[Freeswitch-users] Calls dropping due to SDP change

[Brian :]

Unless you're doing hd audio on these calls your solution is to just use
g711 on calls into this provider.

On Saturday, December 26, 2020, Nicola von Thadden <nico at vthadden.de> wrote:
> Hi,
>
> I'm currently investigating reproducable call drops when calling
> mobile-phone numbers from Deutsche Telekom (T-Mobile Germany).
> My provider has a NGN (SIP) Interconnection with Deutsche Telekom and is
> transparend for the messages involved here (although IP rewriting is
> happening).
>
> The calls contain following SDP in the invite from my FreeSwitch towards
> my provider:
>
v=0
>
> o=FreeSWITCH 1608967203 1608967204 IN IP4 *redacted*
>

>
>
s=FreeSWITCH
>
> c=IN IP4  *redacted*
>

>
> t=0
>
0
>
> m=audio 32256 RTP/AVP 9 8 0
>
101
>
> a=rtpmap:9
>
G722/8000
>
> a=rtpmap:8
>
PCMA/8000
>
> a=rtpmap:0
>
PCMU/8000
>
> a=rtpmap:101
>
telephone-event/8000
>
> a=fmtp:101
>
0-16
>
> a=ptime:20
>
> Once the call is established, FS sends a re-invite after 50% of the
> expiration timer is elapsed, 15 minutes in this case. The re-invite
> contains a slightly modified SDP:
>
v=0
>
> o=FreeSWITCH 1608967203 1608967204 IN IP4
>
*redacted*
>
>
s=FreeSWITCH
>
> c=IN IP4
>
*redacted*
>
> t=0
>
0
>
> m=audio 32256 RTP/AVP 8 101 9
>
0
>
> a=rtpmap:8
>
PCMA/8000
>
> a=rtpmap:101
>
telephone-event/8000
>
> a=fmtp:101
>
0-16
>
> a=rtpmap:9
>
G722/8000
>
> a=rtpmap:0
>
PCMU/8000
>
> a=ptime:20
>
> The new codec on position 1 (PCMA) is not necessary the chosen one for
> the session, that call was using G.722 (verified via 'show channels').
>
> Telekom does not like my SDP change and responds with:
> SIP/2.0 488 SDP Parameter Error In SIP
>
Request
>
>
> The freeswitch console only logs:
> 2020-12-26 16:32:49.578925 [DEBUG] sofia.c:7326 Channel
> sofia/external/*redacted*entering state [calling][0]
> 2020-12-26 16:32:49.618925 [DEBUG] sofia.c:7319 Channel
> sofia/external/*redacted* skipping state [ready][488]
>
> The call is disconnected 15 minutes later because the session timer has
> expired:
> 2020-12-26 16:47:53.838925 [NOTICE] sofia.c:1089 Hangup
> sofia/external/*redacted* [CS_EXCHANGE_MEDIA] [NORMAL_CLEARING]
>
> This does not happen when I only allow PCMA (or any other codec) since
> the SDP can't get mixed up.
>
> I have reproduced that behaviour with
> 1.10.5~release~6~25569c1631~buster-1~buster+1 and
> 1.6.20~37~987c9b9-1~jessie+1.
>
> Do you have any idea why FS changes the SDP (without reason?) and what I
> can do about it?
>
> Thanks
> Nico
>
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