Network Topology

Content:

• Introduction
• Types
• Mesh Topology
• Star Topology
• Bus Topology
• Ring Topology
• Tree Topology

Introduction:

Topology is a way of connecting devices with each other either physically or logically. Two or more devices make a link and two or more links form a topology. It is basically a geometrical representation of how a network is laid out.
DEF: Topology is a way of connecting several devices with each other on a network.

Types of Topologies

There are five types of topologies and each topology has some advantages and disadvantages.

Mesh Topology:

In mesh topology, each computer is connected with the other computer. There is a point-topoint link between each dedicated node (workstation). In this type of topology, the link carries traffic only between the two connected devices. A fully connected mesh network has n(n–1)/2 links, where n is the total number of connecting nodes.
For example, if there are five computers and each is connected with the other one, then there will be 5(5–1)/2=10 links.

Advantages of Mesh Topology:

1. Each communicating device carries its own data through its own dedicated link, hence eliminating traffic problems.
2. A mesh topology is robust. If one link becomes unusable, it does not affect the entire system.
3. Point-to-point links make fault identification and fault isolation easy.
4. Expansion and modification in topology can be done without disrupting other nodes.

Disadvantages of Mesh Topology:

1. Mesh topology is highly expensive to set up and involves high maintenance costs because of the amount of cabling and the number of I/O ports required.
2. Set-up and maintenance of this topology is very difficult. Even administration of the network is tough.

Star Topology:

In star topology, each communicating device is connected to a central controller called hub. (A hub is a hardware device used to connect several computers together.) Unlike mesh topology, the devices in star topology send and receive data indirectly; the data passes to and from the hub. The most popular and widely used LAN technology, Ethernet, currently operates in Star Topology

Advantages of Star Topology

1. Fewer wires are required as compared to mesh topology which, thus, reduces the number of input/output ports.
2. Installation and maintenance of network is easy and takes less time.
3. Removal or addition of any node in star topology can take place easily without affecting the entire performance of the network.

Disadvantages of Star Topology

1. Extra hardware is required for installation of central controller known as hub.
2. All nodes of star topology are dependent on central hub and, therefore, any problem in the hub makes the entire network shut down.
3. The performance of the entire network is directly dependent on the performance of the hub. If the server is slow, it will cause the entire network to slow down.

Bus Topology:

Bus topology is a multipoint configuration, i.e., several devices are connected to a main long cable which acts as backbone. Nodes are connected by drop lines and taps. The data flows from one end of the cable to the other. However, as the signal travels a long distance, it becomes weaker and weaker.Therefore, there should be a limited number of nodes connected to a line. Ethernet is a common example of bus topology

Advantages of Bus Topology

1. Nodes can be connected or removed easily from bus network.
2. It requires less cable length than a star topology and also easy to implement.
3. It works well for small networks

Disdvantages of Bus Topology

1. If there is a fault or break in the main cable, the entire network shuts down.
2. Fault isolation is difficult to detect if the entire network shuts down.
3. The signal becomes weaker if number of nodes becomes large.
4. Collision of data can take place because several nodes can transmit data to each other at one time.

Ring Topology:

In ring topology, each node is connected to two other nodes on either side of it, forming a ring network. Signal is transmitted only in one direction along the entire ring in a circular fashion. When the data is transmitted from one node to its recipient node, then the intermediate node regenerates the signal and passes the signal to the destined node.Token Ring is an example of ring topology.

Advantages of Ring Topology

1. A central server is not required in ring topology as the data is passed between two nodes which then passes through the entire network.
2. The configuration makes it easy to identify faults in network nodes..
3. In this topology, each node transmits the data to its next node in a ring.
4. It is relatively cheaper as compared to star topology

Disadvantages of Ring Topology

1. The movement or changes made to network nodes affect the entire network’s performance.
2. Transmission speed becomes slower with an increase in the number of nodes.
3. In this topology, each node transmits the data to its next node in a ring.
4. For proper communication between each node, it is required that each computer must be turned on.

Tree Topology:

In tree topology, all or some of the devices are connected to the central hub, called an active hub, and some of the devices are connected to the secondary hub, which may be an active hub or passive hub. An active hub contains the repeater that regenerates the signal when it becomes weaker with longer distances. A passive hub simply provides a connection between all other connecting nodes.

Advantages of Tree Topology

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

Disadvantages of Tree Topology

1. Owing to its size and complexity, maintenance is not easy and costs are high. Also, configuration is difficult in comparison to other topologies.
2. 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.

Reference:

• Informatics practice by sumita arora