Best Computer Network Notes Class 12

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Computer Network Notes Class 12

Computer Network Notes Class 12
Computer Network Notes Class 12

Computer Networks :

A computer network is an interconnection of two or more computers or computing devices. A network allows computers to share data and resources among each other.

Node :

In a communication network, each device that is a part of a network and that can receive, create, store or send data to different network routes is called a node.

Server :

It is a special computer which provide services to other computer/devices in a called clients.

Client :

A computer/device connected in a network sending request to server is called client.

Types of Network :

Based on the geographical area covered and data transfer rate, computer networks are broadly categorised as:

  1. LAN (Local Area Network)
  2. MAN (Metropolitan Area Network)
  3. WAN (Wide Area Network)

Local Area Network (LAN) : It is a network that connects computers, mobile phones, tablet, mouse, printer, etc., placed at a limited distance. The geographical area covered by a LAN can range from a single room, a floor, laboratory, a school, college, or university campus etc.

LAN is comparatively secure as only authentic users in the network can access other computers or shared resources.

Metropolitan Area Network (MAN) : It is an extended form of LAN which covers a larger geographical area like a city or a town. Data transfer rate in MAN also ranges in Mbps, but it is considerably less as compared to LAN. Cable TV network or cable based broadband internet services are examples of MAN. This type of network can be extended up to 30–40 km.

Wide Area Network (WAN) : Wide Area Network (WAN) connects computers and others LANs and MANs, which are spread across different geographical locations of a country or in different countries or continents. A WAN could be formed by connecting a LAN to other LANs via wired or wireless media. The Internet is the largest WAN that connects billions of computers, smartphones etc.

Computer Network Notes Class 12

Computer Network Notes Class 12
Computer Network Notes Class 12

Network Devices :

Those devices which are used to connect computer, laptop, printer etc. to create a network are called networking device. for example Modem, Hub, Switch, Router etc

1. Modem : Modem stands for ‘MOdulator DEMolulator’. It refers to a device used for conversion between analog signals and digital bits. The modem at the sender’s end acts as a modulator that converts the digital data into analog signals. The modem at the receiver’s end acts as a demodulator that converts the analog signals into digital data for the destination node to understand.

2. Ethernet Card : also known as Network Interface Card (NIC card in short) is a network adaptor used to set up a wired network. It acts as an interface between computer and the network. It is a circuit board mounted on the motherboard of a computer. Each NIC has a MAC address, which helps in uniquely identifying the
computer on the network.

3. Repeater : Data are carried in the form of signals over the cable. These signals can travel a specified distance (usually about 100 m). Signals lose their strength beyond this limit and become weak.

A repeater is an analog device that works with signals on the cables to which it is connected. The weakened
signal appearing on the cable is regenerated and put back on the cable by a repeater.

4. Hub : An Ethernet hub is a network device used to connect different devices through wires. Data arriving on any of the lines are sent out on all the others. The limitation of hub is that if data from two devices come at the same time, they will collide.

5. Switch : A switch is a networking device that plays a central role in a Local Area Network (LAN). Like a hub, a network switch is used to connect multiple computers or communicating devices. A switch is called an intelligent hub as it sends signals to only selected devices instead of sending to all.

6. Router : A router is a network device that can receive the data, analyse it and transmit it to other networks. A router connects a local area network to the internet. A router can be wired or wireless. A wireless router
can provide Wi-Fi access to smartphones and other devices.

7. Gateway : As the term “Gateway” suggests, it is a key access point that acts as a “gate” between an organisation’s network and the outside world of the Internet. Gateway serves as the entry and exit point of a network, as all data coming in or going out of a network must first pass through the gateway in order to use routing paths.

A gateway can be implemented as software, hardware, or a combination of both. This is because a network gateway is placed at the edge of a network and the firewall is usually integrated with it.

Computer Network Notes Class 12

Computer Network Notes Class 12
Computer Network Notes Class 12

Networking Topologies

The arrangement of computers and other peripherals in a network is called its topology. Common network topologies are mesh, ring, bus, star and tree.

Mesh Topology : In this networking topology, each communicating device is connected with every other device in the network. Such a network can handle large amounts of traffic since multiple nodes can transmit data simultaneously.

Ring Topology : In ring topology, each node is connected to two other devices, one each on either side. The nodes connected with each other thus form a ring. The link in a ring topology is unidirectional. Thus, data can be transmitted in one direction only (clockwise or counterclockwise).

Bus Topology : In bus topology, each communicating device connects to a transmission medium, known as bus. Data sent from a node are passed on to the bus and hence data can be received by any of the nodes connected to the bus.

In this topology, a single backbone wire called bus is shared among the nodes, which makes it cheaper and easy to maintain.

Star Topology : In star topology, each communicating device is connected to a central node, which is a networking device like a hub or a switch. Star topology is considered very effective, efficient and fast as each device is directly connected with the central device.

Disturbance in one device will not affect the rest of the network, any failure in the central networking device may lead to the failure of complete network.

Tree or Hybrid Topology : It is a hierarchical topology, in which there are multiple branches and each branch can have one or more basic topologies like star, ring and bus. Such topologies are usually realised in WANs where multiple LANs are connected.

The Internet

The Internet is the global network of computing devices including desktop, laptop, servers, tablets, mobile
phones, other handheld devices as well as peripheral devices such as printers, scanners, etc. It is being used by everyone in the society as is evident from the increasing use of online tools for education, creativity, entertainment, socialisation and e-commerce.

Applications of Internet

Following are some of the broad areas or services provided through Internet:

  1. The World Wide Web (WWW)
  2. Electronic mail (Email)
  3. Chat
  4. Voice Over Internet Protocol (VoIP)

1. The World Wide Web (WWW) or web in short, is an ocean of information, stored in the form of interlinked web pages and web resources. The resources on the web can be shared or accessed through the Internet.

Sir Tim Berners-Lee — a British computer scientist invented the revolutionary World Wide Web in 1990 by defining three fundamental technologies that lead to creation of web:

A. HTML : — HyperText Markup Language or HTML is a language which is used to design standardised Web
Pages so that the Web contents can be read and understood from any computer across the globe.

B. URI : — Uniform Resource Identifier or URI is a unique identifier to identify a resource located on the web.
URI identifies a resource (hardware or software) either by its location or by its name or by both.

URL is Uniform Resource Locator and provides the location and mechanism (protocol) to access the resource. Examples of URI identifying resources using location (i.e., URL) are:,, etc. URL is sometimes also called a web address.

C. HTTP : — The HyperText Transfer Protocol is a set of rules which is used to retrieve linked web pages
across the web. It’s more secure and advanced version is HTTPS.

2. Electronic Mail (Email) : Email is the short form of electronic mail. It is one of the ways of sending and receiving message(s) using the Internet. An email can be sent anytime to any number of recipients at anywhere. Some of the popular email service providers are Google (gmail), Yahoo (yahoo mail), Microsoft (outlook), etc. An existing file can be sent as an attachment with the email.

3. Chatting or Instant Messaging (IM) over the Internet means communicating to people at different geographic locations in real time through text message(s). It is a forum where multiple people connect to each other, to discuss their common interests. Applications such as WhatsApp, Slack, Skype, Yahoo Messenger, Google Talk, Facebook Messenger, Google Hangout, etc., are examples of instant messengers.

4. Voice over Internet Protocol or VoIP, allows us to have voice call (telephone service) over the Internet. VoIP works on the simple principle of converting the analogue voice signals into digital and then transmitting
them over the broadband line.

There are two major advantages of a VoIP—

  1. These services are either free or very economical, so people use them to save on cost.
  2. VoIP call(s) can be received and made using IP phones from any place having Internet access. Hence, VoIP has increased the portability and functionality of the voice calling system.

The only disadvantage of VoIP is that its call quality is dependent on Internet connection speed. Slow Internet
connection will lead to poor quality voice calls.

Computer Network Notes Class 12

Computer Network Notes Class 12
Computer Network Notes Class 12


A website is a collection of web pages related through hyperlinks, and saved on a web server. A visitor navigates from one page to another by clicking on hyperlinks. To access a website, one has to type the address of the website (URL) in the address bar of a browser, and press enter. The home page of the website will be displayed.

Purpose of a Website

Some of the common purposes for which websites are designed are listed below:

  1. Selling products and delivering services
  2. Posting and finding information on the internet
  3. Communicating with each other
  4. Entertainment purposes
  5. Disseminating contents and software

Web Page

A web page is a document on the WWW that is viewed in a web browser. Basic structure of a web page is created using HTML (HyperText Markup Language) and CSS (Cascaded Style Sheet). A web page is usually a part of a website and may contain information in different forms, such as:

  1. text in the form of paragraphs, lists, tables, etc.
  2. images
  3. audio
  4. video
  5. software application
  6. other interactive contents

Static and Dynamic Web Pages

Static Web PageDynamic Web Page
A static webpage is one whose content does
not change for person to person.
A static webpage is one whose content changes
for person to person.
Static web pages are generally written in HTML.Dynamic web pages can be created using various
languages such as JavaScript, PHP, ASP.NET, Python,
Java, Ruby, etc
They are simple and easy to design. They are complex and difficult to design.
Computer Network Notes Class 12

Web Server

A web server is used to store and deliver the contents of a website to clients such as a browser that request it. A web server can be software or hardware. If the server is not able to locate the page, it sends a page containing the error message (Error 404 – page not found) to the client’s browser.

Hosting of a Website

Web hosting is a service that allows us to put a website or a web page onto the Internet, and make it a part of the World Wide Web. Once a website is created using a hardware server, we need to connect it to the Internet so that users across the globe can access.

Steps to host a website

  1. Select the web hosting service provider that will provide the web server space.
  2. Identify a domain name, which best suits our requirement.
  3. Create logins with appropriate rights and note down IP address to manage web space.
  4. Upload the files in properly organised folders on the allocated space.
  5. Get domain name mapped to the IP address of the web server.

Computer Network Notes Class 12


A browser is a software application that helps us to view the web page(s). Some of the commonly used web
browsers are Google Chrome, Internet Explorer, Mozilla Firefox, Opera, etc. A web browser essentially displays
the HTML documents which may include text, images, audio, video and hyperlinks that help to navigate from
one web page to another.

Browser Setting

Every web browser has got certain settings that define the manner in which the browser will behave.

Let’s learn how to change the browser settings using the open source browser, Mozilla Firefox. Open Mozilla Firefox, and on the top right corner of the browser window, click the Menu button. From the drop down button, select Options. The preferences and Options window will be displayed in the browser.

On the left side, there are multiple Panels like.

General Panel: Some of the options that the panel contains are as follows:
• setting the default browser
• language and appearance of text
• downloading files and applications
• firefox update settings
• browsing and network settings

Home Panel: This panel contains options to set the home page of the browser, browser window and tab settings.

Search Panel: This panel contains options to edit the settings of the search engine used by Firefox.

Privacy and Security Panel: This panel contains options to secure the browser and data. It includes the
• enhanced tracking protection
• forms and passwords
• history and address bar
• cookies and site data

Sync Panel: This panel contains options to set up and manage a Firefox account which is needed to access all
services given by Mozilla.


A plug-in is a complete program or may be a third-party software. For example, Flash and Java are plug-ins. A Flash player is required to play a video in the browser.


An add-on is not a complete program and so is used to add only a particular functionality to the browser. An add-on is also referred to as extension in some browsers. Adding the functionality of a sound and graphics card is an example of an add-on.


A cookie is a text file, containing a string of information, which is transferred by the website to the browser when we browse it. This string of information gets stored in the form of a text file in the browser.

It helps in customising the information that will be displayed, for example the choice of language for
browsing, allowing the user to auto login, remembering the shopping preference, displaying advertisements of
one’s interest, etc.

Computer Network Notes Class 12

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Computer Network Notes Class 12

MCQ of Computer Science Chapter Wise

1. Functions in Python

2. Flow of Control (Loop and Conditional statement)

3. 140+ MCQ on Introduction to Python

4. 120 MCQ on String in Python

5. 100+ MCQ on List in Python

6. 50+ MCQ on Tuple in Python

7. 100+ MCQ on Flow of Control in Python

8. 60+ MCQ on Dictionary in Python

100 Practice Questions on Python Fundamentals

120+ MySQL Practice Questions

90+ Practice Questions on List

50+ Output based Practice Questions

100 Practice Questions on String

70 Practice Questions on Loops

70 Practice Questions on if-else

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

Computer Network Notes Class 12

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