What does it mean if a leased telephone line has a bandwidth of 3kHz? Does it mean any signals travelling alone that line must have frequency components less than or equal to 3kHz? Or does it mean that all the signals' frequency components (assuming time multiplexed) must add up to be less than 3kHz? Also is bandwidth just the range of frequencies? So if a signal had frequencies from 1kHz to 3kHz, its bandwidth would be 2kHz? Because in my signal theory classes they seem to use "highest frequency" and "bandwidth" interchangeably. For example some say the nyquist sampling rate is "twice the bandwidth", while others say it's "twice the highest frequency", but technically it should be twice the highest frequency right?