Toward more reliable telecom systems

A word currently in vogue in software engineering is quality. Quality involves many factors, and it would be time-consuming to address all of them in one paper. Instead, only one is addressed: reliability. Specifically, this paper presents the use of redundant software as a means of improving the software reliability of telecom systems at the operational phase. Redundant software acts as a supervisor by monitoring both inputs and outputs of a target system and checking them against the target system´s specification. A case study involving a PBX (private branch exchange) illustrates the use of Statecharts as a formalism to specify the software supervisor. Benefits in terms of quality improvement and cost reduction are discussed