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How can the Initial Congestion Window be increased to 10? It seems it can be done with TCP_INIT_CWND, but I don't know how to do that.

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You can use ndd to tweak the tcp parameters. Get a list:

ndd /dev/tcp \?

The only one I see that looks similar is tcp_cwnd_max (I'm not well versed in the guts of TCP) and it's set to 1048576:

ndd /dev/tcp tcp_cwnd_max

You can also use ndd to change the parameters dynamically. To make them stay changed after a reboot, add a set line in /etc/system

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Max is not the same as initial so I don't think that is it. Perhaps I could add one that is not in the list. I will try later. – George Bailey Mar 30 '11 at 12:15

The new features in Solaris Express 1/06 seems to suggest that an application can change this parameter and then points to the TCP(7P) man page which itself suggests it can be set by an application

 An appli cation can use this option to set  the  initial cwnd  
 to a specified  number of TCP segments. This applies to the cases
 when the connection first starts and restarts after an  idle

As this seems to be application related you may get a better answer on

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