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

[c.savinovich at itntelecom.com]

  I don't see where it is difficult to figure out.

  First of all, system keeps looking up on the table as user dial each
number.

  When number starts with 1, expect USA. When number doesn't start with
either 1 nor 0, expect USA too.

  When number starts with 011, and as country code and city code is
identified, expect as many numbers as determined by country+city code
(once you know country and city code, you know how many local digits to
expect)

CS

>>>Question:
How does the local Telco know you're done dialing a seven digit number?
Easy you may say:  If your dial string begins with 1, the parser expects
11 digits total, otherwise seven, 011 is international.

The reason suspect it's more complex is that:
1) International numbers can vary widely in length and
2) Our local analog Telco will route a ten digit NANP numbers with no
leading 1 and with no terminator--seemingly instantly

Obviously this could be done with 'timeouts'--implicitly 'sending'
after a delay.  But it works so well I suspect there's more logic in
there.   For example I have dozens of ATA's provisioned with timeouts,
and I find it difficult or impossible to replicate the Telco dialing
experience (Either the delay is too long, or you have frequent 'reorder'
tones because it 'sent' before you were finished).

Therefore I assume that there is something more 'fancy' going on.  Can
someone validate, debunk or clarify this?

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 possibleto 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.

-Karl