[asterisk-dev] Fwd: T38 and codecs negotiation

[Theo Belder]

Hi Federico,

We have encoutered the same problem. We have made a patch for this, so you
can send T38 only invites. You can find the patch here:
https://issues.asterisk.org/view.php?id=17966. You should grep the latest
patch (rev3)!

BR. Theo



2010/9/22 federico cabiddu <federico.cabiddu at gmail.com>

>
>
> ---------- Forwarded message ----------
> From: federico cabiddu <federico.cabiddu at gmail.com>
> Date: 2010/9/22
> Subject: [asterisk-users] T38 and codecs negotiation
> To: asterisk-users at lists.digium.com
>
>
> Hi,
> I'm working with asterisk 1.4.35 and found an issue regarding codecs
> negotiation when T38 is enabled (t38pt_udptl=yes).
> In particular if the INVITE sdp contains no allowed codec the call is not
> rejected with "488 - Not acceptable here" but it goes through and the 200 OK
> SDP is as follows:
>
> v=0
> o=root 27285 27285 IN IP4 xxx.xxx.xxx.xxx
> s=session
> c=IN IP4 xxx.xxx.xxx.xxx
> t=0 0
> m=audio xxxxx RTP/AVP
> a=silenceSupp:off - - - -
> a=sendrecv
>
> or
>
> v=0
> o=root 27285 27285 IN IP4 xxx.xxx.xxx.xxx
> s=session
> c=IN IP4 xxx.xxx.xxx.xxx
> t=0 0
> m=audio xxxxx RTP/AVP 96
> a=rtpmap:96 telephone-event/8000
> a=fmtp:96 0-15
> a=silenceSupp:off - - - -
> a=sendrecv
>
> if in the originating INVITE there was the a line for telephone-event
> mapping.
> Looking chan_sip.c I understood that the problem is related to t38
> capabilities and in particular at row 5636:
>
> if (!newjointcapability) {
>         /* If T.38 was not negotiated either, totally bail out... */
>         if (!p->t38.jointcapability || !udptlportno) {
>                 ast_log(LOG_NOTICE, "No compatible codecs, not accepting
> this offer!\n");
>                 /* Do NOT Change current setting */
>                 return -1;
>         } else {
>                 if (option_debug > 2)
>                         ast_log(LOG_DEBUG, "Have T.38 but no audio codecs,
> accepting offer anyway\n");
>         }
>  }
>
> As I understand if t38 is globally enabled p->t38.jointcapability
> and udptlportno are always true even so the call is never rejected.
> As this behavior caused me some problems with a customer I modified, for
> the moment, the line 5638 as follows:
>
> if (!p->t38.jointcapability || !udptlportno || p->t38.state ==
> T38_DISABLED)
>
> cause if I understand well the code if there is no fax request in the
> INVITE SDP p->t38.state is set to T38_DISABLED.
> This did the trick for me but I don't know the implications of such change
> and if it is correct to manage it this way.
>
> Kind regards,
>
> Federico Cabiddu
>
>
>
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