What are good and bad SNR and Line Attenuation numbers?

SNR

• 6bB or below = Bad and will experience no line synchronization 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

Line Attenuation

• 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

This information has been copied and reposted all over the internet. It seems to be pretty accurate, but I cannot independently vouch for it.