Network Topologies

The layout of a LAN design is called its topology. There are three basic types of topologies: the star topology, the bus topology, and the ring topology. Hybrid combinations of these topologies also exist.

• In a network based on the star topology, all computers and devices are connected to a centrally located hub or switch. The hub or switch collects and distributes the flow of data within the network. When a hub is used, data from the sending host are sent to the hub and are then transmitted to all hosts on the network except the sending host. Switches can be thought of as intelligent hubs. When switches are used rather than hubs, data from the sending host are sent to the switch which transmits the data to the intended recipient rather than to all hosts on the network.

FIGURE: The Star Topology

• In a network based on the bus topology, all computers and devices are connected in series to a single linear cable called a trunk. The trunk is also known as a backbone or a segment. Both ends of the trunk must be terminated to stop the signal from bouncing back up the cable. Because a bus network does not have a central point, it is more difficult to troubleshoot than a star network. Furthermore, a break or problem at any point along the bus can cause the entire network to go down.

FIGURE: The Bus Topology

• In a network based on a ring topology, all computers and devices are connected to cable that forms a closed loop. On such networks there are no terminating ends; therefore, if one computer fails, the entire network will go down. Each computer on such a network acts like a repeater and boosts the signal before sending it to the next station. This type of network transmits data by passing a "token" around the network. If the token is free of data, a computer waiting to send data grabs it, attaches the data and the electronic address to the token, and sends it on its way. When the token reaches its destination computer, the data is removed and the token is sent on. Hence this type of network is commonly called a token ring network. Of these three network topologies, the star topology is the most predominant network type and is based on the Ethernet standard.

FIGURE: The Ring Topology