on the local access link. A popular analogy that explains local addressing is that there can be
only a single street address of 2000 Pennsylvania Avenue, Washington, D.C., but there can be
a 2000 Pennsylvania Avenue in every town in the United States. Likewise, DLCIs must be
unique on each access link.
header, which meets the requirement that the addresses be unique on that access link. Likewise,
for all VCs terminating at Router B, unique DLCI values must be used for each one. Because
there is only one VC to Router B in Figure 8-7, there is no possibility of an overlap.
revised network of Figure 8-8, in which DLCI 41 and 42 are still used by Router A on the access
link. Before the frames are forwarded on the access links to Router B and Router C, the Frame
Relay switches convert the DLCI to a value of 40 in each case. The DLCI values are chosen by
the service provider; the only requirement of local addressing can be summarized as follows:
VC on one access link has no bearing on the value that is chosen to identify the VC
on the access link at the other end of the VC.