2.5 Tree Topology

Tree Topology

Tree Topology

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.

Advantages

1. The tree topology is useful in cases where a star or bus cannot be implemented individually.
2. It is most-suited in networking multiple departments of a university or corporation, where each unit (star segment) functions separately, and is also connected with the main node (root node).
3. The advantages of centralization that are achieved in a star topology are inherited by the individual star segments in a tree network.
4. Each star segment gets a dedicated link from the central bus. Thus, failing of one segment does not affect the rest of the network.
5. Fault identification is easy.
6. The network can be expanded by the addition of secondary nodes. Thus, scalability is achieved.
7. It is an extension of Star and bus Topologies, so in networks where these topologies can't be implemented individually for reasons related to scalability, tree topology is the best alternative.
8. Expansion of Network is possible and easy.
9. Here, we divide the whole network into segments (star networks), which can be easily managed and maintained. 
10. Error detection and correction is easy.
11. Each segment is provided with dedicated point-to-point wiring to the central hub.
12. If one segment is damaged, other segments are not affected.

Disadvantages

1. As multiple segments are connected to a central bus, the network depends heavily on the bus. Its failure affects the entire network.
2. Owing to its size and complexity, maintenance is not easy and costs are high. Also, configuration is difficult in comparison to that in other topologies.
3. Though it is scalable, the number of nodes that can be added depends on the capacity of the central bus and on the cable type.
4. Because of its basic structure, tree topology, relies heavily on the main bus cable, if it breaks whole network is crippled.
5. As more and more nodes and segments are added, the maintenance becomes difficult.
6. Scalability of the network depends on the type of cable used.