1、 International Telecommunication Union ITU-T Y.2172TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2007) SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Next Generation Networks Quality of Service and performance Service restoration priority le
2、vels in Next Generation Neworks ITU-T Recommendation Y.2172 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 aspects Y
3、.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, netwo
4、rk capabilities and resource management Y.1200Y.1299 Transport 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 NEXT GENERATION NETWORKS Frameworks and f
5、unctional 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 addressing Y.2300Y.2399 Network
6、management Y.2400Y.2499 Network control architectures and protocols Y.2500Y.2599 Security Y.2700Y.2799 Generalized mobility Y.2800Y.2899 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. Y.2172 (06/2007) i ITU-T Recommendation Y.2172 Service restoration priority leve
7、ls in Next Generation Networks Summary ITU-T Recommendation Y.2172 proposes three levels of restoration priority for services in Next Generation Networks. This indicator is intended as a guidance for the development of appropriate signalling protocol extensions and the restoration/re-route mechanism
8、s. Source ITU-T Recommendation Y.2172 was approved on 13 June 2007 by ITU-T Study Group 13 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. Y.2172 (06/2007) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of teleco
9、mmunications. 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 standardizing telecommunications on a worldwide basis. The World Telecomm
10、unication 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 by the procedure laid down in WTSA Resolution 1. In some areas
11、 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 both a telecommunication administration and a recognized opera
12、ting 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 all of these mandatory provisions are met. The words “shall“
13、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 RIGHTS ITU draws attention to the possibility that the practi
14、ce 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 by ITU members or others outside of the Recommendation developm
15、ent 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 this may not represent the latest information and are therefore
16、 strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2007 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. Y.2172 (06/2007) iii CONTENTS Page 1 Scope 1 2 References.
17、 1 3 Definitions 1 4 Abbreviations and acronyms 2 5 Conventions 2 6 Introduction and rationale. 2 7 Recommendation for restoration priority levels. 3 8 Security considerations. 3 Appendix I Illustrative example of restoration priority use for call/session setup with RACF 4 Bibliography. 6 ITU-T Rec.
18、 Y.2172 (06/2007) 1 ITU-T Recommendation Y.2172 Service restoration priority levels in Next Generation Networks 1 Scope As stated in ITU-T Y.1271, enhanced priority treatment is an essential requirement for the assured capabilities needed for emergency telecommunications. One critical component is a
19、dmission control and associated priorities as described in ITU-T Y.2171. Another critical component is service restoration particularly during emergency conditions with potentially reduced network bandwidth/resources. Under such conditions, emergency telecommunications interrupted by network failure
20、s require preferential restoration treatment. In the NGN, assured restoration can be enabled by: 1) development of service restoration priority levels based on the criticality of services; 2) development of the necessary extensions in signalling protocols that can indicate the restoration priority l
21、evels during call/session set-up; 3) development of restoration mechanisms that can recognize the signalled priority levels and undertake the necessary restoration/re-routing action. The scope of this Recommendation is limited to the development of priority levels for service restoration in the NGN.
22、 This guidance can be helpful in the development of the subsequent signalling extensions and restoration mechanisms. Administrations may require operators and service providers to take into account national regulatory and national policy requirements in implementing this Recommendation. 2 References
23、 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 Recommendations and other references are subject to revision; users of
24、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 regularly published. The reference to a document within this Recommendation
25、 does not give it, as a stand-alone document, the status of a Recommendation. ITU-T E.361 ITU-T Recommendation E.361 (2003), QoS routing support for interworking of QoS service classes across routing technologies. ITU-T Y.1271 ITU-T Recommendation Y.1271 (2004), Framework(s) on network requirements
26、and capabilities to support emergency telecommunications over evolving circuit-switched and packet-switched networks. ITU-T Y.1291 ITU-T Recommendation Y.1291 (2004), An architectural framework for support of Quality of Service in packet networks. ITU-T Y.2171 ITU-T Recommendation Y.2171 (2006), Adm
27、ission control priority levels in Next Generation Networks. 3 Definitions This Recommendation defines the following terms: 3.1 emergency telecommunications: An umbrella term for telecommunications of an “extraordinary nature“ under abnormal and potentially adverse network conditions. 2 ITU-T Rec. Y.
28、2172 (06/2007) 3.2 service restoration: A set of automated or manual methods, invoked after a network failure, to enhance the ability of successful communications reroute and completion around the failed network element(s). 4 Abbreviations and acronyms This Recommendation uses the following abbrevia
29、tions and acronyms: DS-TE DiffServ-Aware MPLS-Traffic Engineering G-MPLS Generalized Multi-Protocol Label Switching IP Internet Protocol ISP Internet Service Provider LSP Label Switched Path MIB Management Information Base MPLS Multi-Protocol Label Switching NGN Next Generation Network PD-FE Policy
30、Decision Functional Entity RACF Resource Admission Control Functions SCF Service Control Function SLA Service Level Agreement TRC-FE Transport Resource Control Functional Entity VoIP Voice over IP VPN Virtual Private Network 5 Conventions None. 6 Introduction and rationale All forms of communication
31、s traffic are expected to be carried by NGN networks control plane traffic (e.g., routing and signalling messages), emergency telecommunications, real-time voice and video services, data services, virtual private network (VPN) services, as well as traditional “Best effort“ traffic. In such an enviro
32、nment, it is important to assign priority classifications and establish rules for service restoration such that critical services (e.g., control plane traffic and emergency telecommunications) are recognized and restored over other services in case of network overloads or failures ITU-T E.361, ITU-T
33、 Y.1291. As service flows can be expected to traverse multiple network domains, priority classification is an important step in the development of the necessary signalling protocol extensions as well as of the mechanisms for enabling preferential restoration of critical services b-IETF RFC 4090. The
34、 priority level classification is based on the following premise: Under reduced bandwidth conditions resulting from network failure, the critical issue for an NGN is the ability to recognize and restore higher priority traffic flows over others. The priority level recommendations proposed in this Re
35、commendation strictly relate to the relative importance of traffic classes from this perspective. They do not reflect implementation-specific priority definitions. For example, there are mechanisms utilizing generalized multi-protocol label switching (G-MPLS)-based recovery that define specific reco
36、very capabilities such as 1+1 protection and 1:N protection b-IETF RFC 4426. ITU-T Rec. Y.2172 (06/2007) 3 Such mechanism-specific priority definitions do not apply to the recommendations in this Recommendation. To summarize, the priority levels being recommended in this Recommendation are completel
37、y independent of the restoration mechanisms that a network operator may utilize. 7 Recommendation for restoration priority levels Three restoration priority levels are recommended for traffic in NGN: Priority level 1: Traffic with this priority receives the highest assurance of restoration. This cla
38、ss must include control services crucial to the operation of a network and emergency telecommunications. Other services may be included depending on availability of restoration capacity and service level agreements (SLA) between network operators and customers for the desired service. Priority level
39、 2: Traffic with this priority will receive lower assurance than priority level 1 traffic but will receive higher assurance than priority level 3 traffic for restoration. Examples include real-time services (VoIP, video), VPN and data services. The selection of this priority class is expected to be
40、determined by appropriate SLA agreements between network operators and customers for the desired service. Priority level 3: Traffic with this priority receives the least assurance for restoration. Examples include “traditional“ Internet service provider (ISP) services (e-mail, web surfing). The sele
41、ction of this priority class is expected to be determined by appropriate SLA agreements between network operators and customers for the desired service. The choice of the offered priority levels and the priority implementation mechanisms in the transport stratum is up to the network operator. The to
42、tal number of restoration priority levels may be extended in the future. 8 Security considerations The nature of this Recommendation does not raise new security considerations. 4 ITU-T Rec. Y.2172 (06/2007) Appendix I Illustrative example of restoration priority use for call/session setup with RACF
43、(This appendix does not form an integral part of this Recommendation) b-ITU-T Y.2111 defines the functional architecture for the resource and admission control functions (RACF) for NGN. RACF is intended to serve as the arbitrator between the service control function (SCF) and the transport function
44、in the NGN for QoS-related transport control in access and core networks. Arbitration decisions will be based on transport subscription information, SLAs, network policy rules, service priority, and transport resource status and utilization information. Restoration priority levels can be used in the
45、 RACF decision-making process to determine appropriate resource allocation for incoming calls/sessions depending on the type of the underlying transport technology. To illustrate the usage, consider the example of how two types of incoming video applications IPTV and multimedia video conferencing ar
46、e considered by RACF based on the following assumptions: The transport technology deployed is a DiffServ-Aware MPLS-TE (DS-TE) network b-IETF RFC 3564 having an aggregated set of Label Switched Path (LSP) tunnels, each with an assigned class type attribute, into which incoming calls/sessions are dir
47、ected based on the traffic type and admission control priority ITU-T Y.2171 of the incoming call/session. A network operator may decide to group all video applications in tunnels of the same class type (e.g., class type 2). This may be necessary as the total number of class types for DS-TE tunnels i
48、s restricted to eight. The DS-TE tunnels are protected against failures by the MPLS-Fast Reroute b-IETF RFC 4090 mechanism whereby each tunnel is assigned backup tunnels having pre-determined set-up and holding priority attributes. These tunnel attributes are stored in appropriate management informa
49、tion bases (MIB) b-IETF RFC 3812. This flexibility allows for DS-TE tunnels of the same class type to have different restoration priorities. An IPTV session is initiated requiring level 2 (normal) admission control priority and level 1 (high) restoration priority. The high level 1 restoration priority is necessary due to very stringent availability requirements for IPTV sessions b-ID-ServClasses. A multimedia video conferencing session is initiated requiring level 2 (normal) admission control priority and lev
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