[e2e] [Iccrg] Re: Reasons not to deply TCP BIC/Cubic

[Mirja Kuehlewind]

Hi everybody,

I know I'm quite late to enter this discussion, but I would like to raise 
another question. I guess there was already a lot explanation on the e2e list 
saying (more or less) that Cubic is more aggressive but it is also able to 
react more quickly on network changes (mainly sudden increases in bandwidth). 

With e.g. TCP Reno the time between two loss events is increasing with the 
network capacity. So it might take a long time to actually detect that there 
is more bandwidth available in a network with large capacity. If we want to 
speed up this probing process we would need more frequent loss events causing 
a higher loss rate...? I guess one solution to this problem would be ECN. 
That means having a high probing rate but no losses. I'm wondering if there 
is any other solutions?

Mirja


On Wednesday 30 November 2011 12:56:46 Michael Welzl wrote:
> This should really go to ICCRG, I'd say (added to recipients). May I ask
> to continue this (interesting!) discussion there?
>
> On 11/30/11 12:10 PM, mascolo at poliba.it wrote:
> > Dear all,
> >
> > we know that TCP BIC/Cubic is default in Linux and as a consequence
> > 50% of servers employs TCP BIC/Cubic.
> >
> > Our measurements say that there could be reasons not to deploy TCP
> > BIC/Cubic. These reasons  are in our opinion rooted in its more
> > aggressive probing phase. In particular, in common network conditions,
> > TCP BIC/CUBIC exhibits: 1. a larger RTT average wrt to TCP NewReno or
> > TCP Westwood+; 2. a larger number of retransmission wrt to TCP NewReno
> > or TCP Westwood+; 3 larger throughput but same goodput wrt to TCP
> > NewReno or Westwood+.
> >
> > In other terms, it seems that its more aggressive probing increases
> > both throughput and retransmissions but leaving unchanged the goodput.
> > This is  neutral for the users but negative for the network.
> >
> > I appreciate your views.
> >
> > Thanks for the attention and best regards,
> >
> > Saverio Mascolo
> >
> > ----------------------------------------------------------------
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>
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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 at ikr.uni-stuttgart.de
web: www.ikr.uni-stuttgart.de
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