Policy Statement on Address Space Allocations

}-- End of excerpt from Vadim Antonov

Regular telephone service is indeed generally multihomed except for the
final loop from the central office.

SS7 is a major pain partly because of the multiple routes it supports.
- Multiple links in linksets (partly for capacity, partly for reliability)
- Multiple linksets in routesets, where each linkset terminates on a
   different node

Typically the CO is "multihomed" to two mated STPs for signaling traffic,
and user traffic is routed through multiple tandems based on load,
availability, cost and destination. Of course SCPs are also deployed in
pairs. All this is in addition to the redundancy built into each piece
of equipment, or the underlying transport (e.g. sonet). Of course none
of this stuff comes for the price of a Cisco router either.

What *is* true is that the telephone network is more or less a static
network in terms of routing (although becoming less so). It would be
big news indeed if a new CO just popped onto the network and started
"announcing" itself!

This "static routing" idea makes for ultimate control and predictability
even with multiple routes.