Principles Digital Communication System & Computer Networks (Charles River Media Computer Engineering)

Frame Relay provides fast switching of packets by reducing the protocol overhead. Due to fast packet switching, multimedia services at very high data rates can be supported. Frame Relay networks are now becoming popular for wide area networking. In this chapter, we will study the details of Frame Relay.

28.1 ADVANTAGES OF FRAME RELAY

Using X.25 protocols for wide area networks (WANs) results in delay mainly because X.25 protocols have lots of overheads. The packet sequence number, acknowledgements, supervisory frames, and so on create processing overhead at each packet switch. In Frame Relay, this protocol overhead is reduced to achieve fast switching.

In Frame Relay networks, the protocol overhead is reduced by eliminating the sequence number, acknowledgements, flow control, and error control. Hence, switching of packets is done very fast to support multimedia services.

In Frame Relay networks, each packet is called a frame. The frame contains user information, a 2-Byte Frame Relay header, a frame check sequence, and a flag. The protocol overhead is eliminated using the following strategy:

• There is no sequence number for the frames.

• The Frame Relay switch does not send an acknowledgement after receiving a frame.

• Multiplexing and switching of logical channels is done at layer 2, hence there is no need for layer 3 protocol. One complete layer of processing is eliminated.

• Call control signaling is done on a separate logical connection, so intermediate switches need not process messages related to call processing.

• There is no flow control or error control. End-to-end flow control and error control need to be done by higher layers. If a switch receives a frame and there are errors, the frame is discarded.