What use is delta modulation to the transmission engineer?

MOST of the transmission methods used today are rather elementary. The signal to be transmitted is made to vary the amplitude or phase of a sine wave, or perhaps the height, width, or position of a pulse. The variation is continuous, and at each repeater some noise, cross-talk or distortion is added to the signal, causing some deterioration in quality. By the time the signal has gone through hundreds of repeaters, it is a miracle that there is any quality left.