Multicast

Multicast has been a large research area since the 90s, and it has presented some usesful insights into how to get a subset of hosts in the Internet to communicate effectively. Multicast has traditionally been done at the network layer. The motivation for network-layer multicast is twofold. First, it reduces the amount of work done at the application and transport layers. Second, because packets are not duplicated until they must traverse multiple flows, duplicate data transmission is avoided and unnecessary congestion is reduced.

Because of the difficulties involved with the expanding nature of the Internet and integrating multicast into routers, multicast has not always been deployed at the network level. Instead, multicast is often implemented at the application layer. While this involves more overhead, multicast is still able to be deployed. Perhaps our experience deploying it at the application layer will give us further insights that will make it possible to deploy multicast at the network layer in the future as an optimization.