1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.1010 (I 1/2001) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Quality of service and performance - End-user multimedia QoS categories ITU-T Recommendation G. 1 O1 O INTERNATIONAL TE
2、LECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.1010 (I 1/2001) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Quality of service and performance End-user multimedia QoS categories ITU-T Recommendation G. 1 O1 O ITU-T G-SERIES RECOMMENDATIONS TRA
3、NSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS TRANSMISSION SYSTEMS INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES GENERAL CHARACTERISTICS OF INTERNATIONAL CARRER TELEPHONE METALLIC LINES COORDINATiO
4、N OF RADIOTELEPHONY AND LINE TELEPHONY TESTING EQUIPMENTS TRANSMISSION MEDIA CHARACTERISTICS DIGITAL TERMINAL EQUIPMENTS DIGITAL NETWORKS DIGITAL SECTIONS AND DIGITAL LINE SYSTEM GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRER- SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH
5、 UALITFOF SERVICE AND PERFMAc II TRANSMISSION MEDIA CHARACTERISCTICS G. 100-G. 199 G.200-G.299 G.300-G.399 G.400-G.449 G.450-G.499 G.500-G.599 G.600-G. 699 G.700-G.799 G.800-G. 899 G.900-G.999 /I DIGITAL TERMINAL EQUIPMENTS G.7000-G.7999 I For further details, please refer to the list of ITU-T Recom
6、mendations. ITU-T Recommendation G.1010 End-user multimedia QoS categories Summary This Recommendation defines a model for multimedia Quality of Service (QoS) categories fiom an end-user viewpoint. By considering user expectations for a range of multimedia applications, eight distinct categories are
7、 identified, based on tolerance to information loss and delay. It is intended that these categories form the basis for defining realistic QoS classes for underlying transport networks, and associated QoS control mechanisms. Source ITU-T Recommendation G. 10 1 O was prepared by ITU-T Study Group 12 (
8、200 1-2004) and approved under the WTSA Resolution 1 procedure on 29 November 200 1. ITU-T Rec. 6.1010 (11/2001) i FOREWORD The International Telecommunication Union (IT) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (IT
9、U-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
10、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 IT-Ts purview, the ne
11、cessary standards are prepared on a collaborative basis with IS0 and EC. 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 IT draws attention to the
12、possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Propem Right. IT takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the
13、 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 infor
14、mation and are therefore strongly urged to consult the TSB patent database. o ITU 2002 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. G.lO1O (11/2001) 11 CONTENTS 1 2 3 4 4.1 4.2 4.3 5 5.1 5.2 5.3 5
15、.4 6 Scope References User-driven performance requirements Delay . Delay variation . Information loss Key parameters impacting the user Performance considerations for different applications . Audio 5.1.1 Conversational voice . 5.1.2 Voice messaging . 5.1.3 Streaming audio . Video 5.2.1 Videophone .
16、5.2.2 One-way video 5.3.1 Web-browsing . High-priority transaction services (E-commerce) . Data . 5.3.2 Bulk data . 5.3.3 5.3.4 Commandcontrol 5.3.5 Still image . 5.3.6 Interactive games . 5.3.8 E-mail (server access) . 5.3.9 Instant messaging Background applications Low priority transaction service
17、s 5.3.7 Telnet . 5.4.1 Fax . 5.4.2 5.4.3 Email (server-to-server) 5.4.4 Usenet Classification of performance requirements into end-user Quality of Service categories Appendix I . Performance targets . Appendix II . Bibliography . Page 1 1 1 2 2 2 2 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 8 10 . IT
18、U-T Rec . 6.1010 (11/2001) 111 ITU-T Recommendation 6.1010 End-user multimedia QoS categories 1 Scope The intent of this Recommendation is to provide guidance on the key factors that influence Quality of Service (QoS) from the perspective of the end-user. By considering a range of applications invol
19、ving the media of voice, video, image and text, and the parameters that govern end-user satisfaction for these applications, a broad classification of end-user QoS categories is determined. It is intended that these categories be used as the basis for deriving realistic QoS classes and associated Qo
20、S control mechanisms for the underlying transport networks. 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. Al
21、l 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 re
22、gularly published. NOTE - The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 11 ITU-T Recommendation F.700 (2000), Framework Recommendation for multimedia services. 2 3 4 ITU-T Recommendation G. 13 1 (1 996), Control of
23、 talker echo. ITU-T Recommendation G. 114 (2000), One-way transmission time. ETSI TS 1 O 1329-2 (ZOOZ), Telecommunications and Internet Protocol Harmonization Over Networks (TIPHON) Release 3; End-to-end Quality of Service in TIPHON Systems; Part 2: DeJinition of speech Qualiy of Service (QoS) class
24、es. 3 User-driven performance requirements A major challenge for emerging wireline and wireless IP-based networks is to provide adequate Quality of Service (QoS) for different services. To do this requires a detailed knowledge of the performance requirements for particular services and applications.
25、 The starting point for deriving these performance requirements must be the user. A typical user is not concerned with how a particular service is implemented. However, the user is interested in comparing the same service offered by different providers in terms of universal, user- oriented performan
26、ce parameters. This implies that performance should be expressed by parameters that: o Take into account all aspects of the service from the users point of view; Focus on user-perceivable effects, rather than their causes within the network; Are independent of the specific network architecture or te
27、chnology; Can be objectively or subjectively measured at the service access point; Can be easily related to network performance parameters; o o o o ITU-T Rec. G.lO1O (11/2001) 1 0 Can be assured to a user by the service providers(s). 4 Key parameters impacting the user 4.1 Delay Delay manifests itse
28、lf in a number of ways, including the time taken to establish a particular service om the initial user request and the time to receive specific information once the service is established. Delay has a very direct impact on user satisfaction depending on the application, and includes delays in the te
29、rminal, network, and any servers. Note that from a user point of view, delay also takes into account the effect of other network parameters such as throughput. 4.2 Delay variation Delay variation is generally included as a performance parameter since it is very important at the transport layer in pa
30、cketised data systems due to the inherent variability in arrival times of individual packets. However, services that are highly intolerant of delay variation will usually take steps to remove (or at least significantly reduce) the delay variation by means of buffering, effectively eliminating delay
31、variation as perceived at the user level (although at the expense of adding additional fixed delay). 4.3 Information loss Information loss has a very direct effect on the quality of the information finally presented to the user, whether it be voice, image, video or data. In this context, information
32、 loss is not limited to the effects of bit errors or packet loss during transmission, but also includes the effects of any degradation introduced by media coding for more efficient transmission (e.g. the use of low bit-rate speech codecs for voice). 5 Performance considerations for different applica
33、tions 5.1 Audio A general classification of audio into five levels of quality, and a mapping to various services, is given in i. More specific details are given below. 5.1.1 Conversational voice Requirements for conversational voice are heavily influenced by one-way delay. In fact, there are two dis
34、tinct effects of delay. The first is the creation of echo in conjunction with two-wire to 4-wire conversions or even acoustic coupling in a terminal. This begins to cause increasing degradation to voice quality for delays of the order of tens of milliseconds, and echo control measures must be taken
35、at this point (provision of echo cancellers etc 2). The second effect occurs when the delay increases to a point where it begins to impact conversational dynamics, i.e. the delay in the other party responding becomes noticeable. This occurs for delays of the order of several hundred milliseconds 3.
36、However, the human ear is highly intolerant of short-term delay variation (jitter). As a practical matter, for all voice services, delay variation due to variability in incoming packet arrival times must be removed with a de-jitterizing buffer. Requirements for information loss are influenced by the
37、 fact that the human ear is tolerant to a certain amount of distortion of a speech signal. In IP-based transmission systems a prime source of voice quality degradation is due to the use of low bit-rate speech compression codecs and their performance under conditions of packet loss. 2 ITU-T Rec. G.10
38、10 (112001) 5.1.2 Voice messaging Requirements for information loss are essentially the same as for conversational voice (i.e. dependent on the speech coder), but a key difference here is that there is more tolerance for delay since there is no direct conversation involved. The main issue, therefore
39、 becomes one of how much delay can be tolerated between the user issuing a command to replay a voice message and the actual start of the audio. There is no precise data on this, but based on studies related to the acceptability of stimulus-response delay for telecommunications services, a delay of t
40、he order of a few seconds seems reasonable for this application. In fact, a distinction is possible between recording and playback, in that user reaction to playback is likely to be the more stringent requirement. 5.1.3 Streaming audio Streaming audio is expected to provide better quality than conve
41、ntional telephony, and requirements for information loss in terms of packet loss will be correspondingly tighter. However, as with voice messaging, there is no conversational element involved and delay requirements for the audio stream itself can be relaxed, even more so than for voice-messaging, al
42、though control commands must be dealt with appropriately (see 5.3.4). 5.2 Video A general classification of video into six levels of quality, and a mapping to various services, is given in i. More specific details are given below. 5.2.1 Videophone Videophone as used here implies a full-duplex system
43、, carrying both video and audio and intended for use in a conversational environment. As such, in principle the same delay requirements as for conversational voice will apply, i.e. no echo and minimal effect on conversational dynamics, with the added requirement that the audio and video must be sync
44、hronised within certain limits to provide “lip-synch“ . Once again, the human eye is tolerant to some loss of information, so that some degree of packet loss is acceptable depending on the specific video coder and amount of error protection used. It is expected that the latest WEG-4 video codecs wil
45、l provide acceptable video quality with frame erasure rates up to about 1%. 5.2.2 One-way video The main distinguishing feature of one-way video is that there is no conversational element involved, meaning that the delay requirement will not be so stringent, and can follow that of streaming audio. T
46、aking into account the above considerations, performance targets for audio and video applications are shown in Table I. 1. 5.3 Data From a user point of view, a prime requirement for any data transfer application is to guarantee essentially zero loss of information. At the same time, delay variation
47、 is not generally noticeable to the user, although there needs to be a limit on synchronisation between media streams in a multimedia session (e.g. audio in conjunction with a white-board presentation). The different applications therefore tend to distinguish themselves on the basis of the delay whi
48、ch can be tolerated by the end-user fiom the time the source content is requested until it is presented to the user. ITU-T Rec. G.lO1O (11/2001) 3 5.3.1 Web-browsing In this category we refer to retrieving and viewing the HTML component of a Web page, other components e.g. images, audiohideo clips a
49、re dealt with under their separate categories. From the user point of view, the main performance factor is how quickly a page appears after it has been requested. Delays of several seconds are acceptable, but not more than about 10 seconds. 5.3.2 Bulk data This category includes file transfers, and is clearly infuenced by the size of the file. As long as there is an indication that the file transfer is proceeding, it is reasonable to assume somewhat longer tolerance to delay than for a single Web-page. 5.3.3 High-priority transaction services -commerce) The ma
