This is a very interesting issue. Strange that there are no other replies so far. I studied the case a bit and thus the following remarks:
When do the routers need to know about TCP window size? Their main task is IP routing, which requires packets only to be examined at layer 3. The window size is something that is negotiated between the end nodes that have a TCP connection established. Exeptions to this occur when the router does something like protocol translation, tunneling through TCP or when a router on one end is also the termination point for the TCP connection. So I would not think that an upgrade will help you much.
Another remark is that the actual speed is much lower than what might be expected from the calculations. 13 Mbps should equal an FTP-rate of about 1Mbyte/s. So your achieved results are 4 to 5 times lower than they should.
When you get this straight, you will just need three simultaneous connections to fill the link almost completely. That should be pretty sufficient as this type of link is never installed to serve only one end node.
Goodluck with it, and please let me know if you solved the issue somehow.
I had similar issues. Of course I agree with the previous concensus, that the TCP WINDOW size in the router only needs to be adjusted for TCP connections that are made to the router (rsh, rlogin, rcp, telnet, tacacs, dlsw, etc).
I increased TCP Window Size to 256950, enabled Window Scaling, RFC 1323, disabled TimeStamps, enabled PathMTU discovery, and blackhole detection. This was on two Windows 2000 Servers, seperated by ATM WAN, using 20 Mbps SCR.
Previously the hosts were only able to transfer at about 1.6 Mbps, increasing the settings from default to the above, I was able to reach a transfer rate of 8mbps.
I tested with multiple FTP servers, and multiple FTP Clients, and found that other FTP Clients do not utilize the RFC1323 options. Microsofts FTP client does for certain.
I used a quick little utility called DRTCP from dslreports.com.. Supposedly they say that cisco recommends them, but I have never seen mention of DRTCP anywhere else.. At any rate it worked well and quick, and there is a definition of the settings there as well.
I am actually looking for advanced information on the RFC1323 options and how they affect DLSW if anyone has any information on that, it would be greatly appreciated.
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