How to troubleshoot your broadband connection

Make sure you're getting the speed you expect

If you’re having intermittent connection problems then there’s often useful information to be gleaned from your router. Check the log, which lists the date and time of each reconnection. In the above screenshot, the router has just reconnected and the router log records each stage of the connection process.

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Every router has a connection status display that lists information such as uptime – both for the ADSL connection and the router. Most routers are capable of measuring the quality of your phoneline, too. Two parameters listed here are important: the amount of signal lost (line attenuation) and how ‘loud’ the signal is compared to background noise.

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Line attenuation should be low (60dB is bad; 20dB is good), while the signal-to-noise ratio should be high (20dB is good; 6dB is rock-bottom). A low SNR ratio makes it difficult for the router to sync with the DSLAM card at the telephone exchange. The screenshots above and left show how line quality can change in just a few minutes.

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Since ADSL Max is rate adaptive, you can’t be sure what connection speed you’ve actually got. There are many broadband speed test sites, but we advise the one offered by BT. To try it, head to speedtester.bt.com using the broadband line you want to test, enter your phone number and click on Go.

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It works by checking the broadband connection of the phoneline you enter, although you can’t test your line speed remotely. On the second screen you’ll need to enter your ADSL login name and, from then on, the progress bar at the top of the screen will indicate where you are in the process.

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As you can see from the results, my ‘up to 8Mbps’ connection is in fact just 5.5Mbps. And you will notice that the profile for my line reduces this to 4.5Mbps. Worse still, my actual IP throughput is a mere 2.8Mbps. The same test run a few hours earlier produced an actual IP throughput of 4.1Mbps.

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Don’t take the results you get at online speed-testing sites as gospel. You can get different results from other sites. Here, you can see such a result from Speedtest.net, performed just a few minutes after the BT test. This site measured my connection speed at a little over 2Mbps.

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XPNetDiag is a much improved network diagnostic tool capable of fixing many connectivity problems. It comes as part of the Internet Explorer 7.0 update and you may already have it in your Windows, Network Diagnostic folder. Otherwise, you can download it from .

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If you’ve got Internet Explorer 7.0, load Network Diagnostics by clicking on Tools, Diagnose connection problems. You could also click on the Diagnostics link of a web page that can’t be displayed. This will analyse your connectivity, which takes less than a minute.

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Very often XPNetDiag can fix problems it finds all by itself. It will automatically renew the IP address of your PC’s network adaptor – which fixes many problems – and it will display a log of all the discovered problems and their fixes. Here, it is having trouble connecting to a test website, Microsoft’s FTP site.

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You can also tweak your TCP/IP settings to maximise your broadband connection. The most important is MTU (maximum transfer unit) which defines the largest data packet size you can transmit in one go across a network. For BT ADSL, the recommended MTU setting is 1458.

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It’s easy to check the optimum MTU system. Open a command prompt (Start, Run, type command) and enter the following: ping www.pcadvisor.co.uk -f -l 1492 . The 1492 is the MTU value and, as you can see, using this value the ’Packet needs to be fragmented’. Our packet value is too big.

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Reduce the packet value using trial and error until you obtain a normal ping response. Here, 1430 is effective. The MTU is actually 1458 – the extra 28bits account for data in the packet header. To change your settings to reflect this, you can download a tool from tinyurl.com/2raka3 or from the cover disc.

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Tracert is another essential diagnostic tool that can help pinpoint network bottlenecks. Open a command prompt and enter: Tracert www.pcadvisor.co.uk . Here it took 1ms to reach my router and then 45ms per ‘hop’ to the PCA site, which is fine. Note abnormally large timings but take distance into account.

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Roger Gann

PC Advisor (UK)
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