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An IP multicast is a communication technique used for one-to-many and many-to-many real-time communication over a TCP/IP network.
Data is often simultaneously communicated from a server toward many clients who have requested the data. The technique can scale to a large receiver population because the server does not need to know the identities of the receivers or the number of receivers, unlike in traditional TCP/IP communication which requires a sort of handshaking where a separate connection is required for each source-destination pair.
An IP multicast is also known as multipoint communication.
An IP multicast serves to transmit data to multiple hosts. The network nodes, like routers and switches, take care of replicating the data packets to be sent to the receivers in such a way that data is sent over each link only once. Three things are required for this method:
The IP multicast group address is used by both sources and receivers for messaging. Sources or senders use the group address to transmit their packets while receivers ask the network to join that group address using the Internet Group Management Protocol (IGMP) so that they can receive the packets being sent to that group address.
This is an efficient way of sending data to a multicast group compared to unicast and broadcast methods. In a unicast, the sender transmits data to each receiver separately in a multicast group, which makes it very inefficient when there are many recipients. On the other hand, in the broadcast method the sender transmits to every host on a network, and the hosts who have no need for the data simply drop it. This wastes a resources and is really only applicable to hosts within the same network or LAN.