The book provides practical and compact insights into important fundamental concepts and standards of data communication in today's computer networks. After an introduction to reference models and protocol mechanisms, it first presents the technical foundations of networks as well as selected technologies and communication protocols of the lower layers. In the main part of the book, the concepts and protocols of the network and transport layers are explored in depth, particularly through the example of the TCP/IP protocol family. Important protocols and systems of the application layer, such as DNS and HTTP, are also explained. Finally, the fundamental concepts of mobile communication are introduced, and the programming of communication applications based on TCP and datagram sockets is discussed. The sometimes complex protocol mechanisms are illustrated with many examples for clarity.