On Sun, 19 Jul 2009 14:34:12 +0100, Roland Perry
wrote:

In message , at 14:15:56 on
Sun, 19 Jul 2009, Recliner remarked:
There *is* an underlying technical issue, in that out-of-area codes
don't scale, because they involve running wires from one exchange to
the other.

Surely it's all done with software now? In any case, the exchanges are
now connected by high bandwidth glass, not copper wire.

The software switches calls within the exchange, but they have to get
there first.

I'm not sure if it does any more. ISTR the exchange "owning" the
number now rejects the call and instructs the originating exchange
where to send it (all done in milliseconds) BICBW. The older version
on some exchanges required use of a directory number at the exchange
actually serving the subscriber to which calls were silently diverted
by the exchange which "owned" the number; IIRC that became unneccesary
once everything was replaced by System X or newer.

The originating exchange can only send to the receiving
exchange specified by the code (there won't be an "exception routing
table" for the out-of-area numbers). And that exchange then has to
deliver the call to a distant POTs line.

ITYF that like 0345, 0845 etc. it can deliver to a "numberless"
circuit.

That latter connection might
well be done by a MUX at both ends and fibre in between, but that too
doesn't scale very well, and isn't inherently cheaper than a leased line
between those two points.