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

Magnus Westerlund <magnus.westerlund@ericsson.com> Mon, 17 January 2011 10:52 UTC

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Date: Mon, 17 Jan 2011 11:55:08 +0100
From: Magnus Westerlund <magnus.westerlund@ericsson.com>
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To: "Ali C. Begen (abegen)" <abegen@cisco.com>
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Cc: "draft-ietf-avt-ports-for-ucast-mcast-rtp@tools.ietf.org" <draft-ietf-avt-ports-for-ucast-mcast-rtp@tools.ietf.org>, IETF AVT WG <avt@ietf.org>
Subject: Re: [AVT] WGLC comments on draft-ietf-avt-ports-for-ucast-mcast-rtp-11: Part 3 Binding of C2->P4 RTCP to correct RTP session
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Ali C. Begen (abegen) skrev 2011-01-14 19:33:
> 
> 
>> -----Original Message-----
>> From: Magnus Westerlund [mailto:magnus.westerlund@ericsson.com]
>> Sent: Friday, January 14, 2011 5:43 PM
>> To: IETF AVT WG; draft-ietf-avt-ports-for-ucast-mcast-rtp@tools.ietf.org
>> 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,
>>
>> 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.
> 
> Correct, there could exist multiple clients sending rtcp to p4.
>  
>> 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.
> 
> 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.

Great, that seems to close on this issue.

-- 

Magnus Westerlund

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[AVT] WGLC comments on draft-ietf-avt-ports-for-u… Magnus Westerlund
Re: [AVT] WGLC comments on draft-ietf-avt-ports-f… Ali C. Begen (abegen)
Re: [AVT] WGLC comments on draft-ietf-avt-ports-f… Magnus Westerlund