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FreePBX: the D-Modem module

FreePBX is a web interface for running an Asterisk phone system. D-Modem's FreePBX module (for FreePBX 16 and 17) lets you set up D-Modem from that web interface instead of editing configuration files. It adds Applications > D-Modem to the menu and a fwconsole dmodem command.

It works with either dmodem-ari (the default, and the one you can share) or app_dmodem on an Asterisk you built yourself.

For the generated files, the code and the tests, see the technical details.

Installing

  1. Install dmodem-ari beside Asterisk, and add an ARI user in Settings > Asterisk REST Interface Users.

  2. Build the module package:

    cmake --build build --target freepbx_module

This makes build/freepbx/dmodem-<version>.tgz. 3. Upload it in Admin > Module Admin. FreePBX will warn that it is unsigned; that is expected.

Using it

  • Profiles. A profile says where a modem call's data goes: a BBS server, a program such as pppd, or a login. Each profile appears as a destination ("D-Modem") you can pick in inbound routes, IVRs, time conditions and so on.
  • Fax. The fax destination (on unless you turn it off in the settings) has D-Modem answer as a fax machine and save faxes to a folder.

  • Dial out. Make D-Modem call a remote modem (a BBS or a provider) with a profile, from the page or from a script:

    fwconsole dmodem dial

  • Line check. Shows the settings on your trunks and extensions that would spoil a modem call (see below).

  • Backup. D-Modem's settings and profiles are included in FreePBX's Backup & Restore. fwconsole dmodem export and import do the same from the command line.

After changing anything, click Apply Config. If you use dmodem-ari, restart it afterwards so it reads the new settings.

Getting good modem calls

Fast modem calls (V.90 especially) need the call's audio to reach the modem untouched. In FreePBX:

  • On the trunk and the modem's extension, allow one codec only: ulaw in North America and Japan, alaw elsewhere. Your provider must not convert it either.
  • Set DTMF to RFC 4733, and turn Fax Detect off.
  • On the modem's inbound route: no fax detection, no call recording, no music or announcement before the call is answered.

The line check page shows what is still set wrongly.