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General Router FAQ

ADSL Line Status

What do the ADSL line signal figures mean ?

The router's online status screen (as well as the telnet logs) will show two figures which relate to ADSL line signal level/quality. A good ADSL signal is more reliable and produces less errors. When you order your ADSL line, the telephone company will test your line, and if the attenuation is too high (because you are too far from the exchange) you cannot have ADSL. The two measures indicated by the router of the line quality are Signal to Noise Ratio (SNR) and Loop Attenuation.

SNR is, as its name suggestions the ratio of signal (the bit we want) with noise (the bits we don't want). Noise can be introduced by poor quality lines, bad wiring (including your own extension wiring) etc. The ratio is expressed as in dB and the higher the number, the better (i.e. if the number is higher, there is much more signal than noise). An average SNR is around 30dB..

Loop Attenuation is a measure of the quality of the line from the point of view of how much the signal is impeded. The longer a line, the higher the attenuation will be (hence the 'quieter' the signal). BT will generally not provide ADSL service if your Attentuation is over 55. Typical attenuation values from a good working ADSL line are between 30 and 40, but if yours is higher, this isn't anything to worry about if it works fine.

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