1、 International Telecommunication Union ITU-T G.1040TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 1(10/2007) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Quality of service and performance Generic and user-related aspects Network contribution to transaction time
2、Amendment 1: New Appendix I Network contribution to SIP set-up time ITU-T Recommendation G.1040 (2006) Amendment 1ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO
3、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 WITH METALLIC LINES G.400G.
4、449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY 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 USE
5、R-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA 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.1040 (2006)/Amd.
6、1 (10/2007) i ITU-T Recommendation G.1040 Network contribution to transaction time Amendment 1 New Appendix I Network contribution to SIP set-up time Summary ITU-T Recommendation G.1040 defines a performance metric for typical data transactions, called the network contribution to transaction time (N
7、CTT). Session initiation protocol (SIP) produces data transactions that resemble a typical call signalling flow between an originating and terminating station, and sometimes several other entities located within the service providers network. Appendix I to ITU-T Recommendation G.1040 describes how N
8、CTT can be adapted for use with SIP session flows to estimate the network contribution to session set-up time. Source Amendment 1 to ITU-T Recommendation G.1040 (2006) was agreed on 11 October 2007 by ITU-T Study Group 12 (2005-2008). ii ITU-T Rec. G.1040 (2006)/Amd.1 (10/2007) FOREWORD The Internat
9、ional 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, opera
10、ting 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, pr
11、oduce 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 In t
12、his 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. in
13、teroperability 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
14、 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 evidenc
15、e, 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
16、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 may be r
17、eproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. G.1040 (2006)/Amd.1 (10/2007) iii CONTENTS Page Amendment 1 New Appendix I Network contribution to SIP set-up time 1 I.1 Introduction 1 I.2 SIP set-up compared with a data transaction 1 I.3 Revised equations
18、for SIP set-up 2 I.4 Additional measurement considerations for SIP Set-up. 2 ITU-T Rec. G.1040 (2006)/Amd.1 (10/2007) 1 ITU-T Recommendation G.1040 Network contribution to transaction time Amendment 1 New Appendix I Network contribution to SIP set-up time I.1 Introduction Session initiation protocol
19、 (SIP) packet exchanges are data transactions that resemble a typical call signalling flow between an originating and terminating station. Sometimes these exchanges include several other entities located within the service providers network. This appendix describes how NCTT calculations can be adapt
20、ed for use with SIP session flows to estimate the network contribution to session set-up time. Set-uptimeG.1040Amd.1(07)_F.AppI-1UA PS PS UAINVITE180 ringing200 OKP1 P2 P3d1, p1 d2, p2 d3, p3P6 P5 P4d6, p6 d5, p5 d4, p4One-waypaths withloss anddelayFigure I.1 Typical SIP session flow with proxy serv
21、ers (PS) I.2 SIP set-up compared with a data transaction One-way packet transfers: A typical and generic data transaction is illustrated in Figure 2/G.1040, where a client is communicating with a host across one or more IP networks. The main difference between a SIP set-up transaction and Figure 2/G
22、.1040 is that the INVITE and other SIP messages proceed to their intended destination and the “desired reply“ cannot arrive until the INVITE (and its corresponding reply) has proceeded successfully to all devices in the signalling path. There may be some provisional responses conveyed, but these are
23、 not the “desired reply“ of Ringing or other state information. The figure above illustrates a SIP set-up between two user agents (UA) with two proxy servers (PS) in the signalling path. Links in the signalling path have different characteristics: The typical transaction in ITU-T Rec. G.1040 assumes
24、 point-to-point communication between client and host over a single stable path with the same delay and loss characteristics for every exchange of the transaction. SIP messages may use several different paths as they travel from user agent to proxy server, proxy to proxy, and proxy to another UA (pa
25、ths P1, P2, , P6 in Figure I.1). It is likely that both the average one-way delay and loss will be different on the path between each signalling entity. 2 ITU-T Rec. G.1040 (2006)/Amd.1 (10/2007) Time-out assessed at the originating agent: The UA that originates the INVITE waits to receive some defi
26、nitive reply, and then re-starts the entire set-up process by sending another INVITE. In the typical data transaction illustrated in Figure 3/G.1040, any exchanges completed prior to a time-out are effective in progressing the transaction. With SIP however, failure at some point in the set-up result
27、s in the progress of the INVITE being discounted, and the set-up must be attempted again from the start. Note however that the time for the set-up (contributed by the network) remains the sum of time-outs plus the time for the INVITE and reply to traverse the network. In other words, equations for N
28、CTT still hold for either case. Variable time-out with exponential back-off: We have assumed a constant time-out value (RTO) for our typical data transaction in ITU-T Rec. G.1040. SIP conforms to the IETFs mantra that all protocol designs be congestion-aware. The default initial time-out value is 50
29、0 ms, and this value is doubled on every successive attempt to set up a session. I.3 Revised equations for SIP set-up One approach to adapting the NCTT calculations for SIP is to treat the multiple link exchange as a single transaction. In the example UA-UA signalling path with two proxy servers as
30、shown above, the network contribution to the average loss-less set-up time would be: Average NCTTno loss= d1 + d2 + d3 + d4 + d5 + d6 = RTT where d1 through d6 are the average delays for the six one-way paths. This is the same quantity as round-trip time (RTT) calculated in clause 4.3/G.1040. The ov
31、erall set-up loss probability can be calculated from the individual loss probabilities (p1, p2, , p6) for each path between signalling entities: ()()()()()()6151413121111 ppppppp = With the number of exchanges, E = 1, the Expected number of losses, L, reduces to: ()ppLE=1A weighted average time-out
32、can be computed by calculating the probabilities of L = 1, 2, 3, etc., and construct various ratios that result in different weights for each of the different time-out values. Several schemes to determine a set of weights have been examined. However, for any reasonably small value of p, such as p =
33、0.001, the weight of the default time-out is much larger than all others. Therefore, a good approximation is to use the default initial time-out value as the RTO under this condition. With all components now known, it is possible to calculate the average network contribution to SIP set-up time, as:
34、( ) ()( )()RTOLERTTNCTTNCSIPupset+=1AverageAverage I.4 Additional measurement considerations for SIP set-up Clause 5/G.1040 gives general measurement considerations for data transactions. Additional considerations for measuring network contribution to SIP set-up include: One-way measurements are ass
35、umed above, but it may be possible to use round-trip measurements of each path, as long as both directions of transmission follow the same path that the signalling packets will take. Packet size: Some SIP INVITEs may be large enough that they are fragmented at the IP layer. Measurement packet size s
36、hould take this into account. Printed in Switzerland Geneva, 2008 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 telecommun
37、ication services Series G Transmission systems and media, digital systems and networks 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 aga
38、inst 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 Specificat
39、ions of measuring equipment Series P Telephone transmission quality, telephone installations, local line networks 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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