1、 International Telecommunication Union ITU-T G.1050TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2007) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Quality of service and performance Generic and user-related aspects Network model for evaluating multimedia transmission
2、 performance over Internet Protocol ITU-T Recommendation G.1050 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.2
3、99 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 WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPH
4、ONY G.450G.499 TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA
5、CHARACTERISTICS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.1050 (11/2007) i ITU-T Recommendation G.1050 Network model for eva
6、luating multimedia transmission performance over Internet Protocol Summary ITU-T Recommendation G.1050 describes a model for evaluating multimedia transmission performance over an IP network. It is a statistical model in which likelihood of occurrence values are assigned to all network elements and
7、impairments. Test results using these statistical models are expressed in terms of network model coverage. Testing to a comprehensive statistical model suggests how communications devices may perform over an IP network in terms of network model coverage. This Recommendation focuses on the impact of
8、impairments on layer 3 performance. IP streams from any type of network device can be evaluated using this model. Emphasis is given to the fact that manufacturers of communications equipment and service providers are interested in a specification that accurately models the IP network characteristics
9、 that determine performance. Evaluators desire a definitive set of simple tests that properly measure the performance of communications devices from various manufacturers. Therefore, the objective of this Recommendation is to define a technology-independent model that is representative of the IP net
10、work, that can be simulated at reasonable complexity, and that facilitates practical evaluation times. Source ITU-T Recommendation G.1050 was approved on 13 November 2007 by ITU-T Study Group 12 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. G.1050 (11/2007) FOREWORD The Int
11、ernational 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,
12、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 tur
13、n, 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-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE
14、 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.
15、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 s
16、uggest 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 e
17、vidence, 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, whic
18、h 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 2008 All rights reserved. No part of this publication ma
19、y be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. G.1050 (11/2007) iii CONTENTS Page 1 Scope 1 2 References. 2 3 Definitions 2 4 Abbreviations and acronyms 4 5 Description of the model 5 6 IP impairment level setup . 6 6.1 Service test profiles 6 6.2 N
20、etwork impairments . 7 6.3 Test set-up 8 6.4 Impairment combination tables 9 6.5 Network model coverage 18 Appendix I Rationale for IP network model. 22 I.1 Wireless LANs . 22 I.2 Structured wiring 22 I.3 Hubs versus switches 22 I.4 Access rates 22 I.5 Router delays 23 I.6 Impairment data from anony
21、mous IP network service providers 23 Appendix II Packet delay and loss algorithms 24 II.1 General IP network model 24 II.2 Packet loss model . 24 II.3 Delay variation model 25 II.4 Core packet reordering . 25 II.5 Model output 26 II.6 Model parameters . 26 Bibliography. 28 iv ITU-T Rec. G.1050 (11/2
22、007) Introduction Previous network transmission model standards for evaluating modem performance (see bibliography) have been statistical models in which likelihood of occurrence (LOO) values were assigned to all network elements and impairments. Test results using these statistical models were expr
23、essed in terms of network model coverage (NMC): the percentage of network connections over which a particular level of performance is achieved. This is an example of a statistical model. Testing to a comprehensive statistical model suggests how communications devices may perform over an IP network i
24、n terms of network model coverage. Unlike the previous models, which focused on physical-layer (layer 1) impairments, this Recommendation focuses on the impact of impairments on Internet Protocol (IP) layer 3 performance. IP streams from any type of network device can be evaluated using this model.
25、Emphasis is given to the fact that manufacturers of communications equipment and service providers are interested in a specification that accurately models the IP network characteristics that determine performance. Evaluators desire a definitive set of simple tests that properly measure the performa
26、nce of communications devices from various manufacturers. Therefore, the objective of this Recommendation is to define an application-independent model (e.g., data, voice, voiceband data, video) that is representative of the IP network, that can be simulated at reasonable complexity and that facilit
27、ates practical evaluation times. The IP network model presented herein represents a snapshot of actual network data provided by anonymous IP service providers and IP network equipment manufacturers in the 2007 time-frame and will continue to evolve as more statistical information becomes available a
28、nd as the IP network evolves. In developing this model, certain assumptions have been made based on the best available statistical information. These assumptions are given in Appendix I. The following are parameters and impairments that affect quality of service and IP network performance: Network a
29、rchitecture; Types of access links; QoS controlled edge routing; MTU size; Network faults; Link failure; Route flapping; Reordered packets; Packet loss (frame loss); One-way delay (latency); Variable delays (Jitter); and Background traffic (congestion, bandwidth, utilization, network load, load shar
30、ing). ITU-T Rec. G.1050 (11/2007) 1 ITU-T Recommendation G.1050 Network model for evaluating multimedia transmission performance over Internet Protocol 1 Scope This Recommendation specifies an IP network model and scenarios for evaluating and comparing communications equipment connected over a conve
31、rged wide area network. The IP network model consists of many impairment combinations that are scenario-based and time-varying. IP streams from any type of network device can be evaluated using this model. The test scenarios combine LAN, access and core network elements in a realistic way to create
32、layer 3 IP network impairments that cause packets to experience varying delay or loss. These scenarios are based on actual network data provided by anonymous IP service providers and IP network equipment manufacturers. Examples of the types of equipment that can be evaluated using this model include
33、: IP-connected endpoints: IP network devices (such as: user agents, call agents, media servers, media gateway controllers, gatekeepers, application servers, edge routers, etc.); IP video (IPTV, video conferencing, telepresence, etc.); IP phones (including soft phones); IAF (Internet-aware fax). PSTN
34、-connected devices through IP gateways: POTS through voice-over-IP (VoIP) gateways; T.38 facsimile devices and gateways; V.150.1 and V.152 (voiceband data, VBD) modem-over-IP gateways; V.151 textphone-over-IP gateways. The models include parameters that can be used to configure and set up suitable e
35、mulator equipment. This Recommendation includes mandatory requirements, recommendations and options; these are designated by the words “shall“, “should“ and “may“, respectively. Limitations of this model: This IP network model is not intended to represent any specific IP network. Rather, it provides
36、 a range of test scenarios that could represent a wide range of IP network characteristics, such as those experienced in well-managed (QoS-managed), partially-managed (non-QoS) and unmanaged (Internet) networks. Some VoIP networks may utilize PSTN at one or both ends of the connection through a medi
37、a gateway. This model only addresses the IP portion of the network and does not address the PSTN portion of the end-to-end connection. The network models represented in this Recommendation do not model all possible connections that can be encountered between devices. The IP network model presented h
38、erein is based on an informal survey of anonymous IP service providers and IP network equipment manufacturers in the 2007 time-frame and will continue to evolve as more statistical information becomes available and as the IP network evolves. 2 ITU-T Rec. G.1050 (11/2007) 2 References The following I
39、TU-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 Recommendat
40、ion 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 i
41、t, as a stand-alone document, the status of a Recommendation. ITU-T G.107 ITU-T Recommendation G.107 (2005), The E-model, a computational model for use in transmission planning. ITU-T G.108 ITU-T Recommendation G.108 (1999), Application of the E-model: A planning guide. ITU-T G.114 ITU-T Recommendat
42、ion G.114 (2003), One-way transmission time. ITU-T T.38 ITU-T Recommendation T.38 (2007), Procedures for real-time Group 3 facsimile communication over IP networks. ITU-T V.150.0 ITU-T Recommendation V.150.0 (2003), Modem-over-IP networks: Foundation. ITU-T V.150.1 ITU-T Recommendation V.150.1 (2003
43、), Modem-over-IP networks: Procedures for the end-to-end connection of V-series DCEs. ITU-T V.151 ITU-T Recommendation V.151 (2006), Procedures for the end-to-end connection of analogue PSTN text telephones over an IP network utilizing text relay. ITU-T V.152 ITU-T Recommendation V.152 (2005), Proce
44、dures for supporting voice-band data over IP networks. ITU-T Y.1541 ITU-T Recommendation Y.1541 (2002), Network performance objectives for IP-based services. 3 Definitions This Recommendation defines the following terms: 3.1 burst loss: A high density of packet loss over time, or loss of sequential
45、packets, due to congestion, bandwidth limitation or rerouting (delay translated into loss due to implementation) on the network. 3.2 delay: The time required for a packet to traverse the network or a segment of the network (see latency). 3.3 downstream: A transmission from a service provider toward
46、an end user. 3.4 end-to-end network: Pertaining to an entire path from one endpoint to another. Metrics may refer to a single segment (example: core delay) or to the entire path (example: end-to-end network delay). 3.5 E-model: A standard-based (ITU-T G.107, ITU-T G.108) model for planning the trans
47、mission quality of telephone networks. The output of the E-model is a transmission rating factor called the R-Factor. The scale for the R-Factor is between 0 and 100, where 0 is low and 100 is high transmission quality. 3.6 gateway: A network device that acts as an entrance to another network. One f
48、unction is to convert media provided in one type of network to the format required in another type of network. ITU-T Rec. G.1050 (11/2007) 3 For example, a gateway could terminate bearer channels from a switched circuit network (e.g., DS0s) and media streams from a packet network (e.g., RTP streams
49、in an IP network). 3.7 IP network: A network based on the Internet Protocol, a connectionless protocol. 3.8 jitter: Variation in packet delay. 3.9 jitter buffer: A shared data area where packets can be collected, stored and sent to the processor in evenly spaced intervals to improve the end-user experience. 3.10 latency: An expression of how much time it takes for a packet of data to get from one designated point to another (see delay). 3.11 layer 3: The third layer of the International Organi
