Defects Per Million (DPM): A user-oriented perspective of telecommunication systems

Defects Per Million (DPM), defined as the number of calls dropped out of a million calls due to failures, is used by the telecommunication systems community as a user-perceived dependability metric. As new standards evolve, with built-in mechanisms to handle and recover from failures, the need for an accurate estimation of metrics like DPM become essential. In this paper, we illustrate the computation of the DPM metric using a system supporting Voice over IP functionality using the Session Initiation Protocol (SIP) as an example to illustrate how the fault-handling mechanisms of the protocol can be accurately reflected in the dependability evaluation. We discuss how can we extend our approach and underlying models to other types of service-oriented environments.