Broadband Optimizer for Revolution?

[Mark Wieder]

Dar-

Tuesday, May 31, 2005, 2:34:59 PM, you wrote:

DS> I don't think that a large MTU would hurt the receive window.

No, but...

DS> Perhaps Andre is right in that these mean buffer sizes for transmit.
DS> (To me it seems strange to call the MTU a transmit window.)

Here's my understanding of this - I'm sure someone will correct me if
I'm too far off - there's a maximum transmit window size and a maximum
receive window size. You can crank your receive window up without too
much problem. However, if you start messing with your transmit window
one of several things may happen:

1. You'll get the size too low (I think windows enforces a minimum
88-byte window even if you try to set it lower), in which case you'll
be sending out lots of small packets and the packet overhead will
significantly affect your transmission speed.

2. You'll set the size too high, which should theoretically increase
your throughput - sending lots of data with low overhead. However, if
there are any routers in between (i.e., you're on some system other
than a two-computer point-to-point system) then somewhere along the
line some device will have an MTU smaller than the size you've set and
it will break up the packet into smaller pieces, again probably
slowing things down for you.

Of course, these are *maximum* windows sizes - TCP is constantly
testing performance and adjusting the window sizes as necessary, but
it won't go above the MTU.

The only real reason I've seen for messing around with the maximum
window sizes is when switching between dialup and broadband
connections, and you'll see a real difference there. There are speed
tests at www.dslreports.com (look in the tools section) that can
report on current settings and allow you to tweak them for optimal
performance. On Windows machines anyway - there's some minimal
tweaking you can do in OSX, but I haven't found it to affect things
very much - it already seem optimized. Windows seems to need a lot
more handholding.

-- 
-Mark Wieder
 mwieder at ahsoftware.net