Does attenuation and SNR margin still matter ?
A. Yes. Attenuation reduces the signal that reaches you from the exchange. If your attenuation is less than 30 dB you should get the full speed, although you may achieve it at higher attenuations providing the noise is low enough to achieve the target SNR margin (initially 6 dB). At 40 dB you may get 6M, 50 dB 4M and 60 dB 2M etc. The SNR or noise margin will be lower than before, and the modem will sync at 6 dB (BT increase this to 9, 12, or 15 dB if the line is unstable). The SNR margin target is achieved by increasing speed – its a simple trade-off with lower margin giving more speed and probably an increase in error rate too.
