Digitalization of the telecommunications networks is now progressing from switches to access networks and subscribers’ equipment. ISDN plays a large role in this process, though it uses the same wiring that comes into your home or business as does the POTS (Plain Old Telephone Service) system. In short POTS – ordinary analogue telephony – uses the well-known communications medium of twisted copper pair. Because of this fact telephone operators all over the world still face the same problem in the digital age that they faced in analogue times – a chronic shortage of available copper cables and wiring.