[e2e] Are we doing sliding window in the Internet?
detlef.bosau at web.de
Tue Jan 2 11:52:03 PST 2007
Venkata Pingali wrote:
> Server end (i.e, end that has large
> amount of data to transfer):
> - Most connections are short (90% < 1sec)
Do you have any knowledge of the number of "rounds" the TCP connection
has seen? A couple of years ago I saw some similar result (don´t no the
source at the moment) where 90 % of connections consist of not more than
Now, consider the initial slowstart, IIRC we start with 2 MSS (?) then
total of 14 packets up to now
total of 24 packets up to now,
thus many flows will finisch before the end of the fourth round which
would correspond to a CWND of about 6 kByte, 1500 byte MSS assumed.
In short words: Quite a few connections are finished before the end of
the fist slow start period.
Does this match your observations?
> - MaxCwnd is < 5KB in > 80% of cases
> - MaxRTT is distributed almost uniformly
> in the 0-400ms range.
> Client end (i.e., the end receiving data):
> - ~ 90% of connections see MaxCwnd < 5KB
> - < 1% connections see MaxCwnd > 10KB
> - 90% of connections have MaxRTT < 100ms
Oh, I love it :-)
Last year I had a long argument with someone who told me about the
benefits of window scaling :-) He talked about extremely large CWNDs by
several dozens or hundreds of MByte :-)
O.k., that´s a different story because we are talking about greedy
sources than. However, if that colleague was the only one to activate
window scaling while surfing from the US and A to good ol´ Europe and
Cisco et al. had buried hundreds of megabytes of useless queue memory in
their hardware *blush* this guy perhaps filled the queues the first time
ever, following the good old paradigm: "Keep the queue full" and that
way of course outperformed his competitors hopelessly ;-)
> There are some problems with the data:
> - limited scenarios (web based)
> - small sample sizes (21K for server, 150K
> for client)
> - the website has non-standard distribution
> of file types and sizes
At least it exists. And reality is often more convincing than standards.
Particularly in cases were both disagree.
> You can find the various graphs here:
Just a question: Is it possible to export those slides to a common
readable format like PDF? I don´t have any M$ products in use here and
when I opten PowerPoint slides with OpenOffice the results are sometimes
interesting, sometimes surprising, sometimes hopeless, but nearly always
quite different from what you wrote :-)
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