Frame Relay provides connection-oriented data link layer communication. This means that a defined communication exists between each pair of devices and that these connections are associated with a connection identifier. This service is implemented by using a Frame Relay virtual circuit, which is a logical connection created between two data terminal equipment (DTE) devices across a Frame Relay packet-switched network. Frame relay is an extremely efficient data transmission technique used to send digital information such as voice, data, local area network (LAN), and wide area network (WAN) traffic quickly and cost-efficiently to many destinations from one port. It is especially effective for the bursty traffic typical of most LAN interconnection applications.
Similar to X.25, frame relay uses the concept of virtual circuits to provide maximum bandwidth utilization and connectivity flexibility. A physical frame relay port can have multiple virtual circuits, each connecting to a different destination port. Virtual circuits belonging to the same physical port can share all the available bandwidth so that applications can borrow from the unused idle bandwidth for short periods of time when dealing with traffic burst.
To further optimize efficiency, frame relay takes advantage of the improvements in quality of digital transmission facility by using only the bottom two OSI protocol layers, rather than three (in the case of the X.25 protocol). By restricting its use to Layers 1 and 2, frame relay performs error detection only, whereas X.25 performs both error detection and retransmission. Frame relay leaves retransmission up to the intelligent devices at each end of the network.
In the event of errors, frame relay simply drops bad frames to reduce overhead and enable greater throughput. Congestion is handled through vendor implementation of the congestion management techniques described in the frame relay standards. Standards-compliant congestion management means that, even during congestion, each end user device has guaranteed access to a defined amount of bandwidth.
Frame relay also provides tremendous flexibility in terms of the types of devices that can be connected to the network. Because it is protocol transparent above Layer 2, the data link layer, most types of traffic can ride over a frame relay network without realizing that frame relay is being used. Because it is an access technique, frame relay is concerned only with the network interface; protocols determine the transfer of information on and off the WAN.