In telecommunication networks, a tree network is a combination of two or more star networks connected together. Each star network is a local area network (LAN) in which there is a central computer or server to which all the workstation nodes are directly linked. The central computers of the star networks are connected to a main cable called the bus. Thus, a tree network is a bus network of star networks.
The illustration shows a tree network with five star networks connected to a common bus. The workstations are shown as small spheres, the central computers of the star networks are shown as larger spheres, connections within star networks are shown as short lines, and the bus is shown as a long, heavy line. The connections can consist of wire cables, optical fiber cables, or wireless links.
The tree network topology is ideal when the workstations are located in groups, with each group occupying a relatively small physical region. An example is a university campus in which each building has its own star network, and all the central computers are linked in a campus-wide system. It is easy to add or remove workstations from each star network. Entire star networks can be added to, or removed from, the bus. If the bus has low loss and/or is equipped with repeaters, this topology can be used in a wide area network (WAN) configuration.
In a tree network, a cable failure in one of the star networks will isolate the workstation that it links to the central computer of that star network, but only that workstation will be isolated. All the other workstations will continue to function normally, except that they will not be able to communicate with the isolated workstation. If any workstation goes down, none of the other workstations will be affected. If a central computer goes down, the entire portion of the network served by it will suffer degraded performance or complete failure, but rest of the network will continue to function normally. If the bus is broken, serious network disruption may occur. If redundancy is needed, the central computers of the star networks can be interconnected in a mesh network topology.