[Asterisk-Users] Dial to Answer -- Can this be done?

[John Todd]

At 7:20 PM -0400 on 5/15/04, Jim Rosenberg wrote:
>Let's suppose you have a PSTN line with multiple extensions. One of 
>these extensions is connected to an Asterisk FXO port. For reasons 
>that I won't go into, the "normal" configuration of the system is 
>that when a call comes in on the PSTN line, Asterisk *does not 
>answer* -- the other extensions do whatever they would do if there 
>were no Asterisk system there.
>
>When I hear one of these extensions ringing, I want to be able to 
>dial an extension on the Asterisk phone system that will allow the 
>Asterisk FXO port to answer, and from there on Asterisk takes the 
>call.
>
>Any thoughts on how to do this?
>
>-Thanks, Jim

The answer to your description is "No, I don't know how to do that." 
It may be possible, since the chipset on an X100P or other Tigerjet 
chip _might_ be able to look at line voltage without actually seizing 
the line, at which point it might be possible to detect a pickup 
event somewhere else on the loop, which in turn then might be able to 
activate a "silent pickup" which could listen for DTMF.

However, I doubt that is feasible unless you really want to dig into 
the Zap drivers and/or the code logic on the Tigerjet chips.

A more reasonable way to do it would be to buy a TDM4xx card from 
Digium, and put one FXO and one FXS interface daughtercard(s) on it. 
Run the line from the phone company into the FXO line.  Create a 
dialplan that pushes any inbound call on the FXO directly out to the 
FXS.  I am guessing (though I don't know for sure) that it will not 
pick up the FXO until the FXS is answered.  At that point, you can 
manipulate the dialplan with the # button (yuck - see my previous 
rants on why Dial needs to be extended to do more stuff with 
single-digit keypresses, but that's another story.)

JT