[sllug-members]: Phones and hardware for Asterisk

[Corey Edwards]

On Mon, 2006-08-07 at 16:17 -0600, Walter Scott wrote:
> We have a T1 coming in to the building and have it split into 14 lines (12 
> voice, 2 fax) and the rest is data.  They are converted over to analog and 
> wired to an outdated Telrad System that controls all the phones.  My take on 
> the Asterisk is that it will control the calls from the 12 voice and 2 fax 
> lines coming in and give us more functionality than our current system.  I 
> only mentioned a 12 line phone due to my ignorance on these.

What you need to do is separate the idea of lines and phone numbers.
This is one of the coolest tricks to a phone system, I think. It's not
specific to Asterisk. I'm currently running a (piece of junk) NEC PBX
that does this same thing.

Let's say you've got 20 people in your office. You want all of them to
have their own phone number. Fine, you'll need 20 phone numbers. No way
around that.

But, does that mean you need 20 lines? Maybe not. How many of them will
be on a call at the exact same time. 5 maybe? 10? That's how many phone
lines you would need. 12 might be that magical number. Kinda just
depends on your usage.

So, how does the phone system match phone numbers and lines up? It's
call Direct Inward Dial, or DID. The phone numbers are often referred to
as DIDs. Back to our scenario of 20 DIDs and 12 lines, a call could come
in on any one of those 12 lines. With the call, the phone company's
switch will set the Dialed Number Information Service (DNIS) so that
your switch sees the DID that was called. Now the PBX can route it to
the user's extension.

Would an example be useful? Your users have phone numbers 555-0100
through 555-0120. You have a T1 with 12 lines, numbered A-M. For
simplicity's sake, your users' extensions are 100-120.

Somebody calls 555-0110. The telco's switch routes it to your PBX on
line J. Your PBX picks up the line and see the DNIS contains 555-0110.
It knows that 555-0110 should route to extension 110 so it rings 110.
When that user picks up, the calls are bridged and away they go.

Sounds nifty, no? It gets even better. A DID doesn't have to correspond
to a single extension. It could be a call queue, or a group extension,
or a phone menu (IVR), or voicemail. With Asterisk's Applicaton Gateway
Interface (AGI) you can write your own code to handle phone calls, so
the sky is really the limit. Multiple calls to the same DID can arrive
at the same time, so you can have a single number for your company but
be able to take more than one call without resorting to weird remote
forward on busy magic.

>   Does anyone 
> have one of these systems set up in the area around Midvale that would be 
> willing to show me how this works?  How to visually see the lines and make a 
> transfer?  I just need to know if this is going to be a viable solution for 
> us.

I can't speak to showing a system off in Midvale, but the way a transfer
would work is that once a call is connected to extension 110, that user
could send the call to say 115. The call would still be on the T1 on
line J. The PBX just bridges line J to a new extension. Is that what you
were looking for?

Corey

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