Digital PABX

Abstract

This report documents the design, construction and testing of a small digital private telephone exchange. This field of telecommunications has undergone a revolution by the introduction of new technologies and techniques. The aim of this project was to gain an insight into this technology by designing and building an experimental prototype system. The design of the PABX centres around an integrated digital switch which is interfaced to an IBM compatible P.C. The **86 assembly language is used to run the switch control software. The system is equipped to handle twenty four channels which can be configured according to the needs of the user. However, due to the experimental nature of the project and the limited budget and time, the prototype system is equipped with only five extension lines and one central office line interface. Incoming calls are routed to a particular extension identified by a single digit number code. The PABX is designed such that timeslots 0-4 are allocated to the five telephone channels, and timeslot 9 is reserved for the central office interface channel. A Direct Dialing In (DDI) facility is also embedded in the design.