Please note that a TcpWindowSize of 65536 in decimal value is
1 0000 in Hexadecimal. Win NT 4.0 does not realize this is and sets
the window size to 0. When sending a packet to a host with a
TcpWindowSize of zero, the host follows the TCP spec and sends back 1 byte to
respond to the zero window size. The Win NT host then proceeds to advertize a
no-zero window size and the communications begin. The rest of the packet which
trails the initial 1 byte originaly sent is fragmented and minimizes throughput.
To provide a band-aid fix, you can set 1 back the TcpWindowSize to 65535 which
is ffff in hex and does fit in the 16 bit tcp parameter.
Windows advertizes correctly and communications is possible to a full
theoretical
64 Kbyte * 8 bit/Byte / .250 ms(average sat delay) = 2.048 Kbit/sec
Longterm fix - Use Solaris or Windows 2000 with the scaling option.
Loay Oweis
COMSAT Corp
[email protected]
____________________Reply Separator____________________
Subject: Fwd:RE: nt to nt tcpsat problems
Author: Rob Kibler
Date: 2/11/00 9:16 AM
____________________Forward Header_____________________
Subject: RE: nt to nt tcpsat problems
Author: <[email protected]>
Date: 2/10/00 6:04 PM
Gentlemen,
I did a week long study on this exact problem and the simple answer is "YOU
ARE OUT OF LUCK." I have a ticket open with MS on this problem as it is how
the CIFS protocol works. CIFS will only negotiate a 4K transfer size when
the latency and bandwidth are small (if you are very very ... lucky maybe
upto 12K). Basically, in short your throughput will be about equal to
4K/RTT (excluding other various factors). Thus, window size only needs to
be 4K for this. It is a higher layer problem!!!
While I cannot give you a copy of my report, I do have a couple of graphs I
can get to you.
Greg
-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Robert Schellhase
Sent: Thursday, February 10, 2000 1:18 PM
To: [email protected]
Cc: [email protected]
Subject: RE: nt to nt tcpsat problems
Hi Graham,
I see you have found that Windows supports a registry key for TcpWindowSize.
The sad news is that it has no effect, in spite of the fact that Microsoft
has a white paper on its own TCP implementation that claims otherwise.
You might try the NetManage OnNet kernel for Windows 95/98 at
http://www.netmanage.com/products/onnetkernel4/index.asp
I don't know what they charge for it, but I think it's affordable and they
offer a free demo.
Best regards,
Robert Schellhase
Senior Engineer
INTELSAT
-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Graham Street
Sent: Thursday, February 10, 2000 9:04 AM
To: [email protected]
Subject: nt to nt tcpsat problems
Hi all,
We're trying to run windows file sharing protocols over a tcp sat link
and getting miserable performance, even after setting TcpWindowSize to
65536. We can get about 100-250k max. We are trying to get at least
one megabit out of it. Is this even possible? We can get 1-2 megabits
ftping from a sun box over satellite...
does anyone know of any clever (cheap) solutions (spoofing nacks?,
translating
to udp?)
Thanks,
Graham Street
[email protected]
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From: "Greg Otto" <[email protected]>
To: "'Robert Schellhase'" <[email protected]>,
<[email protected]>
Cc: <[email protected]>
Subject: RE: nt to nt tcpsat problems
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