITU-T Recommendations.

ITU-T Recommendation G.107

    The E-model, a computational model for use in transmission planning

Summary

    This ITU-T Recommendation 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.

    This revision provides an enhanced version of the E-model to better take into account the effects of room noise at the send side, and quantizing distortion.

Source

    ITU-T Recommendation G.107 was revised by ITU-T Study Group 12 (1997-2000) and approved

    under the WTSC Resolution 1 procedure on 18 May 2000.

     ITU-T G.107 (05/2000) i

    FOREWORD

    The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. 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 Conference (WTSC), 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 WTSC 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.

    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, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database.

    ? ITU 2001

    All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. ii ITU-T G.107 (05/2000)

    CONTENTS

     Page

    1 General ................................................................................................................... 1

    1.1 Scope ...................................................................................................................... 1

    1.2 References .............................................................................................................. 1

    2 The E-model, a computational model for use in transmission planning .................... 2 2.1 Introduction ............................................................................................................ 2

    2.2 Source code ............................................................................................................ 2

    3 The structure and basic algorithms of the E-model .................................................. 2 3.1 Calculation of the transmission rating factor, R ....................................................... 3

    3.2 Basic signal-to-noise ratio, Ro ................................................................................. 4 3.3 Simultaneous impairment factor, Is ......................................................................... 4 3.4 Delay impairment factor, Id .................................................................................... 5 3.5 Equipment impairment factor, Ie ............................................................................. 7 3.6 Advantage factor, A................................................................................................. 7 3.7 Default values ......................................................................................................... 7

    Annex A Conditions of using the E-model ........................................................................ 8 Annex B Quality measures derived from the transmission rating factor R ......................... 10

    Annex C Source code for G.107_2 in BASIC ................................................................... 12 Appendix I Bibliography .................................................................................................. 16

     ITU-T G.107 (05/2000) iii

ITU-T Recommendation G.107

    The E-model, a computational model for use in transmission planning

    1 General

    1.1 Scope

    This ITU-T 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

    1several transmission parameters that affect conversational 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). Accordingly, the model described here is intended to be used to do relative comparisons of transmission conditions.

    This revision provides an enhanced version of the E-model to better take into account the effects of room noise at the send side, and quantizing distortion. Because of this users should be aware that the computational algorithm has changed slightly see Annex C.

    The E-model has not been fully verified by field surveys or laboratory tests for the very large number of possible combinations of input parameters. For many combinations of high importance to transmission planners, the E-model can be used with confidence, but for other parameter combinations, E-model predictions have been questioned and are currently under study. Accordingly, caution must be exercised when using the E-model for some conditions; for example, the E-model may give inaccurate results for combinations of certain types of impairments. Annex A provides further information in this regard.

    1.2 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; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published.

    [1] ITU-T Recommendation G.100 (1993), Definitions used in Recommendations on general

    characteristics of international telephone connections and circuits.

    [2] ITU-T Recommendation G.108 (1999), Application of the E-model: A planning guide.

    [3] ITU-T Recommendation G.109 (1999), Definition of categories of speech transmission

    quality.

    [4] ITU-T Recommendation G.113 (1996), Transmission impairments.

    ____________________

    1 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 ITU-T Recommendation is not intended to model transmission impairments during double talk situations.

     ITU-T G.107 (05/2000) 1

[5] Recommendation G.113 Appendix I (1999), Transmission impairments Appendix I:

    Provisional planning values for the equipment impairment factor Ie.

    2 The E-model, a computational model for use in transmission planning

    2.1 Introduction

    The complexity of modern networks requires that for transmission planning the many transmission parameters are not only considered individually but also that their combination effects are 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 Recommendation G.113 [4] gives guidance about specific impairments, including combinations effects based upon a simplification of the model. However, the output can also give nominal estimates of user reactions, for instance in the form of percentages finding the modelled connection "Good or Better" or "Poor or Worse", as described in Annex B. Furthermore, detailed guidance on the proper application of the E-model as described in this ITU-T Recommendation is provided in

    ITU-T Recommendation G.108 [2]. In addition, the definition of categories of speech transmission quality can be found in ITU-T Recommendation G.109 [3].

    2.2 Source code

    Annex C contains the source code in BASIC of the E-model described in this ITU-T Recommendation. The purpose of this code is to ensure that users of the E-model are using consistent implementations of the formulae.

    3 The 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 in 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.

    2 ITU-T G.107 (05/2000)

    Connection

    quality as Receive sideperceived at Send sidereceive side

    OLR

    RLRSLR

    0 dBr point

    Weighted Echo -FactorDs-FactorDrPath Loss WEPL

    RoomRoomRound-TripNoise PsNoise PrDelay Tr

    Sidetone Masking

    Rating STMR

    Circuit Noise Nc Listener Sidetonereferred to 0 dBrRating LSTR= + (LSTR STMR Dr)Mean one-way Delay T

    Absolute Delay Ta

    Talker EchoQuantizing Distortion qduLoudness RatingEquipment Impairment Factor IeTELRExpectation Factor A

    T1208390-96

    Figure 1/G.107 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 send side and receive side and may be of different amount. The parameters SLR, RLR and circuit noise Nc are referred to a defined 0 dBr point. All other input parameters are either considered as values for the overall connection such as OLR (in any case the sum of SLR and RLR), number of qdu, equipment impairment factors Ie and advantage factor A, or referred only to the receive side, such as STMR,

    LSTR, WEPL (for calculation of Listener Echo) and TELR.

    There are three different parameters associated with transmission time. The absolute delay Ta

    represents the total one-way delay between send side and receive side and is used to estimate the impairment due to too-long 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.

    3.1 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 Bibliography, Supplement 3 to P-series]:

    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:

     (1) RRoIsIdIeA

     ITU-T G.107 (05/2000) 3

Ro represents in principle the basic signal-to-noise ratio, including noise sources such as circuit noise

    and room noise. The 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 equipment impairment factor Ie represents impairments caused by low bit rate codecs. The advantage factor A allows for compensation of impairment factors when there are other advantages of access to the user. The term Ro and the Is and Id values are subdivided into further specific impairment values. The following subclauses give the formulae used in the E-model. 3.2 Basic signal-to-noise ratio, Ro

    The basic signal-to-noise ratio Ro is defined by:

    ;?Ro151.5SLRNo (2)

    The term No [in dBm0p] is the power addition of different noise sources:

    NcNosNorNfo??

    ?10101010No10lg10101010 (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:

    2 (4) ;?NosPsSLRDs1000.004PsOLRDs14

    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.

    2 (5) NorRLR121Pre0.008(Pre35)

    The term Pre [in dBm0p] is the "effective room noise" caused by the enhancement of Pr by the

    listener's sidetone path:

    (10LSTR)??

    10?PrePr10lg110 (6) ?

    ??

    Nfo [in dBm0p] represents the "noise floor" at the receive side,

    NfoNforRLR (7)

    with Nfor usually set to 64 dBmp.

    3.3 Simultaneous impairment factor, Is

    The factor Is is the sum of all impairments which may occur more or less simultaneously with the voice transmission. The factor Is is divided into three further specific impairment factors:

    IsIolrIstIq (8)

    Iolr represents the decrease in quality caused by too-low values of OLR and is given by:

    1??8?8?XX????Iolr201 ? (9) (??88)?????????

    4 ITU-T G.107 (05/2000)

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