Explore a comprehensive tutorial on communications and network systems, covering fundamental concepts, network topologies, protocols, hardware components, and transmission technologies. Learn about the communications system framework, network basics, and various topologies including point-to-point, bus, ring, star, tree, and mesh. Dive into CSMA/CD protocol, network resources, operating systems, and account management. Understand the differences between LANs and WANs, and explore networking devices such as bridges, gateways, NICs, cables, repeaters, hubs, switches, and routers. Discover wireless technologies like infrared, Bluetooth, Wi-Fi, NFC, and cellular networks. Examine terrestrial microwaves and satellite communications. Gain insights into network performance metrics, signal rates, and various cable types. Finally, learn about error detection techniques including parity checks, checksums, and cyclic redundancy checks.