Editing Multicast (section)

{{Short description|Computer networking technique}}
{{About|one-to-many communications in computer networks|radio systems|Point-to-multipoint communication|broadcasting multiple programs using a single channel|Multicast channel}}

[[Image:multicast.svg|right|250px]]
{{routing scheme}}

In [[computer networking]], '''multicast''' is a type of group communication where [[data transmission]] is addressed to a group of destination computers simultaneously.<ref name="app_layer">[https://books.google.com/books?id=I4excGQVTVkC&dq=multicast+%22one+to+many%22+%22group+communication%22+-IP_multicast&pg=PA302 Media-communication based on Application-Layer Multicast]</ref> Multicast can be [[point-to-multipoint communication|one-to-many]] or [[many-to-many]] distribution.<ref>Lawrence Harte, ''[https://books.google.com/books?id=EUUqAAAACAAJ&q=multicast+%22one+to+many%22+television Introduction to Data Multicasting]'', Althos Publishing 2008.</ref><ref>{{Cite journal |last1=Li |first1=Bing |last2=Atwood |first2=J. William |date=2016-06-19 |title=Secure receiver access control for IP multicast at the network level: Design and validation |url=https://www.sciencedirect.com/science/article/pii/S1389128616300706 |journal=Computer Networks |language=en |volume=102 |pages=109–128 |doi=10.1016/j.comnet.2016.03.010 |issn=1389-1286|url-access=subscription }}</ref> Multicast differs from physical layer [[point-to-multipoint communication]].

Group communication may either be [[application layer]] multicast<ref name=app_layer/> or network-assisted multicast, where the latter makes it possible for the source to efficiently send to the group in a single transmission. Copies are automatically created in other network elements, such as [[router (computing)|routers]], [[Network switch|switches]] and [[base station subsystem|cellular network base stations]], but only to network segments that currently contain members of the group. Network assisted multicast may be implemented at the [[data link layer]] using one-to-many addressing and switching such as [[multicast address#Ethernet|Ethernet multicast addressing]], [[Asynchronous Transfer Mode]] (ATM), point-to-multipoint virtual circuits (P2MP)<ref name="p2mp">{{Cite web |title= DCCast: Efficient Point to Multipoint Transfers Across Datacenters |author= M. Noormohammadpour|display-authors=etal|date= July 10, 2017 |publisher= USENIX |url= https://www.researchgate.net/publication/316921061 |via=ResearchGate |access-date= July 26, 2017 }}</ref> or [[InfiniBand]] multicast. Network-assisted multicast may also be implemented at the [[Internet layer]] using [[IP multicast]]. In IP multicast the implementation of the multicast concept occurs at the IP routing level, where routers create optimal distribution paths for [[datagram]]s sent to a multicast destination address.

Multicast is often employed in [[Internet Protocol]] (IP) applications of [[streaming media]], such as [[IPTV]] and [[videoconferencing#Multipoint videoconferencing|multipoint videoconferencing]].