[SR-Users] Parallel forking - first responder wins

[Ivan Ribakov]

Just thought of a follow up question - is it possible to find out which of the branches Kamailio chose as the winner? According to RFC multiple 200 OK could arrive before CANCEL is sent. Do I need to look for an outgoing ACK to know for sure which branch was chosen for sure or is there a way I could “catch” a winning branch through some sort of custom branch route (thinking along the lines of “t_on_branch_success”)?

Thanks,
Ivan

> On 20 Apr 2020, at 15:28, Ivan Ribakov <i.ribakov at zaleos.net> wrote:
> 
> Thanks for pointing me to the specific section, Giovanni! I was searching RFC for the “fork” and “merge” keywords so I never got even close to this part of RFC.
> 
> 
>> On 20 Apr 2020, at 13:27, Giovanni Maruzzelli <gmaruzz at gmail.com <mailto:gmaruzz at gmail.com>> wrote:
>> 
>> ( and is implemented in automatic: when receive the 200 OK for a branch (the winning one), Kamailio sends CANCEL to the other branches )
>> 
>> 
>> On Mon, Apr 20, 2020 at 12:48 PM Giovanni Maruzzelli <gmaruzz at gmail.com <mailto:gmaruzz at gmail.com>> wrote:
>> Maybe is not very explicit, but I believe section 16.7(10) of RFC 3261 deal with it (sends CANCEL to branches)
>> -giovanni
>> 
>> 
>> On Mon, Apr 20, 2020 at 11:48 AM Ivan Ribakov <i.ribakov at zaleos.net <mailto:i.ribakov at zaleos.net>> wrote:
>> As far as I understand, RFC3261 is not providing any instructions on how to deal with forked INVITES specifically. It just says that forking can result in multiple dialogs that are part of the same original call. I couldn’t find any prescriptions on how/when to deal with these multiple dialogs specifically which makes me think it depends on the application. Once again, please correct me if I’m wrong.
>> 
>> So, in the same way as RFC3261 is not talking about forked INVITE priorities or parallelism, but Kamailio (TM module) is providing a mechanism for forking in parallel/serial modes (advanced feature that is not part of RFC3261, but is built on top of it), I’m wondering whether Kamailio (TM module) is providing any advanced features for dealing with forked INVITE responses.
>> 
>> Thanks,
>> Ivan
>> 
>> 
>>> On 20 Apr 2020, at 11:13, Olle E. Johansson <oej at edvina.net <mailto:oej at edvina.net>> wrote:
>>> 
>>> 
>>> 
>>>> On 20 Apr 2020, at 10:31, Ivan Ribakov <i.ribakov at zaleos.net <mailto:i.ribakov at zaleos.net>> wrote:
>>>> 
>>>> Hi all,
>>>> 
>>>> What I’m trying to achieve is to have Kamailio fork an INVITE to multiple endpoints in parallel but only maintain the branch that responds first (first to respond with 200 OK I guess).
>>>> 
>>>> I’ve read the TM module documentation on forking (https://www.kamailio.org/docs/modules/stable/modules/tm.html#tm.serial_forking <https://www.kamailio.org/docs/modules/stable/modules/tm.html#tm.serial_forking>) and as far as I understood a combination of “seturi()” + “append_branch()” + “t_relay()” command calls will allow me to send multiple forked INVITEs in parallel. 
>>>> 
>>>> What I couldn't find information about in the documentation (please point me to it in case I missed it) is what controls (if any) do I have over forked requests. Do I need to keep track of the branches myself and cancel others when first succeeds or does Kamailio have some kind of setting for implementing such behaviour?
>>> 
>>> It’s all implemented according to the RFC 3261 where you can read all the cool details!
>>> 
>>> /O
>>> 
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>> 
>> -- 
>> Sincerely,
>> 
>> Giovanni Maruzzelli
>> OpenTelecom.IT
>> cell: +39 347 266 56 18
>> 
>> 
>> 
>> -- 
>> Sincerely,
>> 
>> Giovanni Maruzzelli
>> OpenTelecom.IT
>> cell: +39 347 266 56 18
>> 
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