Scalable Application Layer Multicast

S. Banerjee, B. Bhattacharjee, C. Kommareddy, "Scalable Application Layer Multicast," ACM SIGCOMM Conference, (August 2002).

This paper presents an application layer multicast protocol specifically designed for low-bandwidth, data streaming applications with large receiver sets. Being based on hierarchical clustering of application-layer multicast nodes, it is highly scalable and is not very sensitive to churn. The authors claim that 2 measures of goodness of any application layer multicast overlay network can be per-link stress (no. of identical packets sent by the protocol over each underlying link in the network) and a per-member stretch (ration of path length from the source to the member along the overlay to the length of the direct unicast path). 

The authors propose NICE application-layer multicast scheme. It reduces the control overhead at any member to O(log N). Additionally, they also showed that the average member maintains state for a constant number of other members and incurs constant control overhead for topology creation and maintenance. The overall idea of the NICE scheme is as follows. All receivers are divided into various groups (of size between k and 3k-1 where k is a constant and consists of hosts that are closer to one another). Each cluster has a cluster leader that is preferably geometrically equidistant from all other nodes in the group. The cluster leaders of all the groups are further divided into groups in a higher hierarchy and this goes on until there is only one node at the top of the hierarchy. Data is sent in an hierarchical manner to the topmost node that forwards it to its corresponding children which again forward the data down the tree. It can be shown that on an average the control overhead incurred by the nodes is O(k) while in the worst case it could be upto O(k log N).

The simulation results consisted of a comparison on average link stress between NICE and Narada-5 and average path length (hops) between NICE, Narada-5, IPMulticast and Unicast. NICE performed better than Narada-5 over long periods of time. The results clearly showed a promising implementation of the application layer multicast protocol.