Hierarchical Path QoS on a QoS-based Multicast Protocol SRSVP Takaaki Sekiguchi † , Kenji Fujikawa †† , Yasuo Okabe †† and Kazuo Iwama † † Department of Communications and Computer Engineering †† Department of Intelligence Science and Technology, Graduate School of Informatics, Kyoto University Abstract In this paper, we argue a method to collect information of each existing multicast flow on hierarchical networks. SRSVP, a QoS-based multicast routing protocol, is designed as it collects flow-specific information, called PQ, by putting it into signaling messages, so that the derived QoS path becomes more efficient. HQLIP, an underlying QoS-based uni- cast routing protocol, handles a network as a hierarchical structure for scalable QoS-based routing. We have designed and implemented an algorithm to compute PQ (hierarchical PQ) corresponding to aggregated link information on hierarchical networks for SRSVP to compute better QoS paths. We have attempted to make the algorithm more efficient by examining behaviors of routers. called HQLIP 6) , protocol, have been pro- 1. Introduction posed by Real Internet Consortium (RIC, IP multicasting is designed to enable the de- http://www.real-internet.org/). SRSVP uses a livery of packets to a set of hosts that have been mechanism to collect flow-specific information, configured as members of a multicast group 1) . called PQC (Path QoS Collection) 7) , to com- Various protocols for IP multicast routing such pute better QoS routes in order to let receivers as PIM-SM 2) have been developed. But these join multicast distribution trees. HQLIP han- existing protocols are based on the best-effort dles a network as a hierarchical structure so service, so QoS guarantees are not considered. that it archives a scalable QoS-based routing. On the next-generation Internet, it is neces- In this paper, we argue an algorithm to sary to accomplish some services, for example, collect PQ on hierarchical networks, so that multi-site video conferences and broadcasting SRSVP compute better QoS routes moreover over the whole of the Internet. Therefore IP on hierarchical networks handled by HQLIP. multicast routing with QoS guarantees on a 2. A Framework for QoS Multicasting large-scale network is required. Routing Traditional routing protocols such as OSPF 3) distribute single arbitrary metric, while QoS- 2.1 PQC based routing protocols distribute additional PQC is a mechanism to collect flow-specific routing metrics such as transmission delay and information for QoS-based routing. available bandwidth. If any of these metrics In any QoS-based multicast routing model, change frequently, routing updates may become it is important how routers collect flow-specific more frequent and they consume more network information. That is, how much information resources. That is, there exists a scalability is- routers have about existing multicast trees af- sue in QoS-based routing on a large-scale net- fects routing heuristics very much. work. One of techniques for the issue is to For example, in the PNNI signaling protocol, aggregate local information by handling a net- QoS routes are determined without collecting work as a hierarchical structure 4) thereby avoid flow-specific information. For QoS-based mul- flooding messages over the whole network. ticast routing with such mechanisms, it is im- For scalable QoS-based multicasting, a possible to compute efficient routes reflecting QoS-based multicast routing protocol, called current multicast trees. Because of a lack of SRSVP 5) , and a QoS-based unicast routing information about resources consumed by mul- -1-
ticast flows, it may appears that there exists no tribution tree become like Figure 2(a). routes accommodating the requested QoS, and route determinations may fail. S S On the other hand, QOSPF 8) attempts to R1 R1 f f 3 3 collect all information. It advertises flow- 3 3 a 4 a 8 e e 3 3 b 3 b 3 specific information on links by messages called 3 3 k k C d C d RRA. Routers are notified all states of multi- 4 8 8 4 j j i i cast flows by them and they will compute ef- 4 8 4 4 ficient routes 9),10) . h h But the number of RRA 4 4 messages can easily become large as the num- R2 R2 g g ber of flows increase. There exists a scalability (a) (b) issue on a large-scale network, so it will be un- (a) Reservations without PQC / (b) Fig. 2 realizable. Reservations with PQC PQC is a mechanism as it collects flow- specific information on links, called PQ (Path PQC works as follows. When the Path mes- QoS), by putting it into Path messages of sig- sage is sent from S , each router investigates naling protocols. Using this information, each more precise QoS information on links for the router updates link-state information flooded flow, puts it into the Path message, and for- by QoS-based routing protocols and computes wards the message downstream to the receivers. better QoS routes. PQ includes transmission By PQC, the routers g , h , and i can know the delay and available bandwidth for a flow. For links among d , e , and f are available for the example, assuming that there exists a flow con- flow, that is, these links have 8Mbps available suming 3Mbps bandwidth on a link and QoS- bandwidths. Then the Resv message will be based routing protocol advertises the link has routed along the path g − h − i − d − e − f and 6Mbps available bandwidth, then PQ indicates the link states and the multicast tree becomes that the link has 9Mbps available bandwidth. like Figure 2(b). Reservations with PQC con- The following figures illustrate examples of sume network resources more efficiently than PQC. Figure 1 illustrates a network and its link those without PQC. states. The numbers beside links indicate avail- 2.2 SRSVP able unidirectional bandwidths on each link. SRSVP is a QoS-based multicast routing For simplicity, bandwidths on links are consid- protocol that combines a resource reservation mechanism like RSVP 11) with a multicast rout- ered to be the same value as the opposite direc- tion, originally they are different in directions. ing scheme like PIM-SM. Traditional multicast routing protocols such as DVMRP 1),12) and MOSPF 13) are based on S broadcasts for receiver discovery, so they have a :router f 8 scalability issue. SRSVP employs the concept S:sender 8 a 8 e 8 b 8 of a rendezvous point (RVP) like PIM-SM to 8 k C d solve the issue. In SRSVP, multicast packets 8 8 j i are transferred from a sender to a rendezvous 8 8 h point by unicasting and to receivers by multi- 8 casting. That is, reservations between a sender g and a rendezvous point and those between a Fig. 1 A network rendezvous point and receivers are established First, when a receiver R 1 requests 5Mbps to independently. S that is a sender of a multicast flow, the Resv The mechanism of resource reservations and message for the resource reservation is routed multicast routing are as follows. A receiver along the path a − b − c − d − e − f computed sends a Resv message, called Resv0. Each by a QoS-based routing protocol. Next, an- router forwards it along the best-effort path to other receiver R 2 requests 4Mbps to S . The a sender. A sender sends a Path message in re- Resv message is sent to S . The path will be sponse to the Resv0 message. Each router for- g − h − i − j − k − f because other paths have wards it with PQ along the reverse path of the insufficient bandwidths and cannot grant the Resv0 message. The receiver sends a second request. Then link states and the multicast dis- Resv message, called Resv1. Using PQ, each -2-
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