Current definition of "in use" is the one proposed by Holmberg yesterday:
"Whatever session parameters (SDP) have been negotiated, AND preconditions are met on both sides for those parameters."
But as the two sides can have different view of when "preconditions are met". The problem is still exist.
What I talked here is just signaling concerned. And I admit that combine with the "signalling-media synchronization", it will be more complex.
| Gonzalo Camarillo <Gonzalo.Camarillo@xxxxxxxxxxxx>
2009-02-27 15:50 |
|
Hi,
> 1. the situation of inconsistent media level(perhaps it is impossible)
there is a situation we need to clarify regarding how to configure the
endpoint's media tools at a given point. However, this is a general
issue, not specific to the rollback issue we are discussing here. We
discussed this issue a long time ago but clarifying it at this point may
be a good idea. The issue is the following:
Two endpoints involved in a session perform a successful offer/answer
exchange in a re-INVITE or in an UPDATE to change the media parameters.
When can the endpoints stop using the old parameters and start using the
new parameters? This synchronization-related issue is caused by the fact
that signalling and media are only loosely coupled. The typical answer
is that the endpoint stops using the old media parameters (e.g., stop
listening on the old port) when it starts receiving media with the new
parameters. Of course, the endpoint can also implement a timer to cope
with delayed media packets using the old parameters.
When preconditions are used, the period where the endpoint acting as the
UAC needs to be prepared to receive media with both the old and the new
parameters is longer because once its preconditions are met, the UAS may
take a while to meet its own preconditions. In any case, the solution is
the same. The UAC stops using the old configuration when it starts
receiving media with the new configuration. The UAC can also request
confirmation of the preconditions so that the UAS lets the UAC know when
In any case, as you can see, this is a general SIP issue on
signalling-media synchronization, not specific to the rollback issue we
are discussing here.
Cheers,
Gonzalo
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