[asterisk-users] Seemingly easy question: NPA/NXX

[Jay R. Ashworth]

----- "Karl Fife" <asterisk-users at kfife.mailworks.org> wrote:
> Theory 1
> Is it all done with timeouts, but they're CONDITIONAL timeouts.
> i.e. give a LONG timeout if the number:
> -did not start with a 1 and is still shorter than 7 digits, 
> -started with a 1 and is still shorter than 11 digits
> -started with a 011 and is shorter than the theoretical international
> minimum lenght
> 
> Theory 2
> As you know, a few years ago the 2nd digit of the NPA was always 1 or
> 0.
>  Therefore the switch could easily determine(without the leading 1)
> if
> your first three digits were an NPA or just an NXX (exchange).  They
> were nationally unambiguous.   Now that's no longer true.  STILL, it 
> could be possible to consider all known valid NPA's and exchanges so
> they
> can determine via context what you're trying to do, and thereby
> optimize
> the dialing experience?  
> 
> Can anyone speak to this?  I would very much appreciate any
> knowledgable input.

Well, my input is knowledgeable, though not authoritative.

Yes, each NANP switch actually does have a routing table loaded locally
(they call them "translations") that tells it where to route calls for 
each and every valid NPA-NXX in the NANP, and this could be used to
authenticate the first 3/6 digits of 7/10/11 digit dialled numbers for
intra-NANP calls, and in fact, I would bet that you're correct that that's
how they accomplish it.

I have never actually seen live switch code on this, but I think I could
locate some people who have -- but yes, you'll play hell duplicating it
exactly on something with as small a brain as an ATA.

Cheers,
-- jra
-- 
Jay R. Ashworth                   Baylink                      jra at baylink.com
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