A network whose basic task is to move files from one place to another can transmit data packets at an uneven rate. If portions of a file arrive slowly or out of order, that is not a problem. Multimedia requires that data packets arrive at the client on time and in the proper order. Second, multimedia requires transmitting large amounts of data over the network, and thus uses more of the network's bandwidth than basic network operations such as file transfer. Multicasting, the subject of this paper, addresses this issue.
Networks also support broadcasting.
When data is broadcast, a single copy of the data is sent to all clients on the network. When the same data needs to be sent to only a portion of the clients on the network, both of these methods waste network bandwidth. Unicast wastes bandwidth by sending multiple copies of the data. Broadcast wastes bandwidth by sending the data to the whole network whether or not the data is wanted. Broadcasting can also needlessly slow the performance of client machines.