There have been many posts regarding SNR and Line Attenuation.
SNR means Signal to Noise Ratio. Simply put divide the Signal value by Noise Value and you get SNR. You need high SNR for a stable connection. In general, a higher signal to noise ratio will result in less errors.
- 6bB. or below = Bad and will experience no line synchronisation and frequent disconnections
- 7dB-10dB. = Fair but does not leave much room for variances in conditions.
- 11dB-20dB. = Good with little or no disconnection problems
- 20dB-28dB. = Excellent
- 29dB. or above = Outstanding
Note that most modems display value as SNR Margin and not pure SNR.
You can think of SNR margin as the measure of quality of the service; it defines the ability of the service to work error free during noise bursts.
This is a measure of the difference between your current SNR and the SNR that is required to keep a reliable service at your connection speed. If your SNR is very close to the minimum required SNR, you are more likely to suffer intermittent connection faults, or slowdowns. You need a high margin to ensure that bursts of interference don’t cause constant disconnections.
With traditional broadband, the higher the SNR Margin, the better. With MaxDSL the faster speeds are only available as a trade-off with what your line can reliably support. The Target SNR Margin is about 6dB. If your broadband is provided through an LLU (Local Loop Unbundled) network, this target SNR Margin may be as high as 12dB.
In gerneral, 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
Line attenuation also affects your speed.
- 75 dB+: Out of range for broadband
- 60-75 dB: max speed up to 512kbps
- 43-60dB: max speed up to 1Mbps
- 0-42dB: speed up to 2Mbps+