LAN topologies

The computers on a local area network must be connected via some form of networking medium. This medium serves as the conduit along which the network signal is transmitted. To a limited extent, the way a network is laid out determines the type of media appropriate for that network.

The layout of the network is referred to as its topology. A topology can be described by the way the workstations are physically connected to the network, or by the way the data appear to flow through the network--its logical topology.

Standard models for topologies are the ring, star and bus.

A physical star topology is one in which all branches of the network are connected through a hub. A logical star topology is one in which the hub contains all of the intelligence of the network and directs all network transmissions

Physical Star topology

A physical ring topology is one in which all branches of the network are connected to a loop. In a logical ring, data flow from one node to the next in an ordered sequence. When the data reach the last node, they are returned to the originating node.

Physical Ring topology

A physical bus topology connects all networked devices to a single continuous cable. Data may pass directly from one station to another without first going through a hub or around the ring. In a logical bus topology all network communications are broadcast to the entire network.

Physical Bus topology

A star network is the most reliable, since the remaining segments of the star can still function if one segment goes bad. In a bus or ring topology, a bad segment can bring down the entire network.

Most networks are a hybrid of the three types. A network's logical topology does not have to match its physical topology. For example, in most token ring networks the network may be set up as a phyical star, with the data and wiring passing through a hub. However, data are transmitted from workstation to workstation, passing through the hub, using the logical ring topology.

Ref: http://supportnet.merit.edu/m-intint/t-lantec/text/lantop.html

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