North American Network Operators Group

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Re: The next broadband killer: advanced operating systems?

  • From: Adrian Chadd
  • Date: Tue Oct 23 04:59:21 2007

On Tue, Oct 23, 2007, Sam Stickland wrote:

> I'm concerned that if Microsoft were to post this as a patch to Windows 
> XP/2003 then we would see the effects of this "all at once", instead of 
> the gradual process of Vista deployment. Anyone agree?

You need both ends to have large buffers so TCP window sizes can grow.

So a few possibilities:

* you're running content servers but you're on training wheels and you're just
  not aware of this. Windows default sizes are small, so you never notice
  as you never grow enough TCP windows to fill your set buffer size.
  These guys would notice if Windows XP was patched to use larger/adaptive

* You're cluey and already have window sizes tuned; these guys won't notice
  any client changes as they'll never negotiate a larger window.

* You're cluey and have assumed X% of your customers (say, the ones >100ms
  away from you) have fixed their window sizes and hedge your bets on that.
  This group is analogous to network engineering based on current, not future
  use - possibly saving money in the short term, but probably going to fund
  the executive bonuses and not put away safely for days like what you're

* .. caveat to the above: until Linux goes and does what Linux does best
  and change system defaults; enabling adaptive socket buffers by default
  during a minor version increment. Anyone remember ECN? :P Then even some
  cluey server admins will cry in pain a little.

* I don't think the proposals are changing TCP congestion avoidance/etc, are

Its easily solvable - just drop the window sizes. In fact, I think the window
size increase/adaptive window size stuff would be much more useful for P2P over
LFN than average websites -> clients. General page HTTP traffic atm doesn't hit
window size before the reply has completed. Sites serving larger content
than HTML+images (say, Youtube, Music sites, etc) would've already given
this some thought and fixed their servers to not run out of RAM so easily.
Those are on a CDN anyway..

Its not just that; there's other things to worry about than just numsockets *
(send size + receive size) memory possibly being consumed but its a good
starting point.