Networking and Internet Notes – Class 11 IT(802) | Quick Revision

Class 11 IT (802) Networking and Internet quick revision notes designed for fast and effective exam preparation. This concise, exam-focused Network and Internet notes of Class 11 IT covers all important concepts including basics of computer networking, internet services and terminologies, Cyber Crime, Cyber Safety, and key terms in a simple and easy-to-understand format. Perfect for last-minute revision, it helps students quickly recall concepts, strengthen understanding, and improve performance in exams with minimal effort and maximum clarity.

Evolution of Networks and Internet

• In 1876, Alexander Graham Bell introduced communication through telephone lines, which led to the development of Public Switched Telephone Network (PSTN) in 1877.
• During the late 1950s, military communications used telephone networks with circuit switching, where a dedicated path was established between two users.
• Later, packet switching was introduced by Paul Baran, Donald Davies, and Len Kleinrock. In this method, data is divided into small packets and sent separately, making communication faster and more efficient.
• In 1969, the US Department of Defense developed ARPANET, the first major computer network.
• In 1970, TCP/IP protocol was developed to enable communication between different networks.
• In 1984, NSFNET was introduced for research and education purposes.
• The interconnection of multiple networks like ARPANET and NSFNET resulted in the formation of the Internet, which is known as a “network of networks.”

Who Governs the Internet

• Internet is a decentralized system, which means there is no single central authority controlling the entire Internet.
• The Internet Engineering Task Force (IETF) is responsible for developing and standardizing core Internet protocols such as IPv4 and IPv6.
• The Internet Corporation for Assigned Names and Numbers (ICANN) manage important Internet resources like:
  • Domain names (e.g., google.com)
  • IP addresses
  • Other unique identifiers
• Internet Service Providers (ISPs) are organizations (government or private) that provide Internet connectivity to users.

Computer Network

• A computer network is a group of interconnected electronic devices such as computers, printers, mobiles, etc., which communicate with each other.
• Each connected device is called a node.
• Networks enable resource sharing, communication, and data exchange.

Components of Communication System

• Sender → The device that sends the data.
• Receiver → The device that receives the data.
• Message → The information being transmitted.
• Channel → The medium through which the data travels (wired or wireless).

Types of Communication

• Simplex Communication → Data flows only in one direction (e.g., TV broadcasting).
• Half Duplex Communication → Data flows in both directions, but only one at a time (e.g., walkie-talkie).
• Full Duplex Communication → Data flows in both directions simultaneously (e.g., phone calls).

Transmission Media

• A transmission medium is the path through which data travels from sender to receiver.
• Guided Media (Wired)
  • Uses physical cables like twisted pair, coaxial cable, and optical fiber
  • Signals travel in the form of electrical or light signals
• Unguided Media (Wireless)
  • Uses electromagnetic waves
  • Examples include radio waves, microwaves, and infrared

Network Devices

Repeater

• A repeater is used when a signal becomes weak or distorted over long distances.
• It regenerates (reshapes and amplifies) the signal to its original form.

Hub

• A hub is a device used to connect multiple devices (cable segments) in a network.
• It contains several input/output (I/O) ports, each connected to a device.
• When data is received on one port, it is broadcast to all other ports.

Bridge

• A bridge is used to connect two or more LANs, even if they operate at different speeds.
• It helps in expanding a network by combining smaller LANs into a larger one.

Switch

• A switch is used to connect individual devices (nodes) within a network.
• Each device is connected to a separate port in the switch.
• It forwards data only to the intended destination device, not to all devices.

Router

• A router is used to connect different networks such as LANs and WANs.
• It transfers data packets from one network to another.
• It uses a routing table to determine the best path for data transmission.

Gateway

• A gateway is used to connect networks that use different protocols.
• This allows communication between completely different types of networks.

Network Types

• On the basis of geographical area covered, computer networks are classified into different types.
• The main types of networks are PAN, LAN, MAN, and WAN.
• Each type differs in terms of coverage area, speed, and purpose.

Personal Area Network (PAN)

• PAN stands for Personal Area Network.
• It is a small network used for communication among devices located close to one person.
• PAN is commonly used to connect personal devices for everyday use.
• Covers a small range of approximately 10 meters
• Suitable for connecting personal devices like Bluetooth headphones, smartwatch, etc.

Examples of devices used in PAN:

• Personal computers
• Mobile phones
• Printers
• Scanners
• Telephones
• PDAs
• Video game consoles

Local Area Network (LAN)

• LAN stands for Local Area Network.
• It connects devices within a limited geographical area, such as a room, office, school, building, or campus.
• LANs are generally private networks owned by a single organization.
• Covers an area of up to 1 kilometer
• High speed network ranging from 10 Mbps to 1 Gbps
• Used for resource sharing like printers, files, and internet connection

Example of LAN

• School computer lab
• Office network

Metropolitan Area Network (MAN)

• MAN stands for Metropolitan Area Network.
• It connects multiple LANs within a city or large town.
• MAN may be managed by a single organization or multiple organizations.
• Covers an area up to approximately 50 kilometers
• Used for connecting offices, branches, or institutions within a city
• Helps in sharing resources among multiple LANs

Example of MAN:

• Cable TV network in a city
• University campuses across a city

Wide Area Network (WAN)

• WAN stands for Wide Area Network.
• It connects networks over a very large geographical area, such as countries or continents.
• WAN is mainly used for long-distance communication.
• Covers an area of around 1000 kilometers or more
• Connects multiple LANs and MANs
• Managed by multiple organizations

Example:

• Banking network across India
• The Internet (largest WAN)

Network Topology

• Network topology refers to the arrangement or layout of nodes (devices) in a computer network.
• It defines how devices are connected and how data flows between them.

Types of Topology (Based on Communication)

Broadcast Topology

• All nodes share a common communication channel (single link).
• When one device sends data, all devices receive it.
• There is a possibility of collision if multiple devices transmit at the same time.
• Special collision handling mechanisms are used.
• Examples: Bus Topology, Ring Topology

Point-to-Point Topology

• Every pair of devices has a dedicated communication link.
• Data is sent directly between two devices.
• Provides better security and performance.
• Examples: Star Topology, Mesh Topology

Types of Network Topologies

Bus Topology

• All devices are connected to a single main cable called the backbone using connectors called taps.
• When a device sends data, it is received by all devices on the network.

Advantages:

• Requires less cabling
• Easy to install and extend

Disadvantages:

• Difficult to detect and fix faults
• Failure of backbone cable can stop entire network

Ring Topology

• All devices are connected in a circular (ring) structure.
• Data travels in one direction, passing through each node until it reaches the destination.

Advantages:

• Easy fault detection and isolation
• Organized data flow

Disadvantages:

• Single point failure can disrupt entire network
• Data transmission may be slower due to multiple hops

Star Topology

• All devices are connected to a central device called a hub or switch.
• Communication between devices happens through the central hub.

Advantages:

• Easy to install, manage, and troubleshoot
• Failure of one device does not affect others

Disadvantages:

• Requires more cabling
• Failure of central hub leads to complete network failure

Mesh Topology

• Each device is connected to every other device in the network.
• Uses dedicated point-to-point connections.

Advantages:

• Highly secure and reliable
• No traffic or collision issues

Disadvantages:

• Requires large number of connections
• Complex and costly to install and maintain

Tree Topology

• A hybrid topology combining bus and star topology.
• The main backbone acts like the trunk of a tree, and star networks act like branches.

Advantages:

• Failure in one segment does not affect other segments
• Suitable for large networks

Disadvantages:

• Complex installation and configuration
• Failure of backbone cable affects entire network

Identification of Computers and Users over a Network

• In a network, multiple devices (nodes) communicate with each other.
• For proper communication, each device must have a unique identity.
• This identification is mainly done using:
  • MAC Address
  • IP Address
  • Domain Name

MAC Address (Media Access Control Address)

• Every device connected to a network has a Network Interface Card (NIC).
• Each NIC is assigned a unique MAC address by the manufacturer.
• It is used to uniquely identify a device at the hardware level.
• It is Permanent and does not change
• It is 48-bit (12-digit hexadecimal) number
• Written in formats like:
  • MM:MM:MM:SS:SS:SS OR MM-MM-MM-SS-SS-SS
  • First half (MM:MM:MM) → Manufacturer ID & Second half (SS:SS:SS) → Unique serial number

IP Address (Internet Protocol Address)

• Every device on a network is assigned an IP address for communication.
• It is used to identify and locate a device on a network.

• 32-bit (IPv4) address
• Written in dotted decimal format (e.g., 59.177.134.72)
• Each part ranges from 0 to 255

Domain Name

• IP addresses are difficult to remember, so domain names are used.
• A domain name is a human-readable name assigned to a server.
• It is used in URLs to identify websites.
• Example: www.cbse.nic.in

Structure of Domain Name:

• Top Level Domain (TLD) → .in, .com, .org
• Subdomain(s) → nic, cbse

Types of Domain Names:

1. Generic Domains

• .com → Commercial
• .edu → Educational institutions
• .gov → Government
• .mil → Military
• .net → Network organizations
• .org → Non-profit organizations

2. Country-Specific Domains

• .in → India
• .us → USA
• .jp → Japan
• .au → Australia
• .ca → Canada

Domain Name Resolution

• Domain Name Resolution is the process of converting a domain name into its IP address.

Steps:

• User enters a URL in the browser
• Browser checks if IP is already stored (cache)
• If not found, request is sent to DNS (Domain Name Server)
• DNS returns the corresponding IP address
• Browser connects to the server using that IP
• Website is displayed to the user

Internet and Its Terminology

• The Internet plays a major role in learning, communication, and digital development.
• It helps people gain knowledge and improve digital literacy, making them capable of using modern technology effectively.

Digital Literacy

• Digital literacy refers to having knowledge and awareness of digital technologies such as computers, smartphones, tablets, and other electronic devices.
• It also includes the ability to use software tools and the Internet efficiently.
• Supports various fields like: Education, Social networking, E-commerce, Healthcare, Tourism
• Provides access to online courses (MOOCs) without limitations of time and place

Internet Services

Electronic Mail (E-Mail)

• Email is used to send and receive messages electronically.
• Messages can include text, images, audio, video, and attachments.
• Emails can be sent to one or multiple recipients.

Types of Email Applications:

• Web-based → Gmail, Yahoo Mail
• Desktop-based → Microsoft Outlook, Thunderbird

Protocols Used:

• SMTP (Simple Mail Transfer Protocol) → sending emails
• POP3 (Post Office Protocol) → receiving/downloading emails

File Transfer (FTP)

• FTP (File Transfer Protocol) is used to transfer files between computers over a network.
• Works on client-server architecture
• Allows users to upload and download files

Remote Login (TELNET)

• TELNET stands for Terminal Network
• It allows a user to access and control a remote computer
• Requires IP address + username + password

World Wide Web (WWW)

• The World Wide Web (WWW) is a collection of web pages stored on servers across the Internet.
• Web pages may contain text, images, audio, videos, and hyperlinks.
• Uses HTTP (HyperText Transfer Protocol)

Internet Protocol Suite (TCP/IP Model)

• The Internet Protocol Suite is a set of rules used for communication over networks.
• Commonly known as TCP/IP, based on:
  • TCP (Transmission Control Protocol)
  • IP (Internet Protocol)

Layers of TCP/IP Model

Application Layer

• Responsible for creating and processing data/messages
• Adds necessary headers to the message
• Protocols:
  • HTTP → web communication
  • POP3 → email retrieval

Transport Layer

• Responsible for end-to-end communication
• Divides data into smaller units called segments
• Adds port numbers and ensures proper sequence and reassembly of data
• Protocols:
• TCP → Reliable, error-free delivery
• UDP → Fast but less reliable

Internet Layer

• Adds IP address of sender and receiver
• Responsible for routing data packets
• Protocol:
  • IP (Internet Protocol)

Link Layer (Host-to-Internet Layer)

• Responsible for physical transmission of data
• Adds MAC (physical) addresses to packets

Cyber Threats and Cyber Security

Malware

• Malware (Malicious Software) refers to harmful programs designed to:
  • Damage a system
  • Disrupt normal functioning
  • Gain unauthorized access
  • Deny access to legitimate users
• Common types of malware include Virus, Worm, and Trojan Horse.

Virus

• A virus is a malicious program that infects files and system areas.
• It can replicate itself and spread by attaching to programs or files.
• It Effects:
  • Corrupts or deletes files
  • Slows down system performance
  • May stop system functioning

Types of Virus:

• Boot sector virus
• File infector virus
• Macro virus

Worm

• A worm is a self-replicating malware that spreads through networks.
• It does not require a host program to function.

• Effects:
  • Creates multiple copies of itself
  • Consumes system memory and bandwidth
  • May crash the system or entire network
• Example: Code Red Worm (spread rapidly within hours)

Trojan Horse

• A Trojan Horse is a malicious program disguised as a useful or legitimate software.

• Gets installed along with genuine applications (e.g., games)
• Creates a backdoor for hackers
• Effects:
  • Allows hackers to monitor activities
  • Can steal or damage data
  • Gives unauthorized control over the system

Eavesdropping

• Eavesdropping is the act of secretly listening to private communications without permission.
• It can occur through phone calls, emails, messaging apps, or networks.
• Leads to loss of privacy and confidential information.

Denial of Service (DoS Attack)

• A denial-of-service attack (DoS attack) is a cyber-attack in which a machine or network resource becomes unavailable to its users by temporarily or indefinitely disrupting its services.
• It is usually carried out by flooding the targeted system or resource with a large number of unnecessary requests.
• This overload prevents the system from processing legitimate requests, making it inaccessible to genuine users.
• A DoS attack can be understood as a situation where a group of people crowd the entrance of a shop, making it difficult for actual customers to enter.

Phishing

• Phishing refers to the act of stealing a user’s personal information through fraudulent emails.
• These emails either contain embedded forms that ask for personal details or include links to web pages that prompt the user to provide such information.
• The information targeted in phishing may include bank account numbers, debit/credit card details, passwords, or any other valuable data.

Cyber Crime

• Cybercrimes are crimes related to the misuse of computers or the Internet such as theft, fraud, and forgery.
• According to the IT Act, cybercrime is an unlawful act in which the computer is used as a tool, a target, or both.

Types of Cyber Crimes:

• Cyber bullying refers to harassment or bullying carried out using electronic devices like computers, mobile phones, or laptops.
• Cyber stalking involves using electronic communication to repeatedly follow or contact a person despite clear disinterest.
• Online job fraud is an attempt to cheat people seeking jobs by offering false promises of better employment and higher salaries.
• Vishing is the act of obtaining personal information such as customer ID, banking passwords, ATM PIN, OTP, or card details through phone calls.
• SMSing involves sending fraudulent text messages to trick users into calling fake numbers, visiting fake websites, or downloading malicious content.
• SIM swap scam refers to obtaining a duplicate SIM card for a registered mobile number to gain unauthorized access.
• Credit or debit card fraud is the unauthorized use of someone else’s card details for transactions or withdrawing money.
• Identity theft is the dishonest use of another person’s electronic signature, password, or unique identification details.
• Spamming involves sending unwanted emails or messages to promote products, services, or websites.
• Ransomware is a type of attack in which the victim is asked to pay money to regain access to their locked or encrypted device.

Network Security Tools and Services

• With the increasing use of the Internet for sharing resources and accessing data, more users are using it for both good and harmful purposes, making security a major concern.
• Every user must be aware of security risks and take proper protective measures while using the Internet.

Network Layer Security

• Network layer security ensures protection of communication over networks using secure protocols.
• TCP/IP protocols can be secured using cryptographic methods and security protocols such as Secure Sockets Layer (SSL).

Firewalls

• A firewall is used to protect an internal network from malicious traffic coming from external networks.
• It can be implemented using a router or a dedicated computer placed between internal and external networks.
• A firewall monitors and filters network traffic, allowing only authorized data to pass through.
• Hardware firewalls (like routers) prevent external threats, while software firewalls protect individual systems.
• Firewalls may also encrypt data to enhance security.

Antivirus

• Antivirus is software designed to protect a system from malicious and unwanted programs.
• It detects harmful programs by scanning files and comparing them with a database of known malware.
• This database is regularly updated to identify new threats.
• Once detected, harmful programs are removed or disabled to protect the system.

Password Managers

• A password manager is a software tool used to store and manage passwords securely.
• It stores passwords in encrypted form, ensuring data safety.
• Users need to remember only one strong master password to access all stored credentials.

Cyber Law

• Cyber laws are rules and regulations for the proper and secure use of electronic resources and the Internet.
• They help prevent cybercrimes and define punishments for offenders.
• The Information Technology Act, 2000 and its amendment in 2008 deal with cyber security and cybercrime issues.
• Cyber police are responsible for handling cybercrime cases and taking necessary legal action.

Protective Measures while accessing Internet

• Never click on suspicious links on web pages or links received through emails if you are not sure about their authenticity, as they may lead to harmful or fake websites.
• Passwords should always be strong and changed regularly because they are used to authenticate users and provide access to systems; weak passwords can be easily cracked.
• Avoid using obvious passwords such as names, mobile numbers, or date of birth, and instead use long passwords with a combination of numbers, symbols, and characters.
• Never share personal information like date of birth, home address, phone number, bank details, passwords, or credit/debit card details with unknown sources.
• Report phishing attempts to concerned authorities or on cybercrime portals, and mark suspicious emails as spam to avoid further risk.
• Always ensure that communication over the Internet is secure by checking for HTTPS in the website URL and a padlock symbol in the address bar, which indicates a secure connection using SSL certificate.
• Make sure your web browser is updated regularly, as updates include important security patches that protect against vulnerabilities.
• Be careful while interacting on social networking sites; do not accept requests from unknown users and trust messages only if you are sure about the sender.
• Avoid posting offensive or inappropriate content online, as it may lead to legal consequences.
• Do not spread rumors or unverified information online, as it can be considered a cybercrime.
• If someone harasses or threatens you online, take a screenshot as proof, block the person, and report the incident to the platform administrator.
• Use updated antivirus software, firewalls, and secure browsing practices to protect your system from threats.
• Always check the website address carefully, as fake websites may look similar to real ones and are often used for phishing.
• Delete cookies regularly, as they store user information and can be misused by hackers to gain unauthorized access; also clear temporary files during browsing.