Re: [Sip] Asking a B2BUA to add a party

["James M. Polk" <jmpolk at cisco.com>]

At 03:44 PM 7/26/2005 -0500, Baniel Uri-CUB001 wrote:
> Say a UA A talks with UA B via B2BUA X. A wants to add an additional 
> party, UA C to the call.
> A wants to "ask" X to initiate the addition of C to the call. I can think 
> of INFO or NOTIFY (w/ implicit subscription) sent from A to X as the 
> simplest way to trigger the necessary action in X. It might be even the 
> method MESSAGE with some text which is meaningful to X...

A sends an INV to C, sending the message at X (perhaps with a Route header 
of X). This might be the normal operation A, btw - based on a Service Route 
in the 200 OK Response to its REGISTER Request. Normally, X will forward 
the INV to C (being a B2BUA, this will look like X did this from C's pov).

The question you have to determine is where does the RTP go? In other 
words, what is the 3-way bridge element for these merged streams? A? or an 
external element like a DSP? It isn't going to be X.

If it's A, then there doesn't need to be anything special in the INV, and 
the SDP from A indicates A as the IP address for C's RTP stream to be set 
up to.

If it's a DSP, B needs to be reINVITEd to this DSP too.


> Is anyone aware of more "standardize" (but simple) way to accomplish that? 
> In general I am asking about a SIP standardized way for a SIP element A to 
> ask another SIP element B to perform an action, which is related to an 
> existing dialog(s), without the need to use an additional protocol.
>
> Thx
> -uri (Baniel)
>
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cheers,
James

                                *******************
                Truth is not to be argued... it is to be presented.

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