Nonvoice-Capable Gateways Remove Extra Costs
Backbone
Router (R1)
3524 Switch
CallManager Unity
Site A
Router (R4)
3524 Switch
T-1
512K
Frame
Relay
Cloud
Site B
Router (R5)
3524 Switch
512K
Site C
Router (R6)
3524 Switch
Frame Relay uses a shared medium “cloud” provided by the telecommunications
carrier.While your circuit goes from your premises to the provider, the circuit
ends and hits the “cloud,” so called because no one really knows (except for
the provider) where the data passes through the network devices. All you know is
that the data arrives at the destination safely. Figure 11.3 shows an example of a
Frame Relay cloud used by many subscribers.
This cloud spans the United States and is typically joined by several telecommunications
carriers.This cloud is really a series of clouds that serve specific areas
of the country, and specific portions of each state as well.These connections are
joined by what is called a Permanent Virtual Circuit (PVC).A PVC is nothing
more than an increment of 64 Kbps channels bonded together to form the
desired capacity of circuit, up to the limit of the carrier. Figure 11.4 shows an
expanded view of the state of Florida to show the frame clouds at each of the
major cities displayed.