Chapter 16. IP Multicast


The Internet was originally designed to carry two types of traffic, unicast and broadcast. Unicast traffic is sent from a single sender to a single host (or receiver), providing one-to-one delivery. Broadcast traffic goes from a single sender to all hosts, providing one-to-all delivery. Multicast traffic offers a third model, sending traffic from a single sender to many hosts (one-to-many delivery) and from many senders to many receivers (many-to-many delivery). Applications—such as streaming audio and video, collaborative groupware, teleconferencing, distributed online games, and “push” technology that sends periodic data delivery, such as stock quotes and sports scores—are well-suited for multicast because from a single source of data, they want to reach a specific, limited audience scattered across the Internet. If these applications use a unicast model, they must set up a session with each individual viewer. This places a heavy overhead burden on the source, which must replicate the video or audio stream for each customer. If these applications instead broadcast a single stream, the burden shifts to devices all across the network, which must replicate the stream regardless of whether there are downstream receivers interested in the video or audio stream. Multicast provides a way for these applications to deliver a single stream to all interested listeners.

Multicast networks consist of servers, which are the sources of a stream ...

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