DOCUMENT:Q138831  13-JUN-2001  [sna]
TITLE   :Disabling TCP/IP Nagle Algorithm Improves Speed on Slow Nets
PRODUCT :Microsoft SNA Server
PROD/VER:WINDOWS:2.1,2.11
OPER/SYS:
KEYWORDS:

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft SNA Server, versions 2.1, 2.11, on platform(s):
    - the operating system: Microsoft Windows NT 
-------------------------------------------------------------------------------


SYMPTOMS
========

This article explains the Nagle TCP/IP algorithm and how to manually disable it
on different the SNA Server client and server releases for different operating
systems. It also mentions how to obtain an update that automatically disables
this algorithm. Microsoft has updated the file <snaroot>\SYSTEM\SNAIP.DLL
to correct this problem.


STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft products that are
listed at the beginning of this article.
This correction is included in the latest U.S. Service Pack for SNA Server for
Windows NT, version 2.11. For information on obtaining the Service Pack, query
on the following word in the Microsoft Knowledge Base (without the spaces):

   S E R V P A C K

MORE INFORMATION
================

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" (without the
   quotation marks) 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.

Additional query words: prodsna 2.10 2.11

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbSNAServSearch
Version           : WINDOWS:2.1,2.11
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 2001.