Subject: RE: [Sip] Changing SSRC/sequence numbers during a call

From: <[email-masked]>
Date: Thu, 12 Oct 2006 09:42:01 +0530

Hi,

SSRC is used per session as an identifier of the source. It will not be
changed in a Session.

In a session, if there is a collision with the SSRC from the other side
it should be changed (This is a very rare case!!)

Ina video call, where you have audio and video for each medium a SSRC is
used.

So what type of call are you making? Is it a multimedia call?

Questions related to RTP can be posted @ [email-masked]

HTH,

Sreeram.

________________________________

From: Dhodapkar Chinmay-C23627 [mailto:[email-masked]] 
Sent: Wednesday, October 11, 2006 9:37 PM
To: [email-masked]
Subject: [Sip] Changing SSRC/sequence numbers during a call

Hi,

Can the SSRC of RTP packets change midway between the call. The scenario
is that the call has been set up using the usual SIP/SDP signalling.

After this there is no further signalling between the two entities, but
the SSRC changes. Is this valid? Since nothing else changed (remote
ip/port, 

remote entity, there is no conflict of SSRCs, etc).

Looking forward to some inputs on this.

Regards,

Chinmay Dhodapkar

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---

From: Colin Perkins <[email-masked]>
Date: Thu, 12 Oct 2006 08:59:55 +0100

On 12 Oct 2006, at 05:12, <[email-masked]> wrote:
> SSRC is used per session as an identifier of the source. It will  
> not be changed in a Session.

The SSRC of a participant can change within a session if there is a  
collision (as noted below), or if the participant generates multiple  
streams within the session. For example, if a participant has two  
cameras and switches between then, the video from each camera should  
use a different SSRC [RFC 3550 section 3].

> In a session, if there is a collision with the SSRC from the other  
> side it should be changed (This is a very rare case!!)
>
>
>
> Ina video call, where you have audio and video for each medium a  
> SSRC is used.
>

Or to the IETF AVT working group <[email-masked]> which designed RTP.

Colin