This course provides an introduction to the architecture and services of modern telecommunication networks. A general introduction illustrates the major features of a network, how they interact and introduce the concept of an intelligent network. Switching is an essential requirement and the ideas behind circuit, packet and cell switching are presented. Contention in switching systems and blocking/non-blocking switching is described. In addition to these, queuing in switching systems, complexity, scalability and traffic issues are explained in engineering aspects. Optical transmission and networking, key features for current and future telecommunication and information networks, are discussed.