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

Thu Mar 1 00:20:40 UTC 2018

Hi,
You can try fax_transfer_rate var
https://freeswitch.org/confluence/display/FREESWITCH/Variables
or configure spandsp
https://freeswitch.org/confluence/display/FREESWITCH/mod_spandsp

On Thu, Mar 1, 2018 at 8:39 AM, Andrew <asims1979 at hotmail.com> wrote:

> Thanks Vallimamod, that gives me some additional info we weren't aware of
> (re: preamble and t38 max bitrate).
>
>
> I noticed you mentioned disabling v17; which would allow the bitrate to
> increase to 14400, which is where we're seeing the problem. We want to
> force/limit the max bitrate under all circumstances (t38 or t30 over g711)
> to 9600, which we know works.
>
> Some additional info;
>
> Doing some further digging; the problem doesn't appear to specifically lie
> with t38; from what we can see some fax calls come in via t30 over g711
> which also fail with a bit rate of 14400.
>
> Given the preamble info you mentioned, could it be we're sending the
> sending fax our capabilities (i.e. max bitrate = 9600) and it's ignoring
> this and sends it across at 14400? I would assume that most, if not all
> faxes have the capability to send at 9600 if requested?
>
> Given our issue relates to incoming (i.e we're the receiving end), is
> there anything else we can do within FS to force the lower bit rate?
>
> cheers,
> A
>
>
>
> ------------------------------
> *From:* FreeSWITCH-users <freeswitch-users-bounces at lists.freeswitch.org>
> on behalf of Vallimamod Abdullah <vma at vallimamod.org>
> *Sent:* Thursday, 1 March 2018 4:34 AM
> *To:* FreeSWITCH Users Help
> *Subject:* Re: [Freeswitch-users] Fax Transmit Rate - force to 9600?
>
> Hi,
>
> From the error message, it looks like the remote fax drops the call when
> it sees no match between capabilities (it's the receiving fax who sends the
> preamble with its capabilities first.)
> According to the source code, with v17 disabled, the max bitrate over t38
> is 9600, else it's 14400. So I guess you need to enable v17 to communicate
> with faxes with min bitrates greater than 9600.
>
> Best Regards,
> --
> Vallimamod Abdullah
> SIP Solutions
> vma at sipsolutions.fr
> .
>
> On 28 Feb 2018, at 02:32, Andrew <asims1979 at hotmail.com> wrote:
>
> 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 thefax_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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