Natural line enhancement

We've been over this already: lines and extensions are not the same thing.  Once again, the USAC News Brief instructs applicants: "Provide the number of lines, including the number of extensions."  The explanation following that instruction make things a little clearer, but not much.

What USAC wants to say is: "Include all the incoming lines on a bill, not just the billed telephone number."  I've never heard a phone company call an incoming line of any sort an "extension."  In telecomese, "extension" means an internal line connected to a phone system, not an external line.  In the case of Centrex, it's not confusing, but otherwise it's going to be the wrong number.

It brings up an interesting question, though.  In the traditional world, you either had a bunch of phone lines (POTS or Centrex) or a PRI.  (What's a PRI, you ask?  It's an Integrated Service Digital Network (ISDN) Primary Rate Interface, a T-1 channelized into 24 channels, meaning up to 24 simultaneous calls. You can associate as many phone numbers as you wanted to that trunk by buying blocks of DID (Direct Inward Dialing) numbers.  You have to have your own PBX to distribute the calls coming in over the PRI.)

Determining the number of lines was straightforward.  In the case of POTS or Centrex, you put down the total number of lines on the bill.  (Tip for figuring out the total number: Most bills have a dizzying array of different types of lines, but there is frequently only one line for "SLC" or "Subscriber Line Charge", sometimes called "FCC SLC" or "FCC line charge" or some other misleading name to make you think it's some kind of tax, when in fact the FCC's involvement is to set the maximum amount that can charged; the phone company is keeping 100% of that money.  So if you find that line on the bill, it will typically show you how many lines there are total.)  In the case of PRI, you put down the number of channels you're using (almost always 24).  Don't put down the number of DIDs.

Along comes VoIP.  There is an architecture analogous to the PRI, called SIP (Session Initiation Protocol) trunks.  You need a PBX to use SIP trunks, and you buy a certain number of trunks (simultaneous calls), so it's easy to determine the number of "lines" (though in reality it's only one line with a bunch of conversations crammed into it, but that's kind of true for PRIs, too).  And vendors offer another service that looks just like regular Centrex: you get as many phone jacks as you want, and you can connect them to regular phone lines; the provider installs a router in your building converting those phone calls to VoIP.  If you want, you can have IP phones in your building, in which case the provider router doesn't have to convert calls, it just routes the IP packets from your phone.  Like with Centrex, you pay a certain amount per phone each month.  And like with Centrex, all call processing takes place on service provider equipment.

In all of those scenarios, it's clear how many "lines" you have.  Either the number of SIP trunks if you have a PBX or the number of phones if you are using the Centrex-like setup.

But there is a new option on the scene that makes the number of lines fuzzy.  It's just like the scenario above, where you have VoIP phones connected to a service provider who handles all the calls.  The difference is that the service provider charges you for simultaneous calls.  This can be an attractive option for schools, since they typically have hundreds of phones in classrooms which get used very rarely.  So a school with 200 phones can probably get by with 12 simultaneous calls, which is a lot cheaper.

But how many lines do you have?  I mean, each and every phone, when you pick up the handset, interacts directly with the service provider to set up the call.  So our hypothetical school has 200 lines.  But if 12 people are on the phone, the 13th person can't make a call.  So is that 12 lines?  Adding to the confusion is that the limit of 12 calls is a setting in the service provider's software.  In reality, the 13th call does reach the service provider's switch, which makes the decision that the school is over it's limit, and gives back a busy signal.

So you'd think 12 lines, but the only difference between a school paying $30/month for each phone set and the school paying $600/month for 12 simultaneous calls is a software setting and maybe once or twice a month someone is the unlucky 13th caller and gets a busy signal.

I guess the right answer in that case really is 200 lines, even though they can't all make calls at the same time.  So now the USAC guidance is right.