[Freeswitch-users] T.38 and Audiocodes or Patton gateway

[Steve Underwood]

On 11/17/2010 03:00 AM, Kristian Kielhofner wrote:
> Dave,
>
>    It's a better parameter for T.38 in general...
>
>    When you look at a T.38 trace (presumably without ECM) you'll see
> that the T.38 data stream is entirely unidirectional.  The sending
> device sends a stream of data - that's it.
Er, no. There is is two way exchange between each page, or between each 
chunk of a page in ECM mode. You should require a single page that takes 
longer than 600s to send for this timer to expire.
>    I first caught on to this with large faxes or faxes with high
> complexity that took a while to send.  I finally found one fax page
> with multiple images that failed 100% of the time when being sent from
> FreeSWITCH to the device.  Once I set the rtp-timeout-sec parameter to
> 600 it succeeded 100% of the time.  This change was (and has been) the
> single biggest change I've made to my configuration to improve my T.38
> success rate.
>
>    Ideally FreeSWITCH could be updated with an "enhanced understanding"
> of the unidirectional flow of T.38 and modify/tweak/remove the RTP
> timeout parameter as necessary (I imagine it does something similar
> with silence suppression/CNG now).  Or maybe I'm completely wrong and
> this change had no effect (I seriously doubt that).
>
> On Tue, Nov 16, 2010 at 11:14 AM, Dave  Redmore
> <dave.redmore at spigotsystems.com>  wrote:
>> I'm curious about your recommendation to use a long (600 sec) media/RTP
>> timeout value in the sofia profile.  Is this a specific need for the
>> Audiocodes device or just generally better for T.38?  I'm assuming you are
>> referring to the "rtp-timeout-sec" parameter?
>>
>> I'm using FreeSwitch as a media proxy to a T38 provider and have had decent
>> success, but usually have problems with longer faxes (8+ pages) and am
>> wondering if this setting might help?
>>
>> Thanks,
>>
>> Dave Redmore
Steve