A Reliable Broadcast Protocol.

Broadcast multipoint communication is the delivery of copies of messages to all nodes in a communication network. In a network with mobile subscribers, for example, the location and connectivity to the network of such subscribers may change frequently and this information must be broadcast to all nodes in the network, so that the corresponding directory list entry can be updated. Broadcast messages are used in many other situations, like locating subscribers or services whose current location is unknown (possibly because of security reasons), updating distributed data bases or transmitting information and commands to all users connected to the communication network. There are certain basic properties that a good broadcast algorithm must have and the most important are: a) reliability, b) low communication cost, c) low delay, d) low memory requirements. Reliability means that every message must indeed reach each node, duplicates should be recognizable upon arrival at a node and only one copy accepted, and messages should arrive in the same order as transmitted. Communication cost is the amount of communication necessary to achieve the broadcast and consists of, first, the number of messages carried by the network per broadcast message (broadcast communication cost), second, the number of control messages necessary to establish the broadcast paths (control communication cost), and, third, the overhead carried by each message (overhead cost). Low delay and a small buffer memory are basic requirements for any communications algorithm, and broadcasts are no exception. (Author)