New TCP/IP Registry Parameter Ignores Push Bit on Receives

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To allow TCP/IP to ignore the push bit on receives, do the following:

1. Start Registry Editor (REGEDT32.EXE) and locate the following Registry subkey in the HKEY_LOCAL_MACHINE subtree:

   \SYSTEM\CurrentControlSet\Services\Afd\Parameters

2. Select the following value name: IgnorePushBitOnReceives
3. From the Edit menu, select DWORD.
4. Change the Data to 1.
5. Click OK and quit the Registry Editor.
6. Shut down and restart Windows NT.

In Windows NT version 3.1, TCP/IP behaved as if the PUSH bit was always set by the sender. In Windows NT 3.5, the receive logic was optimized to use the PUSH bit. This reduces the number of times an application has to wake up for incoming data. However, when Windows NT is communicating with a TCP/IP implementation (or application) that does not set the PUSH bit at the appropriate times, performance can suffer.

Performance degrades because, when data arrives without the PUSH bit set, TCP holds onto the application's recv() while waiting for the rest of the data. Windows NT TCP/IP completes a recv() call when:

• Data arrives with the PUSH bit set.
  
  -or-
• The user recv() buffer is full.
  
  -or-
• 0.5 seconds have elapsed since any data arrived.

When the third test above is required to complete a recv() call, performance degrades.

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