1、 ATIS-0100006 Service Restoration Priority Levels for IP Networks TECHNICAL REPORT The Alliance for Telecommunication Industry Solutions (ATIS) is a technical planning and standards development organization that is committed to rapidly developing and promoting technical and operations standards for
2、the communications and related information technologies industry worldwide using a pragmatic, flexible and open approach. Over 1,100 participants from more than 350 communications companies are active in ATIS 23 industry committees and its Incubator Solutions Program. ATIS-0100006, Service Restorati
3、on Priority Levels for IP Networks Is an ATIS Standard developed by the Network Reliability Task Force (REL) Subcommittee under the ATIS Network Performance, Reliability, and Quality of Service Committee (PRQC). Published by Alliance for Telecommunications Industry Solutions 1200 G Street, NW, Suite
4、 500 Washington, DC 20005 Copyright 2006 by Alliance for Telecommunications Industry Solutions All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher. For information contac
5、t ATIS at 202.628.6380. ATIS is online at . Printed in the United States of America. ATIS-0100006 Technical Report on Service Restoration Priority Levels for IP Networks Secretariat Alliance for Telecommunications Industry Solutions Approved March 2006 Abstract This Technical Report (TR) proposes th
6、ree levels of service restoration priority for traffic in IP networks. It also proposes that all emergency communications (e.g., ETS and E911) be included in the highest priority for service restoration. This report also provides guidance on restoration compliance with the Telecommunications Priorit
7、y System as mandated by the Federal Communications Commission (FCC). The goal is to formalize restoration priority levels in IP networks such that appropriate signaling requirements can commence. ATIS-0100006 ii FOREWORD This Technical Report (TR) proposes three service restoration priority levels i
8、n IP networks. It also proposes that National Security/Emergency Preparedness services are included in the highest restoration priority class. This TR is intended for providers of IP-based communications networks and services, communications equipment suppliers, and government agencies responsible f
9、or addressing emergency situations. The Alliance for Telecommunication Industry Solutions (ATIS) serves the public through improved understanding between carriers, customers, and manufacturers. The Network Performance, Reliability, and Quality of Service Committee (PRQC) formerly T1A1 develops and r
10、ecommends standards, requirements, and technical reports related to the performance, reliability, and associated security aspects of communications networks, as well as the processing of voice, audio, data, image, and video signals, and their multimedia integration. PRQC also develops and recommends
11、 positions on, and foster consistency with, standards and related subjects under consideration in other North American and international standards bodies. Suggestions for improvement of this document are welcome. They should be sent to the Alliance for Telecommunications Industry Solutions, PRQC Sec
12、retariat, 1200 G Street NW, Suite 500, Washington, DC 20005. The Network Reliability Task Force (REL) on Network Performance, Reliability, and Quality of Service, which developed this TR, has the following officers and participants: A. McCain, REL Chair S. Makris, REL Vice-Chair F. Kaudel, REL Chief
13、 Editor P. Tarapore, A. Nguyen, A. Webster; REL Technical Editors C. Underkoffler, ATIS Chief Editor Active Participants: J. Ash C. Bailey J. Bennett M. Dolly C. Dvorak P. Kimbrough S. Makris A. McCain A. Nguyen R. Paterson S. Sayers N. Seitz P. Tarapore A. Webster R. Wohlert ATIS-0100006 ii TABLE O
14、F CONTENTS FOREWORD .II TABLE OF CONTENTS II 1 PURPOSE 1 2 SCOPE 1 3 APPLICATION . 2 4 RELATED WORK 2 5 RESTORATION PRIORITY PRINCIPLES 3 6 RECOMMENDATION FOR RESTORATION PRIORITY LEVELS 4 7 FLEXIBILITY. 4 8 CONCLUSION 5 9 DEFINITIONS. 5 10 ABBREVIATIONS AND ACRONYMS 6 11 REFERENCES 6 ATIS-0100006 T
15、echnical Report on Service Restoration Priority Levels for IP Networks 1 1 PURPOSE Restoration of communications traffic during severe network outages is a critical function for IP-based networks. For service providers with large volumes of traffic involved, prioritizing traffic for restoration acco
16、rding to traffic criticality as determined by Service Level Agreements (SLAs), as well as the availability of fast restoration mechanisms becomes essential. For instance, SONET rings are widely deployed in todays networks and provide fast (200 ms) restoration for all traffic that is routed over them
17、. At the same time, SONET rings may not be universally deployed by a service provider seeking to contain capital expense. It is imperative that the facilities transporting critical traffic such as National Security/Emergency Preparedness (NS/EP) services, are provisioned over rings. Similarly, as IP
18、 networks evolve, the ability to differentiate traffic for restoration priority, signal the desired restoration priority for traffic flows entering an IP backbone as well as traversing multiple backbones, and implementing appropriate restoration mechanisms capable of recognizing restoration prioriti
19、es and taking necessary actions, becomes a critical issue. The ATIS Network Performance, Reliability, and Quality of Service (PRQC) Committee recently published the Technical Report ATIS-0100003, User Plane Priority Levels for IP Networks and Services. 1The goal was to enable the ATIS sub-committee
20、on Signaling and Architecture Control of the Packet Technologies and Systems Committee (PTSC-SAC) to commence development of necessary signaling requirements for priority classifications for admission control and consequently, bandwidth reservation, in IP networks. The purpose of this Technical Repo
21、rt is to extend IP service classification to the important function of service restoration. The goal is to enable PTSC-SAC to include restoration priority in the development of necessary requirements for priority-based signaling extensions. This Report recommends three restoration priority class lev
22、els for IP services. It also recommends that NS/EP services such as Emergency Telecommunications Service (ETS) be included in the highest restoration priority class. 2 SCOPE From the perspective of the network, it is expected that future IP networks will be truly “converged.” That is, all forms of c
23、ommunications traffic will be handled by such networks control plane traffic (e.g., routing and signaling messages), NS/EP (real-time, data, and video) services, real-time voice and video services, data services, Virtual Private Network (VPN) services, as well as traditional “Best Effort” traffic. I
24、n such an environment, it is important to assign priority classifications and establish rules for service restoration such that critical services (e.g., control plane traffic and emergency services) are recognized and restored over other services in case of network overloads or failures. As service
25、flows can be expected to traverse multiple network domains, priority classification is an important step in the development of the necessary signaling protocol extensions as well as the mechanisms for enabling preferential restoration of critical services. ATIS-0100006 2 The scope of this recommenda
26、tion is limited to the determination of restoration priority class levels for communications over IP networks. In particular, the scope of this document is limited to addressing the need for priorities in automated restoration mechanisms in IP networks. The underlying support for this recommendation
27、 is based on the potential impact on IP services due to failure conditions. Specifically, the recommendation seeks to cast a broad view on priority classification, namely: what should the proper number of classes be such that critical services are given the highest probability of successful restorat
28、ion under failure conditions? For example, it is recognized that a class of “emergency services” can comprise Federal ETS (real-time, data, and video) as well as local E911 calls and that this class of traffic requires priority treatment in case of emergency. The goal of this document is to distingu
29、ish this class of traffic from other less critical classes of traffic. However, this document does not seek to “fine tune” the treatment of different traffic types within a broad priority class or level. Thus, the ability to distinguish between service types within any given priority class (e.g., di
30、stinguish between ETS and E911 services in the emergency service class) is beyond the scope of this document. 3 APPLICATION The priority level classification is based on the following premise: under reduced bandwidth conditions resulting from network failure, the critical issue for an IP network is
31、the ability to recognize and restore higher priority traffic flows over others. The priority level recommendations proposed in this document strictly relate to the relative importance of traffic classes from this perspective; they do not reflect implementation specific priority definitions. For exam
32、ple, there are mechanisms utilizing Generalized Multi-Protocol Label Switching (GMPLS) based Recovery that define specific recovery capabilities such as 1+1 protection and 1:N protection 2. Such mechanism-specific priority definitions do not apply to the recommendations in this document. 4 RELATED W
33、ORK A significant amount of work on ETS requirements is ongoing in various standards bodies. A detailed list of such efforts can be found in the ATIS/PRQC Technical Report T1.TR.79-2003, Overview of Standards in Support of Emergency Telecommunications Service (ETS) 3. An ATIS Technical Report origin
34、ated by the PRQC committee T1.TR.84-2004, IP Network Traffic Priorities and ETS documents the need for traffic prioritization from the perspective of emergency services 4. ATIS PRQC has also advanced a Technical Report on restorability aspects of ETS for publication 5 . In the ITU-T, Recommendation
35、E.361 6has progressed work on the definition of reliability and priority parameters for QoS service classes. This Recommendation also provides useful insights on the priority signaling across multiple networks. ITU-T Recommendation Y.1291 7presents a discussion on priority levels for Connection Admi
36、ssion Control (CAC) and service restoration functions in packet networks. ITU-T Recommendation TRQ-QoS-SIG 8also provides additional detail on the signaling aspects of restoration priority levels. In the IETF Next Steps in Signaling (NSIS) Working Group, work is ongoing to define Quality of Service
37、(QoS) modeling parameters in IP networks. Initial efforts include the use of priority parameters as well as a proposal for three levels for restoration priority 9. The goal of this effort is to eventually embrace QoS and priority parameters that apply to specific mechanisms such that these values ca
38、n be signaled throughout an IP network. Also in the IETF, the label distribution for Traffic Engineering and ATIS-0100006 3 QoS (and hence priority) can be accomplished via the Resource Reservation Protocol Traffic Engineering (RSVP-TE) 10. This protocol permits the creation of explicitly routed LSP
39、s and provides fast rerouting 11, traffic and QoS specification, preemption, and other capabilities. 5 RESTORATION PRIORITY PRINCIPLES In todays PSTN networks, restoration priority is influenced by the Telecommunications Service Priority (TSP) System 4, 12as mandated by the Federal Communications Co
40、mmission (FCC). Per these requirements, all TSP services (e.g., NS/EP services), regardless of their restoration priority, are restored before any non-TSP services. Service providers are required to restore TSP services with restoration priority assignments before telecommunications services without
41、 restoration priority assignments. However, control services and order-wires that are wholly owned and operated by a service provider and crucial to the operation of that service providers network are exempted from this requirement. The applicability of TSP procedures to evolving networks having IP
42、backbones (and generally, large cross-section optical transport systems) requires clarification. For instance, TSP procedures were written when only limited automated restoration methods (e.g., protection switching) were in existence. By contrast, todays automated restoration methods work best “in b
43、ulk” faster restoration is achieved when large amounts of impacted bandwidth are restored regardless of the underlying communications traffic. For example: SONET rings in transport networks restore all impacted facilities in less than 200 ms regardless of the type of traffic carried on the failed fa
44、cilities. Thus, a DS-3 that is provisioned for NS/EP private line traffic hence governed by TSP priority rules gets restored at the same time as other less critical DS-3 facilities on the ring. Re-routes in IP backbones work at the packet layer and are governed by OSPF rules in the event of failure.
45、 Packet streams are re-routed in the order of tens of seconds over alternate paths depending on the availability of spare bandwidth regardless of the type/source of packet. Thus, an ETS packet stream is just as likely to get re-routed as other less critical packet streams. The scope of this document
46、 is limited to addressing the need for priorities in automated restoration mechanisms in IP networks. It should be noted that transport restoration methods (e.g., SONET rings) cannot recognize failures in IP backbone routers, and hence, Layer 3 restoration in todays IP networks is done exclusively a
47、t the IP layer. To speed up the restoration process, faster MPLS-based re-route methods 11are being considered with restoration speeds in the sub-second range approaching SONET ring speed. However, it is not clear whether such faster methods can apply universally to all traffic in an IP network the
48、ability of such methods to work efficiently may require that the mechanisms only apply to a limited portion of the total traffic. In that case, it is recommended that all critical traffic, including NS/EP, be assigned to the faster re-route class in the IP network. Less critical traffic can then be
49、re-routed via existing OSPF methods. The above discussion immediately suggests that at least two restoration priorities are desirable in IP networks. However, the evolution of IP networks is driven by the idea of convergence the ability to transmit all types of communications traffic over IP backbones. Thus, service providers are increasingly planning the use of “converged” IP networks to carry real-time services such as Voice over IP (VoIP) as well as video, private data traffic (exemplified by VPN traffic),
