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JSI Tip 1318. Control initial TCP retransmission timeout.

Starting with SP5, a new registry entry allows you to control the initial TCP retransmission time. Previously, it was hard coded to 3 seconds, and retried 2 times, resulting in a timeout of 21 seconds (3+6+12).

To alter the timer, use Regedt32 to navigate to:


On the Edit menu, Add Value name InitialRtt, as a type REG_DWORD, and set the data value to the number of milliseconds, using the Decimal Radix. The default is 3000. The range is 0 - 65535 milliseconds.

InitialRtt controls the initial timeout for connection requests (SYN) and the 1st data segment. On high delay networks, you may want to increase this value, though it may make an application appear to hang.

If you set it to 5 seconds (5000 milliseconds) the timeout will be 35 seconds, if the IP address does not exist.

Conversely, setting InitialRtt to 2 seconds (2000 milliseconds), will reduce the timeout to 14 seconds.

Shutdown and restart your computer for the change to take effect.

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