Networking and Internet Class 11 Notes | IT 802 Unit-2

IT 802 Unit 2 Networking and Internet Class 11 Notes designed as per CBSE suggested syllabus covering all topics in easy language and concisely. This Networking and Internet Class 11 Notes is very useful and specially designed by well experienced IT professional for all those students learning IT 802 Class 11.

Session 1:  Computer Networking

Evolution of Networks and Internet

  • In 1876 Bell came forward with the concept of communication through telephone lines leading to development of Public Switched Telephone Network (PSTN) in 1877.
  • In the late 1950s, all the military communications started using telephone networks setting up dedicated connections between the two parties. This dedicated connection made use of technology called circuit switching.
  • Paul Baran along with Donald Davies and Len Kleinrock came forward with the idea of digital packet switching in which the message to be transmitted is divided into small chunks called packets.
  • The US Department of Defense led to the development of Advanced Research Projects Agency Network (ARPANET) in 1969.
  • Need for communication between various heterogeneous networks led to the development of TCP/IP (Transmission Control Protocol/Internet Protocol) in 1970.
  • Along with several smaller networks, another large network called NSFNET was developed in 1984 by NSF, U.S. National Science Foundation for research and education purposes.
  • When ARPANET and NSFNET were interconnected, the network growth increased tremendously. This wide network is an Internet (network of networks).

Who governs Internet

  • The Internet is a global network that comprises many voluntarily interconnected networks. It operates without a central governing body.
  • The standardization of the core protocols, Internet architecture is managed by an International community Internet Engineering Task Force (IETF).
  • To maintain interoperability, the principal name spaces of the Internet are administered by the Internet Corporation for Assigned Names and Numbers (ICANN). ICANN coordinates the assignment of unique identifiers for use on the Internet, including domain names, Internet Protocol (IP) addresses and many other parameters.

Computer Network

Electronic devices such as computers, printers, Fax machines, Mobiles etc which are interconnected with each other to send or recieve data/message. All these interconnected devices are called as node.

Components of Communication System

  • Sender: The node that is responsible for sending the data.
  • Receiver: The node that is responsible for receiving the data.
  • Message: Message is the information or meaningful data that is being communicated in a structured form.
  • Channel: Channel is the communication medium through which message is transmitted

Types of Communication

The communication taking place in a computer network can be categorized as:

Simplex Communication: In simplex mode, information can be transferred only in one direction. This mode is termed unidirectional. In computer networks, the data transmitted using many fiber optics and satellites is simplex in nature.

Half Duplex Communication: Half-duplex mode is a bidirectional communication between the two nodes, however, only one node at a time can transmit the data. This mode is generally used for transferring files between nodes in a low-bandwidth setting.

Full Duplex Communication: In full-duplex mode, both communicating parties can send and receive at the same time. The interactive applications use this mode of communication, thus speeding up the data transfer.

Transmission Medium

A transmission medium refers to the channel of transmission through which data can be transmitted from one node to another in the form of signal.
A transmission medium can be classified in two categories:

Guided Medium: There is a physical link made of wire/cable through which data is transmitted in form of signal between the nodes. These are physical conductors such as twisted pairs, coaxial cable, and fiber optics. In twisted pair and coaxial cable, the signal travels as voltage and current signal whereas in optical fiber, the signal is in the form of light.

Unguided Medium: In unguided medium, data is transmitted in air in form of electro-magnetic waves that do not require a physical conductor. They are also known as wireless media. Examples of unguided medium include microwave, radio wave, and infrared.

Network Devices


With increase in distance, a signal may become weak and distorted. A repeater is used to restore the input signal to its original form, so that it can travel a larger distance. Thus, it is placed between two cable segments as shown in image given below. It is also known as digital generator which reshapes and amplifies the digital signal.


A hub connects several lines, also called, cable segments. A hub comprises several input/output (I/O) ports, each of which connects to a single cable as shown in image below. Data arriving on an incoming line is output to all lines except the line on which the hub receives the data.


A bridge is a multiport device used for connecting two or more local area networks (LAN), possibly operating at different speeds as shown in image below. Thus, a bridge may be used to produce bigger LAN by combining smaller LANs.


Unlike bridges which connect two or more LAN segments, switches are used to connect individual nodes in the network with each other. Each node within network is connected to a unique port in the switch as shown in image below. On receiving the incoming data frame, it forwards it to only a single line connecting to the destination node. All the nodes connected through switch forms only one LAN.


Routers are used for connecting various networks (LAN or WAN) with each other as shown in image below. A router transmits data from incoming network to another network. Based on the destination address, the router determines to which network the incoming packet should be transmitted


A gateway connects networks based on different protocol technologies to communicate with each other. Data coming from one network operating on one protocol is converted according to the protocol of the outgoing network, and then forwarded. Thus a gateway may be thought of as a router equipped with software for protocol conversion.

Network Types

Personal Area Network (PAN)

It is a network formed by connecting a few personal devices like computers, laptops, mobile phones, smart phones, printers etc., as shown in image below. All these devices lie within an approximate range of 10 meters. A personal area network may be wired or wireless.

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, an office having one or more buildings in the same premise. Local Area networks are private networks and can span a radius of up to 1 Km.

Metropolitan Area Network

MAN stands for Metropolitan Area Network. It may be owned by a single organization or by many individuals or organizations. These networks are used to establish links within a city, and span an area of radius up to 50 Km.

Wide Area Network

WAN stands for Wide Area Network. Typically a WAN spans a segment of about 1000 Km. They are used for long distance communication and are well suited for connecting remote areas. They establish links within a country or continent. A WAN may be owned and managed by several organizations. It connects various local and metropolitan area networks.

Network Topology

Topology refers to geometric arrangement of connected nodes in a computer network. Basically topologies are categorized as:
Broadcast topologies: In this all nodes share the same physical link. Data transmitted from one node is received by all nodes. Popular broadcast topologies are Bus and Ring.
Point to Point topologies: In this every pair of nodes has a dedicated link. Data transmitted from one node is received by the only specified (pointed) node. Popular point to point topologies are star and mesh.

Bus Topology

In bus topology, there is a long cable, called backbone that connects various nodes through a connector called tap as shown in image below. In this, a message sent by one is received by all devices connected to backbone cable. This topology requires less cabling and is easy to install and extend the network laid using it. However, fault detection and isolation is difficult.

Ring Topology

In ring topology, all the devices are attached through a cable in the form of ring as shown in image below. In a ring topology, data travel from one node to the next until they reach their destination. Addition and deletion of devices, and fault detection and isolation is easy. However, the topology suffers from the limitation of single point failure leading to disruption of the entire network. Sending a message from one node to another node may take more time.

Star Topology

In star topology, all the devices are connected to the central controller called hub as shown in image below. Communication between any two devices takes place through the hub responsible for relaying messages. Star network can be easily installed and configured. Also, fault detection and isolation is easy. However, it requires more cabling as compared to bus and ring topology. Also, hub failure will lead to network failure.

Mesh Topology

In mesh topology, every node is connected with every other node in the network as shown in image below Because of dedicated point to point connection between every possible pair of nodes, the topology provides secure data transfer without any traffic problem. it requires a large number of connections to establish the topology. This leads to difficulty in installation as the number of nodes grow as the network grows.

Tree Topology

Tree topology is a hybrid topology using a combination of star and bus topology. Backbone cable in a bus topology acts like the stem of the tree, and star networks (and even individual nodes) are connected to the main backbone cable like the branches of tree as shown in image below. Damage to a segment of a network laid using tree topology will not affect other segments. Installation and configuration is difficult as compared to other topologies. Also, if the backbone cable is damaged, the entire network communication is disrupted.

Identification of computers and users over a network

MAC Address

Each NIC has a universally unique address assigned to it by its manufacturer. This address is known as the MAC (Media Access Control) address of the card. It means that a machine with an NIC can be identified uniquely through its NIC’s MAC address. The MAC address of an NIC is permanent and does not change.
MAC addresses are 12-digit hexadecimal (or 48 bit) numbers. The first half (MM:MM:MM) of a MAC address contains the ID number of the adapter manufacturer. The second half (SS: SS:SS) of a MAC address represents the serial number assigned to the adapter (NIC) by its manufacturer.

IP Address

Every machine in a network has another unique identifying number, called its IP Address. An IP address is a group of four bytes (or 32 bits), each of which can be a number from 0 to 255. A typical IP address looks like this:

On a network, the IP address of a machine, and not the MAC address of its NIC, is used to identify it.

Difference between IP Address and MAC Address

IP AddressMAC Address
It is group of 4 Bytes (or 32 bit) expressed in Decimal NumberIt is 12 digit Hexadecimal (or 48bit) number.
It is assigned by the network administrator or ISPIt is assigned by manufacturer
IP Address may be changedMAC address remains same
it is usually possible to track the tentative location with IP AddressTracking tentative location is not possible with MAC Address

Domain Name

Over the Internet, Its very difficult to remember IP address of the computer one may have to communicate. Therefore, a system has been developed which assigns names to some computers (web servers) and maintains a database of these names and corresponding IP addresses. These names are called Domain Names.

For example:,

Parts of Domain Name

List of Primary (Generic) Domain Name:

·com – commercial business
·edu – Educational institutions
·gov – Government agencies
·mil – Military
·net – Network organizations
·org – Organizations (nonprofit)

Country Specific Domain Names:

.in – India
·au – Australia
·ca – Canada
.ch – China
.nz – New Zealand
.pk – Pakistan
.jp – Japan
.us – United States of America

Domain Name Resolution

It is the process of getting the corresponding IP address from domain name.

Networking and Internet Class 11 Notes


Digital literacy

Digital literacy refers to raising knowledge and awareness about technology such as desktop computers, smartphones, tablets, and other electronic gadgets. It also includes familiarity with software tools and the Internet. This knowledge facilitates people to acquire, analyze, share, create, and deliver information in an efficient and constructive way. Digital literacy also aids people in several arenas such as education, social networking, e-commerce, healthcare, and tourism.

Internet Services

There are several applications of Internet such as e-mail, file transfer, remote login, and World Wide Web (WWW).

Electronic Mail (E-Mail)

  • An email may be a written text and may include multimedia attachment consisting of text, audio, image, or video.
  • Senders of the e-mail may send it to one or more intended recipients.
  • Sending and receiving of mails can take place through web based email application also called webmail application, (such as, Gmail, Windows Live Hotmail, and Yahoo), or a desktop based email applications (such as, Microsoft outlook, Thunderbird).
  • Transferring mail over the Internet is governed by a set of rules known as email protocols such as SMTP (Simple Mail Transfer Protocol) and POP3 (Post Office Protocol).

File Transfer

Transferring files from one machine to another through a TCP based network is done using FTP (File Transfer Protocol). File Transfer Protocol is based on client server architecture. Using FTP, local hosts (clients) can download or upload files to and from remote hosts (server).

Remote Login (TELNET)

TELNET stands for TErminaL NETwork. It is a client server based application that allows the user working on one system to access a remote system. For initiating remote login, the user (client) should specify the address of the remote system, and should authenticate himself/herself using username and password mechanism. On successful login, the client can access the remote system.

World Wide Web (WWW)

World Wide Web popularly called ‘Web’ is a leading information sharing service of the Internet, which  give user access to wide range of documents called web pages that are connected to each other by hyperlink and written in HTML.

  • Content of HTML documents (Web Page) can be any text, graphics, audio or video.
  • Every HTML Document can be accessed by its unique address known as URL.
  • To read HTML Documents Web Browser is used.
  • HTTP is used to transfer documents from Server to Client.

Internet Protocol Suite

  • The Internet Protocol Suite is set of protocols used in the Internet and computer network for data communication. It is popularly known as TCP/IP as it consists of Transmission Control Protocol (TCP) and Internet Protocol (IP).
  • Data communication over the network is accomplished by several sub-tasks such as specifying address of sender and receiver, diving data into smaller packets, taking measures for secure and error free communication.
  • These sub-tasks or functions are performed by different layers of TCP/IP as shown in image below.

Application layer
It is responsible for:

  • Creating Data/message at the sender’s end, analyzing and processing at receiver’s end.
  • Enveloping the message to be sent with the header.
  • Protocols such as HTTP (HyperText Transfer Protocol), POP3 (Post Office Protocol version 3) operate on this layer.

Transport layer

  • Application layer passes the message to the Transport layer which appends the information about the source and destination ports of the processes at two ends.
  • Two end-to-end protocols TCP and UDP are operated on this layer.

Difference between TCP and UDP

Stands for Transmission Control ProtocolStands for User Datagram Protocol
It provides reliable connection for data communicationIt is considered as unreliable connectionless protocol
It is needed when error free data communication important than immediate responseIt is used when immediate response is more important than assured delivery

Internet Layer

  • Transport layer hands over the packets to the Internet layer which adds source and destination machine network address (also termed IP address).
  • In the Internet layer, Internet Protocol (IP) is used.
  • IP defines the format of packets exchanged over the Internet.

Link layer

  • Is also called Host to Internet layer.
  • This layer includes header containing the sender and receiver physical address to the packet received from the Internet layer.

Networking and Internet Class 11 Notes



Malware stands for MALcious softWARE. These are programs developed with an intention to harm system, steal data, denying access to legitimate users of computing resources or cause any other trouble to the user.
Virus, Worms, Trojan horse are some of the Malwares.


  • A virus is a software code created to hamper your system by overwriting or corrupting the system files.
  • A Virus may make several copies of it by inserting its code onto the system programs, files or boot sector of hard drives and thereby may corrupt them.
  • Virus may cause the system to slow down or even stop functioning like boot sector virus, file infector virus, and macro virus.
  • CryptoLocker, MyDoom, Netsky are examples of virus.


  • Worms are also malwares that has tendency to automatically keep on replicating itself on the hard disk and flooding it.
  • Worms can spread to other computers through the network and may crash system and entire network.
  • A worm does not need a host application to insert its code into.
  • Code Red, Nimda, MSBlast are some of the examples of worms.

Trojan Horse

  • Trojan Horse is a code that looks like a authentic software and useful but when installed by tricking user, ends up harming the system.
  • Trojan horse can attach itself with a safe application and when that application is executed, it creates backdoors to give malicious user access to the system to hamper it.


  • Eavesdropping is the act of secretly or stealthily listening to the private conversation or communications of others without their consent.
  • Eavesdropping is done through telephone lines, cellular networks, email, and instant messaging.

Denial of Service

A Denial-of-Service attack (DoS attack) is a cyber attack in which the targeted machine or resource is flooded with traffic, making the machine or resource overloaded and prevents services from being accomplished for genuine users.


  • Phishing refers to the act of fraudulently obtaining a user’s personal and sensitive information through fraud mails, phone calls or messages.
  • Mostly it is done through emails. These emails prompt you to provide information through link or embedded form it contains.

Cyber Crime & Its Types

  • Cyber crime is an illegal or unlawful act in which computers or computer network can be either a tool or target or both.
  • Cyber crime mostly involves identity theft, data theft, bullying, virus attack, hacking, ransomware etc.
    Some of these crimes are mentioned below:

Cyber bullying

  • Harassing or threatening someone using Internet and electronic devices such as computer, mobile, laptop etc.
  • Mostly it is done on Social Media sites.
  • It includes sending negative, mean, harmful or hate content about someone else.

Cyber stalking

Use of electronic communication by a person to follow a person or attempts to contact a person to foster personal interaction repeatedly despite a clear indication of disinterest by such person.

Identity theft

Illegally stealing someone’s identifiable information like banking credentials, electronic signature, password or any other unique identification feature and misusing on behalf of victim by hacker.


Sending unsolicited messages usually for marketing like emails, SMS, MMS, Internet Post etc to large no of people to persuade recipients to buy a product.


  • Gaining unauthorized access to the users computer by encrypting data and demanding to pay for decrypting it.
  • Sometimes threatening to publish victim’s sensitive information publically if ransom is not paid.

Network Security Tools and Services

Network layer security

SSL i.e. Secured Socket layers and cryptographic methods might be used to secure TCP/IP (Network layer) protocols.


  • A firewall is used to protect the internal network from malicious traffic come from external network.
  • Firewall can be implemented in form of hardware or software.
  • A router or computer is used as hardware firewall that prevents external malicious data or programs from entering your network.
  • Software firewalls are generally installed on personal computers that prevent malwares to gain unauthorized access.


  • Anti-virus is software that helps in detecting and removing malicious and unwanted programs from your system and keeps protected.
  • It has its own databases containing malware definitions, which it uses to detect malware.
  • This database gets updated automatically on real time basis.

Password managers

  • A password manager is a software application that helps a user in storing and managing his/her different passwords.
  • Password managers usually store passwords in encrypted form and requiring the user to create a master password to access his/her entire password.

Cyber Law

  • Cyber laws are the legal measures made by government to prevent cyber crime and take actions against those involved in such crimes.
  • The Indian Government’s IT Act 2000 amended in 2008 also defines offences and penalties for cyber crime.

Protective Measures while accessing Internet

  • Never click on a suspicious link specified on a web page or send through a mail for which you are not sure about its authenticity.
  • Make sure that passwords you created are strong and keep changing frequently.
  • Never disclose personal information such as personal phone number, account details, passwords, credit and debit card details with anyone.
  • Mark spam to all unsolicited emails you received. You can report phishing issue to the concerned authorities.
  • Always use or open websites having SSL implemented and HTTPS.
  • Be selective in social media platform. And never respond to strangers.
  • Use updated antivirus and firewall, secure browsing, and password management techniques.
  • Delete cookies periodically. A cookie is a small piece of information about the client browsing a website.
  • If someone is harassing or threatening you, take screenshot of it as a proof, and block that person. Also inform to parents and concerned authorities.

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