Page 93 - Optical Switching And Networking Handbook

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78 Chapter 3

Figure 3-20
OC-N OC-N
ADMs installed
along the way

OC-N
OC-N

Insert
1 OC-1
Drop off
1 OC-1

Hub and Spoke

The hub and spoke method (sometimes referred to the star network)
enables some added flexibility in the event of unpredicted growth or
constant change in the architecture of the network. SONET multi-
plexers can be hubbed into a digital cross-connect, where the signal
is concentrated and then forwarded on to the next node. This is used
in many larger organizations where regional offices are located at
some distance, and district or branch offices are tied into the net-
work through the hub. Once again, the flexibility is available if a
major change occurs in the network architecture or in the event of
major campaigns in the organization. Hubs will act as the cross-con-
nect points to link the various echelons in the network together.
These may be developed in a blocking or nonblocking manner. Typi-
cally, some blocking may be allowed. The hub and spoke arrange-
ment is shown in Figure 3-21.

Ring

Next comes the real glory of SONET. In a ring architecture, where
SONET automatic protection switching is employed, the best of all
worlds comes to fruition. In this topology,ADMs are used throughout
the network, and a series of point-to-point links is installed between
adjoining neighbors. The bidirectional capability provides the most
robustness for the network; however, unidirectional services also can
be installed. The primary advantage of the ring architecture is sur-