ADSL >> ADSL Tweaks

Introduction

By tweaking your ADSL connection settings, you have the potential to get an improvement in speed. It is certainly worth attempting as it can be undone should it make no difference, and there is a good chance that it will in fact increase the speed of your connection. This tweaking process involves changing some Windows registry values. However, this can be more easily achieved using a GUI known as Dr. TCP.

Before you begin, you will need to download the latest version from http://www.dslreports.com/front/drtcp.html. I would recommend also completing and noting the results of a speed test before altering any settings so that a comparison can be made between the different settings. The best speed test is ADSLguide's located at http://www.adslguide.org.uk/tools/speedtest.asp. It is advisable to backup before making any changes to the registry - you make any changes at your own risk.

MTU and RWIN

The settings that will be altered in order to tweak your connection are known as MTU (Maximum Transmission Unit) and RWIN (Receive Window). There are various methods used to calculate the optimal RWIN, but this guide concerns the two most popular settings for RWIN and MTU only.

Running Dr. TCP

When you run Dr. TCP for the first time, it will look very similar to the screenshot below.

The adapter shown in Adapter Settings will vary depending on the adapter(s) you have installed.Settings

1. Select an adapter

Select the adapter under Adapter Settings that is concerned with your ADSL connection. If you are using an Ethernet-based connection, then this will be your Network Interface Card (NIC). For those using an ADSL modem (such as SpeedTouch USB) there is no need to select an adapter. In this case, the Adapter Settings field can either be left blank (if no adapters are installed) or, if there are other adapters installed, it may display one of these. Either way, it makes no difference as settings will only be altered for an adapter if it relates to the ADSL connection.

2. Set MTU and RWIN

Many different MTU and RWIN combinations have been tried and tested by a number of different users. However, there are two combinations that have given the best results all round. These MTU and RWIN settings respectively are:

• 1458 and 12762
• 1430 and 13900

If using an Ethernet-based connection, enter the MTU value in MTU in Adapter Settings. If using an ADSL modem (such as SpeedTouch USB) enter the value in Dial Up (RAS) MTU in General Settings. You need not do both, and should only enter the value in one or the other depending on your hardware. Lastly, enter the respective RWIN value in Tcp Receive Window in General Settings.

3. Save settings and test

Save the settings by clicking Save, followed by Exit to close Dr. TCP. If you are using Windows 2000 or XP, you will need to restart networking in order for the settings to take affect. Windows 95, 98, or Me requires a restart.Once again, carry out a speed test and note the new result. It is recommended to also try the other MTU and RWIN combination in the same way, and then compare the original against the two new results. If neither of the new settings make a difference for the better, do the same, but remove the values from the MTU or Dial Up (RAS) MTU and Tcp Receive Window, save the settings, and restart networking or Windows entirely.

Results

Prior to tweaking, my downstream was on average 467. Altering MTU to 1458 and RWIN to 12762 gave me an average downstream of 471. Altering the MTU and RWIN further to 1430 and 13900 respectively gave me an average downstream of 477.

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