The lecture gives a broad introdution to the architecture, protocols and algorithms used in communication networks, including the current Internet but also other network technolgoies (optical, SDN, wireless). In addition, the protocol specific background will be taught, so that the students can learn the qualitative performance methods. Starting from the Data Link Layer, several mechanisms of the error and overload control are studied. On the basis of the IP protocol stack and widely used IP routing protocols, the established funktionality of the Internet will be covered in detail. These will be completed with a detailed view of the funtionality and performance of the tranport layer protocols (TCP/UDP). Finally, the class also gives an introduction to the network security.