Subject: [AVT] Additional requirement in Congestion control for the "draft-kristensen-avt-rtp-h264-rcdo-00"

From: <[email-masked]>
Date: Mon, 23 Jul 2007 23:16:59 +0100

Hi

I just skimmed the draft-kristensen-avt-rtp-h264-rcdo-00 draft and
section 6 that deals with congestion control puzzled me somewhat. The
reference to the main congestion control in RFC3550 in the first
sentence is fine but I don't understand the relationship to the rest of
the paragraph. As the media in a sip sense has been 'offered and
answered' therefore congestion techniques will not apply to this
'session' as congestion control traditionally only applies to the setup
of new 'sessions'. 

The packet loss could be as a result of congestion and could be used as
a indicator to apply congestion control at this entity that is suffering
the packet loss but this is not the only indication of congestion.
Presumably one of the entities monitoring the packet loss is the UE
which I hope is not under congestion but could still be suffering from
packet loss does it then report this loss to the entity sending the
higher resolution video. I think that some clarification of what the
additional requirement to monitor packet loss is needed.

Regards

Steve Norreys

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

---

From: "Tom Kristensen" <[email-masked]>
Date: Tue, 24 Jul 2007 00:36:31 +0200

On 24/07/07, [email-masked] <[email-masked]> wrote:
> Hi
>
> I just skimmed the draft-kristensen-avt-rtp-h264-rcdo-00
> draft and section 6 that deals with congestion control puzzled me somewhat.
> The reference to the main congestion control in RFC3550 in the first
> sentence is fine but I don't understand the relationship to the rest of the
> paragraph. As the media in a sip sense has been 'offered and answered'
> therefore congestion techniques will not apply to this 'session' as
> congestion control traditionally only applies to the setup of new
> 'sessions'.

The text in section 6 is stolen from the draft "How to Write an RTP
Payload Format" (draft-ietf-avt-rtp-howto-01) - where the text is
proposed as an initial text for this section in the template provided.
However, an RTP payload format specification is not written solely for
SIP applications - so other scenarios apply as well.

> The packet loss could be as a result of congestion and could be used as a
> indicator to apply congestion control at this entity that is suffering the
> packet loss but this is not the only indication of congestion. Presumably
> one of the entities monitoring the packet loss is the UE which I hope is not
> under congestion but could still be suffering from packet loss does it then
> report this loss to the entity sending the higher resolution video. I think
> that some clarification of what the additional requirement to monitor packet
> loss is needed.

Thanks for the input, it's possible to expand and elaborate the text
in the H264-RCDO RTP payload format draft.

-- Tom

-- 
# TANDBERG R&D
## http://www.tandberg.com

---

From: Magnus Westerlund <[email-masked]>
Date: Tue, 24 Jul 2007 01:24:54 +0200

> 'session' as congestion control traditionally only applies to the setup 

Here you are wrong. Congestion control is needed for the complete 
session in any best-effort network. Only in cases when you have end to 
end QoS agreements with the network can you avoid doing congestion 
control. Even when using QoS should you monitor that the agreement is 
fullfilled by the network.

Please read RFC 2914 to understand why congestion control is needed in 
the internet.

> additional requirement to monitor packet loss is needed.

Normally you will not get any feedback from any entity within the 
network. That is why receivers need to report to the sender about losses 
so that the sender can react to the congestion that is somewhere on the 
path from the sender to the receiver.

Cheers

Magnus Westerlund

IETF Transport Area Director & TSVWG Chair
----------------------------------------------------------------------
Multimedia Technologies, Ericsson Research EAB/TVM/M
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: [email-masked]
----------------------------------------------------------------------