digital networks: X.25, ISDN, LAN and cellular networks, International Standards Organisation-Open Systems Interconnectivity (ISO-OSI)
A digital network is one in which all data is transferred by the change of a voltage on a wire. For example, a digital 1 may be +5 volts and 0 may be 0 volts or - 5 volts depending on the system.
In simple terms, any wire between two devices over which a change in voltage can be applied is considered a digital communication system. The introduction of standards allows the interconnectivity of devices that are not specific manufacturer defined. The X.25 standard relates to the connectivity of systems via the POTS and similar communications systems. The I430/1 relates to the connection to ISDN services and the 802.3 standard relates to the interconnection between networks.
Mike Leishman