n a router. This opens up design possibilities allowing connectivity to multiple sites at a significant cost savings over point-to-point circuits. Figure 23-5 shows three sites networked together with Frame Relay. On the left, Router B and Router C are both connected to Router A, but are not connected to each other. This design is often referred to as a partial mesh or hub and spoke network. In this network, Router B can communicate to Router C only through Router A. On the right side of Figure 23-5 is an example of a fully meshed network. The difference here is that all sites are connected to all other sites. Router B can communicate directly with Router C in the fully meshed network. Meshed networks are not strictly the domain of Frame Relay. As you can see in Fig- ure 23-6, a fully meshed network can easily be created with point-to-point T1s. In a Frame Relay network like the one shown on the left side of Figure 23-6, each location needs a router that can support a single T1. Each PVC can be configured as separate virtual interface called a subinterface. Subinterfaces allow VCs to terminate into separate logical interfaces within a single physical interface. With point-to-point links (T1s, in this case), each router must be able to support two T1 interfaces. Routers that support two T1s are generally more expensive than Frame Relay Network Design Router B Router B Router A Router A Router C Router C Partial mesh or hub and spoke Full mesh Figure 23-5. Meshed Frame Relay networks Router B Router B Router A Router A Router C Router C Frame Relay Point-to-point full mesh T1 full mesh Figure 23-6. Frame Relay versus point-to-point T1 meshed networks single-T1 routers. Additionally, point-to-point T1s cost more than Frame Relay T1 services, especially over long distances. The example in Figure 23-6 is relatively simple, but what about larger networks? Fig- ure 23-7 shows two networks, each with six nodes. On the left is a fully meshed network using Frame Relay, and on the right is a fully meshed network using point