Subject: Re: [siprec] Multiplexing different participants' streams on the sameport

From: "Sid Rao" <[email-masked]>
Date: Fri, 18 Mar 2011 06:33:57 -0400

Just out of curiosity, apart from the extra socket this saves, what are
the actual technical drivers for such a solution?

Sid Rao

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of Elwell, John
Sent: Friday, March 18, 2011 4:11 AM
To: [email-masked]
Subject: [siprec] Multiplexing different participants' streams on the
sameport

Something Charles mentioned in another thread triggered me to raise
this.

We consider different participants in the CS as potentially producing
separate media streams that the SRC sends to the SRS, where the SRC can
send them mixed or unmixed.

When sending them unmixed, up till now I think we have considered
sending them to separate ports on the SRS and identifying them as
separate m= lines in the SDP. Another possibility might be to multiplex
the different streams on the same port and identify them by different
SSRC values. I am not sure whether this would be a correct use of SSRC,
and I suspect we would need to check with AVTCORE. Recent discussions in
other contexts (telepresence, RTC-Web) have also drawn my attention to
such possibilities. See also
https://datatracker.ietf.org/doc/draft-perkins-rtcweb-rtp-usage/.

Of course, it would mean that we would have to rethink how we reference
the different streams from metadata.

I am not necessarily proposing such a change - I just want to make sure
we have given it due consideration.

John (as individual)

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From: "Parthasarathi R (partr)" <[email-masked]>
Date: Fri, 18 Mar 2011 16:10:36 +0530

John/Charles,

To make my query in the single thread, I'm re-posting my earlier
question here:

"I wish to get more clarity for this scenario. In the mentioned
scenario, whether RFC 5576 ssrc attribute or some other attribute is
used in CS SDP to indicate RTP muxing in m-line. If so, the same
attribute shall be extended for RS session as well. There is no need to
push the information to metadata XML. In case there is no indication of
multiple stream in CS, it is possible that SRC may not able to indicate
explicitly in RS signaling but RTP muxed passed to SRS with different
SSRC or CSRC."

Thanks
Partha 

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of Sid Rao
Sent: Friday, March 18, 2011 4:04 PM
To: Elwell, John; [email-masked]
Subject: Re: [siprec] Multiplexing different participants' streams on
thesameport

Sid Rao

-----Original Message-----

John (as individual)

---

From: "Elwell, John" <[email-masked]>
Date: Fri, 18 Mar 2011 14:59:16 +0100

Those who have proposed this in other contexts are concerned about:
- excessive use of NAT port bindings, which some feel might become a scarce resource in some situations;
- the amount of ICE work that needs to be done.

Of course, these considerations will not apply to all deployments of SIPREC, so a one stream per port solution might be considered adequate. But it is better to have this discussion now than later.

John

> From: Sid Rao [mailto:[email-masked]] 
> Sent: 18 March 2011 10:34
> Subject: RE: [siprec] Multiplexing different participants' 
> streams on the sameport
> 
> From: [email-masked] 
> [mailto:[email-masked]] On Behalf
> Of Elwell, John