[Spce-user] T.38 <-> G.711 Transcoding

[Richard Fuchs]

Thanks for the suggestions, I'll pass them on to see what we can do.

Cheers


On 03/09/2020 02.21, Gabriel Kuri wrote:
> The reason for rejecting T.38 from the carrier is that it sucks... 
> Faxes work sometimes and other times don't when using T.38 with them. 
> They also disable ECM which is a bad idea. Using G.711 is a reliable 
> option since we're on-net with them and there's no latency or jitter, 
> which is why we'd want to keep the call on G.711 and not switch to 
> T.38. From the ATA perspective, that's an unreliable connection 
> susceptible to latency and jitter and must be T.38.
>
> If I may make a couple suggestions, it would be good if there were 2 
> additional options in C5 or rtpengine:
>
> - t38_refuse
> This option would refuse a T.38 Invite on a leg with a 488 and keep 
> the call at the current codec. This would be used on the leg facing 
> the carrier to reject their T.38 invite and keep the call on the 
> current codec (ie PCMU or PCMA).
>
> - t38_send_invite
> This option would force C5 to send a T.38 invite on a leg of the call 
> to get that leg to switch over to T.38 rather than relying on the ATA 
> or other endpoint to make the switchover. The main reason is to 
> eliminate the late T.38 reinvite issue that occurs and causes Faxes to 
> fail at times. If C5 did the T.38 invite within a very short interval 
> at the start of the call (assuming you know it's always a Fax call), 
> it would eliminate the late reinvite issue associated with T.38. This 
> would be used on the leg facing the ATA or other device you want to 
> use T.38 and ensure the T.38 invite comes early enough into the call 
> to switchover and have a successful Fax.
>
>
>
> On Wed, Sep 2, 2020 at 6:08 AM Richard Fuchs <rfuchs at sipwise.com 
> <mailto:rfuchs at sipwise.com>> wrote:
>
>     On 02/09/2020 01.37, Gabriel Kuri wrote:
>     > Hi Richard,
>     >
>     > Thanks for the info, I tried those settings and it seems to
>     transcode.
>     > However, sometimes the carrier does a T.38 Re-INVITE before the ATA
>     > does the T.38 Re-INVITE, and C5 passes the T.38 Re-INVITE
>     through to
>     > the ATA rather than rejecting it and staying on G.711 on the
>     carrier
>     > side. Is it possible to reject the T.38 from the carrier side
>     and stay
>     > G.711 so that only the ATA side of the call does T.38 and the
>     call is
>     > transcoded?
>
>     I'm afraid that's not a use case we had envisioned -- We expected
>     people
>     would want to use T.38 when available and not reject it. :) So the
>     options we were designed for cases where one side just doesn't
>     support T.38.
>
>     May I ask why you want to reject the T.38 offer from the carrier?
>
>     Cheers
>
>
>     -- 
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>
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