[Freeswitch-users] Fax Transmit Rate - force to 9600?

[Andrew]

Hi all,


We've been trying to get our fax implementation as reliable as possible using FS; we've had some great results with inbound faxes with the following items set in the incoming dial-plan:


action application ="answer"/>
action application="playback" data="silence_stream://2000"/>
action    set    ignore_early_media=true
action    set    absolute_codec_string='PCMU,PCMA'
action    set    fax_enable_t38=true
action    set    fax_verbose=true
action    set    fax_use_ecm=true
action    set    disable-v17=true
action    set    fax_v17_disabled=true
action    set    fax_disable_v17=true
action    set    fax_enable_t38_request=true
application    rxfax    /tmp/FAX-IN-${uuid}.tif

application    hangup

The one thing that we have identified with this configuration is that 99% of inbound faxes come through fine when the fax transfer rate is negotiated at 9600 bps (as a result of the fax_v17_disabled=true setting).


However, we still see quite a few incoming faxes reported as coming in with a fax transfer rate of 14400 bps, which have a 100% fail rate.


I understand that the two ends need to negotiate a rate; but how do we force (or only offer) the rate of 9600 or lower? My understanding is that the fax_v17_disabled=true setting should cover that? My first thought was that the remote end was forcing the rate at 14400, regardless of what we were sending back in terms of fax capabilities.


Not sure if it helps, but the two error messages we receive when faxes fail due to the 14400 rate are:

- Unexpected DCN while waiting for DCS or DIS, and
- The call dropped prematurely

My thought was, If we could find a way to get all faxes coming in at 9600, we'd be able to improve the reliability.

Looking through the wiki and previous list messages, the fax_disable_v17=true setting seems to be the documented approach, but I'm not sure why we're still seeing faxes come in at a higher rate.

Any advice on this or are we missing something with regards to locking in the lower speed?

cheers,
A

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