What is a computer Network?





A computer network is a group of computers and associated peripheral devices connected by communication network technologies. And computer networking is one of the best concepts to study in the field of computers. A computer network is used for files, resources, software sharing and sharing the hardware like printers among different users working on different locations. Computers located in different locations use telecommunication networks to connect to each other in a computer network. Computer networks require a physical channel or medium such as copper wires, optical cable, wireless radio frequencies etc. for communication. Computer networks use different network topologies to form telecommunication networks.

Following are the different types of networks:
LAN (Local Area Network)
MAN (Metropolitan Area Network)
WAN (Wide Area Network)



Local Area Network

This type of network is very small. It is used in a single campus, school and building. In local area network computers are connected in a limited geographical area. The transmission medium used for LAN is generally copper-based or fiber-based. To operate LAN systems LAN operating system is required.
Three most common network topologies found in LANs are star, ring, and bus.

LAN has following characteristics-
Data transmission speed of LAN network is very fast and higher than MAN and WAN. It ranges from 1-1000 Mbps.
LAN has low error rates.
LAN network interconnection medium is privately owned so it maintains security of data.

Metropolitan Area network

This network is used to connect a whole city. MAN is made after connecting different LANs in a city. This network is bigger than LAN and smaller than WAN. Data transmission speed of MAN is slower than LAN. MAN use optical fiber for the transmission medium mostly. A single person and organization cannot own the MAN it is owned by group or network provider.

MAN has following characteristics-
It covers a wider area than LAN such as a town or entire city.
MAN provide uplinks from LANs to WANs and the Internet.

Wide Area Network

Wide area networks connect computers over large geographical areas by connecting states and countries. It uses microwave relays and telephone networks for communication. This network is used for transferring large amounts of data to users over long distances. It is used for video, voice and image transmission. The working of WAN is like working of LAN, but it works on a larger scale.

WAN has following characteristics-
WAN network can be made up of multiple LAN and MAN networks.
TCP/IP (Transmission Control Protocol/Internet Protocol) is used in WAN for devices such as modem (modulator/demodulator), routers.
It can connect large numbers of devices over a large geographical area.
Data transmission speed of WAN is comparatively slow than LAN and MAN.


NETWORK TOPOLOGIES

Topology- There are different ways to connect computers in a network. The way in which computers are connected in a network is called topology. Topology defines the actual physical structure in which computers are connected to each other.

Types of network topologies-
Star topology
Ring topology
Tree topology
Bus topology
Mesh topology


Star topology- In star topology network topology computers and peripherals are connected to one centralized hub. The central computer is called server and the other computers and peripherals connected to it are called clients. While communication data is transmitted to the hub first, which means hub controls the data flow to client computers and ensures which computer will fetch the data.
It gives control to the hub. Fault finding in star topology is easy. But when the central computer gets damaged none of the other computers can communicate anymore. Which is the weakness of star topology. If all the computers are connected to a central computer even if they don't resemble a star, it will still be called a start topology.

Ring topology- When computers or devices are connected in a closed loop using a single communication channel it is called ring topology. In ring topology there is no central computer. The data flow in ring topology is unidirectional. Which means data flows only in one direction. If the data is meant to be sent to the last computer in ring.
The data packets will travel from sender computer to receiver though all the computer in the middle of the path. Which causes the data loss. To prevent data from being lost, repeaters are used in the network. If one computer gets damaged the entire network will collapse. Because if data cannot flow through the damaged computer, then it cannot reach another computer until the damaged computer starts working again. Ring topology can be made bidirectional as well but for that network requires two communication channels between each computer. In bidirectional ring topology one computer failure does not cause the failure of the whole network because data is sent through the opposite direction using another channel. A switch is attached in the network which is used to automatically switch the routes in case of channel failure.

Tree topology- In tree topology computers are linked in a hierarchical form for data flow. In tree topology all the computers are connected to a central computer in a hierarchy. And all the other additional computers are branched from the higher-level main computers. The network connects all the additional computers to the main computer without loops. Lower-level computers are controlled by the higher-level computers. The network is simple to control, but it is sure if the main computer fails the entire network can fail.

Bus topology- Bus topology is also known as horizontal topology. In bus topology all the computers in the network are connected to a single communication channel.
All the computers in the network can receive data simultaneously using the common channel. Bus topology supports bidirectional transmission of data. If the backbone or the transmission channel fails, the topology crashes. Bus topology uses only one channel or wire so that it is less costly to establish than other topologies. Computers in bus topology are connected to channel via drop lines.

Mesh topology-
In mesh topology every device has a dedicated point to point connection to one or more than one device in the network.



Fully Connected Mesh- A mesh topology in which every computer device is directly connected to every other computer using a dedicated link in the network is called a fully connected mesh.
Mesh topology is very reliable because the failure of a single computer does not affect the working of the entire network. And mesh topology is very secure as well. Fault finding in mesh topology is easy because of point-to-point links between computers. Communication and data transmission in mesh topology is very fast. Cabling cost is high in mesh topology because every device needs to be connected by a dedicated wire. So, mesh topology is suitable for less numbers of devices.



Data Transmission Modes in Computer Networks


Transmission Mode- It refers to the mechanism or the way in which data is transmitted from one computer to another. Digital data transmission modes are classified into the following three different categories.

1. Simplex Transmission Mode- It is a unidirectional transmission mode of digital data transmission. Which means if two computers or nodes are connected to each other via a transmission channel or medium only one computer can transmit the data and another computer can only receive data but cannot transmit data. Data transmission is always in one direction. The entire channel capacity is used only for the transmission of data in one direction.
Example- Keyboard used only for input, radio station broadcasting etc.

2. Half Duplex Transmission Mode- It is a bidirectional mode of digital data transmission. Data transmission can take place in both directions. It means if two computers are connected to each other both computers can transmit and receive data from each other, but the data transmission is not simultaneous data transmission. Which means computers can either transmit or receive data at a time. When one computer is transmitting data, another can only receive and vice versa.
Example- Walkie-talkie, two-way radios, Browsing the internet etc.

3. Full Duplex Transmission Mode- In full duplex data transmission mode computers can transmit data in both directions simultaneously. Full duplex data transmissions divide the transmission medium or channel capacity in both directions. It requires two separate transmission mediums, one for signal transmission, another for receiving signal.
Example- Telephone conversation between two people or telephony.