1、 International Telecommunication Union ITU-T J.283TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2006) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Digital transmission of television signals IP network architecture with network layer rout
2、e diversity providing resilient IP multicast video distribution ITU-T Recommendation J.283 ITU-T Rec. J.283 (11/2006) i ITU-T Recommendation J.283 IP network architecture with network layer route diversity providing resilient IP multicast video distribution Summary This Recommendation proposes an IP
3、 network architecture supporting network layer route diversity to construct resilient video distribution infrastructure using IP multicast. Source ITU-T Recommendation J.283 was approved on 29 November 2006 by ITU-T Study Group 9 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec
4、. J.283 (11/2006) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tar
5、iff 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 Recomm
6、endations 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 Recommen
7、dation, 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. interoperabili
8、ty 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 compli
9、ance 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
10、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 received notice of intellectual property, protected by patents, which may be required to i
11、mplement 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 2007 All rights reserved. No part of this publication may be reproduced, by an
12、y means whatsoever, without the prior written permission of ITU. ITU-T Rec. J.283 (11/2006) iii CONTENTS Page 1 Scope 1 2 References. 1 2.1 Normative references 1 2.2 Informative references 1 3 Terms, definitions and acronyms 1 4 IP multicast network. 1 5 Considerations of router/link failure. 2 6 R
13、equirements 3 7 IP network architecture with network layer route diversity . 3 iv ITU-T Rec. J.283 (11/2006) Introduction IP multicast is a promising technology for providing IP-based video distribution because of its bandwidth efficiency that accommodates millions of clients. The construction of a
14、stable IP multicast network is a very important issue to meet the service quality requirement of IP-based video distribution. This Recommendation describes a set of architectural concepts for constructing an IP multicast network with high availability. ITU-T Rec. J.283 (11/2006) 1 ITU-T Recommendati
15、on J.283 IP network architecture with network layer route diversity providing resilient IP multicast video distribution 1 Scope Highly available IP multicast network architecture will be discussed in order to maintain sufficient service quality for IP-based video distribution. This Recommendation co
16、ncerns network layer (Layer-3) route diversity between the server edge routers and the client edge routers. Note that Layer-3 route diversity is independent of Layer-2 resiliency, i.e., protection and/or restoration. As Layer-2 resiliency does not cover Layer-3 route diversity, e.g., Layer-2 resilie
17、ncy cannot handle a routers failure. This Recommendation focuses on Layer-3 architectural issues. Coordination with Layer-2 resiliency would contribute to even higher reliability. 2 References 2.1 Normative references None. 2.2 Informative references RFC 2328 IETF RFC 2328 (1998), OSPF Version 2. RF
18、C 2362 IETF RFC 2362 (1998), Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification. 3 Terms, definitions and acronyms This Recommendation defines the following terms: 3.1 multicast: A packet delivery mechanism from one source to many clients supported by IP routers. 3.2 video d
19、istribution: Digital video services for an unspecified number of clients. 3.3 Protocol Independent Multicast-Sparse Mode (PIM-SM): A multicast routing protocol based on an explicit join model for multicast groups that may span a wide area. 3.4 RP: A Rendez-vous Point among multicast sources and grou
20、p members. Packets transmitted from multicast sources are distributed via an RP router at the beginning of multicast transmission. 3.5 Open Shortest Path First (OSPF): A unicast routing protocol for large-scale intra-domain networks. OSPF is a link state based routing protocol specified according to
21、 the ISO IS-IS routing protocol. 3.6 cost: A cost is a parameter configured by an operator in order to make a network resource utilization effective. Example definition is described in RFC 2328. 4 IP multicast network Figure 1 shows an example of an IP multicast network. Each IP router replicates pa
22、ckets conveying video stream and forwards them to downstream routers or clients along multicast trees. A Multicast 2 ITU-T Rec. J.283 (11/2006) tree is established from client-edge routers to the multicast source1on a hop-by-hop basis by a multicast routing protocol such as PIM-SM (Protocol Independ
23、ent Multicast Sparse Mode) running on each router. In PIM-SM, each router decides an upstream router using unicast routing information destined for the multicast source. Figure 1/J.283 Example of IP multicast network 5 Considerations of router/link failure On the other hand, Figure 1 has only one un
24、icast route between the client-edge routers and the multicast source. When an intermediate router or link between them fails as shown in Figure 2, multicast packets do not arrive at the client until recovery of the failure. In detail, from the viewpoint of the network layer, the following procedures
25、 occur in the routers below the failure point. a) A unicast routing protocol such as OSPF (Open Shortest Path First) detects the failure and withdraws the unicast route for the multicast source. b) PIM-SM recognizes that there is no unicast route for the multicast source. As a result, the correspond
26、ing multicast trees are broken. c) OSPF detects the failure recovery and recalculates the unicast route for the multicast source. d) PIM-SM knows the reappearance of this unicast route and reconstructs the multicast trees. _ 1The multicast source can be an RP (Rendez-vous Point) router in PIM-SM. IT
27、U-T Rec. J.283 (11/2006) 3 Figure 2/J.283 Example of router failure scenario 6 Requirements In order to prevent long-time service disruption due to single router or link failure on multicast trees as described in clause 7, this clause describes requirements and recommendations of IP network architec
28、ture for resilient IP multicast video distribution. The most important point is that the route diversity of multicast trees is provided dynamically. a) In order to avoid long-time service disruption due to one router or link failure on multicast trees, an IP multicast network is required to be const
29、ructed with unicast route diversity from any client-edge router to the multicast source. That is, an alternative unicast route is required to appear automatically when the original route is withdrawn. b) Multicast trees are required to be reconstructed dynamically along the alternative unicast route
30、 after failure. c) For quick convergence of the reconstruction of multicast trees, it is recommended that at least two equal-cost unicast routes are arranged from any client-edge router to the multicast source so that one or other of the unicast routes can be always preserved. 7 IP network architect
31、ure with network layer route diversity This clause categorizes the following three types of IP network architecture realizing network layer route diversity. 1) Category 1: A client-edge router has only one best route destined for the multicast source. Another route(s) is possible, but its cost is gr
32、eater than the best route. 2) Category 2: A client-edge router has at least two best routes, i.e., equal-cost routes, destined for the multicast source. However, other routers such as core routers do not always have equal-cost routes for the multicast source. 3) Category 3: A router except for serve
33、r-edge routers has at least two best routes, i.e., equal-cost routes, destined for the multicast source. 4) Category 2+1, 3+1: In addition to Category 2 or 3, another route(s) destined for the multicast source is possible in every router, but its cost is greater than the best routes. 4 ITU-T Rec. J.
34、283 (11/2006) Figures 3 through 7 depict examples of IP network architecture. All the categories satisfy Requirements a) and b) in clause 6. However, only Category 1 does not satisfy item c) in clause 6. Figure 3/J.283 Example of IP network architecture (Category 1) Figure 4/J.283 Example of IP netw
35、ork architecture (Category 2) ITU-T Rec. J.283 (11/2006) 5 Figure 5/J.283 Example of IP network architecture (Category 3) Figure 6/J.283 Example of IP network architecture (Category 2+1) 6 ITU-T Rec. J.283 (11/2006) Figure 7/J.283 Example of IP network architecture (Category 3+1) In all the categori
36、es, the following procedures are performed to reconstruct multicast trees if a router/link failure occurs on them. a) OSPF detects the failure and withdraws the corresponding unicast route for the multicast source. Unicast route recalculation occurs. b) (Category 1) As a result, an alternative route
37、 is recalculated, and then appears on the unicast routing table for the first time. b) (Categories 2, 3, 2+1, 3+1) Even during the route recalculation phase, the other equal-cost unicast route remains as an alternative route on the unicast routing table. Therefore, the router can rapidly proceed to
38、Step c). c) PIM-SM reconstructs the multicast trees according to the alternative unicast route if they have been established along the withdrawn route. After recovery of the failure, similar procedures to Steps c) and d) in clause 5 are conducted. Comparing Category 3 with Category 2, the network re
39、siliency will increase because more network layer route diversity is provided in Category 3. For example, even if two routers fail simultaneously at different levels, e.g., the core and server-edge, Category 3 can continue multicast distribution, but Category 2 cannot. However, the network topology
40、is more complicated and may be expensive in Category 3 considering the incidence of such a failure scenario. Printed in Switzerland Geneva, 2007 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
41、 service, service operation and human factors Series F Non-telephone telecommunication 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 t
42、elevision, sound programme and other multimedia signals Series K Protection against 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: interna
43、tional sound programme and television transmission circuits Series O Specifications 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 equi
44、pment 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
