If you have a Windows machine which acts as a server and it have many connections per seconds, you can get in the situation when you have a lot of half-open connections owned by the system (PID 0) process. To resolve this if the communication hosts have high speed connections with one another (like a local LAN), you can use the following tweak to reduce the timeout value:
Change the DWORD value (create it if you don’t have one) TcpTimedWaitDelay in HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipParameters to 30. This is in seconds and the accepted range is between 30 and 300 seconds.
Tip taken from the WinGuides site.
The official documentation can be found over at the MS technet site
As a side note: why are all those connections owned by the system process? Because if a process exists, its half open connections are inherited by the system process (probably this is something like the init process under Linux which inherits processes whose parents have exited).