1、 International Telecommunication Union ITU-T Y.1221TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2010) SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Architecture, access, network capabilities and resource managemen
2、t Traffic control and congestion control in IP-based networks Recommendation ITU-T Y.1221 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 middlewar
3、e Y.200Y.299 Network aspects 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.11
4、99 Architecture, access, network capabilities and resource management Y.1200Y.1299Transport Y.1300Y.1399 Interworking Y.1400Y.1499 Quality of service and network performance Y.1500Y.1599 Signalling Y.1600Y.1699 Operation, administration and maintenance Y.1700Y.1799 Charging Y.1800Y.1899 IPTV over NG
5、N Y.1900Y.1999 NEXT GENERATION 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.229
6、9 Numbering, naming and 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
7、to the list of ITU-T Recommendations. Rec. ITU-T Y.1221 (06/2010) i Recommendation ITU-T Y.1221 Traffic control and congestion control in IP-based networks Summary Recommendation ITU-T Y.1221 provides a general description as well as objectives and procedures for traffic control and congestion contr
8、ol for IP-based networks. In particular, it describes the concepts of the traffic contract between a user and the network. It specifies the IP transfer capabilities (IPTCs) including, for each IPTC, the service model, the associated traffic patterns and conformance definition. History Edition Recomm
9、endation Approval Study Group 1.0 ITU-T Y.1221 2002-03-16 13 1.1 ITU-T Y.1221 (2002) Amend. 1 2004-03-29 13 1.2 ITU-T Y.1221 (2002) Amend. 2 2005-11-29 12 1.3 ITU-T Y.1221 (2002) Amend. 3 2007-10-11 12 2.0 ITU-T Y.1221 2010-06-29 12 ii Rec. ITU-T Y.1221 (06/2010) FOREWORD The International Telecommu
10、nication 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, operating and tariff
11、 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, produce Recommend
12、ations 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 this Recommendat
13、ion, 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., interoperability
14、 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 that complian
15、ce 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 evidence, validity or
16、 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 received notice of intellectual property, protected by patents, which may be required to imp
17、lement 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 2010 All rights reserved. No part of this publication may be reproduced, by any
18、means whatsoever, without the prior written permission of ITU. Rec. ITU-T Y.1221 (06/2010) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 1 3.1 Terms defined elsewhere 1 3.2 Terms defined in this Recommendation . 1 4 Abbreviations and acronyms 2 5 Conventions 3 6 General 3 7 Traffic param
19、eters and descriptors . 4 7.1 Definitions 4 7.2 Requirements on traffic parameters and traffic descriptors . 5 7.3 Traffic parameter specifications . 5 8 IP transfer capabilities 5 8.1 Dedicated bandwidth transfer capability 6 8.2 Statistical bandwidth transfer capability 6 8.3 Best effort transfer
20、capability . 8 8.4 Delay-sensitive statistical bandwidth transfer capability . 8 8.5 Conditionally dedicated bandwidth transfer capability 9 9 Functions for traffic control, congestion control, and overload treatment . 12 9.1 Traffic control functions . 12 9.2 Functions for congestion control and ov
21、erload treatment 13 10 Methods and tools for IP traffic engineering 14 10.1 MPLS traffic engineering . 14 10.2 DiffServ-aware MPLS traffic engineering . 14 Annex A The token bucket and the generic byte rate algorithm 15 A.1 The token bucket 15 A.2 The continuous-state token bucket . 15 A.3 The gener
22、ic byte rate algorithm 16 A.4 The virtual scheduling byte rate algorithm . 16 A.5 The continuous-state leaky bucket byte rate algorithm 17 A.6 Throughput behaviour of the GBRA algorithm . 17 Annex B Behaviour of two coordinated generic byte rate algorithms 19 iv Rec. ITU-T Y.1221 (06/2010) Page Appe
23、ndix I Illustration of token bucket behaviour . 20 I.1 Characterization of a flow with a single rate and a single token bucket 20 I.2 Characterization of a flow with two rates and two token buckets (Bp Bs) . 23 Appendix II Relation between IPTC/QoS class and IETF IntServ/DiffServ-specification 25 II
24、.1 Dedicated bandwidth IPTC associated with a suitable QoS class 25 II.2 Statistical bandwidth IPTC associated with a suitable QoS class 26 Appendix III Guidelines for support of services using IP transfer capabilities in a differentiated services environment 27 III.1 Guidelines applicable to all IT
25、U-T Y.1221 transfer capabilities . 27 III.2 DBW guidelines . 27 III.3 SBW guidelines 28 III.4 BE guidelines 28 Appendix IV Example methods for determining token-bucket parameters . 29 Bibliography. 31 Rec. ITU-T Y.1221 (06/2010) 1 Recommendation ITU-T Y.1221 Traffic control and congestion control in
26、 IP-based networks 1 Scope This Recommendation describes traffic control and congestion control procedures for IP-based networks. Such control procedures are necessary in order to support services with quality of service (QoS), where the QoS is negotiated between a user and the network. Traffic cont
27、rol refers to all network actions aiming to meet the negotiated performance objectives in an IP-based network and to allow the avoidance of congested conditions. Congestion control refers to all network actions to minimize the intensity, spread and duration of congestion. This Recommendation provide
28、s a general description, as well as objectives and procedures, for traffic control and congestion control. In particular, it describes the concepts of the traffic contract between a user and the network. It specifies the IP transfer capabilities (IPTCs) including, for each IPTC, the service model, t
29、he associated traffic patterns and conformance definition. 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. All
30、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 regu
31、larly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T I.371 Recommendation ITU-T I.371 (2000), Traffic control and congestion control in B-ISDN. ITU-T Y.1241 Recommendation ITU-T Y.1241 (2001), Suppo
32、rt of IP-based services using IP transfer capabilities. ITU-T Y.1540 Recommendation ITU-T Y.1540 (1999), Internet protocol data communication service IP packet transfer and availability performance parameters. ITU-T Y.1541 Recommendation ITU-T Y.1541 (2002), Network performance objectives for IP-bas
33、ed services. 3 Definitions 3.1 Terms defined elsewhere None. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 conformance: Conformance is the application of one or more criteria, at a given standardized interface, to a flow. 2 Rec. ITU-T Y.1221 (06/2010
34、) 3.2.2 congestion: Congestion is defined as a state of network elements (e.g., router, switches) in which the network is not able to meet the network performance objectives and the negotiated QoS commitments for the already established flows. 3.2.3 IP congestion control: Refers to all network actio
35、ns to minimize the intensity, spread and duration of congestion. 3.2.4 IP flow: An IP flow at a given interface is defined as the occurrence at that interface of the set of IP packets which match a given classification (see clause 7.1.2). 3.2.5 IP traffic control: Refers to network actions aiming to
36、 meet the network performance objectives and negotiated QoS commitments. 3.2.6 IP transfer capability: An IP transfer capability is a set of network capabilities provided by an IP-based network to transfer IP flows. 3.2.7 overload: Overload is defined as a state of a network element in which buffer
37、overflow results in packet discard for flows with no QoS commitments. 3.2.8 packet classification: The process of distinguishing IP packets for the purpose of applying appropriate traffic control and congestion control mechanisms (see clause 7.1.1). 3.2.9 traffic contract: For a given IP flow, the s
38、elected IP transfer capability (see clause 8), the traffic descriptor at a given interface and the QoS class ITU-T Y.1541 define the traffic contract at that interface (see clause 7.1.5). 3.2.10 traffic descriptor: A traffic descriptor is the set of traffic parameters that is used to capture the tra
39、ffic characteristics of an IP flow at a given standardized interface as part of the traffic contract (see clause 7.1.4). 3.2.11 traffic parameter: A traffic parameter describes one aspect of a flow (see clause 7.1.3). 4 Abbreviations and acronyms This Recommendation uses the following abbreviations
40、and acronyms: BE Best Effort Bp Bucket size of peak token bucket Bs Bucket size of sustainable token bucket CBR Constant Bit Rate CDBW Conditionally Dedicated Bandwidth (IP transfer capability) CDV Cell Delay Variation CSPF Constrained Shortest Path First DBW Dedicated Bandwidth (IP transfer capabil
41、ity) DS Differentiated Services (IP header field) DSBW Delay-sensitive Statistical Bandwidth (IP transfer capability) FRR Fast Reroute GBRA Generic Byte Rate Algorithm GCRA Generic Cell Rate Algorithm IP Internet Protocol IPDV IP Delay Variation IPLR IP Loss Ratio Rec. ITU-T Y.1221 (06/2010) 3 IPTC
42、IP Transfer Capability IPTD IP Transfer Delay LR Line Rate LSP Label Switched Path MPLS Multiprotocol Label Switching OSPF Open Shortest Path First PC Parameter Control PCR Peak Cell Rate QoS Quality of Service Rp Rate of peak token bucket Rs Rate of sustainable token bucket SBW Statistical Bandwidt
43、h (IP transfer capability) SDP Session Description Protocol SIP Session Initiation Protocol TAT Theoretical Arrival Time TB Token Bucket TC Transfer Capability ToS Type of Service (IP header field, see DS) 5 Conventions This Recommendation uses the following conventions: B: Bucket size of a token bu
44、cket; M: Maximum allowed packet size; N: Size (in bytes) of an IP packet; R: Rate of a token bucket. 6 General The primary role of traffic control and congestion control procedures is to protect the IP network and the traffic entering the network in order to achieve the IP network performance object
45、ives and QoS commitments. Traffic and congestion control allows the use of IP network resources to be optimized. In IP-based networks, congestion is defined as a state of network elements (e.g., routers, switches) in which the network is not able to meet the network performance objectives and the ne
46、gotiated QoS commitments for the established flow. Congestion is to be distinguished from the state where buffer overflow causes IP packet loss, but the negotiated quality of service is still met. For services with no QoS commitments, such as best effort services, the term overload is used rather th
47、an congestion. This Recommendation defines a set of traffic control and congestion control capabilities. It may be appropriate to consider additional sets of such capabilities, for which additional traffic control mechanisms will be used to achieve increased network efficiency. 4 Rec. ITU-T Y.1221 (
48、06/2010) It should be noted that traffic control procedures apply to IP packet flows. For some IP flows, the network commits to meet QoS objectives, assuming the user-generated IP packet flow conforms to a traffic contract. For IP flows without a traffic contract between the user and the network, th
49、e network may provide a best effort service. 7 Traffic parameters and descriptors 7.1 Definitions 7.1.1 IP packet classification Typically, IP packets from many different sources may cross a given interface to many different destinations. For the purpose of IP traffic control and congestion control, it is essential that not all IP packets are treated the same way but differently, depending on the objectives and on the commitments made. Therefore, it is useful to distinguish IP packets into relevant cate
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