Opaque to Internet end users until they encounter problems with their service is the issue of the reliability of digital switching systems. For telecommunications design engineers, service providers, and software engineers familiar with the basics of telephony, Ali (senior engineer, Bell Communications Research; Piscataway, NJ) tours switching system fundamentals (including the architecture of networked systems), system software and quality analysis tools (e.g. sensitivity analysis), reliability modeling techniques (e.g. advanced Markov models), and maintenance (firmware and software). Also discusses the major DSSs in the North American network, and his own generic model in the context of up-and-coming trends. Annotation c. by Book News, Inc., Portland, Or.