Maintainability: The Hidden Side of System Reliability

Telecom power systems are designed for high reliability, often characterized as 5 or 6 "9s" for availability. The initial designers selected the architecture and reliable components to achieve this. Mean time to repair (MTTR) is one key to reaching the objective once the architecture and component reliability (MTBF) have been determined. What is not factored into the system reliability is the maintainability of the system. This does not affect the availability calculation per se, but impacts how the system or the components will be maintained, upgraded, expanded, or replaced. We often see weak or flawed designs which look reliable at the initial deployment, but subsequent design decisions to address growth or operational decisions are made that cause problems later. This paper will discuss a number of typical problems observed and present practical options to avoid or deal with the problems, if they are an existing situation.