Overview
Routing in Telephone Networks
The national telephone network is structured as a three-level hierarchy:
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Subscribers (telephones, modems, fax machines)
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Central offices
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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.
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The Routing Algorithm Used:
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If a call's source and destination are within a central
office, directly connect them.
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If the call is between central offices within a local
exchange carrier, use a one-hop path between central
offices.
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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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