As an interface between user and
network equipment,
Frame Relay provides a means for multiplexing many
logical data conversations, referred to as virtual circuits, through a
shared physical medium by assigning DLCIs to each DTE/DCE pair of devices.
Frame Relay's multiplexing provides
more flexible and efficient use of available bandwidth. Therefore,
Frame Relay allows users to share bandwidth at a reduced cost. For
example, say you have a WAN using Frame Relay, and the Frame Relay is
equivalent to a group of roads. The phone company usually owns and
maintains the roads. You can choose to rent out a road (or path)
exclusively for your company (dedicated), or you can pay less to rent
a path on shared roads. Of course, Frame Relay could also be run
entirely over private networks; however, it's rarely used in this
manner.
Frame Relay standards address permanent
virtual circuits (PVCs) that are administratively configured and
managed in a Frame Relay network. Frame Relay PVCs are identified by
DLCIs, as shown in Figure ,
Frame Relay DLCIs have local significance. That is,
the values themselves are not unique in the Frame Relay WAN. Two DTE
devices connected by a virtual circuit might use a different DLCI
value to refer to the same connection.
Frame Relay provides a means for multiplexing many logical
data conversations. The service provider's switching equipment constructs a table mapping
DLCI values to outbound ports. When a frame is received, the switching device analyzes the
connection identifier and delivers the frame to the associated outbound port. The complete
path to the destination is established before the first frame is sent.
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