Subject: [Megaco] SSRC field

From: "Wainwright, John \(Com US\)" <[email-masked]>
Date: Fri, 10 Nov 2006 09:17:07 -0800

Assume there is a call set up between A & B both using unique ssrc
values in the RTP stream.  If party A, with the help of the MGC,
invokes a  call transfer type scenario such that party B now speaks to
Party C via a Modify message with the Remote Descriptor/SDP data
indicating party C, can party B continue with the same ssrc value ?
If it is used to identify the source then nothing has changed - only the
termination data  has changed.
 
Thanks
John
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---

From: [email-masked]
Date: Mon, 13 Nov 2006 17:34:26 +0100

John,

guess you question is for the avt list, rather than megaco, because SSRC
values are not exchanged via H.248.

I'm not very familiar with RTP, but I think the starting point would be the
correspondent RTP model (e.g. mixer, translator; two translators; modeling
of each half call by a separate RTP session; etc.) applied for a specific
supplementary service.

Nevertheless, I think B may continue the "next call phase" with the same
SSRC value, assuming the basic rule of § 7.1/RFC3550:

   Similarly, all RTP end systems that can communicate through one or
   more RTP translators or mixers share the same SSRC space, that is,
   the SSRC identifiers MUST be unique among all these end systems.
   Section 8.2 describes the collision resolution algorithm by which
   SSRC identifiers are kept unique and loops are detected.

Cannot see any requirement for an SSRC value update of B in such a service.
Of course, C's SSRC may clash with B (or SSRC values of the H.248 RTP
terminations dependent on model ...), but then normal collision resolution
algorithm applies as in any 2-party service.

- Albrecht

                      "Wainwright, John                                                                                                 
                      \(Com US\)"                To:      <[email-masked]>                                                             
                      <john.wainwright@s         cc:                                                                                    
                      iemens.com>                Subject: [Megaco] SSRC field                                                           
                                                                                                                                        
                      10.11.2006 18:17                                                                                                  

Assume there is a call set up between A & B both using unique ssrc values
in the RTP stream.  If party A, with the help of the MGC,  invokes a  call
transfer type scenario such that party B now speaks to Party C via a Modify
message with the Remote Descriptor/SDP data indicating party C, can party B
continue with the same ssrc value ?
If it is used to identify the source then nothing has changed - only the
termination data  has changed.

Thanks
John_______________________________________________
Megaco mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/megaco