Frame Relay PVC Concepts

Typically, the service provider preconfigures all the required details of a PVC. For instance, in Figure 15-3, the switches knew to forward frames with DLCI 102 to Cincinnati, and frames with DLCI 103 to Boston.

One reason that drawing the PVCs is important is that when you order Frame Relay service, you do not have to have a PVC between each pair of routers. For instance, Figure 15-3 shows three sites, and frames going from one site (R1) to the other two sites (R2 and R3). That network does not have to have a PVC between R2 and R3. The choice of which sites need to have a PVC depends on where the network engineers think that traffic needs to flow in the network. When routers use Frame Relay, and there is a PVC between each pair of routers, the PVCs are in a full mesh, as shown in Figure 15-5; when not all routers have a PVC, it's called a partial mesh, as was shown in Figure 15-3.