Establishment communication systems: LAN's or PABX's—which is better?

In the sixties and early seventies, major activities in networking were focused on private and public data networks using either circuit and packet-switching technology or integrating both switching methods into a single network. In this time frame, manufacturers of main frames defined and implemented network architectures, ISO started work on the reference model of the Open-System Interconnect Architecture, and CCITT recommended the X-series of interfaces.

Local-area communication networks (LAN's) represent a comparatively new field of activity which can be viewed as an extension to data networks for making high-speed packet-switching services available to the in-house domain. Currently, much research and development work is being pursued in this field, both at universities and in industry. The term local refers to communication on the users' premises, i.e., within a building or among a cluster of buildings.

Local data and voice communication are not new. A typical example of a system widely used today for local data communication between hosts and display terminals is a star configuration where the terminals are attached to control units tightly coupled to a processor via I/O channels. The necessary terminal control functions are provided in the control unit and shared among a set of terminals. The most widely used local communication system is the Private Automatic Branch Exchange (PABX). Most PABX's installed today are optimised for real-time voice, and use analog technology.