Re: [SR-Users] about rtpengine-[offer-answer] via-branch flag

[Sebastian Damm]

Hi,

On Tue, Jul 18, 2017 at 9:42 AM, Juha Heinanen  wrote:
> Is the note about "serial forking" correct or should it be about
> "parallel forking" instead?  In case of serial forking, it would not
> matter if the whole call is deleted, because a new offer would be issued
> for the next branch.  Or perhaps I just don't understand the meaning of
> the note?

If the proxy that does the parallel forking is the same that issues
the rtpengine call, it shouldn't matter because there won't be a
delete command for the cancelled branch. If you have a scenario where
the proxy sends out multiple branches and for example a load balancer
does the rtpengine stuff, then the load balancer should use the via
branch flag or the cancelled branch will kill the call.

In serial forking, the new INVITE could go out before the CANCEL is
sent out. If that happens, the Via branch is needed to not kill the
whole call.

So one can think of scenarios with both serial and parallel forking,
where the via-branch flag can be useful.

Regards,
Sebastian

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[SR-Users] about rtpengine-[offer-answer] via-branch flag

[Juha Heinanen]

rtpengine-offer function documentation tells this about via-branch flag:

 via-branch=... - Include the “branch” value of one of the “Via” headers
 in the request to the RTP proxy. Possible values are: “1” - use the
 first “Via” header; “2” - use the second “Via” header; “auto” - use the
 first “Via” header if this is a request, or the second one if this is a
 reply; “extra” - don't take the value from a header, but instead use
 the value of the “extra_id_pv” variable. This can be used to create one
 media session per branch on the RTP proxy. When sending a subsequent
 “delete” command to the RTP proxy, you can then stop just the session
 for a specific branch when passing the flag '1' or '2' in the
 “rtpengine_delete”, or stop all sessions for a call when not passing
 one of those two flags there. This is especially useful if you have
 serially forked call scenarios where the RTP proxy gets an “offer”
 command for a new branch, and then a “delete” command for the previous
 branch, which would otherwise delete the full call, breaking the
 subsequent “answer” for the new branch.

Is the note about "serial forking" correct or should it be about
"parallel forking" instead?  In case of serial forking, it would not
matter if the whole call is deleted, because a new offer would be issued
for the next branch.  Or perhaps I just don't understand the meaning of
the note?

-- Juha

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