In the introductory part of this course, the principles of routing in packet networks are discussed. The key properties of the distance vector and link-state routing protocols are analyzed. Subsequently, the mechanisms ensuring the Quality-of-Service in data networks and possible implementations of these mechanisms in active network elements designed for wired and wireless data communication are discussed. Based on the hierarchical network division, the switching nodes operating on individual layers are described in more detail. The properties of switching nodes using time division multiplex and space channel division are given. The issue of inner blocking, output port competition, queue blocking, multicast transfer, and cell selection algorithms are discussed.