Influence of software and hardware failures with imperfect fault coverage on PONs OPEX

Passive Optical Networks (PONs) are one of the preferred technologies to deploy broadband access networks. As time passes, end users presuppose network connectivity to be always available, and expect PONs to be highly dependable. Yet operators, from an economic view, are interested in the costs related to failures. Thus, PONs dependability and associated costs have been extensively studied, but only focusing on hardware failures. Contrarily, this paper performs a thorough analysis of the impact of software failures in failure-related costs. Based on real empirical data, software failures are thoroughly characterized and classified in four different categories according to their severity. Also, the effect of software failures on the behavior of PON´s fiber protection and recovery mechanisms is detailed. Software failures are included into a Markov cost model, implementing a comprehensive cost framework. This way, the dependability-related costs of PONs are analyzed, accounting for hardware and software failures, as well as for the consequences of software failures on well-known PON protection mechanisms. Moreover, how the testing phase duration and user profile (residential or business) impact these costs is pinpointed.