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Overview

Routing in Telephone Networks

The national telephone network is structured as a three-level hierarchy:

  1. Subscribers (telephones, modems, fax machines)
  2. Central offices
  3. Long distance offices (toll switching offices)

A local exchange carrier (i.e. Bell Atlantic), provides local telephone services and manages many central offices interconnected with one-hop links.

The Telephone Network


Figure 10:





Subscribers are served by central offices, which are in turn linked at the core at toll-switching offices.

The Routing Algorithm Used:

  1. If a call's source and destination are within a central office, directly connect them.
  2. If the call is between central offices within a local exchange carrier, use a one-hop path between central offices.
  3. Otherwise, send the call to the appropriate core (or cores).

The only major decision in the selection of a path between two toll switches for a long-distance call is between a one-hop path and a two-hop path. (Paths longer than two hops usually are not considered).

 
 
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