Reliability models for facilities switching

Facilities switching has been proposed for use in remote line units in telecommunication systems as a means of reducing both maintenance cost and customer-perceived failure rate. The authors present mathematical models of the cost/availability/modularity tradeoffs involved. Numerical methods are used to plot these cost-availability tradeoffs for several scenarios, including an electronic cross-connect frame in an electronic remote unit, and an optical cross-connect frame in an optical remote unit. It is demonstrated that it is possible to model the reliability of a given configuration of linecards and facilities switches in closed form for some service schedules, notably a deterministic scheduled maintenance discipline. For a set of four switch-cost functions, the optimum modularity is insensitive to the linecard failure rate. The optimum modularity of a facilities switch was also insensitive to the parameters chosen for a particular type of cost function over the range of parameters modeled