In article <[EMAIL PROTECTED]>, Andy
Davidson <[EMAIL PROTECTED]> writes
Tunnels all over the place seems like the only way it'd even be
halfway practical. It's more-or-less how phone number portability
works anyway, from what (little) I know.
I don't know about the USA, but in the UK it's done with something
similar to DNS. The telephone system looks up the first N digits of
the number to determine the operator it was first issued to. And
places a query to them. That either causes the call to be accepted and
routed, or they get an answer back saying "sorry, that number has been
ported to operator FOO-TEL, go ask them instead".
Not quite, the simplistic overview is that operators have an obligation
to offer porting wherever practical, so operate ports on a
accept-then-forward principal. If I port my number from CarrierA to
CarrierB, then my calls still pass through A's switch, who transits the
call to B without charging the end user.
For the benefit of completeness, the regulator has mandated that this
situation must change, as CarrierB's inward-port customers are not
protected from the technical or commercial failure of CarrierA. The
industry [www.ukporting.com] has responded and is building a framework
to support all-call-query style lookups to handle number ports.
Apologies, I should have made it clear that I was following up the
remark about cellphone number portability. Described in 2002 (at the
beginning of the discussion about migrating to the new system that's
currently still being built):
"To deliver a call a routing enquiry is made to a Home Location Register
(HLR) to determine where the subscriber is located and to obtain a
routing number. The solution for mobile number portability, known as the
Signalling Relay Function (SRF), is that the donor network sends the
routing enquiry signal addressed to a ported number to the appropriate
recipient network for treatment. In this way the recipient network can
provide the routing number to complete the call."
Although that is also apparently known as "onward routing", even though
the subsequent call traffic isn't routed onwards.
--
Roland Perry
