4.5 Frame Relay

Frame Relay is a link-layer protocol used for large networks. It is specified in the following standards: I.122, I.441, and ANSI TI.606 and mostly in the standards of the Frame Relay Forum (FRF) group. See http://www.mfaforum.org.

Frame relay is usually used in permanent virtual circuits (dial-up lines are theoretically possible as well, but haven’t seen them in reality yet). A permanent virtual circuit is similar to a leased line. A user would rent virtual circuits in his or her particular locality from a Frame Relay provider.

A Frame Relay is a datagram-oriented and connectionless service; so unnumbered frames are transferred by it. The provider doesn’t guarantee the frame delivery. Each frame contains a checksum, so it is possible to check that the packet wasn’t changed during the transfer. A damaged packet is discarded.

The primary parameter of a virtual circuit is the amount of data that can be transferred by the user to the virtual circuit within...