A human-machine interface has been created for an integrated services digital network (ISDN) network control unit (I-NUU). I-NUI is a sophisticated terminal device that allows a voice communication channel and two data channels to be connected through an ISDN I-series interface. ISDN communication functions and network control operations were analyzed to determine the required characteristics of I-NCU. I-NCU features the minimum number of control buttons and a liquid crystal display. Visual and audible information are used to keep the operator fully informed about the state of the communication channels.>

In addition to the present voice communications services, more diverse digital telephone services are in very strong demand. Among the critical system requirements for designing digital telephone sets are how to economically realize new telephone services and how to ensure the continuity of existing analog telephone services. This paper describes the system requirements from both the service and technical points of view in the design of telephone sets. Based on these requirements, it further describes a method of designing network interface and telephone function blocks. An outline of the configurations and characteristics of digital telephone sets which can be operated by remote power feeding is presented as a design example.