[VoiceOps] Ambiguous dial plan pattern matching

Faisal Imtiaz faisal at snappydsl.net
Mon Dec 3 13:10:55 EST 2012

Quick FYI.... (you need to hit reply all, if you want the thread to 
continue on the list)    :)
(I always get tripped by this..different  lists are configured 
differently ! )

DUAL NPA with 7 digit dialing, ....I would say that your situation would 
be rather unique. We do see that at times, especially in border areas.
(Best option is to re-train the customer.... btw.. .how do the Cell 
phones in the area handle this ?)

As far as timeouts are concerned, they are an age old balancing act... 
there is no easy answer other than tweak it till you are happy with it.

We often tell our clients that the phone service works like the Cell 
Phone, put in the tel # and then press dial.

Unless others can chime in with suggestions !   :)

Faisal Imtiaz
Snappy Internet & Telecom

On 12/3/2012 12:49 PM, Nathan Anderson wrote:
> Not true...I live in an area where we (Moscow, ID; NPA 208) sit a couple of miles from the state border, and there is a town immediately across the border from us (Pullman, WA; NPA 509), and the same telco (Frontier) is the ILEC in both towns.  It is considered a local call when dialing Pullman from Moscow and vice-versa, *and* Frontier's customers can dial numbers in the opposite town as 7 digits, leaving off the NPA!
> I realize it might be a unique scenario, and it is not the same as an NPA overlay, but it does exist.
> Also, just to clarify, we do the same thing too: we accept any 7-digit destination and automatically tack on the caller's NPA to the number before patching it through.  That's not the problem.  The problem is that the CPE gear that the client has will wait several seconds before realizing that the caller has stopped dialing if they only dial 7 digits, because after only hearing 7 digits, the gear can't know for sure whether to match NXXXXXX or NXXNXXXXXX without waiting for a timeout to expire first; it's ambiguous.  In contrast, somehow the ILEC's switch is able to recognize that the caller is done dialing much faster and resolve the ambiguity to its satisfaction.  The question is, how?
> -- Nathan
> -----Original Message-----
> From: Faisal Imtiaz [mailto:faisal at snappydsl.net]
> Sent: Monday, December 03, 2012 9:18 AM
> To: Nathan Anderson
> Subject: Re: [VoiceOps] Ambiguous dial plan pattern matching
> Something to keep in mind....   7 digit dialing only works in areas
> (LATA) where there is only one NPA. Any area with multiple NPA are 10
> digit dialing.
> We address this,  as close to the CPE as possible (Hosted PBX, or on
> IAD/Phone/CPE) .  Since one knows what is the 'local' NPA for the DID of
> that CPE / Client.
> We use a conversion rule to take all 7 digit dial strings and convert
> them 10 digit dialing, by adding the NPA.
> The switch is setup for 10 digit dialing.
> Lots of folks are now going to 1+ (aka 11 digit) dialing on the switch
> to stay consistent, using similar techniques.
> Hope this helps clearing it up.
> Regards
> Faisal Imtiaz
> Snappy Internet & Telecom
> On 12/3/2012 11:55 AM, Nathan Anderson wrote:
>> 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?

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