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Broadcast networking refers to a type of networking that is done on shared-media networks such as Ethernet where multiple nodes are attached to the same LAN. It is a one-to-many method of transmitting information. All the devices attached to the network that receive the broadcast are part of the same broadcast domain.

In contrast, a point-to point link is an unshared connection between two systems. On a point-to-point link, there is no contention for the cable because it connects only the sender and receiver, not a number of shared devices. There are also NBMA (Nonbroadcast Multiple Access) networks such as ATM (Asynchronous Transfer Mode), frame relay, SMDS (Switched Multimegabit Data Service), and X.25. NBMA networks are the opposite of broadcast networks. They are constructed of a mesh of connections or a switching fabric, and virtual circuits are established to transmit information between two endpoints. There is no broadcasting. Data is sent directly across the circuit as if a physical wire connected the endpoints.

A transmission on a broadcast network consists of frames that include the MAC (Medium Access Control) address of the destination node. Network interface cards have built-in MAC addresses that are programmed at the factory. A sender puts the destination system MAC address in a frame and transmits it on the network. Each node listens to traffic on the network and reads the destination address in the frames. If a node receives a frame that has been addressed to it, it accepts the frame. Other nodes ignore the frame. There is also a broadcast address that is used to address frames to every node on the network.

Applications that produce broadcast messages include ARP (used by hosts to locate IP addresses on a network), routing protocols like RIP, and network applications that "advertise" their services on the network. Multicasting is a selective form of broadcasting that allows broadcasts to be directed to users who request to see the broadcast and limits broadcasts to only those parts of the network where users have requested it, thus controlling traffic where it is not needed.

A discussion of broadcasting may be found in RFC 791 (Internet Protocol, September 1981) and RFC 919 (Broadcasting Internet Datagrams, October 1984).

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
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