1、 INTERNATIONAL TELECOMMUNICATION UNION G.109TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (09/99) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS International telephone connections and circuits General definitions Definition of categories of speech transmission quality ITU-
2、T Recommendation G.109 (Previously CCITT Recommendation) ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS For further details, please refer to ITU-T List of Recommendations.INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 General definitions G.10
3、0G.109 General Recommendations on the transmission quality for an entire international telephone connection G.110G.119 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
4、 national extension circuits G.130G.139 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 cir
5、cuits G.160G.169 Transmission plan aspects of special circuits and connections using the international telephone connection network G.170G.179 Protection and restoration of transmission systems G.180G.189 Software tools for transmission systems G.190G.199 INTERNATIONAL ANALOGUE CARRIER SYSTEM GENERA
6、L CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION
7、 WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TESTING EQUIPMENTS TRANSMISSION MEDIA CHARACTERISTICS G.600G.699 DIGITAL TRANSMISSION SYSTEMS TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 Re
8、commendation G.109 (09/99) i ITU-T RECOMMENDATION G.109 DEFINITION OF CATEGORIES OF SPEECH TRANSMISSION QUALITY Summary This Recommendation defines five categories of end-to-end speech transmission quality for 3.1 kHz handset telephony. These categories are defined as ranges of speech transmission q
9、uality in terms of “user satisfaction“, tied to the ratings given by the transmission planning tool of Recommendation G.107 which takes into account the combined effects of various transmission impairments. The definitions provided here are independent of any specific technology that may be used in
10、different types of network scenarios under consideration. Source ITU-T Recommendation G.109 was prepared by ITU-T Study Group 12 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on 30 September 1999. Keywords E-Model, speech transmission quality, user satisfaction, voice qualit
11、y. ii Recommendation G.109 (09/99) FOREWORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technic
12、al, 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,
13、in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a coll
14、aborative basis with ISO and IEC. NOTE In this Recommendation the term recognized operating agency (ROA) includes any individual, company, corporation or governmental organization that operates a public correspondence service. The terms Administration, ROA and public correspondence are defined in th
15、e Constitution of the ITU (Geneva, 1992). INTELLECTUAL PROPERTY RIGHTS The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or ap
16、plicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, the ITU had not received notice of intellectual property, protected by patents, which may be required t
17、o 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. Ge3 ITU 2000 All rights reserved. No part of this publication may be reproduced or utilized in any form or by a
18、ny means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. Recommendation G.109 (09/99) iii CONTENTS Page 1 Scope. 1 2 References. 1 3 Abbreviations 1 4 Key parameters affecting speech transmission quality . 2 5 Definition of categories of s
19、peech transmission quality . 2 6 Examples of speech transmission quality provided in typical scenarios 3 7 Qualifications to the definitions provided in this Recommendation 4 8 Guidance for detailed transmission planning 4 iv Recommendation G.109 (09/99) Introduction A general trend that has taken p
20、lace over many decades is that end-to-end speech transmission quality in telecommunications networks has improved because of technological advances in terminal and network equipment, especially the deployment of digital technologies. In particular, digital long-haul facilities have allowed the trans
21、mission quality of very long distance calls to approach that of local calls, provided that excessive delay and echo are controlled. In recent years, however, various new access and transport technologies have been used with these digital transport facilities to deliver new capabilities (e.g. wireles
22、s access and packet-based transport) to users and service providers, that can introduce substantial degradation to the speech transmission quality of telecommunication services, as well as other quality-of-service aspects. These new access and transport technologies may present the possibility for u
23、sers and service providers to choose trade-offs between the new capabilities and the resulting speech transmission quality. While each user, service provider and/or Administration must make these trade-offs for themselves, a definition of categories of speech transmission quality is needed to provid
24、e a consistent basis for comparisons. This Recommendation defines five categories of speech transmission quality that can be used as guidance in establishing different speech transmission quality levels in telecommunications networks. Recommendation G.109 (09/99) 1 Recommendation G.109 DEFINITION OF
25、 CATEGORIES OF SPEECH TRANSMISSION QUALITY (Geneva, 1999) 1 Scope This Recommendation defines five categories of speech transmission quality from mouth to ear for 3.1 kHz handset telephony across networks in terms of “user satisfaction“, tied to the ratings given by the transmission planning tool of
26、 Recommendation G.107 for the combined effects of various transmission impairments. The definitions provided here are independent of any specific technology that may be used in different types of network scenarios under consideration. 2 References The following ITU-T Recommendations and other refere
27、nces 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 i
28、nvestigate 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. ITU-T Recommendation G.107 (1998), The E-model, a computational model for use in transmission planning.
29、 ITU-T Recommendation G.108 (1999), Application of the E-Model A planning guide. ITU-T Recommendation G.113 (1996), Transmission impairments. ITU-T Recommendation G.114 (1996), One-way transmission time. ITU-T Recommendation G.131 (1996), Control of talker echo. ITU-T Recommendation G.175 (1997), Tr
30、ansmission planning for private/public network interconnection of voice traffic. ITU-T Recommendation P.11 (1993), Effect of transmission impairments. ITU-T Recommendation P.311 (1998), Transmission characteristics for wideband (150-7000 Hz) digital handset telephones. ITU-T Recommendation P.341 (19
31、98), Transmission characteristics for wideband (150-7000 Hz) digital hands-free telephony terminals. 3 Abbreviations This Recommendation uses the following abbreviations: ECD Echo Control Device ISDN Integrated Services Digital Network PSTN Public Switched Telephone Network 2 Recommendation G.109 (0
32、9/99) 4 Key parameters affecting speech transmission quality Speech transmission quality is an important aspect of quality-of-service for many user applications of many telecommunications services. Recommendation P.11 identifies the key speech quality parameters and gives the subjective effects of v
33、ariations in the parameters. Examples of speech quality parameters are speech level, attenuation distortion, transmission delay, echo path loss and delay, circuit noise, background noise, nonlinear distortion (such as the effects of low bit-rate speech codecs, packet loss, etc) and terminal characte
34、ristics. The G.100 series of Recommendations provides transmission planning guidance, and in particular, Recommendations G.113, G.114 and G.131 provide planning guidance on transmission impairments, delay and echo, respectively. Additionally, Recommendation G.107 provides a practical planning tool f
35、or modelling the speech transmission quality from mouth to ear for 3.1 kHz handset telephony that results from combinations of many of these impairments. While it is strongly recommended that users, Administrations, equipment designers and network planners all refer to these Recommendations for pert
36、inent detail, the following information is provided as summary guidance on the different categories of speech quality, for use in the general assessment of the impact of various technology choices on end-to-end speech transmission quality. 5 Definition of categories of speech transmission quality Wh
37、ile the parameters mentioned above describe the individual factors affecting speech transmission quality, it is the combined effect of all parameters together which leads to the overall level of speech transmission quality as perceived by the user. For transmission planning purposes, the E-model (G.
38、107) is a useful tool for assessing the combined effect of all parameters and hence differentiating between categories of speech transmission quality. The primary output of the E-model is the Transmission Rating Factor, R. Table 1 gives the definitions of the categories of speech transmission qualit
39、y in terms of ranges of Transmission Rating Factor R provided by Recommendation G.107. Also provided are descriptions of “User satisfaction“ for each category. Table 1/G.109 Definition of categories of speech transmission quality R-value range Speech transmission quality category User satisfaction 9
40、0 R 100 Best Very satisfied 80 R 90 High Satisfied 70 R 80 Medium Some users dissatisfied 60 R 70 Low Many users dissatisfied 50 R 60 Poor Nearly all users dissatisfied NOTE 1 Connections with R-values below 50 are not recommended. NOTE 2 Although the trend in transmission planning is to use R-value
41、s, equations to convert R-values into other metrics e.g. MOS, %GoB, %PoW, can be found in Annex B/G.107. Recommendation G.109 (09/99) 3 It is very important to fully understand the principle recommended in this Recommendation. The R-value is a measure of a quality perception to be expected by the av
42、erage user when communicating via the connection under consideration: quality is a subjective judgement such that assignments cannot be made to an exact boundary between different ranges of the whole quality scale. Rather, the quantitative terms should be viewed as a continuum of perceived speech tr
43、ansmission quality varying from high quality through medium values to a low quality as illustrated in Figure 1. 5060708090100T1211030-99linear quality scalehigh qualitymediumqualitylow qualityArea notrecommendedOverallRating “R“Figure 1/G.109 Judgement of a connection on a linear quality scale 6 Exa
44、mples of speech transmission quality provided in typical scenarios To provide a practical context for the categories defined above, Table 2 gives estimates of R-values for a number of service/network scenarios. In these examples, specific parameter values follow the default values of Table 3/G.107,
45、except as noted in column 2 of Table 2. Table 2/G.109 Examples of speech transmission quality provided in typical scenarios Service/network scenario R-value Deviations from Table 3/G.107 ISDN subscriber to ISDN subscriber, local connection 94 Note 1 Analogue PSTN subscriber to analogue PSTN subscrib
46、er, 20 ms delay (average echo path losses; no active echo control) 82 Note 2 Mobile subscriber to analogue PSTN subscriber as perceived at mobile side 72 Note 3 Mobile subscriber to analogue PSTN subscriber as perceived at PSTN side 64 Note 4 Voice over IP connection using G.729A + VAD with 2% packe
47、t loss 55 Note 5 NOTE 1 No deviations. NOTE 2 TELR = 35 dB, WEPL = 50 dB, T = 20 ms, Tr = 40 ms, Ta = 20 ms. NOTE 3 TELR = 68 dB, WEPL = 101 dB (EC with ERLE = 33 dB assumed), T = 110 ms, Tr = 220 ms, Ta = 110 ms, Ie = 20. NOTE 4 TELR = 53 dB, WEPL = 101 dB (EC with ERLE = 33 dB assumed), T = 110 ms
48、, Tr = 220 ms, Ta = 110 ms, Ie = 20. NOTE 5 T = 300 ms, Tr = 600 ms, Ta = 300 ms, Ie = 19. 4 Recommendation G.109 (09/99) 7 Qualifications to the definitions provided in this Recommendation It should be noted that the E-model captures the effects of many of the key transmission parameters, but there
49、 are impairments that the current model of Recommendation G.107 does not directly capture: for example, echo canceller behaviour under double-talk conditions; syllabic clipping caused by the use of voice activity detectors; comfort noise; etc. Additionally, it should be emphasized that while the guidance of this Recommendation applies to 3.1 kHz handset telephony; other audio categories with better quality are possible, such as wideband (150-7000 Hz bandwidth) telephony, for which terminal specifications exist (Rec
