Before we dive right into Frame Relay we need to have a better understanding of what Frame
Relay is, how it is used, and how it came about.
What Is Frame Relay?
Frame Relay
is a telecommunications service designed for cost-efficient data transmission
across a WAN. Frame Relay puts data in a variable-size unit called a
frame
and leaves any
necessary error correction up to the end points. This provides for a high-speed, low-overhead,
efficient network.
Frame Relay is a layer 2 (Data Link layer) connection-oriented protocol that creates virtual circuits
(VCs)—usually permanent virtual circuits (PVCs)—between two end devices such as routers,
through a Frame Relay network. A Frame Relay
bearer service
was defined as a network service
within the framework of ISDN. It was designed to be more efficient and faster than X.25. The
major difference between Frame Relay and traditional ISDN is that in Frame Relay, the control
information needed to keep the link synchronized is not in a separate channel as it is in ISDN, but
instead is included with the data. This single stream of data provides for flow control, congestion
control, and frame routing. Frame Relay is a form of packet switching, whereas ISDN is still considered
circuit switching.
NOTE:You should understand that the error and congestion control works only at the
Data Link layer and that Frame Relay also relies on upper layer protocols and
applications for error correction.