Information Technology

Lecture No 3

By: Khurram Shahid

Network Topology

The way in which a number of computers are connected together in a network is called network topology. It is the physical layout or arrangement of computer in a network.

There five basic topologies for connecting computer in a network.

These are:• Bus Topology• Ring topology• Star topology• Tree topology• Mesh topology

Bus Topology In bus topology, the computer or network nodes are

connected to a common communication medium, called the backbone. A special type of central wire is used as the backbone. This central wire is called the bus. The computers are connected to the bus. The ends of the bus are closed with terminators. These terminators are used to absorb signals. Bus topology is commonly used for small and networks.

Working of Bus Topology

The sending computer attaches the address of the destination computer with the data. It then sends this data to the bus. All computers connected to the bus receive the data but only that computer accepts the data whose address matches the address attached with the data. In this topology only one computer can send data at a time. Therefore, the speed of a network reduces as the number of computer attached to the bus increase.

Advantages

It is simply and reliable for very small networks. It is easy to install. It requires minimum length of communication cable. It is easy to extend as extra cable can be connected to

make a longer bus. A repeat can also be used to extend the length of the bus. If a node is out of order, it does not affect the rest of the

network.

Disadvantages

It can support only a small number of computers. As the number of computer increases, the network gets slower.

It is difficult to troubleshoot a bus. A cable-break, fault in any one computer or a loose connection may cause

breakdown of the whole network.

Star topology In star topology, all computers or nodes are directly

connected to a central device. The device that connects

the nodes is called hub.

Working of Star Topology

Each computer on a star network communication with the central hub. The hub then sends data to the destination computer or computers.

Advantages It is easy to modify a star network. New

computers can be added to the central hub or any computer can be removed without affecting the network.

It is usually easy to troubleshoot a star network. If any computer in the star topology breaks

down, the network is not affected. Since the data rate between the central hub and

a node is relatively low, low specification twisted pair can be used to connect the nodes to the central hub.

Disadvantage

If the central hub fails, the whole network breaks down. Star topology requires more communication cable than

any other topology. Star topology is very costly

Ring topology

In ring topology, each computer or node is connected to the next computer and the last computer is connected to the first. Thus, a ring of computers is formed.

Working of Ring Topology

Every computer receives message from the previous computer and transmits it to the next computer receives the message. Since each computer re-transmits what it receives, signal-loss does not occur.

Advantages

All computers on the ring have equal access to the network.

Disadvantages

Failure of one computer can affect the whole network. It is difficult to troubleshoot a ring network. Adding or removing a computer affects the whole

network.

Tree Topology

A tree topology combines characteristics of linear bus and star topologies. It consists of group of star-configured workstations connected to a linear bus. The

bus works as the backbone cable for the network.

Advantage Point-to-point wiring for individual segments. Supported by several hardware and software

manufacturers.

Disadvantage Overall length of each segment is limited by the type of

cabling used. If the backbone breaks down, the entire network goes

down. It is more difficult to configure and wire than other

topologies.

Mesh Topology

In mesh topology, each device is physically connected to every other device on the network. Thus messages sent on a mesh network can take any of several possible paths from source of destination. Each device is physically connected to every other device on the network. This increases performance and reliability. However the complexity and difficulty of creating a mesh network increase as number of nodes on the network increases.