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Unit Contents
Overview 
Thus far, we have discussed the simplest, smallest broadcast networks, in which each computer is connected to every other through a ring topology, bus, or central hub. In these single-segment networks, every device receives every frame transmitted by any other device. Each device processes frames that are addressed to it, and ignores frames that are not. For this system to work, only one device is allowed to transmit at any time. (Simultaneous signals will garble each other.) As we have seen, different Data Link Layer protocols, such as Ethernet and Token Ring, enforce this rule in different ways. Single-segment networks provide good service to many small and mid-sized businesses. However, as an organization grows, two main factors force changes in the structure of a network:
To solve both of these problems, network designers break a single broadcast network into separate segments. Internetworking devices, such as repeaters, hubs, switches, bridges, routers, and gateways, function as the connectors between the individual segments. These devices manage data traffic as it flows within and between networks, in some cases over great distances. They can also increase the effective transmission capacity of a network and enhance its security. The operation of most of these components can be configured and optimized by a network administrator. For simple devices, network management is conducted with switches on the device itself. More complex "managed" devices are configured and controlled by software, from a separate management console that plugs into one of the device ports, or by management commands sent through the network itself. Each internetworking device operates at a particular layer of the Open Systems Interconnection (OSI) model. As we introduce each device, we will start with Layer 1 (the Physical Layer) and work upward.
Terms You Should Know
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