I'm not sure the telephone network is really that robust. Think about the SS7 network and a world with 50,000 CLEC's. Like most things, you don't want to really know what's in the sausage. Some systems are designed with a high degree of control, so everything works correctly. But they often have the property of catastrophic failure when any part fails to work perfectly, such as the cascading failures of the western power grid last year.
Years ago, it WAS that robust. Virtually not central control. The switches were internally redundant [axe off part of a #1 crossbar switch; like a worm the rest keeps wiggling...], trunking was almost too simple to break in increments greater than one, etc. But we've traded dumb redundancy for speed and efficiency. And we've paid for that. It struck me that the Martin Luther King Day ATT voice crash [?1991?] was chillingly parallel to this year's frame outage -- both went down on DoS from Sorcerer's Apprentice worth of maintenance messages. -- A host is a host from coast to coast.................wb8foz@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433