On 23 Nov, 14:47, "Clive D. W. Feather" cl...@on-the-
train.demon.co.uk wrote:

Mizter T writes

Overlays sound like a pretty ugly 'solution', I'm glad it sounds like
they're probably off the cards.

They're a lot better than the alternatives (area splits, like the London
01 - 071+081, and length changing, like Reading 01734-0118), both of
which affect existing customers as well.

But one could argue that overlays will affect everyone in the area in
that they'll force people into dialling an 11 digit number for some
local calls. Indeed in the US I've read that the FCC mandates 11 digit
dialling in areas where there are overlays so as to ensure that no
telco has a competitive advantage over any others simply because they
can offer new subscribers numbers in the the older established area
code.

Changing area codes shouldn't be done lightly, but my gut feeling is
that it's preferable to overlays.


I wonder whether the earlier projections for a squeeze on available
numbers aren't a bit out now. I'd think there's far less demand for
second residential lines nowadays, as people don't want dedicated
lines for fax machines or dial-up internet access. Of course, business
still likes direct-dial numbers which certainly has driven demand for
new numbers in certain locations.

The overwhelming cause of number shortages is new telephone companies,
because numbers are allocated in blocks of 1000 (formerly 10,000). So if
five new VoIP providers start up and want numbers in Cambridge, that's
5,000 numbers gone just like that (and a couple of years ago, 50,000
gone just like that).


May I enquire what the forthcoming central portability database is all
about?

Let's suppose you started with a BT line, but then moved to Virgin Media
while keeping your number. At present, when somebody calls you, the call
is sent to the BT exchange handling your old (now removed) line. This
notes that you're a ported customer, sticks a prefix (say 527724) on the
front of your number, and re-injects the call into the trunk network.
This prefix means that it's now routed to the VM exchange handling your
line, which can deliver the call to you. This technique is called
"onward routeing" and is relatively inefficient.

Yes, I'd heard about this method.


The new database will contain every telephone number in the UK together
with a code indicating which exchange it is connected to. When someone
calls you, *their* telephone exchange looks up your number in the
database and adds the code on the front. The rest of the network will
then route on the basis of the code, not your number.

OK. It's almost like each exchange will have the equivalent of their
own DNS server.


One effect of this is that ported calls are routed more efficiently. It
also means that numbers don't need to be allocated in blocks - there are
no problems with giving consecutive numbers to different telephone
companies. And, finally, it makes it trivial to port your number to a
different place.

Does this mean that say a London number could be ported to Cambridge
when someone moves? Would that actually be allowed?

I've certainly lost numbers when moving in London, between different
exchange areas. It'd have been handy to have kept the number - but
that would have broken the number/place linkage, and I also find it
most useful being able to have a broad idea of which area a particular
phone number relates to. Of course, with VOIP, there's no guarantee
that a number relates to any particular place these days - especially
as one can now port a geographic landline number to a VOIP provider -
but nonetheless it is still broadly true that much of the time the
number relates to a farily specific area (especially with regards to
BT geographic numbers).

I'm almost of the opinion that VOIP numbers should all occupy their
own number range (such as 04), rather than masquerade as geographic
numbers. Perhaps this ultimately shows that I'm living in the past,
and any notion of a firm link between telephone numbers and an area is
now old hat!

Anyway, thanks for your reply Clive.