Slow internet speed is often a result of a bad attenuation and SNR margin figure. If you are one of those people who have problems with their internet speed, then you are in the right place. Have you installed an ADSL / VDSL line recently, and you get a slow internet speed? Often the line is disconnecting, and you are wondering… why God!?!?!
Actually God has nothing to do with it: Internet Service Providers are offering ADSL / VDSL speeds up to some bandwidth: it could be 16Mb, 24Mb, 50Mb, 100Mb. Unfortunately the term up-to is not chosen by luck: Internet speed depends on many factors which I am planning to explain.
Slow internet speed and distance
Have you ever heard about line attenuation?
Leaving out some technical jargon: the line attenuation describes the distance between you and ADSL / VDSL provider’s exchange. It’s expressed in dBs, and you can check this number in your ADSL / VDSL statistics of your home / corporate router. In short, the lower this number – the better:
|Attenuation ||Performance |
|<20dB ||Outstanding |
|20dB – 30dB ||Excellent |
|30dB – 40dB ||Very good |
|40dB – 50db ||OK |
|>50dB ||Bad |
The “slow internet speed” of your ADSL / VDSL 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 / VDSL exchange.
Is your line noisy? Check SNR and SNR margin!
Have you ever tried to speak to a friend of yours that is 100m away in a noisy street? I bet he would be struggling to hear you. If the street was empty, communication would be drastically improved.
VDSL / ADSL line are susceptible to noise. This could be because of the electromagnetic noise (cars, music, dogs barking) or the ADSL / VDSL exchange’s load (people talking).
Signal-to-noise ratio (SNR) is another figure you can check in the ADSL / VDSL stats of your home / corporate router. 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 – the better, as your speaking voice outperforms the noise.
|SNR ||Performance |
|<10dB ||Bad |
|10dB – 20dB ||OK |
|20dB – 29dB ||Excellent |
|>29dB ||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 figures below 6dB may cause problems.
SNR margin above 6dBs is good
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 actual 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.
As you’re probably thinking, noise is a subject of change according to various sources. On-peak hours, the noise increases as your provider’s exchange becomes crowded (people talking in the street) and the SNR margin gets worse.
Florescent light sources, telephone devices installed on your phone line, your mom’s cake-blender, all these may decrease the SNR margin.
Luckily, there are some things you can do to improve the SNR margin:
Replace your router with a better one
Install a good quality ADSL / VDSL filter to your router
Try to change Internet provider, as some providers are less crowded than others. You can check with your neighbours to see how they perform with their ISP
Change the in-building cabling. Poor, low-quality cabling can introduce noise. You can check if you have a problem with the in-building cabling, by placing the router (temporarily) directly to the intrusion point (probably at the basement) and by checking router’s statistics.