Connecting to a remote server with dial up - Asterisk 1.4.21

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. Asterisk v1.4.2 I have tested the lines and can dial out normally with a phone but the modem says “remote party disconnected call, timeout looking for connection” I tested the modem by plugging it directly into the trunk bypassing Asterisk and it connects to the remote server without problems. It looks like it is failing at the far end point because of missmatched signals. Any ideas?

It’s not 100% clear, but I presume that there is no VoIP involved her.

doesn’t look like a typical message from a modem.

Enable the speaker on the modem, and describe what sounds you hear. Make a call using a terminal emulator and AT commands and provide the output from the modem itself. In both cases, provide the Asterisk console output at a reasonable verbosity level, say at least 5.


It sounds like the modem isnt training to a speed that they can both work on.

I wouldnt expect a modem to work much above 9600 baud reliably through asterisk.

try fixing the speed that low and see what happens


As it sounds like you have analogue lines on both FXS and FXO side, you certainly will not be able to get beyond 33.6k. 55k modems only work if there is exactly one D/A conversion between the server “modem” and the user modem, so you would need to have ISDN on the PSTN side. (The server modems are purely software - they never generate an analogue signal; that is only generated on the local loop.)

To maximise the speed of non-56k modems, you need to ensure that the codec used by Asterisk is the same as that used by your PSTN network. I think that is mu-law in North America and A-law everywhere else.

56k modems can be forced not to negotiate 56k mode, and hopefully the server end will accept such negotiation.