IP unicast packets are transmitted with a source and destination address, which enable routers to find a path from sender to receiver. IP multicast packets are transmitted with a source and group address, which extend this functionality to provide delivery to a set of receivers.
IP multicast enables efficient many-to-many datagram distribution. It is one of the basic building blocks of the Internet multimedia architecture. For most conferencing purposes, for example, unicast is viewed as being a special case of multicast routing. It adds functionality to the Internet so that it can provide services resembling those in television broadcast networks, as well as those in CB radio networks and other, as yet unforeseen communication patterns.