Internetworking and Layered Models

The Internet today is a widespread information infrastructure, but it is inherently an insecure channel for sending messages. Networking technology includes everything from local area networks (LANs) in a limited geographic area such as a single building, department, or campus to wide area networks (WANs) over large geographical areas that may comprise a country, a continent, or even the whole world. Connecting devices are used to connect the segments of a network together or to connect networks to create an internetwork. These devices are classified into five categories: switches, repeaters, bridges, routers, and gateways. Each of these devices except the first one (switches) interacts with protocols at different layers of the Open Systems Interconnect (OSI) model. Both the OSI model and the TCP/IP layered model are based on many similarities, but there are philosophical and practical differences between the two models. However, they both deal with communications among heterogeneous computers.