[Asterisk-Users] Some questions regarding T1's

[Tom Rymes]

On Oct 20, 2005, at 1:15 PM, Michaël Gaudette wrote:

> I'm a computer engineer with basic knowledge of telecom.  Actually,  
> less then basic to be honest.  I've been playing around with  
> Asterisks for a few weeks with 2 FXS and 2 FXO cards, and having a  
> bit of fun making a home PBX. I'd like to know how I could apply  
> this new knowledge to, for example, developping a PBX solution for  
> this following hypothetical company:

Welcome! Asterisk can definitely do what you are looking for, and  
save this hypothetical company money in the process, I bet. (The T1  
should be cheaper than 72 analog phone lines, if that's how they are  
doing it...).
> - Exactly 72 employees each with a direct telephone number that  
> goes directly to their phone.  Ex: Bob is 444-555-6666 and Lisa is  
> 444-555-6667. Let's say they don't have a PBX yet.
> - Statistically, the max number of outside lines ever busy at the  
> same time was 24 (how conveniently T1-like)

Well, this is a hypo, but 24 simultaneous calls is a bit close to the  
maximum for comfort. I would want a few extra lines available for  
growth, unexpected peak calling usage, etc. (What happens in an  
emergency/serious problem at multiple customers, or anything else  
unexpected where call volume spikes?)

> .  They don't want to change their business cards, so 444-555-6666  
> should still reach Bob, but now by going to the PBX first.  The PBX  
> should recognize that the call was made to 444-555-6666 and switch  
> it to Bob automatically.  Bob should see the Caller ID of the  
> caller on his phone.

Yes, this will easily work via the T1. Your Provider will send the  
DNIS information when the call comes in. Normally they provide the  
last 4 or last 7 digits of the dialed number (Choose seven. We used  
to have 4, but we ended up with two numbers that had the same last 4  
digits.) Asterisk uses this info to route the call to the correct  
phone. CallerID will come in, too, but a T1 can only provide CallerID  
Number, not name. A PRI is necessary for CallerID Name.

> This is it.  Conceptually, not very complicated.  My guess is I  
> would need (and this is where I need confirmation from somebody in  
> the know):
> - Asterisk PBX
> - A Digium T1 line for a connection to the phone service provider  
> (I'm in Canada, so let's say Bell Canada for argument's sake)

Yes, but you could use a Sangoma card, too.

> - A T1 line from Bell Canada (or other)
> - Something (not sure what) on the outside to connect to those 72  
> phones (3 T1 cards internally connecting to a wire panel, in turn  
> connected to 60 phones?

You could use:
1.) IAX or SIP softphones
2.) SIP Hardphones (Cisco, Polycom, etc.)
3.) Analog phones connected to a Channel bank, connected to a T1 card.

If you choose option 3, you could buy a quad-span T1 card from  
Sangoma or Digium and use one port for the incoming T1 or PRI and the  
other three for extensions. Then if you need to add another incoming  
T1 for incoming/outgoing calls or extensions, you could add another  
T1 card. you could also use ADSI screenphones if you choose, though  
many would prefer SIP hardphones at that point.

> Is this it?  Do I need anything else?

Well, experience, patience, and a working dialplan will all be  
important! I would personally recommend a GUI configuration tool,  
such as AMP, IPManager, or something of the like. This, of course,  
depends on your preferences, though, so feel free to hand-code if you  
so desire.

For something like this as your first serious production install, you  
might want to consider hiring a consultant.

> Follow-up questions:
> a) Is is possible to have 72 numbers associated to a single T1  
> (more numbers than lines)?

Yes. You will have to port the existing analog numbers to the T1,  
which will disconnect the existing analog line. What you might want  
to do is start with one phone number and port it to the T1. plug the  
user's phone into the asterisk server, and make sure it works as  
expected. Then port another ten numbers and make sure that they all  
work. Keep porting numbers in groups of ten, twenty, or whatever you  
feel comfortable. That way if something doesn't work, you will only  
have 1, 10, or however many people whose phones are not functional,  
not all 72.

> b) Will Asterisk be able to recognize (and how?) which number the  
> call came on, so it can run the right dial plan?

Yes, see comment about DNIS above.

> c) This migth be a Canada-specific answer, but I'll try:  When  
> leasing a T1 line, does the regional code  have to be based on  
> geohraphy?  Could I have a T1 with 416 (Toronto) numbers located in  
> Montreal (514)?

Not certain. We have phone numbers from throughout the state (all in  
the same Area Code) ported to our T1, so a customer can dial a local  
number but the call still comes in to our central office. Whether  
this is possible between area codes, though, I don't know.

> I sure hope my questions weren't too "newbie-like".  I fear they  
> are, but I've really tried finding the info on  the web. I  
> certainly wouldn't be insulted if the only reply I got was a link  
> to a decent Web site explaining all this.

No, but again, you might want to consider hiring a consultant before  
you tackle something like this. At the very least, take it slowly as  
I suggested above.

Tom

------------------------------------
Tom Rymes
Cascade Link Systems
www.cascadelinksystems.com
(603) 375-1414

Technology solutions for small & medium sized businesses