[asterisk-users] Fwd: Re: Asterisk T.38 Pass-Through doesn't work

[Zoltán Fekete]

2013/8/1 Joshua Colp <jcolp at digium.com>

> Larry Moore wrote:
>
>> On 31/07/2013 8:08 PM, Joshua Colp wrote:
>>
>>> Zoltán Fekete wrote:
>>>
>>>> Thank You Larry!
>>>>
>>>> I have discussed with my provider. They are not able to insert the
>>>> T38MaxBitRate value into the sip answer. :(
>>>> https://gist.github.com/**anonymous/6120148<https://gist.github.com/anonymous/6120148>(line 559)
>>>>
>>>> That means we are not able to passtrough T38 Faxes with any asterisk
>>>> version at all?
>>>> What do you mean? Am I able to modify and compile the source? Is it
>>>> compicated? (I'm not a developer)
>>>>
>>>
>>> Based on the SDP in your gist the remote implementation has given no
>>> attributes with the T.38 stream which makes it pretty broken
>>> (T38FaxRateManagement is mandatory) and fun. The two hard parts really
>>> would be 1. Modifying Asterisk in a sane fashion to cope and 2.
>>> Determining the exact settings to make the implementation happy.
>>> Defaults as defined in the spec are fine and good, but my experience has
>>> taught me to throw those out the window when it comes to actual
>>> implementations.
>>>
>>>
>> It would seem that having a configurable option would be an idea for
>> this scenario.
>>
>
> That implies it would solve the problem, which my gut and experience tells
> me... it wouldn't. I think the T.38 implementation is just cobbled together
> and without knowing exactly how it behaves getting it to work would likely
> be a nightmare (trust me, I've spent time in those deep dark reaches).
> Throwing assumptions and defaults at it to try to make it work is of course
> an option.
>
>  My testing with Asterisk 1.8 and T.38, I obserevd that setting
>> FAXOPT(minrate) or FAXOPT(maxrate)had no effect, I concluded that when
>> Astrerisk is receiving it uses hard coded values - is this a sane thing
>> to do?!
>>
>
> When Asterisk is receiving the stack implementation offers what it wants,
> with the ability to override. So Asterisk doesn't hard code those values,
> the stack provides them. What is hard coded is the default values if none
> are received.
>
> I would even say it's a bug that the negotiation doesn't fail, since the
> remote side isn't providing a mandatory attribute.
>
> --
> Joshua Colp
> Digium, Inc. | Senior Software Developer
> 445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
> Check us out at:  www.digium.com  & www.asterisk.org
>
> --
> ______________________________**______________________________**_________
>
>
Yes you're right! As I know FAXOPT() value affect only when asterisk woks
as gateway.
We need passtrouh because my endpoints and also my provider supports T38.

https://wiki.asterisk.org/wiki/display/AST/T.38+Fax+Gateway
"Using T.38 Gateway mode

T.38 Gateway mode should be used when one leg of a call is not capable of
T.38 mode. In the event that both legs are capable and Gateway mode is
configured, then the Gateway will step out of the way, allowing *transparent
T.38 passthrough*."

The main problem is that I can't use G711 for the entire fax session
because the endpoints has 20-30ms response time.

When I try to use my Asterisk as FAXOPT gateway (endpoint leg T38 and
provider leg G711) can I force somehow to not accept the T38 re-INVITEs
from the provider?
They have ~1ms response time, so G711 on that leg would be fine but they
also detect fax CED tones and sends the re-INVITEs.

Regards,

Blaxy
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