Network Topology - Bus Topology, Line Topology

Bus Topology

A bus topology is characterized by a main trunk or backbone line with the networked computers attached at intervals along the trunk line. This topology type is considered a passive topology because the computers on a bus just sit and listen. When they “hear” data on the wire that belongs to them, they accept that data (they actually listen using their network interface cards). When they are ready to transmit, they make sure no one else on the bus is transmitting and then send their packets of information.

Bus networks typically use coaxial networking cable (it looks like the same coaxial cable used for cable television, but it is actually slightly different) hooked to each computer using a T-connector. Each end of the network is terminated using a terminator specific to the cable type (if you use 50 – Ohm cable, you use 50 – Ohm terminators). Because the bus network is rally just a collection of cable, connectors, and terminators, there is no amplification of the signal as it travels on the wire. This means that the size of the network will be limited by the maximum distance the cable type can actually move the signal that holds the data.

Bus networks are easy to assemble and are easy to extend. They require a fairly limited amount of cabling when compared to other topologies. Bus networks are prone to cable breaks, loose connectors, and cable shorts that can be very difficult to troubleshoot. One physical problem on the network, such as a detached connector, can actually bring down the entire bus network. Although at one time a bus network would have been the cheapest and easiest way to connect a small group of computers for peer-to-peer networking, the drop in the price of hubs and the ease of using twisted-pair wire have really pushed the coaxial cable bus network to the edge of extinction.

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