A computer network is a system in which multiple computers are connected ,to share information and resources.
Characteristics
Share Resources from one computer to another
Create files and store them in one computer, access those files from the other
computer(s) connected over the network
Connect a printer , scanner, or a fax machine to one computer within the network and
let other computers of the network use the machines available over network.
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Topology
The topology of a network refers to the configuration of cables, computers, and other peripherals.
Four most common topologies are :-
*Bus
*Star
*Ring
*Mesh
Bus topology
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All the devices on a bus topology are connected by one single cable.
When one computer sends a signal , all the computers on the network receive the information, but only one accepts the information.
The rest regrets the message.
One computer can send a message at a time.
A computer must wait until the bus is free before it can transmit.
When the signal reaches the end of the wire, it bounces back and travels back up the wire. When a signal echoes back and forth along an unterminated bus, it is called ringing.
Advantages and disadvantages of network topology:
advantage of network topology
* The bus is simple.
* Reliable in small network.
* It is easy to use and understand.
*Requires the least amount of cable to connect the computers and less expensive
*Easy to extend the bus
Disadvantage of network topology
* Heavy network traffic can slow a bus considerably
* Each barrel connector weakens the electrical signal
*Difficult to troubleshoot a bus Topology.
Star Topology
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*All the cables run from the computers to a central location.
*where they are all connected by a device called a hub.
*Each computer on a star network communicates with a central hub that resends the message either to all the computers or only to the destination computers.
*We can expand a star network by placing another star hub.
Advantages:
*Easy to modify and add new computers to a star network.
*Center of a star net is a good place to diagnose network faults
*Single computer failure do not necessarily bring down the whole network.
* Several cable types can be used with the hub.
Disadvantages
* If Central hub fails, the whole network fails to operate
* Many star networks require a device at the central point to rebroadcast or switch network traffic.
* Costs more for cabling in star net than bus.
Ring Topology
Each computer is connected to the next computer ,with the last one connected to the first. Every computer is connected to the next computer in the ring, and each retransmits what it receives from the previous computer. The message flow around the ring in one direction. Some ring networks do token passing. It passes around the ring until a computer wishes to send information to another computer. The computer adds an electronic address and data and sends it around the ring. Each computer in sequence receives the token and the information and passes them to the next until either the electronic address matches the address of the computer or the token returns to the origin. The receiving computer returns a message to the originator indicating that the message has been received. The sending computer then creates another token and place it on the network, allowing another station to capture the token and being transmitted.
Advantages:
* No computer can monopolize the network.
* The fair sharing of the network allows the net to degrade gracefully as more user are added.
Disadvantages:
* Failure of one compute can affect the total network.
*Difficult to troubleshoot.
*Adding or removing Computers disrupts the network .
Mesh Topology
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The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance. It is used in WANs to interconnect LANs and for mission critical networks like those used by banks and financial institutions. Implementing the mesh topology is expensive and difficult.
Advantages
*Fault tolerance.
*Guaranteed communication channel capacity.
* Easy to troubleshoot.
Disadvantages
*Difficulty of installation and reconfiguration.
*Cost of maintaining redundant link.
*Bus
*Star
*Ring
*Mesh
Bus topology
All the devices on a bus topology are connected by one single cable.
When one computer sends a signal , all the computers on the network receive the information, but only one accepts the information.
The rest regrets the message.
One computer can send a message at a time.
A computer must wait until the bus is free before it can transmit.
When the signal reaches the end of the wire, it bounces back and travels back up the wire. When a signal echoes back and forth along an unterminated bus, it is called ringing.
Advantages and disadvantages of network topology:
advantage of network topology
* The bus is simple.
* Reliable in small network.
* It is easy to use and understand.
*Requires the least amount of cable to connect the computers and less expensive
*Easy to extend the bus
Disadvantage of network topology
* Heavy network traffic can slow a bus considerably
* Each barrel connector weakens the electrical signal
*Difficult to troubleshoot a bus Topology.
Star Topology
*All the cables run from the computers to a central location.
*where they are all connected by a device called a hub.
*Each computer on a star network communicates with a central hub that resends the message either to all the computers or only to the destination computers.
*We can expand a star network by placing another star hub.
Advantages:
*Easy to modify and add new computers to a star network.
*Center of a star net is a good place to diagnose network faults
*Single computer failure do not necessarily bring down the whole network.
* Several cable types can be used with the hub.
Disadvantages
* If Central hub fails, the whole network fails to operate
* Many star networks require a device at the central point to rebroadcast or switch network traffic.
* Costs more for cabling in star net than bus.
Ring Topology
Each computer is connected to the next computer ,with the last one connected to the first. Every computer is connected to the next computer in the ring, and each retransmits what it receives from the previous computer. The message flow around the ring in one direction. Some ring networks do token passing. It passes around the ring until a computer wishes to send information to another computer. The computer adds an electronic address and data and sends it around the ring. Each computer in sequence receives the token and the information and passes them to the next until either the electronic address matches the address of the computer or the token returns to the origin. The receiving computer returns a message to the originator indicating that the message has been received. The sending computer then creates another token and place it on the network, allowing another station to capture the token and being transmitted.
Advantages:
* No computer can monopolize the network.
* The fair sharing of the network allows the net to degrade gracefully as more user are added.
Disadvantages:
* Failure of one compute can affect the total network.
*Difficult to troubleshoot.
*Adding or removing Computers disrupts the network .
Mesh Topology
The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance. It is used in WANs to interconnect LANs and for mission critical networks like those used by banks and financial institutions. Implementing the mesh topology is expensive and difficult.
Advantages
*Fault tolerance.
*Guaranteed communication channel capacity.
* Easy to troubleshoot.
Disadvantages
*Difficulty of installation and reconfiguration.
*Cost of maintaining redundant link.
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