Frame Relay

Frame Relay is a high-performance WAN protocol that operates at the physical and data link layers of

the OSI reference model. Frame Relay originally was designed for use across Integrated Services Digital

Network (ISDN) interfaces. Today, it is used over a variety of other network interfaces as well. This

chapter focuses on Frame Relay's specifications and applications in the context of WAN services.

Frame Relay is an example of a packet-switched technology. Packet-switched networks enable end

stations to dynamically share the network medium and the available bandwidth. The following two

techniques are used in packet-switching technology:

* Variable-length packets

* Statistical multiplexing

Variable-length packets are used for more efficient and flexible data transfers. These packets are

switched between the various segments in the network until the destination is reached.

Statistical multiplexing techniques control network access in a packet-switched network. The advantage

of this technique is that it accommodates more flexibility and more efficient use of bandwidth. Most of

today's popular LANs, such as Ethernet and Token Ring, are packet-switched networks.

Frame Relay often is described as a streamlined version of X.25, offering fewer of the robust

capabilities, such as windowing and retransmission of last data that are offered in X.25. This is because

Frame Relay typically operates over WAN facilities that offer more reliable connection services and a

higher degree of reliability than the facilities available during the late 1970s and early 1980s that served

as the common platforms for X.25 WANs. As mentioned earlier, Frame Relay is strictly a Layer 2

protocol suite, whereas X.25 provides services at Layer 3 (the network