[SIPForum-discussion] Early Media

[XuRui]

Hi,

[RFC3261 14 Modifying an Existing Session]
   This modification can involve changing addresses or ports,
   adding a media stream, deleting a media stream, and so on.  This is
   accomplished by sending a new INVITE request within the same dialog
   that established the session.  An INVITE request sent within an
   existing dialog is known as a re-INVITE.

In my opinion, there's only one way to modify an existing Session defined in 
RFC3261.
That is "re-INVITE".

So I think there's no sense that 183 and 200 have different SDP.
Even if they have different SDP, it makes no sense to UAC(the caller).
So the sip device(UAC) may choose not to used the changed SDP from 200.

Thanks.

Regards,
Xu Rui

----- Original Message -----
From: "Siva M-Q16748" <sivam at motorola.com>
To: "Robert Mansfield" <RJM at Redwoodtech.com>; <discussion at sipforum.org>
Sent: Friday, April 20, 2007 1:06 PM
Subject: Re: [SIPForum-discussion] Early Media

>
> Hi
>
> Would anybody be able to point out any Logical Reason why a 183 and 200
> should not have same SDP ??
>
> May be some scenario in which it creates issues ..
>
> I hope there should be a Logical reason why RFC says so ..
>
> Siva M
>
> -----Original Message-----
> From: Robert Mansfield [mailto:RJM at Redwoodtech.com]
> Sent: Thursday, April 19, 2007 2:55 PM
> To: Siva M-Q16748
> Subject: RE: [SIPForum-discussion] Early Media
>
> Siva,
>
> If the use of early media is in the 'Gateway' model then I believe the
> SDP descriptor in the 183 and 200 will be the same.
>
> The scenario you describe is more akin to the Application Server model
> (both models described in RFC 3960).
>
> "Application Server sends the SDP info he got from Media Server to A in
> the
> 183 message A gets a Music played by media"-In this case the B2BUA AS
> could make use of the 'early-session' extension tag in the
> 'Content-Disposition'
> header. This allows for the establishment of an early session with a
> descriptor that is different from the SDP returned in the 200 OK.
>
> "Server Now Application server forwards the call to C If C answers , A
> should get the SDP info of C ( I thought it would be sent in 200 OK )"
> Ok so now A needs to talk to C. The SDP descriptor is different and
> represents the normal session represented by the INVITE/200/ACK.
>
> I only have experience of this RFC in terms of the GATEWAY model so what
> I'm not staking my life on the accuracy of this explanation however I
> would be interested in your thoughts from RFC 3960 Application Server
> model.
>
> Hope this helps,
>
> Rob.
>
> -----Original Message-----
> From: Siva M-Q16748 [mailto:sivam at motorola.com]
> Sent: 19 April 2007 09:56
> To: Robert Mansfield; discussion at sipforum.org
> Subject: RE: [SIPForum-discussion] Early Media
>
>
> Hi
>
> If the 183 and 200 OK should have same SDP . How does the following
> scenario
> work ??
>
> A calls ( throgh a B2BUA AS) B
> B doesnot answer
> Application Server sends INVITE to Media Server
> Application Server sends the SDP info he got from Media Server to A in
> the
> 183 message A gets a Music played by media Server Now Application server
> forwards the call to C If C answers , A should get the SDP info of C ( I
> thought it would be sent in 200 OK )
>
> If 200 OK sent to A should have the same SDP as that of 183 , How can A
> and
> C talk in this case ..
>
> Thanks
> Siva M
>
> -----Original Message-----
> From: Robert Mansfield [mailto:RJM at Redwoodtech.com]
> Sent: Thursday, April 19, 2007 1:54 PM
> To: Siva M-Q16748
> Subject: RE: [SIPForum-discussion] Early Media
>
> Siva,
>
> I'm not 100% sure but my understanding is that the early media WILL
> contain
> the same SDP descriptor as the 200 OK. There is a 'early-session' header
> (look at RFC 3959 and 3960 for some guidance) that is used in an
> Application
> Server model for early media. This allows for different SDP descriptors
> during session establishment.
>
>>From my experience with PSTN-SIP Gateways (Gateway model) the descriptor
> will be the same.
>
> Rob.
>
> -----Original Message-----
> From: Siva M-Q16748 [mailto:sivam at motorola.com]
> Sent: 19 April 2007 06:49
> To: discussion at sipforum.org
> Subject: [SIPForum-discussion] Early Media
>
>
>
> Hi
>
> In case of Early Media for announcements
>
> Can 183 and 200OK have different SDP info
>
> Thanks
> Siva M
>
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