BT Wholesale has produced a small application for MS Windows based PC's that simply tweaks your MTU size to 1458. Currently it is on trial with two ISPs, BT Openworld and one other unnamed ISP, other ISPs should have it for next week. In the meantime we thought it was worth sharing the tool with our visitors, as it is a lot simpler to use than DrTCP or registry editing.
If you are reading this and do not know what MTU is, or why you need to tweak it, we would advise reading this previous news article. Essentially by changing this figure to 1458 on your PC, you can reduce the level of fragmentation. By reducing fragmentation you can speed up your connection, and until BT Wholesale produces a full fix it will reduce the load on their network, as your traffic will flow more efficiently. As an example I took an untweaked XP Pro machine and tested it at www.dslreports.com/tweaks and it reported 2 retransmitted packets with an MTU of 1492, which is the XP Pro default value. Changing the MTU to 1458 using this new tool resulted in no retransmitted packets and to confirm this I changed between the two values several times and got consistent results each time.
How to use this new tool, firstly visit BT Wholesale website and download the tool and run it. Once it is running it will detect the various modems and network cards attached to the computer (USB modems show up as WAN Miniport(IP) usually) and it will automatically set the MTU to 1458 for the devices it detects (this can be overridden to other values if you want to experiment). Once the application is run you can view a text file with the changes it did and finally it tells you to reboot so that the changes can take effect. The neat part of the tool is that when you run it a second time it simply undoes the previous changes, allowing you to revert to your previous settings if you do not like the results. BT Openworld has added a short FAQ to the download page covering most questions.
Disclaimer: Making modifications to the system registry or using this software is performed at your own risk. If you do not understand the implications, or how to recover from registry changes, you should not attempt the steps outlined above.
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