A study of the architectures of the systems that provide telephone service, including a look at architectures for future systems. It describes the hardware and software of five different systems in detail, offering communications professionals the information they need to understand switching systems in historical context and in relation to regulatory frameworks. The book also examines how factors such as customer services and modern computer applications have affected switching systems, and it provides background discussions on relevant theory and boundary conditions - such as transmission systems, telephone operation, and the human element.