Subject: [AVT] WGLC comments on draft-ietf-avt-ports-for-ucast-mcast-rtp-11: Part 3 Binding of C2->P4 RTCP to correct RTP session

From: Magnus Westerlund <[email-masked]>
Date: Fri, 14 Jan 2011 17:42:31 +0100

Hi,

This third issue was also brought up before and also Tom Van Caenegem
comment on it.

The RTCP reports going from C2->P4 from a receiver is not obvious on how
to correlate with the Unicast RTP session it is reporting on that are
sent P3->C1.

The issues that may arise are the following. First there might be a NAT
with port and address dependent mapping between them. Thus, even if
C2=C1, the externally seen address+port can be different between traffic
going to P3 and P4. In addition we shall not forget that there might be
multiple clients behind the same NAT that participate in the same
multicast session. So several RTCP flow might go to P4 from this IP
address.

I think some details on how to correlate this RTCP flow needs to be
included in the document. What are the determining factors? SSRC can't
be it unless we couple the multicast and unicast session. Which I think
is a bad idea. CNAME is likely the only method that is directly
applicable and would match from the C1->P3 request to the C2->P4 one.
But this needs to be stated as a requirement.

Cheers

Magnus Westerlund

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From: "Ali C. Begen (abegen)" <[email-masked]>
Date: Fri, 14 Jan 2011 10:33:03 -0800

> -----Original Message-----
> From: Magnus Westerlund [mailto:[email-masked]]
> Sent: Friday, January 14, 2011 5:43 PM
> To: IETF AVT WG; [email-masked]
> Subject: WGLC comments on draft-ietf-avt-ports-for-ucast-mcast-rtp-11: Part 3 Binding of C2->P4 RTCP to correct RTP
> session
> 
> Hi,
> 

Correct, there could exist multiple clients sending rtcp to p4.
 
> applicable and would match from the C1->P3 request to the C2->P4 one.

Yes, via a CNAME. And since we now have a good CNAME guideline document, this should work just fine.

Report correlation is about the individual unicast sessions, but I agree it is a good idea to state this explicitly in this draft, too and also require the new CNAME guideline document so that cnames are unique.

> But this needs to be stated as a requirement.

+1.
-acbegen

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From: Magnus Westerlund <[email-masked]>
Date: Mon, 17 Jan 2011 11:55:08 +0100

>> But this needs to be stated as a requirement.

Great, that seems to close on this issue.

-- 

Magnus Westerlund