T.38 (PRI) Fax Debugging

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Asterisk Users 2 Comments

1) Does anyone know of any software to debug the g711cap audio files Asterisk’s res_fax generates? Google has not been very helpful.

2) These files are in WAV format, but my Windows Media Player cannot play them. The Linux “file” command reports “RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 8000 Hz” Does anyone have a solution? Is it a bug?

2 thoughts on - T.38 (PRI) Fax Debugging

  • Neither of your questions relate to T.38 🙂 Maybe you meant T.30 instead.

    That will depend a lot on what you mean by ‘debug’. We have found them useful to determine whether the audio path was ‘clean’ or not. For example, loading them into Audacity and looking at a spectral plot will tell you whether there were any extreme spikes, which usually are indicative of packet loss. You can also use them to look at the timing of the protocol interactions (delay between transitions between sending and receiving).

    If your goal is to actually demodulate the audio into data and then interpret the T.30 transactions, I’m not aware of any easily available tools for doing that. Commetrex (the vendor of the FAX stack in res_fax_digium) has one that they use for helping to analyze problems, but I don’t believe they make it available outside their company. There might be something in spandsp, but I haven’t looked.

    I have never attempted to open them with Windows Media Player, so can’t be of much help there. I know that Audacity will open them and play the audio properly, because that’s what we used when we developed this
    ‘audio capture’ feature.

  • Indeed, I did mean T.30.

    I’ve opened the files in Audacity, they look clean. I’m trying to figure out why I sometimes get FAXOPT(statusstr)=remote channel hungup, FAXOPT(error)=HANGUP, and FAXOPT(status)