28.7 FRAME RELAY VERSUS X.25

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28.7 FRAME RELAY VERSUS X.25

X.25 was used extensively for wide area networks for many years. With the introduction of Frame Relay for wide area networks, the significance of X.25 reduced drastically. A comparison of the X.25 and Frame Relay protocol architectures reveals the reasons.

Figure 28.5: Comparison of X.25 and Frame Relay protocol standards.

In X.25, above the physical layer, LABP and X.25 packet layer protocols will be running that will take care of flow control and error control. A number of acknowledgements are exchanged between the end systems and the switches. Lots of supervisory information also is sent over the network. In the case of Frame Relay, the datalink layer contains only the LAPF protocol, which is a very lightweight protocol with little overhead. Flow control and error control need to be taken care of by the higher layers, such as the TCP layer in TCP/IP networks. The end systems have the necessary processing power so this will not be a problem. Secondly, in Frame Relay networks the physical medium is generally optical fiber, so there are fewer errors.

Compared to X.25 protocols, Frame Relay protocols have less overhead, so switching is very fast in Frame Relay networks. However, Frame Relay is more suited for less noisy transmission media such as optical fiber.

Frame Relay protocols are much more simplified than X.25 and, if used over transmission media with high bandwidths and low errors, they will be very efficient. Frame Relay–based networks are becoming very popular with the advent of optical fiber communications.

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