[asterisk-users] "Legacy" analog data modems and Asterisk

[Don Pobanz]

Erik Jacobs wrote:
> Options (in no particular order):
> 
> 1) Connect Asterisk to existing 6 PSTN lines using FXO.  Connect existing
> modems to Asterisk using FXS.  Data speeds will probably be sub 14.4k, which
> is not acceptable.

Yes, this would connect modems at slow speeds (or not at all) due to the 
additional A/D conversion into * and the D/A conversion out of * to 
interface the pots lines.

> 2) Upgrade PSTN to PRI.  Connect Asterisk to PRI and connect modems to FXS.
> Anyone have an idea about the potential data speeds here?
> 

We have been doing this and it has worked well for us. Because we are 
dialing to another modem that is on a pots line and not directly into a 
modem bank on another digital T1 like ISP would have, the speeds will 
never approach the upper ends of a 56k modem speeds. From my foggy 
memory I believe we were seeing around 28k.

> 3) Connect Asterisk *AND* modems to PSTN using splitters.  Does anyone know
> what happens if someone is using a PSTN with the modem and Asterisk tries to
> use an FXO?  Is Asterisk "smart" enough to detect that the PSTN is currently
> in use?  Or is it like your little sister and it will pick up the phone
> while you're dialed into a BBS and knock you offline.... (ahh, those were
> the days).

Asterisk is NOT smart enough to know the line is already in use and so 
avoid using it.

> 
> 4) We make PPP connections to our customers with the existing modems (for
> the most part), so I'm not sure that there would be any way to somehow hook
> the modems up to the Asterisk box and have the Asterisk make the connection.
> This would very likely involve some extraordinarily complex routing tasks
> and, as we're looking to a 3rd party Asterisk PBX provider, I don't think
> we'll have the access to the guts of the hardware to do this.

??

> 5) The most simple and least elegant -- unplug the phone line you want to
> use for modem from the FXO and plug it into your modem.  Que sera, sera.

Yes, this unsophisticated way would work. However if you go this route, 
get one of the A/B switches and just press A for modem or B for *. I did 
this at home for a while!

Don Pobanz