ADSL technology each channel bandwidth 4312.5 Hz, if the sampling frequency is 4 k potter, should according to the bandwidth of the sampling theorem can accept only 2 KHZ, the channel 4 KHZ bandwidth waste a half?
And the sampling frequency is described here, for to send and receive analog signal sampling?

Just learning network, the concept of sampling frequency is not very understanding
The sampling frequency is in view of the harmonic sampling channel of transmission, or the original analog signal sampling
Consult a great god