A little orange wire..

The quality of Internet in our house has been dubious to say the least for some time and we've long associated it with poor street cabling and distance from the exchange.  It is also made worse by bad weather (rain, usually) so we were putting up with the poor performance as being beyond our control. Recently, however, the service had become very frustrating prompting me to investigate further. The symptoms vary, but the usual ones are:

• Long delays waiting for the browser to start downloading a page
• Pauses when clicking on a link for the new link to start
• Page loads taking a long time

What was (slightly) odd was that these delays did not seem to be restricted to the evening (the traditional Internet 'slow time' in the UK). They were occuring throughout the day - even in the quiet times in the early morning.

Brief Investigation

The first thing I did was to look at our ADSL router, a third-generation NetGear DG834G.  There seemed to be no errors on the set up of the router - I even rebooted it to see if it had got itself confused - but it was when I looked at the router statistics that I saw the seriousness of the problem:

The figure that set my alarm bells ringing was the Downstream Noise Margin, showing here as 2dB but regularly this figure was flitting between 0dB, 1dB and 2dB.  That's bad!  Noise Margin is a measure of how much headroom the router has to maintain a good quality ADSL connection and according to these statistics my router doesn't have any!!
 

Noise Margins and Signal to Noise Ratios

Let me try to explain this.  Your broadband ADSL service is delivered from the exchange by a piece of equipment called a DSLAM which works by putting a signal onto the phone line to your house.  Your router needs to reliably decode this signal so that it can link you to the Internet.  If there is noise on the phone line this signal will be degraded and your router will have difficulty decoding it.  The impact of this is that the quality and speed of your broadband ADSL will suffer.  The more noise; the more your service will suffer.  You can probably see then that the ratio of your ADSL signal level to the phone line noise level can be used to measure the quality of your ADSL service.  This ratio is well-known in communication systems engineering and is referred to as the signal-to-noise ratio or SNR.  The higher the SNR is; the better your signal is and therefore the better your service will be.  As a good analogy, think of yourself trying to listen to your friend talk to you at a football match or in a loud pub.  It's very difficult to hear every word he says unless you listen very hard or if your friend shouts.  This is a situation where there is a very poor SNR.  Now imagine your friend talking to you in a coffee shop or a restaurant.  You would expect to have no problems hearing everything that your friend says.  This is a situation where there is a reasonably good SNR.

Signal to Noise ratio or SNR is a term used to describe the ratio of wanted signal strength to that of unwanted noise levels and is measured in units called dB (decibels).  This is a logarithmic scale where each 3dB of SNR doubles the ratio of signal to noise.  For example, if the noise level was about 1/100th of the level of the signal then the SNR would be 20dB.  If we double the level of noise, the SNR would decrease to 17dB.  However, if we increase the signal to 1000x the level of the noise the SNR would increase to 30dB.  More info can be found here

Having established what SNR is, we can now introduce the Noise Margin.  This is a sort of buffer zone on top of the SNR that allows the router to cope with all the variations in noise levels that occur through the day.  On a 'good' ADSL line this figure is usually around 6dB. So, with our Noise Margin being measured as 0dB to 2dB, our Broadband router had no headroom and that from time to time the level of noise would increase to a level that affected our service.  Indeed, it is perhaps a wonder that our ADSL was working at all - never mind with the poor performance we were experiencing.  Just goes to show that the NetGear hangs on to that signal in the noisiest of environments!

Further Investigation

So now we know what the poor performance is caused by - it's too much noise or interference - the next steps are to try to understand what's causing the noise and then to attempt to correct it.  As usual, you begin with a couple of searches on a search engine and I was fortunate to quickly find the excellent kitz.co.uk that in their own words ... "contains a wealth of adsl information such as how adsl broadband works".  On that site I found a section devoted to poor noise and the likely causes. On this site was a page dedicated to 'Low SNR problems' and this page has a wealth of details I could step through.  I worked through the steps that are listed and came upon "~ One last trick - remove the ringwire." The 'ringwire' is a left over from days gone by when it was used to supply the ringing current to older phones.  Most modern phones don't need this wire and in modern installations it can actually be removed as all it does is act as an antenna for electrical noise.

Here you can see our incoming NTE5 faceplate with the front cover unscrewed and the orange/white wire disconnected from the faceplate connector pin 3.  The blue/white (pin 2) and white/blue (pin 5) wires are NOT touched.  (Note that in some installations you may have a white/orange wire on pin 4.  This can be removed also.)

Result!

Having done this and re-assembled the faceplate the internet router was rebooted and immediately the following router statistics were recorded:

Note how much better the noise margin is.  Note also how much greater the connection speed is.  Just disconnecting this single orange wire has improved our download speed by 14%  And the problems we've had since then have largely disappeared.

Now to tune the MTU - but that's a subject for another time.

Happy Surfing!