Frame Relay is a simple Layer 2 non-broadcast multiaccess (NBMA) WAN technology used to interconnect enterprise LANs. A single router interface can be used to connect to multiple sites using PVCs. PVCs are used to carry both voice and data traffic between a source and destination, and support data rates up to 4 Mb/s, with some providers offering even higher rates.
An edge router only requires a single interface, even when multiple virtual circuits (VCs) are used. The short-leased line to the Frame Relay network edge allows cost-effective connections between widely scattered LANs.
Frame Relay creates PVCs which are uniquely identified by a data-link connection identifier (DLCI). The PVCs and DLCIs ensure bidirectional communication from one DTE device to another.
For instance, in the figure, R1 will use DLCI 102 to reach R2 while R2 will use DLCI 201 to reach R1.