[e2e] Are we doing sliding window in the Internet?

[Venkata Pingali]

Detlef Bosau wrote:
> 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 
> 20 packets.


Our sample shows that 94% of connections
have < 20 packets - when observed from the
server end.

     Number of Packets       Percentile of Connections

      3                         4%
      4                         55%
      5                         69%
      10                        87%
      20                        94%


I have included the new graph and generated pdfs.

http://www.isi.edu/aln/e2e.pdf
http://www.isi.edu/aln/e2e.ppt

> 
> Now, consider the initial slowstart, IIRC we start with 2 MSS (?) then 
> we have:
> 
> Round    CWND
>    1              2
>    2              4
>    3              8
>                            total of 14 packets up to now
>    4             16
>                            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?

Yes.

About 90-95% finished before slow start
completed - often within the first two round
trips. About 3-4% of connections lasted for a
long time (several secs - minutes). But there
is an interesting category of connections that
last beyond the slow start but not for very
long. These connections, it turns, carry a large
chunk of the data (40+%) and most of the time in
these connections is spent in slow start.


> 
>>     - 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 :-)

Dont know if it is correct to extrapolate from the
same that we have but the MaxCwnd graph seems to
plateau as the connection length increases (bytes
or packets).


> 
> 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:
>> http://www.isi.edu/aln/e2e.ppt
> 
> 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 :-)
> 
> Regards
> 
> Detlef
>