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How to measure your broadband speed

Posted on 16 Jun 2008 at 15:12

Determining the true speed of your internet connection isn't as easy as you may think. There are several, often contradictory, measures of your ADSL connection speed. These include:

Sync speed (or line rate)

This is the speed at which your router connects to the local telephone exchange - the theoretical maximum speed your line could achieve in perfect conditions with a following wind and a deadly virus wiping out your entire neighbourhood. This is the figure that pops up in the little bubble in the Windows System Tray when you first connect to your router.

Maximum Stable Rate (MSR)

After ten days, your ADSL Max connection will be given a Maximum Stable Rate figure. Perversely, this is the lowest stable sync speed your line managed to achieve over that period, during which BT is attempting to find the true speed of your line. ISPs recommend you frequently connect and reconnect during that initial ten-day period so the line can be tested at different times of day.

BRAS profile

The BRAS profile regulates the maximum throughput you'll receive on your connection. BT limits the speed you can download data across your ADSL line based on your recorded sync speeds, to help improve stability. This is initally set to 2Mb/sec, but it will increase if your line can support higher speeds. Your BRAS profile changes only when a stable connection has been made for a period of time, which can be anything between 75 minutes and three days. Sometimes BRAS profiles can get "stuck" at that initial 2Mb/sec speed, artificially choking your connection. If you're worried that may have happened on your line, contact your ISP.

Throughput

This is the "true" speed of your connection - taken by measuring the actual rate at which data is downloaded and uploaded. Naturally, this is slower than the sync rate and often well below the mythical "up to 8Mb/sec". Sites such as www.speedtest.net will accurately determine your actual throughput. If you're running your router off an extension socket, try performing a speed test and then connect your router to the house's master socket and run the speed test again to see how much speed you're losing.

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