Multicast Sockets

Abstract

This chapter describes reflectors and application-layer multicast. Reflectors are essentially designed to receive one transmission and reflect it multiple times. However, application-layer multicast is one-to-many communication supported by application-layer mechanisms. It is noted that multicast that uses router support for building and maintaining trees is typically called native multicast or network-layer multicast. A multicast reflector requires two functions. The first function is to determine the set of receiving IP addresses that require multicast traffic from a particular group. The second function is to join the multicast group and then create an individualized stream for each receiver. Also the reflector needs to be run on a machine that has multicast connectivity and enough bandwidth to create a replicated stream for each receiver. It is observed that application-layer multicast is again becoming popular because the deployment of network-layer multicast has been far slower than expected. IPv6 is the right solution in order to build applications that can be made widely available to users, but it is very hard to deploy.