There are two widespread topologies that are used for Ethernet networks: bus topology and star topology. Those topologies are frequently used together in the same network.
Bus Topology
Bus topology means that all the users, servers etc., are connected to a main backbone conductor. A failure in this conductor stops all transaction on the network. This is the reason why it is recommended to use double cables for redundancy, to protect against cable failure. The disadvantage of this topology is also its biggest advantage. A single bus connecting all the users requires only a single communication line making it cost efficient. There are different media (wires) used in constructing this kind of network: Coaxial cables and fiber optic cables. The advantages and disadvantages of each of these media types are described below (see media types).
Star Topology
Star topology is the most common topology in a LANs today because it is flexible, readily expandable and relatively inexpensive.
The hubs in LANs are not only a connection point for the different devices, but also repeaters that receive signals, increases them, and re-broadcasts them to the net. The hubs also separate the network into
independent
segments that will not affect each other in case of failure of disconnection.
Composite topologies
Most of networks are composed of a few segments; each segment can be considered as a separate
independent
network, with communication links between the different segments. The different segments can be built in different topologies. For example: 6 nodes connected to 3 hubs (2 devices per hub in a star topology), and the hubs connected to a bus, comprises a composed topology network.
