In computer networking, multicast (one-to-many or many-to-many distribution) is group communication where information is addressed to a group of destination computers simultaneously. Group communication may either be application layer multicast 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 routers, switches and 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 Ethernet multicast addressing, Asynchronous Transfer Mode (ATM) point-to-multipoint virtual circuits (P2MP) 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 datagrams sent to a multicast destination address.
Multicast is often employed in Internet Protocol (IP) applications of streaming media, such as Internet television scheduled content (but not media-on-demand) and multipoint videoconferencing, but also for ghost distribution of backup disk images to multiple computers simultaneously.
Multicast should not be confused with physical layer point-to-multipoint communication.
In telecommunication and information theory, broadcasting is a method of transferring a message to all recipients simultaneously. Broadcasting can be performed as a high level operation in a program, for example broadcasting Message Passing Interface, or it may be a low level networking operation, for example broadcasting on Ethernet.
All-to-all communication is a computer communication method in which each sender transmits messages to all receivers within a group. This contrasts with the point-to-point method in which each sender communicates with one receiver.