1、 International Telecommunication Union ITU-T Y.1542TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2010) SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Quality of service and network performance Framework for achievin
2、g end-to-end IP performance objectives Recommendation ITU-T Y.1542 ITU-T Y-SERIES RECOMMENDATIONS GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS GLOBAL INFORMATION INFRASTRUCTURE General Y.100Y.199 Services, applications and middleware Y.200Y.299 Network as
3、pects Y.300Y.399 Interfaces and protocols Y.400Y.499 Numbering, addressing and naming Y.500Y.599 Operation, administration and maintenance Y.600Y.699 Security Y.700Y.799 Performances Y.800Y.899 INTERNET PROTOCOL ASPECTS General Y.1000Y.1099 Services and applications Y.1100Y.1199 Architecture, access
4、, network capabilities and resource management Y.1200Y.1299 Transport Y.1300Y.1399 Interworking Y.1400Y.1499 Quality of service and network performance Y.1500Y.1599Signalling Y.1600Y.1699 Operation, administration and maintenance Y.1700Y.1799 Charging Y.1800Y.1899 IPTV over NGN Y.1900Y.1999 NEXT GEN
5、ERATION NETWORKS Frameworks and functional architecture models Y.2000Y.2099 Quality of Service and performance Y.2100Y.2199 Service aspects: Service capabilities and service architecture Y.2200Y.2249 Service aspects: Interoperability of services and networks in NGN Y.2250Y.2299 Numbering, naming and
6、 addressing Y.2300Y.2399 Network management Y.2400Y.2499 Network control architectures and protocols Y.2500Y.2599 Future networks Y.2600Y.2699 Security Y.2700Y.2799 Generalized mobility Y.2800Y.2899 Carrier grade open environment Y.2900Y.2999 For further details, please refer to the list of ITU-T Re
7、commendations. Rec. ITU-T Y.1542 (06/2010) i Recommendation ITU-T Y.1542 Framework for achieving end-to-end IP performance objectives Summary Recommendation ITU-T Y.1542 considers various approaches toward achieving end-to-end (UNI-UNI) IP network performance objectives. Detailed examples are provid
8、ed as to how some approaches might work in practice, including how service providers might handle cases where the aggregated impairments exceed those specified in a requested QoS class (such as those of Recommendation ITU-T Y.1541). The advantages and disadvantages of each approach are summarized. H
9、istory Edition Recommendation Approval Study Group 1.0 ITU-T Y.1542 2006-07-14 12 1.1 ITU-T Y.1542 (2006) Amend.1 2009-03-19 12 2.0 ITU-T Y.1542 2010-06-29 12 ii Rec. ITU-T Y.1542 (06/2010) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field
10、 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, operating and tariff questions and issuing Recommendations on them with a view to standardizin
11、g 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, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered b
12、y 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 this Recommendation, the expression “Administration“ is used for conciseness to indicate b
13、oth 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., interoperability or applicability) and compliance with the Recommendation is achieved when
14、 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 that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY
15、 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 b
16、y 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, implementers are cautioned that t
17、his 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 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. IT
18、U-T Y.1542 (06/2010) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Terms and definitions . 1 4 Abbreviations and acronyms 2 5 Problem statement and consideration of approaches 2 5.1 Static approaches 4 5.2 Pseudo-static approach . 5 5.3 Signalled approaches 5 5.4 Impairment accumulation approach . 7
19、 6 Advantages and disadvantages of the approaches considered 8 7 Summary of approaches according to the problem statement challenges 10 Appendix I Detailed example of a static divisor approach . 12 Appendix II Detailed example of the static reference allocation approach 13 Appendix III Detailed exam
20、ple of impairment accumulation approach . 15 Appendix IV Performance guidance for providers . 18 IV.1 Qualitative guidance statements . 18 IV.2 Circumstances when guidance is useful . 18 Appendix V Additional considerations for achieving end-to-end performance objectives in an NGN environment 19 V.1
21、 Introduction 19 V.2 Requirements for end-to-end QoS class . 19 V.3 End-to-end QoS performance objectives and multi-domain network 20 V.4 Technologies used at carrier segment . 21 V.5 Interface of QoS class and terminal equipment 21 V.6 Interface of QoS class and enterprise networks . 21 Bibliograph
22、y. 22 iv Rec. ITU-T Y.1542 (06/2010) Introduction Compared to networks and systems that are circuit-based, those based on IP pose distinctly different challenges for planning and achieving the end-to-end performance levels necessary to adequately support the wide array of user applications (voice, d
23、ata, fax, video, etc.). The fundamental quality requirements for these applications are well understood and have not changed as perceived by the user; what has changed is the technology (and associated impairments) in the layers below these applications. The very nature of IP-based routers and termi
24、nals, with their queuing methods and de-jitter buffers, respectively, makes realizing good end-to-end performance across multiple network operators a very major challenge for applications with stringent performance requirements. Fortunately, Recommendations ITU-T Y.1540 and Y.1541 together provide t
25、he parameters needed to capture the performance of IP networks, and specify a set of “network QoS“ classes with end-to-end objectives specified. It is widely accepted (i.e., beyond the ITU-T) that the network QoS classes of Recommendation ITU-T Y.1541 should be supported by next generation networks,
26、 and thus by networks evolving into NGNs. Thus, while there is general agreement that the IP network QoS classes of ITU-T Y.1541 are what should be achieved, what is missing is the methodology for satisfying the end-to-end objectives over paths involving multiple network operators, and in some cases
27、, unusual topologies and distances. The guidance provided here is intended to accelerate the planning, deployment and management of networks and systems that can interoperate with a clear goal of supporting the end-to-end performance objectives detailed in Recommendation ITU-T Y.1541. Regardless of
28、the approach, there is no guarantee that the end-to-end objectives can be met for a highly congested path through a complex network topology and/or over extremely long distances. However, the guidance provided in this Recommendation should facilitate network design and operation capable of nearly al
29、ways meeting the desired levels of performance. Rec. ITU-T Y.1542 (06/2010) 1 Recommendation ITU-T Y.1542 Framework for achieving end-to-end IP performance objectives 1 Scope This Recommendation includes a broad consideration of approaches toward achieving end-to-end IP performance objectives on as
30、many UNI-UNI paths as possible, including some detailed examples of how some approaches might work in practice. Examples include how service providers might handle cases where the aggregated impairments exceed those specified in a requested QoS class (such as those of ITU-T Y.1541). The advantages a
31、nd disadvantages of each approach are evaluated to the extent currently possible. For the purposes of this Recommendation, dynamic inter-AS routing using border gateway protocol (BGP) is assumed as per current practices. Other approaches for achieving end-to-end IP performance objectives have been m
32、entioned, such as a “Costed Bids Method“ and “Bid Discovery Using a Global Registry“. As these methods differ fundamentally from those treated here, with significantly different implications for deployment, these and other possible approaches are for further study. 2 References The following ITU-T R
33、ecommendations 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 Recommendation ar
34、e 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 it, as
35、a stand-alone document, the status of a Recommendation. ITU-T G.826 Recommendation ITU-T G.826 (2002), End-to-end error performance parameters and objectives for international, constant bit-rate digital paths and connections. ITU-T Y.1540 Recommendation ITU-T Y.1540 (2007), Internet protocol data co
36、mmunication service IP packet transfer and availability performance parameters. ITU-T Y.1541 Recommendation ITU-T Y.1541 (2006), Network performance objectives for IP-based services. 3 Terms and definitions This Recommendation defines the following terms: 3.1 access segment: The network segment from
37、 the customer interface (UNI) to the interface on the customer side of the first gateway router. It is understood that the access segment may be managed by different entities. In the case where network providers deploy and manage their network devices in user segments (e.g., routers, enterprise LAN,
38、 home network), these network devices should be included in “UNI-to-UNI“. 3.2 allocation: Formulaic division or assignment of a performance impairment objective among segments. 3.3 apportionment: Method of portioning a performance impairment objective among segments. 2 Rec. ITU-T Y.1542 (06/2010) 3.
39、4 total transit segment: The segment between gateway routers, including the gateway routers themselves. The network segment may include interior routers with various roles. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations: AS Autonomous System BGP Border Gateway Prot
40、ocol DV Delay Variation ER Edge Router GW GateWay router IPDV IP Packet Delay Variation IPLR IP Packet Loss Ratio IPTD IP Packet Transfer Delay LAN Local Area Network NSIS Next Step In Signalling RSVP Resource ReserVation Protocol UNI User-Network-Interface 5 Problem statement and consideration of a
41、pproaches How can QoS classes (e.g., network performance according to ITU-T Y.1541) be assured for users? The fundamental challenges to achieving end-to-end QoS are present when: multiple network providers are necessary to complete the path; the number of networks in the path will vary request by re
42、quest; distances between users is generally unknown; the impairment level of any given network segment is highly variable; it is desirable to estimate the actual performance levels achieved on a path; the operator must be able to say if the requested performance can be met or not; and the process mu
43、st eventually be automated. Also, solving the problem of delivering UNI-UNI IP QoS through the standards process will require development and agreement on many new tools and capabilities, and the extent of new work required should be assessed for each candidate solution. These too are challenges. Th
44、ere are two basic approaches to solve this problem. One involves allocating performance to a limited number of network segments, which allows operators to contribute known levels of impairments per segment, but restricts the number of operators that can participate in the path. (If a given segment d
45、oes not need to use all of its allocation, the balance is wasted.) The other approach is impairment accumulation, which allows any number of operators to participate in a path. On the surface this may appear too relaxed, but assuming operators in a competitive environment will actively manage and im
46、prove performance, the likelihood of the concatenated segments satisfying the end-to-end objectives can be predictably good. Figure 1 provides the basis for expressing the problem and how various solutions might work. Rec. ITU-T Y.1542 (06/2010) 3 Generally, the approaches that could be taken in all
47、ocating total impairment targets among network segments can be characterized by the amount of information shared among segments. Each approach has advantages and disadvantages. We describe them here with simple examples. (Detailed examples of the various approaches are appended to this Recommendatio
48、n.) For all allocation-based approaches, a “top-down“ or “bottom-up“ method could be applied. That is, percentages of the aggregated target (top-down) or fixed/negotiated values for impairments (bottom-up) may be allocated for each segment. A hybrid of these methods, with percentages for some segmen
49、ts and fixed/negotiated values for others, could also be used. Brief examples for some approaches as applied to Figure 1 below are provided. Note that the provider which sends traffic over a peering link is assumed to be responsible for that links performance and its impairments must be included in the segment total. Accesssegment AUNIProvider A Provider CUser segment ATransitsegment A1Transitsegment C1Transitsegment A2UNIAccesssegment CRegional MetroProvider BRegionalTransitsegment B2Transitsegment B1Total tran
