This subject studies the standard models for the layered approach to communication between autonomous machines in a network and the main characteristics of data communication (transmission protocols) the the lower layers. It introduces several application layer protocols from a distributed systems viewpoint, and considers alternative lower layer methods such as ATM, and problem areas in the Internet protocol suite. The following topics are included: introduction to comunication network architectures; the physical layer (transmission media, signal representation, limits to data capacity); the data link layer (error detection and recover, point-to-point protocols); the medium access layer (protocols for Local Area Networks and satellite communication); the network layer (routing algorithms, congestion control); internetworking (addressing, internetwork routing and protocols, quality of service); the transport layer (connection-oriented trasnport layer services and protocols); application protocols for distributed systems.