On 2007-04-05, David Hearn <dave@NOswampieSPAM.org.uk> wrote:
> Dennis Ferguson wrote:
>> On 2007-04-04, Jon <spam@jonparker.plus.com> wrote:
>> That's not quite the topic I was addressing but, now that you mention
>> it, that bit of interaction with the carrier you are trying to take your
>> business from is definitely more awkward than just skipping that part,
>> going directly to the carrier you are taking your business to and having
>> them do the whole thing for you. And, to tell the truth, I can't imagine
>> what the PAC requirement has to do with GSM networks since other places
>> have GSM networks but don't make you talk to your old carrier about porting
>> a number out.
>
> Considering the number of complaints about people having their gas and
> electricity suppliers switched without their permission - I kinda like
> the idea that you cannot transfer a number without actually contacting
> your existing 'supplier' first. The whole "just put a signature here
> and we'll do the rest" method of switching gas/electricity suppliers
> seems open to abuse (which evidence proves).

I should note that in the two places I've ported numbers through the
receiving carrier (USA and Hong Kong) the requirement was that the
account holder at the old and new carrier be the same person. The
information they matched up at port time to establish this is essentially
the same information required for the credit check for a contract phone.
If it doesn't match (it didn't in Hong Kong) you need to go to the
old carrier to fix that.

If someone knew enough to pretend to be me for the purpose of stealing
my number they'd hence also know enough about me to open a line of
service in my name and then spend the next month making calls to Burma.
This being the case, stealing my phone number would be the very, very
least of my concerns (I'd prefer that they did take the number since
I'd at least find out about it sooner).

To turn the argument around, if there was money to be made stealing your
number I'm pretty sure you'd see those scams in the countries where
porting works this way. In the two countries I'm familiar with this
just doesn't happen; if someone could do it they could also do even
more profitable scams. In the US you can lock your account to prevent
porting (requiring a call to the old carrier to unlock it), but I
don't bother and I'm not sure anyone else does either.

>> The technical bit I find awkward is having your call routing depend on
>> the resources of a provider with whom you no longer have a business
>> relationship. That doesn't seem desirable for anyone involved, and
>> there are existance proofs that you don't have to do number porting
>> this way so, again, I'm wondering what it is about GSM networks that
>> you think requires this?
>
> In the UK each network is issued a number range. This range determines
> the charge of each call. Each range is routed into the relevant network.
>
> The way UK porting works is that the number range never actually leaves
> the original network - so 07974 is always Orange. If that number gets
> ported to T-Mobile, then Orange needs to set up something in their
> number routing tables to say that number is now off-network.

This is the same as the US and Hong Kong. In the US, of course, most
numbering is geographic, so a carrier will have lots of number blocks
(usually 10,000 numbers, though more often 1,000 numbers lately).
All number blocks remain assigned to the original network.

> At first thoughts, it does seem strange that you may port a number of
> times, never returning to Orange, but each time you port, Orange - your
> original provider - has to update their routing tables.

This is the difference. If only your original provider updates its
routing tables with new routing then you are forever dependent on
the original carrier's equipment to signal your new location for
every call you ever receive. If everyone's routing tables are updated
with your individual number and new provider, however, then those calls
are never delivered to your original provider's switches in the first
place, even though the original provider remains in full control of
the (remainder of) its number block's routing. You can eliminate
the extra signalling (forever) by updating everyone's routing table
(just once), at the cost of a bigger global routing data base. It
is a tradeoff; both ways work but have different costs and benefits.

In the US, and in Hong Kong (as I understand it), number porting is
accomplished by adding the number to global routing. Once this
is done you depend on your original provider for nothing. If you
give up the number it goes back to the original carrier, and if
you port back to your original carrier they obviously get to
remove the number from global routing and just follow the block
route, but otherwise the original carrier is nothing special.

> Unless you have a system where networks are not in charge of their
> number ranges (so a central system - owned by who?) and does the divert
> there, it's not going to be any different. And even then, the only
> difference is to do with who is responsible for updating the
> divert/routing tables.

There is no need for a divert from the original carrier if the
individual number is added to global routing.

I'm having trouble believing you could do without a central administrator
tracking the routing of number blocks (though lack of such might
explain why numbers seem to be incompletely routed so often by various
networks in the UK); even if the mobile companies only consume a single
prefix each, there are lots and lots of geographic and special number
blocks and operators need to learn how to route these from somewhere.
Whatever the mechanism is for distributing the global routing of
number blocks, the same mechanism would work for distributing routing
for individual numbers (with the exception that there are likely to
be a lot more of them). In Hong Kong I think a government department
does it. In the USA and (I think) Canada there's a contractor (NeuStar)
which is paid to perform that service. In the USA in particular the
porting process is really efficient. If you, on a whim, go to a store
you're passing and buy new service, the new phone will usually work
within an hour or so of leaving the store. I think the comparison
of account information to ensure you are you takes most of this
time; the actual rerouting is done by computers talking to computers.

> So far, the existing system of the originating
> network seems to work, and in all probability, evens out between all the
> networks pretty well.

I actually didn't mean to imply there was a better way to do this
in the UK. Porting through global routing may work in Hong Kong
because it is small, and while the USA is huge the use of geographic
numbering (and the constraint against porting numbers out of their
geographic area) means that the number of switches which need to be
updated with your ported number's routing is actually fairly small
as well. I only wanted to object to the notion that the divert from
the provider which owns the number block is the only way to do number
porting. There's an alternative.

Dennis Ferguson