Network Topology

Network Topology

Two or more computers connected together through communication media form a computer network. The arrangement of computers in a network is called Network Topology. It is a physical layout of connected computer.

Following are network topologies.

•  Bus topology.
•  Star topology.
•  Tree Topology
•  Ring topology.
•  Mesh topology

1. BUS TOPOLOGY

STRUCTURE OF BUS TOPOLOGY

In the bus topology, the computers are connected through a common communication media. A special type of central wire is used as communication media. This central wire is called Bus. The computer are attached through the bus the ends of the bus are closed with the terminator .The terminators are used to absorb signals. Bus topology use coaxial cables sections are connected to the B. N. C connectors. B.N.C connectors are often use to connect the computer through the main cable. These connectors can connect through two section of cable with the bus extending in both directions. The end devices on the bus have the terminals on one connectors of T

WORKING OF BUS TOPOLOGY

The computers that send data also attach address of the destination computer with the data. All computers connected to the bus receive the data but only that computer accepts it whose address matches the address attached with data.

In this topology only one computer at a time can send a data therefore the speed of network reduces as the number of computers attached to the bus increases.

Advantages of bus topology

• Easy to install and configure
•  Inexpensive
• Easily extended

Disadvantages of bus topology

• Performance decreases
• Weak signals
•  Difficult troubleshooting

2. STAR TOPOLOGY

STRUCTURE of STAR TOPOLOGY:

The star topology uses a separate cable for each work station. The cable connects the work station to a central device typically a HUB. The configuration provides a more reliable network that is easily expended. With star there is no central point of failure in the cable .if there is a problem with the cable only the station connected to that cable is a effected .to add more work stations simply connect another HUB

WORKING of STAR TOPOLOGY

Each computer in a star network communicates with the central hub that resents the messages either to all computers (in a broad cast network) are only to destination computer (in a switch network).

Star network maybe designed to operate in a polled mode where each user is asked in turn .if it has any information to transmit and in case, if it has, the communication controller will either give full attention to that device until it has no more information to send or it will allow the device to send part of its information, give another device a chance and then return back to original device.

ADVANTAGES of STAR TOPOLOGY

• Easily expended and modified
•   Easy to troubleshoot
• Multiple cable types supported by hub

DISADVANTAGES of STAR TOPOLOGY

•  If hub fails then entire network will fail
•  Require more cables
• May require a device to rebroadcast signals across the network

3. TREE TOPOLOGY

What is Tree Topology?

Tree Topology integrates the characteristics of Star and Bus Topology. Earlier we saw how in Physical Star network Topology, computers (nodes) are connected by each other through central hub. And we also saw in Bus Topology, work station devices are connected by the common cable called Bus. After understanding these two network configurations, we can understand tree topology better. In Tree Topology, the number of Star networks are connected using Bus. This main cable seems like a main stem of a tree, and other star networks as the branches. It is also called Expanded Star Topology. Ethernet protocol is commonly used in this type of topology. The diagram below will make it clear.

Advantages of Tree Topology

• 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.
• Expansion of Network is possible and easy.
• Here, we divide the whole network into segments (star networks), which can be easily managed and maintained.
• Error detection and correction is easy.
• Each segment is provided with dedicated point-to-point wiring to the central hub.
• If one segment is damaged, other segments are not affected.

Disadvantages of Tree Topology

• Because of its basic structure, tree topology, relies heavily on the main bus cable, if it breaks whole network is crippled.
• As more and more nodes and segments are added, the maintenance becomes difficult.
• Scalability of the network depends on the type of cable used.

4. RING TOPOLOGY

STRUCTURE of RING TOPOLOGY

In ring topology each computer is connected to the next computer and the last computer is connected to the first computer. Thus a ring of computers is formed as shown in figure below.

WORKING of RING TOPOLOGY

Every computer is connected to the next computer in the ring and each transmits what it receives from the previous computer. The messages flow around the ring in one direction.

Some ring network do ring token passing. A short message called token (memory area) is passed around a ring until a computer wishes to send information to other computers. That computer modifies token, adds an electronic address and data and send it around the ring. Each computer in sequence receives the token and next computer until either the electronic address matches the address of a computer

Or the token return to its origin .The receiving computer returns a message to the sender indicating that message has been received.

ADVANTAGES of RING TOPOLOGY

• It provides an orderly network in which every device has access to the token and can transmit.
• It performs well under a heavy load.

DISADVANTAGES of RING TOPOLOGY

• Failure of one computer can effect the whole network.
• Difficult to troubleshoot.
•  Change mode with adding or removing a device effect the entire network.

5. MESH TOPOLOGY

STRUCTURE of MESH TOPOLOGY

A mesh network or mesh topology uses separate cable to connect each device to every other device on the network, providing a straight communication.

WORKING of MESH TOPOLOGY

For sending messages, check the cable connected into two devices. A message is send directly from sender to receiver because each one has individual and separate connection. 

ADVANTAGES of MESH TOPOLOGY

• Enhance for error tolerance provided by redundant links.
• Easy to troubleshoot.

DISADVANTAGES of MESH TOPOLOGY

• Difficult to install and maintain.