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Re: Sprint Help

  • From: Leo Bicknell
  • Date: Thu Mar 18 13:54:38 2004

In a message written on Thu, Mar 18, 2004 at 12:15:19PM -0500, Joe Marr wrote:
> I have a customer with a large citrix farm at hop 15. The customer has
> several remote offices, one as far away as Japan. One of their offices has
> been experiencing slow performance with their citrix connections. It's not

Your problem is right here:

>  14 urish-pitts-gw.centrepc.net (67.97.250.166) 100 msec *  100 msec

NT in many configs defaults to a TCP Window size of 8k, other NT and
Server 2000 default to 16k.  At one window per RTT that's 80k/sec
or 160k/sec maximum throughput over a 100ms link.

80k/sec is not fast enough to make Citrix (which must send large
portions of the screen) usable.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\TCPWindowSize

Note, bigger is not better, if you go make it 64k you're likely to
just crash your machine.  Google for "TCP Window Size" and read one
of the 50,000 papers available before you tweek the value.

More to the point: This is becoming an acute problem in ISP support
(at least, if you offer more than dial speeds).  We get several
queries per week from customers who put boxes in a New York and LA
colo on GigE, and then can't get more than a 200k/sec FTP and want
to complain about the backbone.  Reality is they can get the full
10000k/sec if they just fix their boxes.  It's purely an end host
issue.

And yes, it is a Windows issue.  Commercial and Free unix systems
are generally all on 32k default windows, with a few at 64k default
windows.  These still need to be tuned for really high speed links,
but don't make people complain.  Microsoft waited too long to up
these values (XP is 32k) so the masses of older servers show "slow"
performance for no good reason.  They really should update with a
service pack.

Cable/DSL providers who have software that tweeks users computer
settings (which I have issues with, but if you do it...) should 
think about tweeking the value up for 98/NT/2000 users as part
of the default software install.

-- 
       Leo Bicknell - bicknell@ufp.org - CCIE 3440
        PGP keys at http://www.ufp.org/~bicknell/
Read TMBG List - tmbg-list-request@tmbg.org, www.tmbg.org

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