Page 227 - Optical Switching And Networking Handbook

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212 Chapter 8

voice over data, data, video, and multimedia on the same communi-
cations channels.This provision enables the long-distance carriers to
allocate and multiplex as much bandwidth as the customer needs in
a private-line service between the two ends, as shown in Figure 8-22.
In the long-distance network, the SONET and SDH services can
be used to provide a series of interconnected ring topologies that
enables the carrier to provide the redundancy and resiliency of the
network as needed. Figure 8-23 shows a series of interlocking rings
used to provide full service and availability in case of a disaster (for
example, backhoe fade when a backhoe digs up the cables). These
interconnected rings may provide a full 1:1 protection circuit for the
entire OC 12/48 network, or they may be 1:n (where n is 3, 4, or 5),
enabling mission-critical services to be covered even though some
lower-priority circuits may not be 100 percent backed up. This
enables the carrier to provision as much as necessary in order to
meet the critical need without overpopulating a network for
nonessential services. This is more of an economic decision than any
other consideration. Regardless of the level of backup coverage, the
carriers use the interconnected rings for their benefit as well as for
that of the customer.

Figure 8-22
The data private
line

Metro Access
Optical Private Line Optical Switch
ILEC/CLEC
Optical Switch OC-3/OC-12

Metro Access
ILEC/CLEC