DOCUMENT:Q246984  11-JUN-2002  [winnt]
TITLE   :Tuning May Benefit RPC Programs That Use Winsock Over TCP/IP
PRODUCT :Microsoft Windows NT
PROD/VER:winnt:4.0
OPER/SYS:
KEYWORDS:kbenv

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The information in this article applies to:

 - Microsoft Windows NT Server version 4.0 
 - Microsoft Windows NT Server version 4.0, Terminal Server Edition 
 - Microsoft Windows NT Server, Enterprise Edition version 4.0 
 - Microsoft Windows NT Workstation version 4.0 
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IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

   Q256986 Description of the Microsoft Windows Registry

SUMMARY
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Remote Procedure Call (RPC) programs that use Winsock over TCP/IP and perform
reads or writes that are over 8 KB in size may benefit from increasing the
Windows NT Winsock driver internal receive buffer size.

MORE INFORMATION
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WARNING: If you use Registry Editor incorrectly, you may cause serious problems
that may require you to reinstall your operating system. Microsoft cannot
guarantee that you can solve problems that result from using Registry Editor
incorrectly. Use Registry Editor at your own risk.

The Windows NT socket driver (Afd.sys) has a default receive buffer size of 8 KB.
When a program receives more data than this buffer is configured to hold, all
data received up to this count must be transferred to the program before
receiving continues. When this happens, RPC sends an acknowledgement to the
computer that is sending the RPC data. In some cases, the program's receive
function may experience a time-out during this period.

Winsock programs can set the size of this buffer on a per-socket basis by calling
the Windows Socket function setsockopt and specifying the new value for the
parameter SO_RCVBUF.

Because programs that use RPC over Winsock do not have access to the Winsock
options, you must set this parameter in the Windows NT registry manually. If you
modify this parameter in the registry, it is in effect for sockets used by all
Winsock programs. The change causes the default receive buffer allocated for
each socket created to be equal to the new size.

NOTE: You should change this parameter only on systems that are reading more than
8 KB of data at a time. For example, if the server side of an RPC programs is
written so that it receives small requests and sends large responses (larger
than 8 KB), only the Windows NT client computers need the DefaultReceiveWindow
parameter increased.

To change the default receive buffer size for Afd.sys:

1. Start Registry Editor (Regedt32.exe).

2. Open the following registry key:

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Afd\Parameters

3. On the Edit menu, click Add Value. Add the following value:

   Value Name: DefaultReceiveWindow
   Value Type: REG_DWORD
   Radix: as appropriate
   Value Data: as appropriate (the buffer size that gives optimal performance)

For example, click Decimal as the radix and type "16384" (without the quotation
marks) to set the DefaultReceiveWindow value.

4. Quit Registry Editor, and then reboot the computer.


Additional query words: tcpip tcp/ip

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Keywords          : kbenv 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400 kbWinNTS400search kbWinNTS400 kbNTTermServ400 kbNTTermServSearch
Version           : winnt:4.0
Issue type        : kbinfo

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