[Freeswitch-dev] mod_fax

Anthony Minessale anthony.minessale at gmail.com
Mon Jan 5 06:17:14 PST 2009

mod_fax is an unfunded work in progress so calling it crude means I guess we
are not off to a very good start.
Your input is nonetheless appreciated as the small group of 3 or 4 coders
continue to try and find time to add t.30 and t.38 support to
FreeSWITCH in our spare time with little or no help.  So eventually your
concerns will probably be addressed but
Rome was not built in a day........

You do seem to have a talent for writing.  May I suggest your volunteer your
skills on our WIKI?

On Sun, Jan 4, 2009 at 9:21 AM, Steve Underwood <steveu at coppice.org> wrote:

> Hi all,
> I finally started to play with mod_fax today. First, a couple of little
> observations. Although there is a config file for fax, modules.conf.xml
> doesn't contain an entry for mod_fax, and dialplan/default.xml doesn't
> contain a demo like
>    <extension name="test_rxfax_stream">
>      <condition field="destination_number" expression="^9011$">
>    <action application="answer" />
>    <action application="playback" data="silence_stream://2000"/>
>    <action application="rxfax" data="rxfax.tif"/>
>    <action application="hangup"/>
>      </condition>
>    </extension>
>    <extension name="test_txfax_stream">
>      <condition field="destination_number" expression="^9012$">
>    <action application="txfax" data="txfax.tif"/>
>    <action application="hangup"/>
>      </condition>
>    </extension>
> as it does for other modules.
> For more serious things.....
> If the far end of a SIP FAX transaction sends a reinvite to switch to
> T.38, FS sends a 488 back and everything fouls up. Other boxes send back
> the previous codec as the new one to use, and everything carries on
> smoothly in audio mode. I'm not a SIP expert, so I don't know the
> details of what it says on the topic, but in the real world successful
> continuance of a call requires a response other than 488. As an aside,
> the called party should be the one to initiate an attempt to use T.38,
> but in the real world the calling party often does.
> If T.38 is not available (which it isn't ever right now), and the call
> starts with a low bit rate codec, we should initiate a reinvite to use
> Alaw or ulaw. If that fails we might as well abandon the call.
> mod_fax currently follows the practice of my old and crude demo programs
> for *, and has apps called rxfax and txfax. This is taking a very narrow
> view of a FAX machine, and I think is too limiting. I think the
> following is how things should be:
>    - One app, probably just called FAX.
>    - It will be started with a flag saying if it should act as the
> calling party or the called party.
>    - The app will be given optional lists of files to send, and files
> to receive.
>    - The app will do its best to exchange all the files it can,
> including the use of poll mode FAXing.
> The module documentation says page by page events should be added (which
> spandsp supports), and this seems a sound idea. FAXback and other
> services might be implemented through this.
> Regards,
> Steve
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Anthony Minessale II

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