[e2e] opening multiple TCP connections getting popular

Matt Mathis mathis at psc.edu
Fri Aug 31 07:38:38 PDT 2007

I believe that default window scales for Windows Vista and the Linux
mainline source are 7 and 6 respectively, except for IE, which sets it down as
indicated in the slides.   This is large enough to support 1 Gb/s on moderate
paths (10 of ms) or 100 Mb/s on global scale paths.

It remains to be seen if the early adopters can apply enough pressure to get
enough of the bugs corrected, before the masses force more conservative

Hint: use large window scales, and report problems, NOW.

Unfortunately the most insidious bugs are home NAT/security boxes that pass
the WSCALE option w/o parsing it, and then toss segments that seem to be out
of window, because the unscaled window is less than 1500 Bytes.  This bug is
insidious because these particular boxes were marketed to non-clued home
users, who have no hope of figuring out why they can not connect to sites
attempting to actually fill their high speed links.

I actually think making the browser use small WSCALE is an excellent migration
strategy because then the clueless users retain the ability to browse help
and download diagnostic tools....  I assume it will be phased out at some point.

I wish I had seen the talk in Pague.

Matt Mathis      http://www.psc.edu/~mathis
Work:412.268.3319    Home/Cell:412.654.7529
Evil is defined by mortals who think they know
"The Truth" and use force to apply it to others.

On Fri, 31 Aug 2007, Michael Welzl wrote:

> 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
>    limit.
> 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.
> Cheers,
> Michael

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