IP Multicast

IP multicast is a method of sending (IP) datagrams to a group of interested receivers in a single transmission. It is a form of point-to-multipoint communication often employed for streaming media applications on the Internet and private networks. IP multicast is the IP-specific version of the general concept of multicast networking. It uses specially reserved multicast address blocks in IPv4 and IPv6. In IPv6, IP multicast addressing replaces broadcast addressing as implemented in IPv4.

IP multicast is described in RFC 1112. IP multicast was first standardized in 1986. Its specifications have been augmented in RFC 4604 to include group management and in RFC 5771 to include administratively scoped addresses.

IP multicast is a technique for one-to-many and many-to-many real-time communication over an IP infrastructure in a network. It scales to a larger receiver population by requiring neither prior knowledge of a receiver's identity nor prior knowledge of the number of receivers. Multicast uses network infrastructure efficiently by requiring the source to send a packet only once, even if it needs to be delivered to a large number of receivers. The nodes in the network (typically network switches and routers) take care of replicating the packet to reach multiple receivers such that messages are sent over each link of the network only once.

The most common transport layer protocol to use multicast addressing is (UDP). By its nature, UDP is not reliable—messages may be lost or delivered out of order. Reliable multicast protocols such as Pragmatic General Multicast (PGM) have been developed to add loss detection and retransmission on top of IP multicast.

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