Obsolescence vs Reliability - Availability - Maintainability: Petri nets modelling for mission-critical systems

Mission-critical systems like telecommunications networks and defence infrastructures are essential due to their significant role in ensuring security and safety. Maintaining their operational availability is crucial, as any downtime can have serious consequences. While inherent system availability is determined during the design phase, operational availability is influenced by reliability and maintainability, impacted by environmental factors, spare parts, and maintenance resources. Rapid obsolescence of electronic components poses a major risk to operational availability of all systems but far critically for mission-critical systems. This necessitates strategic management to mitigate these risks despite the need for substantial initial investments. This research paper explores the challenge of integrating various types of obsolescence into operational availability using Petri Nets (PN). A physical component within a system's structure is categorised into one of four generically defined classes, based on two criteria that directly affect operational availability: "Make-Buy" and "Repairable-Consumable". Each of these four classes is linked to a specific PN model, called a PN brick, which includes (i) an operational PN, noted PN_λμ and (ii) a set of five PNs that represent potential obsolescence scenarios. The complete model of a mission-critical system is constructed through a top-down analysis of its structure, assigning an appropriate PN brick to each component deemed at risk of obsolescence. This approach allows to model obsolescence interactions with the operational dynamics of (mission-critical) systems by synchronising all the individual PNs. Conclusions and perspectives will conclude the article.

Keywords: Obsolescence, Reliability, Maintainability, Availability, Causality, Petri nets.