This course aims at providing the fundamental knowledge needed to understand the key concepts, the architecture, the functional components and the basic services offered by modern telecommunication networks based on packet, cell and or circuit switching. The covered subjects include the evolution of the architecture of the digital telephony network towards ISDN and B-ISDN, and the architecture of optical transport networks SDH and WDM, MPLS and SDN/NFV networks. Several examples of physical networks such as LANs, access networks (xDSL, FTTx), Satellite Networks and Cellular Networks are presented to clarify how they consider the basic architectural functions related to the data/user, control and management planes of a complex network infrastructure.