Changing technology in switching system software

The evolution of software techniques within the context of stored program controlled telephone switching systems is discussed in this paper. The paper starts with the transition from assembler coding to high-level language coding and then goes on to identify the operating system aspects of a telephone switch. Modern operating system concepts are presented in terms of standard telephone switch functions. The paper continues by describing the need for and development of modularity on a "plug-in" basis and closes by a discussion of mechanisms for simplifying on-line growth of telephone switches in terms of both size and feature complement.