[VoiceOps] Ambiguous dial plan pattern matching

Tue Dec 4 12:22:54 EST 2012

Mary Lou, you write some fantastic educational posts on this list.  I
wanted to thank you for the time and effort you put into it.

On Mon, Dec 3, 2012 at 4:14 PM, Faisal Imtiaz <faisal at snappydsl.net> wrote:

> Thanks for an excellent detailed explanation.
> :)
>
>
> Faisal
>
> On Dec 3, 2012, at 5:21 PM, "Mary Lou Carey" <marylou at backuptelecom.com>
> wrote:
>
> > Routing is determined by the NPA type of that area AND by the local
> calling
> > guide established by the LEC. Everyone can set their own local calling
> areas
> > as far as rates are concerned, but you will be charged CABS according to
> the
> > way the LEC established their local calling area for each rate center.
> (Rate
> > centers are established by the NANP and can be a city, a portion of a
> city
> > or a group of cities. They are listed in the LERG, and on several other
> > websites such as localcallingguide.com, nationalpooling.com and
> nanpa.com).
> >
> > Seven digit dialing is only used in areas where there is one NPA for the
> > local area. Ten digit dialing is used in areas where there is an overlay
> > (more than one NPA per local area) and 11 digit (1 plus) is used in areas
> > where there was an area code split. The difference between a split and an
> > overlay is that a split required everyone (existing and new end users) to
> > change their NPA to the new area code. Overlays allow you to assign
> numbers
> > from the new NPA to new end users but allows the existing end users to
> keep
> > their old NPA.
> >
> > LECs typically break up their local and EAS calling areas by rate center
> and
> > while local calling areas are limited by rate center boundaries, local
> > calling areas can vary by rate center. For example, someone in Nashville
> TN
> > can make a local call to both Murfreesboro and Franklin, but a person in
> > Murfreesboro cannot make a local call to someone in Franklin.
> >
> > Every NPA-NXX is assigned to a specific rate center and a specific
> switch. A
> > switch can cover multiple rate centers and local calling areas, so the
> LECs
> > set up call scenarios that detail the dialing requirements and how the
> call
> > will be routed. They begin by adding every NPA-NXX-X associated for that
> > particular switch and map out which NPA-NXX combinations require 7 digit
> > dialing. Then they set up a scenario for each call type determined by
> route.
> > So if your end user calls another one of your end users in the same rate
> > center, it's going to use scenario A in which the switch will route the
> call
> > directly itself and only require 7 digit dialing. If your end user calls
> > someone on the B list (let's say that list contains all the NXXs within
> the
> > same NPA), then require 7 digit dialing and route the call to the local
> > tandem trunks. I could go on and on, but basically the concept is that
> after
> > you determine the dialing requirements for each rate center your switch
> > covers in a particular LATA and the available routes the call has to
> take,
> > you set up call scenarios in your switch to cover each dialing
> requirement /
> > route combination your switch will encounter.
> >
> >
> > Mary Lou Carey
> > BackUP Telecom Consulting
> > marylou at backuptelecom.com
> > Office: 615-791-9969 x 2001
> >
> >
> >
> >
> > -----Original Message-----
> > From: voiceops-bounces at voiceops.org [mailto:
> voiceops-bounces at voiceops.org]
> > On Behalf Of Nathan Anderson
> > Sent: Monday, December 03, 2012 10:55 AM
> > To: 'voiceops at voiceops.org'
> > Subject: [VoiceOps] Ambiguous dial plan pattern matching
> >
> > Sorry for what probably will end up sounding like a rather noob-ish
> > question, but I still consider myself a relative greenhorn...
> >
> > We are a VoSP.  With the advent here in the U.S. of area code overlays,
> > 10-digit dialing, and even carriers/vendors (VoIP and wireless, mostly)
> > continuing to blur the distinction between local and toll calls (at least
> > from the end-user's perspective), it is not an uncommon thing to run into
> > service platforms where both 7- and 10-digit dialing is supported, but
> the
> > 7-digit support feels (again, from the customer's perspective)
> half-assed,
> > at least compared to the ILEC's implementation.  But if the customer
> still
> > lives in an area where 10-digit dialing is not mandatory, he/she expects
> it
> > to work, so we "have" to provide it.
> >
> > It feels inferior because back when when local destinations were always
> > within the same NPA as the caller, the number pattern rules were simple,
> at
> > least for domestic calls: if it starts with a 1, it will be an 11-digit
> > number, and if it starts with 2-9, it will be a 7-digit number; but now,
> if
> > it starts with 2-9, it could be either 7 or 10 digits, and you won't know
> > for sure which one it is unless the caller has entered more than 7
> digits.
> > And in these ambiguous scenarios where two destination patterns partially
> > overlap, it's the "did the caller stop dialing" part that's hard to
> measure,
> > right?  So now you have CPE gear generating dialtone (whether PBX or ATA)
> > which either feels to the caller like it is extremely slow at putting the
> > call through, or which requires the caller to remember to do something
> > special at the end of a 7-digit destination (like dial # or something to
> > signal they're done) if they don't want to wait.  (There's also been a
> > similar phenomenon for a whil!
> > e with PBX systems that use outbound routing prefixes like '9' in order
> to
> > make it unambiguous whether you are dialing an internal extension or an
> > external destination.)
> >
> > Now obviously the CO switch can't read minds either, so in areas without
> > mandatory 10-digit dialing, it seems inescapable that it would have to
> > determine whether the user is done dialing via some kind of timeout
> > mechanism as well.  But it sure seems like most Class 5 switches must
> have a
> > much more intelligent ambiguous number pattern matching algorithm than
> most
> > CPE gear does since, as a general rule, people that still have an analog
> > loop to the CO these days and regularly dial 7 digits don't experience
> > (e.g.) upwards of a 5-second delay between when they've finished dialing
> and
> > when they hear their first ringback.
> >
> > The question is, what's the secret sauce, and why can't that same
> algorithm
> > be implemented in CPE gear?
> >
> > --
> > Nathan Anderson
> > First Step Internet, LLC
> > nathana at fsr.com
> > _______________________________________________
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> >
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>
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-- 
Carlos Alvarez
TelEvolve
602-889-3003
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