Editing Multicast (section)

==IP==
[[file:Multicast Protocols-en.svg|thumb|The relationship between the multicast group management protocol family and the multicast routing protocols family based on the network topology terms.]]
[[IP multicast]] is a technique for one-to-many communication over an IP network. The destination nodes send [[Internet Group Management Protocol]] ''membership report'' and ''leave group'' messages, for example in the case of IPTV when the user changes from one TV channel to another. IP multicast scales to a larger receiver population by not requiring prior knowledge of who or how many receivers there are. 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 take care of replicating the packet to reach multiple receivers only when necessary.

The most common [[transport layer]] protocol to use [[multicast address]]ing is [[User Datagram Protocol]] (UDP). By its nature, UDP is not ''[[Reliability (computer networking)|reliable]]''—messages may be lost or delivered out of order. By adding loss detection and retransmission mechanisms, [[reliable multicast]] has been implemented on top of UDP or IP by various [[middleware]] products, e.g. those that implement the [[Real-Time Publish-Subscribe (RTPS) Protocol]] of the [[Object Management Group]] (OMG) [[Data Distribution Service]] (DDS) standard, as well as by special transport protocols such as [[Pragmatic General Multicast]] (PGM).

IP multicast is always available within the local subnet. Achieving IP multicast service over a wider area requires [[multicast routing]]. Many networks, including the Internet, do not support multicast routing. Multicast routing functionality is available in enterprise-grade network equipment but typically needs to be configured by a network administrator. The Internet Group Management Protocol is used to control IP multicast delivery.