[e2e] opening multiple TCP connections getting popular

Michael Welzl michael.welzl at uibk.ac.at
Fri Aug 31 01:59:34 PDT 2007

On Fri, 2007-08-31 at 11:08 +0900, Lars Eggert wrote:
> On 2007-8-30, at 15:18, ext Michael Welzl wrote:
> > Does anybody know if there's a generally known, agreed upon reason
> > for not using Window Scaling? Google tells me that some broken
> > routers can't handle it... but, interestingly, Wikipedia (via
> > google :-) ) tells me that, since kernel version 2.6.8, the option
> > is enabled in Linux by default, and that it's used (by default? don't
> > know) in Vista...  so what, are we already heading for trouble?
> Microsoft presented their findings related to window scaling (and  
> several other TCP extensions) at the IETF TSVAREA meeting in Prague.  
> See http://www3.ietf.org/proceedings/07mar/slides/tsvarea-3/sld3.htm  
> and the two following slides. Summary: Window scaling is enabled in  
> Vista, but limited to a factor of 2.
> PPT slides are here: http://www3.ietf.org/proceedings/07mar/slides/ 
> tsvarea-3/tsvarea-3.ppt

Thanks, that's very interesting! (and thanks to David Ros too,
who also pointed me to these slides in a private email)

So ... the reasons they give are bugs, bugs, bugs.

I guess this means that we are facing a world where working
on congestion control is rather pointless because:
1) either your personal bottleneck is the limit (and all
   you care about is that your flows fairly share it,
   at least within reasonable boundaries), or
2) (in Japan, as Jon said, or maybe our future networks
   or some other special cases) the receiver window is the

The reason for 2) is the lack of (proper) use of window
scaling, which is due to bugs in firewalls, routers etc.

That's pathetic. What can we do about it? Stop worrying about
CUBIC vs HTCP vs FAST vs WHATEVERTCP, and shut down ICCRG?
Maybe we should dedicate our time to sending emails to the
people responsible for these bugs instead of doing research
on congestion control.

Wow... I'm normally an optimistic person, but that perspective
truly depresses me.


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