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362 Chapter 10: X.25/Frame Relay Topologies
Figure 10-21
Frame Relay Hub and Spoke (Star)
Full Mesh
NBMA, or full mesh, is not very common. It is a very expensive solution for connecting your
sites. The best reason might be for implementing a voice over Frame Relay network or voice
over IP network because there would be fewer delays from one site to another. The number of
hops is one in a full mesh, which is good for voice traffic. Because full mesh can be expensive,
some companies are asking for a CIR of 0 to offset their costs. The provider simply does not
guarantee that any traffic will flow through the network at all. So, if you hear "voice" in the
same sentence you hear "a CIR of 0," you might wind up disappointed.
A number of PVCs do not scale well in a full-mesh environment. The formula to determine the
number of PVCs needed in a full-mesh environment is n * (n ­ 1) / 2, where n is the number of
sites. This equates to a bill for 45 PVCs if you have 10 sites--not very cheap. Remember that
circuits are monthly recurring costs. It should be your goal to keep that cost to a minimum while
providing the company a quality WAN.
Central
Cloud
Virgina
Florida
North Carolina
192 K CIR
DLCI 101
DLCI 102
DLCI 103
DLCI 100 64 K
DLCI 100
64 K
DLCI 100
64 K
87200333.book Page 362 Wednesday, August 22, 2001 2:53 PM