Re: [conex] ConEx as sender side only modification

Hi Ingemar,

that sounds really complicated. From point of view, a policer should not do 
anything like this. The ConEx sender should be aware of the risk of 
underestimating congestion. The current document on TCP modification proposes 
two 'hacks' how to get better feedback from a classic ECN receiver. Moreover, 
the draft says in the section about credits that when a sender which 
experiences on-going losses/ECN marks even though the sending rate was 
reduced due to congestion control, it should think about sending credits as 
those losses might be introduced by an audit device. 

In the meeting there was already a comment/question why more than one 
possibility is needed to cope with classic ECN. The answer is all variants 
have draw-backs (e.g. risk of information loss when ACK loss occurs). But I 
guess some further advisement is needed here what the sender should do to 
avoid underestimating the congestion and/or in which situation which action 
is the right one. But actually I'm not really sure what the right advise 
would be....

Mirja

On Tuesday 15 November 2011 09:25:57 Ingemar Johansson S wrote:
> Thanks
>
> This then means that a policer need to give some extra slack for normal
> TCP. It is perhaps doable with a policer that somehow has access to the TCP
> acks in the reverse direction and then can determine both RTT with a
> reasonable accuracy and also if TCP ECE is modified according to
> (http://tools.ietf.org/id/draft-kuehlewind-conex-tcp-modifications-01.txt)
> Or is this perhaps simpler ?
>
> /Ingemar
>
> PS
> Realized that I got things a bit backwards in my question below, thought
> that ECE is clamped to 1 for an RTT...
>
> > -----Original Message-----
> > From: Mirja Kuehlewind [mailto:mirja.kuehlewind@ikr.uni-stuttgart.de]
> > Sent: den 14 november 2011 17:43
> > To: conex@ietf.org
> > Cc: Ingemar Johansson S
> > Subject: Re: [conex] ConEx as sender side only modification
> >
> > Hi Ingemar,
> >
> > yes there are only sender-side modification needed. If you
> > only have the 'classic' ECN, you will only be able to get (at
> > max) one congestion notification per RTT. If there is more
> > than one CE marking per RTT you will underestimate the congestion.
> >
> > Mirja
> >
> > On Monday 14 November 2011 11:16:04 Ingemar Johansson S wrote:
> > > Hi
> > >
> > > Have not been able to follow the ConEx list in detail but reading
> > > http://tools.ietf.org/id/draft-briscoe-conex-initial-deploy-00.txt
> > > I can see that received side modifications are optional.
> > > This is of course interesting at least if consinder the
> >
> > normal server
> >
> > > client architecture as it is easier to modify a million
> >
> > servers than a
> >
> > > zillion clients. Assuming that I read right...
> > > How does it work with TCP, I know TCP modifications have been
> > > considered to make TCP echo back the exact correct number
> >
> > of ECN-CE to
> >
> > > the server. Does this then mean that a TCP flow (unmodified
> >
> > TCP) will
> >
> > > state a higher congestion level in the dest-opts than the actual ?
> > >
> > > /Ingemar
> > >
> > > =================================
> > > INGEMAR JOHANSSON  M.Sc.
> > > Senior Researcher
> > >
> > > Ericsson AB
> > > Wireless Access Networks
> > > Labratoriegränd 11
> > > 971 28, Luleå, Sweden
> > > Phone +46-1071 43042
> > > SMS/MMS +46-73 078 3289
> > > ingemar.s.johansson@ericsson.com
> > > www.ericsson.com
> > > =================================
> > > _______________________________________________
> > > conex mailing list
> > > conex@ietf.org
> > > https://www.ietf.org/mailman/listinfo/conex
> >
> > --
> > -------------------------------------------------------------------
> > Dipl.-Ing. Mirja Kühlewind
> > Institute of Communication Networks and Computer Engineering
> > (IKR) University of Stuttgart, Germany Pfaffenwaldring 47,
> > D-70569 Stuttgart
> >
> > tel: +49(0)711/685-67973
> > email: mirja.kuehlewind@ikr.uni-stuttgart.de
> > web: www.ikr.uni-stuttgart.de
> > -------------------------------------------------------------------

-- 
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Dipl.-Ing. Mirja Kühlewind
Institute of Communication Networks and Computer Engineering (IKR)
University of Stuttgart, Germany
Pfaffenwaldring 47, D-70569 Stuttgart

tel: +49(0)711/685-67973
email: mirja.kuehlewind@ikr.uni-stuttgart.de
web: www.ikr.uni-stuttgart.de
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