[VoiceOps] Ambiguous dial plan pattern matching

[Hiers, David]

I can't see any secret logic mojo needed... 

The CO switch in a "10 digit optional" area never needs to face an ambiguous situation.  It can know every legitimate 7 digit NXX destination for every subscriber line, so it knows exactly where it is at all times in its digit-by-digit analysis.  I'm guessing here, but the CO switch probably never has to try to work with the handful of IF/CASE statements implied in your question, but has enough config room to store all the rules it needs to implement the required behavior for every line.  Heck, it probably even knows that 7 digits is a likely special case, and has the juice to implement special interdigit timeout rules around the 7 digit mark.

If there is any advantage on the CO side, it is probably (1) room to store and (2) cycles to execute a decision tree that never needs to wait for a long interdigit timeout for any string that does not begin with 011.

Between the LERG and LCADS and the contracts penned by each *LEC, there is no need for mystery, just reasonably sophisticated software and sufficient execute space and cycles.


David

-----Original Message-----
From: voiceops-bounces at voiceops.org [mailto:voiceops-bounces at voiceops.org] On Behalf Of Nathan Anderson
Sent: Monday, December 03, 2012 08:55
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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