|  | 6.1 | Frame Relay Technology
| 6.1.4 | Frame R elay DLCIs
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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