Well, we faced the same issue of call drop when we play announcement over 183 and then handover call to B party when it come online on voip push notification.

Telcos have more rigid systems.
Resolution was introducing B2BUA for topo-hiding in the path IMS (A party) and VoIP service (B & C party).
Check tags of to and from headers of your call traces. That will give you clue.



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abdul basit | p: +92 32 1416 4196 | o: +92 30 0841 1445

On 30 April 2018 at 14:59, Alfonso Pinto <alfonso.pinto@gmail.com> wrote:
Hi Carsten,

I was thinking about the same, but I need to convince people to add another component in the media path, they may be bit reluctant, but the idea is great.
In the meantime, I was able to trick the phones to react how I want playing with precondition and 100rel, for now it's acceptable in our environment.

Thanks for your answer.
Regards,
Alfonso.

On Fri, Apr 27, 2018 at 9:39 AM, Carsten Bock <carsten@ng-voice.com> wrote:
Hi,

likely, the best solution is here to use RTPEngine, so the IP/Port
stays identical for each request... i've tested it with various VoLTE
phones and various PCRF's.

Thanks,
Carsten
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2018-04-26 15:59 GMT+02:00 Alfonso Pinto <alfonso.pinto@gmail.com>:
> Hi Alex,
>
> Thanks for your answer. I was thinking more or less the same, but it seems I
> oversimplified the example and was missing an important point.
> This is IMS, so in the middle there are a lot more in the middle. It seems
> that this behaviour is normal when precondition is set and the only way to
> avoid the network to release the call on A side is to send the update.
> I've seen that in Kamailio 5 a new function was included in TM:
> https://www.kamailio.org/docs/modules/5.1.x/modules/tm.html#tm.f.t_uac_send
> In the code it looks like it's trying to use the current dialog, but that
> gives me doubts about CSEQ handling on the other side.
>
> Anyway, I will try unless someone is faster replying saying it doesn't work
> :)
>
> Thanks,
> Alfonso.
>
> On Thu, Apr 26, 2018 at 2:37 PM, Alex Balashov <abalashov@evaristesys.com>
> wrote:
>>
>> I would instead redirect my focus to why A is dropping the call in this
>> situation. It shouldn't be doing that.
>>
>> Per the standards, the first SDP answer must be the final SDP answer
>> (absent an update or reinvite) *of that endpoint*. There's no rule saying
>> that must be true of the dialog as a whole.
>>
>> -- Alex
>>
>> --
>> Sent via mobile, please forgive typos and brevity.
>>
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>> sr-users@lists.kamailio.org
>> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users
>
>
>
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