This document presents an overview of communication models and network concepts. It introduces a basic model of communication systems including a source, transmitter, transmission system, receiver, and destination. It then discusses network models including local area networks and wide area networks. Common network technologies like circuit switching, packet switching, frame relay, and asynchronous transfer mode are explained. The document also covers protocols, network architectures, and the three-layer model of network communications including the access, transport, and application layers.