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Frame Relay

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Frame Relay

ecently, the high-performance WAN encapsulation method known

as Frame Relay has become one of the most popular technologies in use. It
operates at the Physical and Data Link layers of the OSI reference model and
was originally designed for use across Integrated Services Digital Network
(ISDN) interfaces. But today, Frame Relay is used over a variety of other
network interfaces.

Cisco Frame Relay supports the following protocols:

DECnet

AppleTalk

Xerox Network Service (XNS)

Novell IPX

Connectionless Network Service (CLNS)

International Organization for Standardization (ISO)

Banyan Vines

Transparent bridging

Frame Relay provides a communications interface between DTE (data

terminal equipment) and DCE (data communication equipment, such as
packet switches) devices. DTE consists of terminals, PCs, routers, and
bridges--customer-owned end-node and internetworking devices. DCE
consists of carrier-owned internetworking devices.

Popular opinion maintains that Frame Relay is more efficient and faster

than X.25 because it assumes error checking will be done through higher-
layer protocols and application services.

Frame Relay provides connection-oriented, Data Link layer communica-

tion via virtual circuits just as X.25 does. These virtual circuits are logical
connections created between two DTEs across a packet-switched network,
which is identified by a Data Link Connection Identifier (DLCI). (We'll get
to DLCIs in a bit.) Also, like X.25, Frame Relay uses both permanent virtual
circuits (PVCs) and switched virtual circuits (SVCs), although most Frame
Relay networks use only PVCs. This virtual circuit provides the complete
path to the destination network prior to the sending of the first frame.

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