Unavailability of a repairable system with one or two replacement options [submarine telecommunication network]

The submarine line terminal equipment (SLTE) is part of the land-based equipment of a submarine telecommunications network. It is considered to be a repairable system and is housed in the terminal station (TS). This study is concerned with the methodology for the calculation of the unavailability of the SLTE. The traditionally-accepted method of calculating the unavailability of the SLTE is to assume an unlimited number of spares in the TS. Because of the rapidly increasing capacity of submarine networks, it is becoming more important to quantify accurately the unavailability of the equipment, taking into account the exact limited number of spares provided. Furthermore, the spares replacement policy has a bearing on unavailability. The Markov method is used to model the system and to calculate the unavailability, the results are supported using Monte-Carlo simulations. Simplified formulae are derived to approximate the results. Numerical examples are presented to show the advantage of introducing a central store and to validate the approximations