Network Topologies

The physical layout or the way in which network connections are made is called a topology. It refers especially to the locations of computers and how the cable runs between them. It is important to select the right topology for the proper use of computer networks.

Important Topologies are as follows:

 

Bus Topology

The simplest type of network is the bus topology. In a bus topology, all computers or network nodes are connected to a common communication medium. In a local network, this medium is often a central wire called a bus.

 

Working of Bus Network

If a computer wants to send data to another computer in the network, it sends the data and destination address via the bus. This data and address move from one end of the network to the other. Each computer checks this address and, if it matches with this computer, the computer keeps the data. Otherwise, the data moves to the next computer.

The electrical signal from a computer travels the entire length of the cable. When the signal reaches the end of the wire, it bounces back and travels back up the wire. It is called ringing. To stop the signals from ringing, you have to attach terminators at either end of the segment. The terminators absorb the electrical energy and stop the reflections.

Advantages

1. Simple, easy to use, and suitable for very small networks.
2. The least amount of cable is required to connect the computers so it is less expensive.
3. Easy to extend a bus, two cables can be joined with a connector.
4. Allowing more computers to join the network.

Disadvantages

1. Heavy network traffic can slow the bus considerably.
2. Each connector reduces the strength of the electrical signal.
3. A cable break or loose connector will cause reflections and the entire network will stop.
4. As the number of computers increases, the speed of the network slows down

 

Star Topology

A star network is one in which all the cables run from the computers to a central location, where they are all connected to a device called a hub.

 

Working of Star Network

If two computers want to share data, the sender computer sends data to the hub and the hub sends it to the receiving computer. Each computer on a star network communicates with a central hub. A hub provides a central connection point so that all computers can communicate across the network.

Advantages

1. It is easy to modify and add new computers to a star network without disturbing the rest of the network.
2. Hub can accommodate multiple cable types.
3. Finding faults becomes very simple.
4. Single computer failure does not bring down the whole network.
5. It is more flexible among the remaining topology.

Disadvantages

1. If the central hub fails, the entire network breaks down.
2. It is more expensive because all network cables must be pulled to one central point.

 

Ring Topology

In this topology, each computer is connected to the next computer with the last one connected to the first.

 

Working of Ring Network

Every computer is connected to the next computer in the ring. Each retransmits what it receives from the previous computer. The messages flow in one direction. Since each computer retransmits what it receives, there is no signal loss problems and termination requirement like bus topology because there is no end to the ring.

Advantages

Because every computer is given equal access to the token, no one computer can monopolize the network.

Disadvantages

1. Failure of one computer on the ring can affect the whole network.
2. Difficult to troubleshoot
3. Adding or removing computers disrupts the network

 

Tree Topology

A tree topology combines the characteristics of bus and star topologies. It consists of groups of a computer configured in a star topology. The groups are then connected to a bus backbone cable. Tree topology is used for the expansion of an existing network.

Advantages

1. It provides point-to-point wiring for individual segments.
2. It is supported by several hardware and software vendors.

Disadvantages

1. The overall length of each segment is limited by the type of cabling used.
2. If the backbone line breaks, the entire segment goes down.
3. It is more difficult to configure and wire than other topologies.

 

Mesh Topology

In a mesh topology, every device on the network is physically connected to every other device on the network. A message can be sent on different possible paths from source to destination. Mesh topology provides improved performance and reliability.

Mesh networks are not used much in local area networks. It is mostly used in wide area networks where reliability is important.

Advantages

1. The use or dedicated link guarantees that each connection can tarry. Its own data load it eliminates the traffic problem.
2. It is one link that becomes unusable it does not harm the entire system.
3. It is easy to troubleshoot.

Disadvantages

1. A full mesh network can be very expensive.
2. It is difficult to install and reconfigure.

• Data Communications and Networks