Windows 2003 server doesn't close TCP connection

I work in a company that one of our products is working on windows 2003
server /windows 2000 server.
The product is working on VOIP platform.
It is responsible of VOIP calls using h.323 protocol.

The problem happened when Tandberg end point is participant in VOIP call.
The Tandberg end point always use port 5555 and when the call is complited
it sends TCP RST .
Windows 2003 sp1 server receives the RST but doesn’t recognize release the
TCP connection for about 20 seconds.
The windows 2000 server does recognize the end of the TCP connection.

When I use windows 2003 server without service sp 1 the problem didn’t happed.
Is there any registry key to use so I return to the old time when the
windows 2003 server will close the TCP connection like windows 2000 server?