Multicast is the delivery of information to a group of destinations simultaneously using the most efficient strategy to deliver the messages over each link of the network only once and only create copies when the links to the destinations split.
The Multicast concept can also be used in amateur radio, allowing digital users to bypass the bottlenecks that currently exist in the world-wide high frequency packet radio network. This is a new approach that may increase the efficiency of digital radio communications.
The word "Multicast" is typically used to refer to IP Multicast, which is a delivery method in IP networks for efficiently sending datagrams to multiple receivers at the same time on networks by way of a multicast destination address. It is also commonly associated with audio/video protocols such as RTP.
IP multicast conferencing was first demonstrated on a wide scale when it was used to broadcast several sessions from the 23rd IETF in March, 1992 to researchers and interested observers around the world. IETF sessions had up until recently been available via multicast. A handful of conferences and program content continues to be available, but almost always content tends to be delivered like a TV broadcast, from a single sender and one-way only.
Multicast security has been an active area of interest for some time. Standard, practical, communications security solutions normally employ symmetric cryptography. But applying that to IP Multicast traffic would enable any of the receivers to pose as the sender. The IETF MSEC workgroup is developing security protocols to solve this problem, mostly within the architectural framework of the IPsec protocol suite.
