Disabling TCP/IP Nagle Algorithm Improves Speed on Slow Nets

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The Nagle TCP/IP Algorithm

The Nagle TCP/IP algorithm was designed to avoid problems with small packets, called tinygrams, on slow networks. The algorithm says that a TCP/IP connection can have only one outstanding small segment that has not yet been acknowledged. The definition of "small" varies but usually it is defined as "less than the segment size" which on ethernet is about 1500 bytes.

Manually Disabling the Nagle Algorithm

You can disable the Nagle algorithm by performing the SNA Server client and server modifications mentioned below and following the instructions in the Activating the Modifications section.

SNA Server Modifications

1. Under the subtree HKEY_LOCAL_MACHINE add the subkey SNATCP under the following key:

   SYSTEM\CurrentControlSet\Services\Snabase\Parameters\ 
   					

2. Choose Add Key from the Edit menu and use the following information:

         Value Name: NoDelay
         Data Type:  REG_SZ
         String:     yes
   					

Windows 95 SNA Client Modifications

Add the same registry entry as SNA Server above.

Windows 3.x Modifications

Windows 3.x client always disables the Nagle algorithm and there is no way to enable it.

Activating the Modifications

When the NoDelay is set to yes, the TCP/IP transport DLL uses the TCP_NODELAY option when it opens a socket.

For this to take effect, the client server interface must be stopped and restarted on both the server and client after the registry changes have been made. The following table shows the name of the SNA client server interface program and the corresponding operating system platform:

   Client Server Interface      Platform
   ----------------------------------------
   SNABASE Service              Windows NT
   SNABASE Service              Windows 95
   WNAP.EXE                     Windows 3.x
				

Note: The Nagle algorithm is defined in TCP/IP RFC 896.