Re: [sipcore] About Join and Replaces Headers:

Gao,

I don't understand the problem you are raising.
An INVITE with Join or Replaces has its own offer/answer to negotiate 
the media used. If the new party wants to use less (or more) media than 
the existing call it can just negotiate that.

	Thanks,
	Paul

On 9/25/2010 4:27 AM, gao.yang2@zte.com.cn wrote:
>
> By RFC3911 and RFC3981, the handling object of Join and Replaces headers
> is dialog:
>
> RFC3911: The Join header is used to logically join an existing SIP
> dialog with a new SIP dialog.
> RFC3981: The Replaces header is used to logically replace an existing
> SIP dialog with a new SIP dialog.
>
> Dialog has meaning is signalling level, not for service level. So, if we
> use Join and Replaces's semantics to build call service, the real
> handling object should be session.
>
> For normal usage, such as:
> A and B has a session;
> C send a INVITE with Join header to A;
> A build a basic conference for the three-party.
>
> But if we consider some more complex use case, there might be problems.
> A and B has a audio and video call, and C just want to join to the audio
> part(part of the streams).
>
> Abstractly, the problem is how can we express the semantics, such as
> Join part of the streams in current session or Replaces part of the
> streams in current session?
>
> Thanks,
>
> Gao
>
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