Slow internet speed and distance
Have you ever heard about line attenuation? Leaving out some of the technical jargon, the line attenuation figure describes the distance between you and the exchange of the ADSL provider. It is expressed in dBs and you can check this number on your ADSL statistics of your home / corporate router (show dsl interface atm(something) for Cisco). In short, the lower this number is, the better:
20dB and below is outstanding
20dB – 30dB is excellent
30dB – 40dB is very good
40dB – 50db is OK
50dB and above is bad
The “slow internet speed” of your ADSL line is directly affected by attenuation. Unluckily, you can do nothing about a low attenuation figure, except from moving to a new location closer to the ADSL exchange.
Is your line noisy? Check SNR and SNR margin!
Have you ever tried to speak to a friend of yours that is 100 m away in a noisy street? I bet he would be struggling to hear you. If the street was empty, his hearing capabilities would be drastically improved. Like a street, ADSL lines are susceptive to noise. This could be because of the electromagnetic noise (cars,music,dogs barking) or the ADSL exchange’s load (people talking).
Signal-to-noise ratio (SNR) is another figure you can check in the ADSL stats of your home / corporate router (show dsl interface atm(something) for Cisco). This number is also expressed in dBs and describes the relation between your speaking strength (signal) and the street’s noise strength (noise). The higher this number is, the better, as your speaking voice outperforms the noise.
10dB and below is bad
11db – 20dB is OK
20dB – 28dB is excellent
29dB and above is outstanding
Some routers instead (or additionally) of the signal-to-noise ratio (SNR) figure are displaying the signal-to-noise margin (SNR Margin) which is the difference between the actual SNR and the SNR required to sync at a specific “speed”:
actual SNR = 44dB
SNR to sync at 8Mb = 35dB
SNR MARGIN = 44-35 = 9dB
A higher number is better and the numbers bellow 6dB may cause problems. It is easier to understand if your line is in an acceptable SNR level, by using the margin figure, because you don’t need to know the SNR dB value you should have, for the line to perform at a specific speed. You just need to know that above 6 dBs you are doing just fine.