HP 600 Series, Services And Applications

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Frame Relay Connections
Figure 2 shows another view of the Frame Relay network. All of the routers
are connected together in a fully meshed topology. Each router has a connec-
tion, a permanent virtual circuit (PVC), to each of the other routers in the
network. (The PVC is illustrated by the lines in figure 2 that connect each of
the routers inside the Frame Relay network.) Each connection is referenced
by a Data Link Connection Identifier (DLCI). DLCIs are conventions be-
tween a router and a frame relay switch.
Figure 2. PVCs Connecting Routers
DLCIs are typically 10 bits wide. Were DLCIs unique throughout the
network, the network would be limited to 1024 addresses—too few
addresses for large public networks. However, DLCIs are not globally
unique; instead, they are “locally significant”, which means they are unique
only on the boundary Frame Relay switch. Thus, there are duplicate (or
reused) DLCIs in a Frame Relay network. Also, routers on either end of a
PVC typically have different DLCIs to reference the same connection. DLCIs
100 and 133 in figure 2 are examples of addresses that are reused.
The fully meshed topology shown in figure 2 is the topology that best
exploits the value of Frame Relay. When compared to private-line pricing, a
meshed topology using Frame Relay is often a fraction of the cost.
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Linking Up with Frame Relay
Overview
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