ABSTRACT
ISDN is a digital voice and/or data service that (generally) works over existing copper local loops.
ISDN transmits data digitally and, as a result, is less susceptible to static and noise than analog transmissions, although it is very sensitive to outside interference. To avoid interference you have to be within a given distance of the CO (Central Office) equip ment that serves you (typically 18,000 feet), and there can’t be any other anomalies near the wiring that might interfere with the transmission.
