As carriers build global and national networks, it becomes necessary to systematically partition these networks into control domains, that is, subnetworks in which a particular control paradigm or protocol is employed. Control domains are often referred to simply as domains (see Chapter 5).
From a network control perspective, the motivations for dividing a network into domains are:
To define administrative boundaries
To allow for scalability of routing and signaling
To isolate portions of the network for security or reliability, and
To accommodate technology differences between systems, for example, by partitioning a single carrier's network into separate single vendor subnetworks
Figure 12-1 illustrates the partitioning of a ...