SCAMP : SCAlable Multicast Protocol for Communication in Large Groups

Atul Vadera, Roll Number: 9711105, February, 1999.

This report proposes a new scalable multicast protocol for communication within a large group over Internet. There are many existing and new applications in which the groups involved are very large. An example would be Video-conferencing amongst a large and widely distributed group. The members of such a group can be spread across the entire Internet with no uniformity in their pattern of distribution. In such applications, there will be one or at most a few sources and a large set of destinations or receivers. The existing multicast routing protocols do not support such large groups efficiently. They incur large overheads and do not scale well. In this thesis we have proposed a new protocol that incurs less cost and is scalable.

Most protocols either build source-based trees or shared trees. Source-based trees are those which have their root located at the node sending the data. In shared trees, a few routers in the Internet act as root of the trees and distribute the data among the members of the group which are on this tree. Source-based trees have the advantage that they support high data rate. The advantage of using shared trees is that they can support sparse groups. We have proposed a protocol which combines the advantages of both type of trees. Our protocol builds both the source-based and shared trees. The shared tree is used for signalling purposes. It conveys the information regarding the source to all the members of the group. Only one signalling tree is used for all the existing multicast groups. A multicast group is referred to a set of nodes across the Internet which can be identified by a common identifier. The source-based trees on the other hand are used for data delivery. The building of the source-based tree is initiated by the receivers. It exists as long as the members belonging to that group are present. This helps in reducing the route entries maintained by routers (referred as router state). Further it reduces the concentration of traffic in different parts of the network, the processing cost of the routers and also utilizes the bandwidth efficiently, by distributing the load.

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