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Windows 2003 Server and TCP Delay May Affect Verastream Performance
Technical Note 10032
Last Reviewed 15-Jul-2004
Applies To
Verastream Host Integrator version 5.5 or higher
Microsoft Windows Server 2003
Microsoft Windows XP
Summary
Technical Note 10032
Last Reviewed 15-Jul-2004
Applies To
Verastream Host Integrator version 5.5 or higher
Microsoft Windows Server 2003
Microsoft Windows XP
Summary
When using Verastream Host Integrator (VHI) on Microsoft Windows Server 2003 or Windows XP, you may experience reduced performance (or slowness). This technical note describes the symptom and troubleshooting tips.
Symptom
When using Verastream Host Integrator on Windows Server 2003 or Windows XP, performance may slow because of a TCP delay in acknowledgement (ACK) responses. This delay is the result of the Windows implementation of TCP, which can add 200 milliseconds in delayed ACK responses under certain conditions that for most applications are unnecessary. This delay can cause an application communicating over TCP to be two to four times slower than it would be if the delays were removed.
The troubleshooting suggestions below describe how to edit the Windows registry to eliminate this TCP delay.
Troubleshooting Tips
If you are experiencing this symptom, Attachmate Technical Support recommends trying the following troubleshooting suggestions:
Edit the Registry.
Follow these steps to add a DWORD value to the Windows Registry.
Note the following:
- This registry update must be made for all network adapter cards (even those not in use).
- Proceed with extreme caution when editing the Windows Registry. For full warning information regarding editing the Windows Registry, see Microsoft Article 256986:
http://support.microsoft.com/default.aspx?scid=
It is critical to back up the registry before you proceed. To make a backup copy of the registry, use the Registry Editor (regedit.exe or regedt32.exe) or a full backup program to back up the Windows Registry. Also, run Rdisk.exe to update the system's Emergency Repair Disk.
Adding a DWORD
Add the TcpAckFrequency DWORD for each network adapter card. This DWORD tells the TCP stack how many frames (in the range of 1-3) to wait before a response is given. By setting the count to 1, no delay is used. Follow the steps below to add the TcpAckFrequency DWORD and set its value to 1:
- Open Regedit.exe.
- In the left panel of the Registry Editor window, navigate to the following key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\"Enet Card ID"\Parameters\TcpipWhere "Enet Card ID" is the unique Hexadecimal identification number for the network adapter card. It is typically near the top of the list under \Services and there may be more than one. The adapters can be identified as those with \Parameters\Tcpip directories beneath them. For example,
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\{0B588BF7-F0AC-49C4-8901-70319935F590}\Parameters\TcpipNote the "Enet Card ID" value(s) because you will refer to this again in step 7 below.
- Click Edit > New > DWORD Value.
- In the Name field, type TcpAckFrequency.
- Select the TcpAckFrequency DWORD, right-click, and then click Modify.
- In the Edit DWORD Value dialog box, change the Value data to 1, and then click OK.
- Then, navigate to the following key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\"Enet Card ID" Where "Enet Card ID" is the unique Hexadecimal identification number for the network adapter card (identified in step 2). For example,
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{0B588BF7-F0AC-49C4-8901-70319935F590} - Repeat steps 3-6 to add the TcpAckFrequency DWORD for this key.
- Important: Repeat steps 2-8 for all network adapters, which are identified in step 2.
- Exit the Windows Registry.
- Restart the computer to implement this change.
If appropriate, apply the Windows Server 2003 Hotfix.
If after editing the registry and rebooting the server, you still experience slowness and you are using Windows Server 2003, check the version of the TcpIp.sys file. If the version of the TcpIp.sys file is not 5.2.3790.84 or higher, update this file to a newer version by applying the Windows Server 2003 Hotfix available from Microsoft.
For more information, see Microsoft Knowledge Base Articles 815230 and 328890:
http://support.microsoft.com/default.aspx?scid=
http://support.microsoft.com/default.aspx?scid=
