DNHR
Telephone Networks: Dynamic Non-Hierarchical Routing (DNHR)
A major advance in telephone routing was the development of
dynamic non-hierarchical routing (DNHR). DNHR
makes use of the statistical predictability of aggregated
telephone traffic and the fact that switches and links are usually
available to select two-hop paths when the shortest one-hop path is
blocked.
DNHR divides the day into a number of periods (usually 10 or so), and
for each period, each toll switch is assigned:
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A primary one-hop path to another toll switch,
and
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An ordered set of alternative, two-hop paths.
The Routing Algorithm
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Incoming calls are forwarded on the primary path.
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If the resources are already in use and cannot be delegated to the current call
(this situation is termed spilling or
overflow), try the alternative two-hop path according to the
pre-computed order for the current period
(known as the crank-back).
-
If all alternative paths are busy, the call is rejected.
Warning!
DNHR's performance may suffer if the traffic changes suddenly, so that
the list of alternative paths ought to be changed (but is not). Any
unexpected traffic change may increase the load on some trunk groups
while leaving other trunks underutilized.
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