Speeding up your modem

Speeding Up Your Modem

I’ll admit to being spoiled. I’ve had a cable connection to the Internet for more than three years, now. In fact, I’m not sure I could tell you the last time I connected to the Internet using a dial-up modem. But, having spent the three years before that on a dial-up, I can appreciate the need for any tweak that will speed up Internet access.

There are two key elements in connection speed that can be tweaked in Linux. The first is MTU - Maximum Transmission Units. MTU is a measure of the largest physical packet size in bytes that your network can transmit. Anything larger than this MTU will be divided into smaller packets, increasing the transmission time.

The second is MRU - Maximum Receive Unit. This is the largest packet size your modem will accept. Once again, set this too low and your connect speed will crawl. Set it too large and the packets will be broken up to meet the maximum requirement. The goal in both cases is to tailor the settings to the size of the pipe you’re connecting to. In other words, your goal is to make your connection as efficient as possible.

On any Linux Internet connection, dial-up, cable or DSL, these setting should be adjusted when no connection to the ‘net exists. They’re not runtime adjustments. That’s generally not a problem with dial-ups, as they’re seldom a full-time connection. To tweak your dial-up, execute the following command as root:

    [root@server tony]$ ifconfig ppp0 mtu 576
    [root@server tony]$ ifconfig ppp0 mru 512

These are good default MTU and MRU values to start with on a dial-up connection. One way to check whether these changes are making a difference in your connect speed is to ping a reliable server, watching for lost packets.

After landing on the proper MTU and MRU settings, you can make the changes permanent by editing the /etc/ppp file. Open your text editor and add the following line:

    mtu 576
    mru 512

With a little testing and patience, you should see an increase in your dial-up connection speed.