To trunk or not to trunk – this is the question

SIP Trunking that is…

Let’s analyze the options for a feature VoIP deployment. We have three basic starting points:

1. A small to medium business which currently have POTS as telephony solution (large enterprises are “large” partially because they have seen the light well back in the time and are VoIP already :-))
2. Enterprises that already have local PBX (VoIP or PSTN)
3. Any size business that have hosted VoIP

Georgia Military College failed in the first category – each endpoint directly connected to a Centrex PBX, served by the local phone company. The service, however, was “provided” by the GTA (Georgia Technology Authority – a State agency created with the idea to negotiate the best rate/services with the local Phone Providers and provide high quality services… Really?!?). So, we had a service charge of $23.60 per line, and that is – for the simpler service one can imagine, very close to what Alexander Bell invented. Want Caller ID – no problem, add $14,60 to the service charges – you get my point. Our IT office had 4 lines/numbers which rand on 10 phones simultaneously. Great productivity environment, right? Anyway, it was a “saver” – 10 phones and only 4 lines charged ($94.60). This year, however, the State of Georgia awarded the contract to AT&T, which in return immediately announced “price reduction from $23.60 to $16.00” just… now would be per ENDPOINT. So, the new MRC for the IT office would be… $160.00. Wow!!!

Let’s dissect this. We have NPA.NXX.XXXX where NPA are the area codes, NXX are the Exchange codes (remember, PBX = Private Branch Exchange) and finally XXXX which is the local number within the local Exchange. So, the number 478-445-4705 translates to Area Code = 478, Exchange Code 445 (a PBX located in the office of WindStream in Milledgeville, GA) and extension = 2705 (terminated on mine (and 9 others) desks. When I call 478-225-2706 (another former GMC number), what actually happens is my call gets to the PBX (WindStream office) where a match is found, a digital relay is closed and the copper pair that goes in to my phone is connected to the copper pair that ends in to another phone in the office next to ours. Well, it is a little more complicated than this but… you get the picture. So, we are paying for the ability to connect one termination point to another (even if they are few feet apart).

Now look the tricky part. XXXX equals to 10,000 (the maximum numbers of extensions) i.e. 0000 to 9999. A call within the range is “local” i.e. never leaves the PBX. Because it is internal, there is no problem since the PBX was designed with THIS capacity i.e. 5,000 users on one end of town pick up the phone and call the other 5,000 located in the other part of town. So far, so good.

Let’s look what happens when I dial OUTSIDE my local exchange. WindStream (in Milledgeville) holds the following NPA.NXX: 478 414; 445; 451; 454; 456; 457; 804 i.e. when I dial 478-452-XXXX, the local Exchange (still within WindStream’s infrastructure) will find the matching pair and connects me. Now, if you think WindStream have10,000 copper pairs between each PBX in order to cover (the alleged demand) i.e. all 10,000 users of 478.445.XXXX will dial all 10,000 users of 478.452.XXXX, and another 10,000 copper pairs between 478.445.XXXX and 478.453 .XXXX just in case, you are wrong. There is much “thinner “cable with way less number of copper pairs. Why? Because telephony is like Health insurance – a big gamble with the odds that LESS people will get sick while ALL insured will pay their premiums thus payments for service will be made and profit will be generated at the same time. And here the term TRUNK comes in use. The gamble here is that less people will dial OUTSIDE the local exchange than a pure “local” call. Same rule apply to calls outside the NPA i.e. Long Distance calls.

How this translates in to our situation? GMC have 220 telephone users in Milledgeville campus.
1. Business Office (everyone in the Educational area knows what the BO does – talks on the phone most of the time.)
2. Faculties (in class most of the time), doing “phone business” mostly returning voice mail calls
3. All others

After a long research, I went with a ¼ ratio i.e. one trunk line per every four phone users. Because OCS is now our local Exchange, we should not account for the “internal calls” – GMC user to GMC user but rather OCS - >PSTN and PSTN -> OCS. I got lucky; it worked perfectly for our situation. For the eight months of EV, our logs showed not more than 10 (ten) calls rejected due to “exceeding the trunk capacity” i.e. more than 40 people (our current number of concurrent calls in Milledgeville) attempted to use our SIP trunk (connection with the PSTN network).

A concurrent call trunk with our provider (more in the next post) carries MRC of… $13.00 and so, the total (fixed – your CEO will love this) cost for our Milledgeville campus - $520.00 per month. Can I have Amen?!? A campus with 500 Middle/High School kids and their teacher, 2,500 students and their faculties plus the Business office, Admissions, Alumni etc. for $520.00 a month?!? Can I have Amen again?

More about our journey is to come in the next few days.