Subject: RE: [AVT] Feedback on draft-hdesineni-avt-avpf-ccm-pd-extn-00.txt from Dallas IETF meeting ( Was Draft minutes from Dallas)

From: "Desineni, Harikishan" <[email-masked]>
Date: Tue, 25 Apr 2006 11:02:07 -0700

>Randell Jesup [mailto:[email-masked]] writes:
 
> "Desineni, Harikishan" <[email-masked]> writes:
> >> Also, current congestion control methods rely strongly on
packet-drop
> as
> >> an indirect signal of congestion.  That method is probably not
> >> appropriate for a wireless situation (where packet-drop might be
due to
> >> channel loss, or congestion/channel-bandwidth).
> >
> >I think the point you made is already very well known and understood
by
> >this community. I would like to point you to section13, RFC1368.
> >RFC3168, Sec 13 states "With the increased deployment of applications
> >and transports sensitive to the delay and loss of a single packet
(e.g.,
> >realtime traffic, short web transfers), depending on packet loss as a
> >normal congestion notification mechanism appears to be insufficient
(or
> >at the very least, non- optimal)"
> 
> So, if it's "well known and understood", what's the suggested
solution?
> RFC 3168 is all well and good, but from a cursory reading it appears
that
> until support for it is fairly widespread, it may not survive through
> the network (and is of no use unless the routers that are congested
> support
> it).  Also, there's no definition of how it would work for UDP, just
> TCP and tunnels, etc.  Note also that RFC 3168 doesn't push routers to
> signal until they're nearing the drop-point, which may be later than a
> real-time application would want to know about it, especially wireless
> or other routers that use deep queues to handle variable link
conditions,
> etc.
> 
> Since we can't wave a wand and have ECN implemented, other solutions
> are worth looking into.  ECN should be used when it's possible, I
suspect.

Agreed -- 
Let me summarize some points here
 --RTP/UDP transport (unlike TCP) has no knowledge of ECN
 --ECN requires support from IP routers
 -- ECN based notification might be a too late reaction for a real time
application (especially for the one attached to a wireless link with
deep queues),

Given the above, it looks like ECN may not be a good and/or easy
solution for real time applications. What we proposed in the draft
(which is close to application level ECN) is a possible alternate easy
solution to solve this problem. 

I would like to know if there is any work/evidence to prove that ECN
applied to RTP/UDP transport will actually work well for a real time
application.

Thanks,
Hari

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