switch
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... subscriber lines
are different levels in the hierarchy. In the phone network, a switch
need not keep detailed routing information about every possible
...
... routing information about every possible
subscriber in a distant area code. Instead, the switch usually knows
one routing entry for the entire area code.
...
...
Notice that the effect on scaling is dramatic. If we look at the
space complexity of the different schemes, the switch that knows
about every subscriber in the world needs O(n) space for n worldwide
...
... hierarchical routing has space complexity O(l + e + a + c).
Notice that each of these factors is much, much less than n, and
grows very slowly, if at all. This implies that a phone switch can be
built today that has some hope of not running out of space when it is
deployed.
...
... addresses obtain from its provider, but then later
switches to a different provider (while continuing to use the same
addresses ...
... their current provider, and the provider they switch to in the future
do not require renumbering, renumbering may still be needed to
achieve Internet-wide ...
... CIDR block associated with the provider. Later
the organization may switch to another provider. The previous
provider ...