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

[Detlef Bosau]

On 01/31/2012 05:22 PM, Mirja Kuehlewind wrote:
> 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).

First of all, I would really like to avoid the term "bandwidth" in our 
context.

To make a long story short and come to the point: Bandwidth is given in 
Hertz, throughput is given bin bit per second.
At least in papers, I've read so far, this "sloppiness" has lead to much 
confusion and in some cases to simply wrong results.

We should acknowledge the fact, that there are e.g. wireless networks 
around, where this difference is absolutely crucial.
> 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

It is not a bandwidth, what we detect, but it is network capacity. And a 
tcp flow may share this capacity with others. So, at least one issue is 
the coexistence of different TCP schemes.

> 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?
>

To my understanding, even an ECN is respected only "once a round". 
Please correct me, if I'm wrong.

The more I think about BIC and CUBIC, the more I ask for the appropriate 
problem for this nice solution.
I'm not quite sure whether there exists a suitable problem for just more 
aggressive probing.

And perhaps we should clearly focus the problem - afterwards we may 
propose and discuss suitable solutions.


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