physical and logical topologies in computer network and client server

Physical And Logical Topologies

Physical Topology

BusStarRingMeshHybrid

Physical Topology

The physical layout of devices on a network.

Physical topology refers to the interconnected structure of a local area network (LAN).

 Physical topology is the way that the devices on a network are arranged and how they communicate with each other.

The method employed to connect the physical devices on the network with the cables, and the type of cabling used, all constitute the physical topology.

Bus Topology The bus topology is often referred to as a "linear bus"

because the computers are connected in a straight line. It consists of a single cable that connects all of the

computers in the network in a single line. Computers on a bus topology network communicate by

addressing data to a particular computer and sending out that data on the cable as electronic signals.

Communication on Bus

Sending the signal

Signal bounce

Terminator

1.Sending the signal

Network data in the form of electronic signals is sent to all the computers on the network.

Only the computer whose address matches the address encoded in the original signal accepts the information. All other computers reject the data. 

Because only one computer at a time can send data on a bus network, the number of computers attached to the bus will affect network performance.

The more computers there are on a bus, the more computers will be waiting to put data on the bus and, consequently, the slower the network will be.

2.Signal Bounce

Because the data, or electronic signal, is sent to the entire network, it travels from one end of the cable to the other.

If the signal is allowed to continue uninterrupted, it will keep bouncing back and forth along the cable and prevent other computers from sending signals.

Therefore, the signal must be stopped after it has had a chance to reach the proper destination address.

3. Terminator Terminator is used to stop the signal from

bouncing, a component called a terminator is placed at each end of the cable to absorb free signals.

Absorbing the signal clears the cable so that other computers can send data.

Star Topology In the star topology, cable segments from each

computer are connected to a centralized component called a hub.

Signals are transmitted from the sending computer through the hub to all computers on the network.

The star network offers the advantage of centralized resources and management. However, because each computer is connected to a central point, it requires a great deal of cable in a large network installation.

If the central point fails, the entire network goes down.

If one computer—or the cable that connects it to the hub—fails on a star network, only the failed computer will not be able to send or receive network data. The rest of the network continues to function normally.

Ring Topology The ring topology connects computers on a single circle of

cable.

Unlike the bus topology, there are no terminated ends.

The signals travel around the loop in one direction and pass through each computer, which can act as a repeater to boost the signal and send it on to the next computer

The failure of one computer can have an impact on the entire network.

One method of transmitting data around a ring is called token passing.

Mesh Topology A mesh topology network offers superior redundancy and

reliability.

In a mesh topology, each computer is connected to every other computer by separate cabling.

This configuration provides redundant paths throughout the network so that if one cable fails, another will take over the traffic.

these networks are expensive to install because they use a lot of cabling.

Often, a mesh topology will be used in conjunction with other topologies to form a hybrid topology.

Fig: Mesh Topology

Hybrid Topology Hybrid networks use a combination of any two or

more topologies, in such a way that the resulting network does not exhibit one of the standard topologies (e.g., bus, star, ring, etc.).

For example a tree network connected to a tree network is still a tree network topology.

A hybrid topology is always produced when two different basic network topologies are connected.

Two common examples for Hybrid network are: star ring network and star bus network

Logical topology• IT IS THE ARRANGEMENT OF DEVICES ON A COMPUTER NETWORK AND

HOW THEY COMMUNICATE WITH ONE ANOTHER. HOW DEVICES ARE CONNECTED TO THE NETWORK THROUGH THE ACTUAL CABLES THAT TRANSMIT DATA, OR THE PHYSICAL STRUCTURE OF THE NETWORK, IS CALLED THE PHYSICAL TOPOLOGY. PHYSICAL TOPOLOGY DEFINES HOW THE SYSTEMS ARE PHYSICALLY CONNECTED. IT REPRESENTS THE PHYSICAL LAYOUT OF THE DEVICES ON THE NETWORK. THE LOGICAL TOPOLOGY DEFINES HOW THE SYSTEMS COMMUNICATE ACROSS THE PHYSICAL TOPOLOGIES.

• LOGICAL TOPOLOGIES ARE BOUND TO NETWORK PROTOCOLS AND DESCRIBE HOW DATA IS MOVED ACROSS THE NETWORK.

• TWO OF THE MOST COMMON LOGICAL TOPOLOGIES ARE:BUS TOPOLOGY: ETHERNET USES THE LOGICAL BUS TOPOLOGY TO TRANSFER DATA. UNDER A BUS TOPOLOGY A NODE BROADCASTS THE DATA TO THE ENTIRE NETWORK. ALL OTHER NODES ON THE NETWORK HEAR THE DATA AND CHECK IF THE DATA IS INTENDED FOR THEM.

RING TOPOLOGY: IN THIS TOPOLOGY, ONLY ONE NODE CAN BE ALLOWED TO TRANSFER THE DATA IN A NETWORK AT A GIVEN TIME. THIS MECHANISM IS ACHIEVED BY TOKEN (THE NODE HAVING TOKEN ONLY CAN TRANSMIT THE DATA IN A NETWORK) AND HENCE THE COLLISION CAN BE AVOIDED IN A NETWORK.