How do I configure an extension to be used by a modem?

How do I configure a dial up Modem to dial out through Asterisk?
Currently my dial up modems are set up with an extension on a ZAP channel just like our analog phones. We are using Rhino Channel Banks, Asterisk v1.4.2.
I have tested the lines and can dial out normally with a phone but the modem says “disconnected, line busy”

Huh? Way to few details to even attempt to answer this question.

Type of trunks? What type of audio codecs are being used? etc.

Modems (aka that’s what is in a fax) DO NOT work with codes that do any type of compression of the audio signal. So you’ll only have a chance at making things work is you are using ulaw or alaw (based on where you live).

Modems use analog technology so you’ll need a analog line of some form either from a analog card or a ATA device. But again you are attempting to convert a analog signal to a digital one and modems work on frequency ranges to determine things so if things are not EXACTLY to spec it will just not work. That’s why faxing works some times and not others.

If you are attempting this over a SIP connection then there is even less chance.

The modems I am using are currently set up with their own ZAP extension the same way I set up the analog phones. I don’t know wht codec I am using how can I find out? Thanks

Modem with built-in VoIP termination? What brand/model?

Thanks
Bill/W5WAF

A zap extension will not use a codec as it’s analog. But what type of trunks are you using? Zap, iax, sip? iax and sip will. and those codecs will be defined in the setup for them.

The trunk is also Zap. The modem is a Motorola SM56 Data Fax Modem in an HP laptop. I set up an extension for it thinking it would be able to dial out just like the analog phones but I guess there is more to it than that.

If the line is analog and the trunk is analog then you have a shot at it working and it “should” work just like a regular phone assuming you have it dial the proper strings to get out (9 if you require it, etc). If a regular phone can get out so should it basically.