A major improvement in the area of telecommunications networks is the implementation of ISDN. It is very difficult to define ISDN. Broadly speaking, when its evolution is complete, ISDN will be a worldwide public telecommunication network. It will provide end-to-end digital connectivity and integrated access to both circuit-switched and packet-switched networks.

The main advantage of ISDN is integrated access. At present, if a personal computer user requires access to a packet-switched network, it must be connected to the packet network through an instrument, namely the Packet Assembler and Disassembler, which conforms to certain standards.