Local loop - Analog vs Digital
A digital signal is conveyed through discrete changes in the state of the signal such as the presence or absence of voltage (1 or 0) or discrete changes in voltage (+3, 0, -3) thereby making the information content of a digital signal less susceptible to electrical noise.
Since a digital signal consists of 1s and 0s, it is easy to identify the signal sent (1 or 0) and re-create the signal and transmit it further.
This is the primary reason digital communications improve the quality, reliability and speed of communications. Any noise or distortion introduced along the circuit is eliminated when the signal is regenerated.