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Windows 2000 Modem Tweak Guide [Page 3/4]

Posted: March 12, 2000
Written By: Keith "Farrel" McClellan

Port Tweaks

From within the "new" device manager (at least new to Win2K) (System Directory/Hardware tab) you can edit the settings for your serial ports. Select each COM port on your system and give it the following settings (under the Port Settings tab) [Note: you may have to be logged in as the Administrator to make these changes stick]:

Bits per Second - 115200+ (if you have compatibility or connection problems with higher settings, return to 115200)
Data bits: 8
Parity: None
Stop Bits: 1
Flow control: Hardware*

*You may get the same or better performance with this set to None - but it will depend on your system.

Under the Advanced button, make sure that the FIFO Receive and Transmit buffers are on and are turned up to their highest settings (14 & 16 respectively).

Registry Settings

Windows 2000 is a little stubborn about letting you change some of the most important networking (and hence internetworking) settings on your computer. If you even search your registry for the following keys, you simply won't find them. Because of this, none of them have defaults (unless they are hard-wired into the system), so if you have problems, simply delete the keys.

All of the following tweaks can be easily installed on your computer using this registry file.

If you would like to install the keys manually, follow these steps:

- Start Menu => Run => Regedit
- Browse to the appropriate key
- Right click and select New Dword
- Type in the name for the setting
- Right click on the new setting and select modify
- Input value

All of the following keys should be added to the key [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters].

"EnablePMTUBHDetect"=dword:00000000 "Tcp1323Opts"=dword:00000003 "SackOpts"=dword:00000001 "DefaultTTL"=dword:00000020 "EnablePMTUDiscovery"=dword:00000001

EnablePMTUBHDetect - This key enables Black Hole Detection over your TCP/IP connections. It applies to all of your TCP/IP stacks. It is best to disable this feature.
0 - Disabled 1 - Enabled

Tcp1323Opts - This key enables large TCP window support. Disabling this setting limits the window to 64K. This setting may not apply to modems but it shouldn't hurt your connection to have it enabled.
0 - Disabled 1 - Window Scaling w/o Timestamp 2 - Unknown 3 - Windows Scaling w/ Timestamp

SackOpts - This setting enables selective acknowledgement support. This setting is more important to connections with large TCP Windows.
0 - Disabled 1 - Enabled

DefaultTTL - This setting determines the default Time to Live setting for your connection. 32 is the standard, but 64, 96, and 128 are also common. There are special instructions for modifying this key. Input the data as binary and then click on the hexadecimal radial button to convert to Hex before saving the setting.

EnablePMTUDiscovery - This setting enables MTU Auto Detect within Win2K. This setting is best enabled.
0 - Disabled 1 - Enabled

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