On operational availability of a large software-based telecommunications system

Modern telecommunications systems are dependent on software for their successful operation. In many cases, the software operates on an established hardware platform and subsequent releases of the system offer primarily in the software component. Because of the increased dependence of the society on advanced telecommunications systems, the reliability and availability of network switching elements are very important. Empirical information on the operational unavailability due to total system outages of a large software-based telecommunications system is presented and discussed. About 50% of these outages are reported as being caused by software. The data is used to show that the unavailability of this system can be described well using a classical two-state availability model. >