View source for ADSL Line Connection Speed

==SNR Margin==
In general, a higher signal to noise ratio will result in less errors.

*6bB. or below = Bad and will experience no line synchronisation or intermittent synchronisation problems.
*7dB-10dB. = Fair but does not leave much room for variances in conditions.
*11dB-20dB. = Good with little or no synchronisation problems
*20dB-28dB. = Excellent
*29dB. or above = Outstanding

==Attenuation Rates==

In general, attenuation is the loss of signal over distance. Unfortunately, dB loss is not just dependent on distance. It also depends on cable type and gauge (which can differ over the length of the cable), the number and location other connection points on the cable.

*20bB. and below = Outstanding
*20dB-30dB. = Excellent
*30dB-40dB. = Very Good
*40dB-50dB. = Good
*50dB-60dB. = Poor and may experience connectivity issues
*60dB. and above = Bad and will experience connectivity issues

==Distance==

And for distance, the equation I have seen suggests that downstream attenuation divided by 13.81 will roughly equal KM from the exchange. For example; if you had a downstream attenuation of 40dB...

40dB / 13.81 = 2.896 KM


For me, 17 / 13.81 = 1.2KM