This document defines and describes several types of communication networks and networking devices. It discusses simplex, half-duplex, and full-duplex communication, as well as examples like broadcasts, CB radios, and telephone networks. It also defines local area networks (LANs), metropolitan area networks (MANs), wide area networks (WANs), and the internet. Additionally, it provides descriptions of common networking devices like hubs, switches, routers, and their functions. Finally, it briefly discusses network addressing at the network layer.