UC@GMC - The extensions puzzle

Hopefully by now you are already convinced that Unified Communications concept has great practical application(s) in EDU sector. It is time to look closer as of how it was implemented in GMC.


***If you expect to see a screenshots of installation and configuration – this is not happening. OCS 2007 R2 and Exchange 2007 (including UM role) is very well documented, you can find it all over Internet and having it here (again) would be a waste of time. My idea is to share the path, the line of thinking and the steps we went through in order to complete the deployment.

Oh, once Microsoft lifts the NDA over Wave 14, it will be different story…

The first challenge – extensions schema. Current users of Centrex or any hosted PBX are familiar with the Enterprise Extensions concept. Basically, the user dials three or four digits and connects to another user in the same location. What happens is: a normalization rule takes place to “convert” the 4 digit number to “full”, in some cases E.164 format, phone number. For example – 2704 was converted to 478-445-2704, a match is found and the called party is ringed. This is because all numbers are typically within the same PBX (remember, NPA-NXX-XXXX) where XXXX is the “internal” extension.

This is valid for all our offices. However, one problem - user in Milledgeville dials 4 digits to call colleague in Milledgeville, user in Valdosta dials 4 digits to call colleague in Valdosta, while calls cross-campus required fill 10 digit number. Of course, a long distance charge would occur due to the fact they reside in different Local Calling Area.

Since we will now host (and control) the environment, we wanted to make “dial by extension” available for cross-campus calls as well. OCS is E.164 compliant. In order a call to be processed, the number must be presented as +1 NPA NXX XXXX. A call (as we know it at home) is typically 7 digits (445 2704) for local calls, 10 digits (478 225 2704) for some local area calls and 11 digits (1 478 445 2704) for long distance. OCS uses RegEx (Regular Expressions) to capture, evaluate and manipulate the input and convert it to E.164 format. For example: ^(\d{7})$ to be translated to +1478$1

On English, this means “Match numbers that are exactly 7 digits long. Prepend '+1478'.” With other words, when users dial 4452704, the number will be presented as +12784452704 for further processing.

Now, we know that Local Area Codes/Prefixes are different for our remote offices, for example 478-387-XXXX for Milledgeville and 229-269-XXXX for Valdosta. So, if I assign a “location” code for every campus (2 for Milledgeville, 3 for Warner Robins, 4 for Valdosta and so on), I could build a RegEx to capture 5 digits input and translate it to E.164:

^4(\d{4})$ to be translated to +1229269$1 i.e. “Match numbers that start with '4' and are a total of 5 digits long. Remove 1 digits from the beginning and add '+1229269'.” Now Milledgeville user would dial 40001 and call Valdosta user whose phone number is actually (229) 269-0001.

Number manipulation is a very powerful tool. A full deployment of UC, including Exchange UM, introduces Auto Attendant feature which can be used as “Dial by name” – the caller speaks the name of the called party and if match is found, the call is connected without further interaction. This come very handy especially in our case (we changed ALL phone numbers – a very downing task indeed, and a separate post will be dedicated to it). We created a RegEx to translate *99 to the Auto Attendant’s E.164 number and so, while in the middle of the changeover confusion, our users found easier to dial *99 and dial by name vs. wander around if the user’ number was changed yet or not.

Our remote offices are connected to Main Campus with VPN links (as to any other campus as well), and so, since now the calls are placed over the IP Network, the LD charges which normally occurred in the past, were completely eliminated. Furthermore, by carefully evaluation the Local Calling Areas and creating proper call routes, a further reduction of LD charges was achieved. Now is this possible:

We established already that (in US), there is something called Local Call (free), where IF the caller and the called party are within the same Local Calling Area, no charges will occur. So, with RegEx, we evaluate the number against the Call Routing table and forward the call to the (most) appropriate gateway:

When a user from Valdosta dials ANY number beginning with 478-387, the system will determine that the most appropriate gateway is the one in Milledgeville because the call will be FREE since appears to ordinate from Milledgeville. Translate this to a large business with office(s) on another continent… This is, by the way, the magic behind dialing US number and “John” with Indian accent takes your customer support call…