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