Construction Of Reservation-based Multicast TreesFor Networked Multimedia Services

Abstract

Distributed multimedia applications make extensive use of real-time multicast streams to implement a new class of services based on the distribution of digital audio and video. Examples of these services are those offered by video-on-demand servers and videoconferencing systems. In such applications, the source delivers a continuous data stream to multiple destinations. This can be logically represented as a tree-shaped communication channel in which the source is the root of the tree and the destinations the leaves .A general problem in this area is the construction of the multicast tree that connects the data source with the destinations. This task is normally accomplished by so-called reservation protocols (e.g., RSVP or ST2+). These protocols not only select the connection paths based on a routing algorithm, but also reserve critical resources (e.g., network bandwidth) over such links. Insufficient resources availability over the selected path causes a connection rejection. This paper discusses an improvement to this scheme. In particular, when a reservation should be rejected because of the unavailability of the requested resource, an alternative could be to try the same reservation on a different path. To this end, the routing protocol should be capable of redrawing the Shortest Path Tree (SPT) without the links or nodes that have provoked the rejection. In the paper, we discuss a strategy for minimising the computational effort by exploiting the knowledge of an initial SPT as calculated for the network without resource reservation constraints. The strategy is based on a centralised version of the Bellman-Ford algorithm, and assumes a linear representation of the above SPT as the scan order for propagating the lowest costs. In such a context, we demonstrate the efficiency of this approach compared with the time performances of the Dijkstra algorithm. The experiments were carried out over sample Transactions on Information and Communications Technologies vol 15, © 1997 WIT Press, www.witpress.com, ISSN 1743-3517