Informatics Practices: Class 12 — Chapter 5: Internet and Web

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

• Network Size: Can vary from small (connecting a few computers in a single room) to large (connecting millions of devices globally).
• Hosts/Nodes: Any device that is part of a network and can receive, create, store, or send data is called a node or host (e.g., server, desktop, laptop, cellular phone, printer, scanner, modem, router).
• Data Transmission: For communication, data in a network is divided into smaller chunks called packets , which are carried over wired media (cables) or wireless media (air).

A LAN connects computers, mobile phones, tablets, printers, and other devices placed at a limited distance.

• Geographical Area: Ranges from a single room, a floor, an office, a school, to a college or university campus (up to 1 km).
• Connectivity Media: Wires, Ethernet cables, fibre optics, or Wi-Fi.
• Data Transfer Rate: High speed, usually varying from 10 Mbps (Ethernet) to 1000 Mbps (Gigabit Ethernet).
• Security: Comparatively secure as only authentic users in the network can access shared resources.

A MAN is an extended form of LAN that covers a larger geographical area like a city or a town.

• Geographical Area: Can extend up to 30–40 km. Often formed by connecting multiple LANs together.
• Data Transfer Rate: Ranges in Mbps, but is considerably less compared to a LAN.
• Examples: Cable TV networks, cable-based broadband internet services.

A WAN connects computers, LANs, and MANs spread across different geographical locations of a country, or across different countries and continents.

• Geographical Area: Global span, connecting devices via wired or wireless media (satellites, fiber-optic undersea cables).
• Examples: Large business, educational, and government networks. The Internet is the largest WAN in existence.

A Modem is a device used for conversion between analog signals and digital bits.

• Modulation: Converts digital data from the sender's computer into analog signals for transmission over communication lines (like telephone lines).
• Demodulation: Converts incoming analog signals back into digital data for the receiver's computer to understand.

An Ethernet Card (or NIC) is a network adaptor used to set up a wired network. It acts as an interface between the computer and the network.

• Physical Form: A circuit board mounted on the motherboard of a computer.
• MAC Address: Each NIC has a unique physical address called a MAC address , which helps in uniquely identifying the computer on the network.
• Speed Support: Supports data transfer rates between 10 Mbps and 1 Gbps.

A Repeater is an analog device that works with signals on the cables to which it is connected.

• Purpose: Signals lose strength beyond a certain distance (usually 100 m). A repeater regenerates the weakened signal and puts it back on the cable to extend the transmission range.

An Ethernet Hub is a network device used to connect multiple devices through wires.

• Working Principle: It is a non-intelligent broadcasting device. Data arriving on any port is sent out to all other ports.
• Limitation: If data from two devices arrive at the same time, they collide, leading to transmission errors.

A Switch is an intelligent networking device that plays a central role in a Local Area Network (LAN).

• Working Principle: When data arrives, the switch extracts the destination address from the packet, looks it up in an internal table, and forwards the packet only to the selected destination device (unicast).
• Advantages: Avoids data collisions, forwards multiple packets simultaneously, filters out noisy or corrupted packets, and requests retransmission.

A Router is an advanced network device that can receive, analyze, and transmit data packets across different networks.

• Working Principle: Connects a local area network to the Internet. It can analyze data packets, decide or alter how they are packaged, and route them to another network of a different type.
• Wired vs Wireless: Wireless routers provide Wi-Fi access to mobile devices while also containing physical ports for wired connections.

A Gateway is a key access point that acts as a "gate" between an organization's private network and the outside world of the Internet.

• Purpose: Serves as the entry and exit point of a network. All data coming in or going out must pass through the gateway to use routing paths.
• Implementation: Can be implemented as software, hardware, or a combination of both. A router is often configured to work as a gateway device.

In a mesh topology , each communicating device is connected directly to every other device in the network.

• Formula for Wires: To build a fully-connected mesh topology of $n$ nodes, it requires $n(n-1)/2$ physical wires.
• Advantages: Highly reliable (no single point of failure), secure (dedicated channels), and handles high traffic.
• Disadvantages: Complex wiring and high cabling cost.

In a ring topology , each node is connected to exactly two other devices, one on either side, forming a closed circular loop.

• Data Flow: Unidirectional (data travels in one direction only, either clockwise or counterclockwise).
• Disadvantage: If a single node or cable breaks, the entire network goes down.

In a bus topology , all communicating devices connect to a single common transmission medium known as the bus (backbone wire).

• Data Flow: Data sent from a node travels along the backbone in both directions and can be received by any node.
• Advantages: Cheap, simple to install, and easy to maintain.
• Disadvantages: Less secure, less reliable (if the backbone cable fails, the entire network fails).

In a star topology , each communicating device is connected directly to a central node (a hub or a switch).

• Advantages: Highly effective, fast, and easy to troubleshoot. Failure of one device does not affect the rest of the network.
• Disadvantages: If the central hub or switch fails, the entire network collapses.

A tree topology is a hierarchical topology where multiple branches exist, and each branch can contain one or more basic topologies like star, ring, or bus.

• Application: Commonly used in Wide Area Networks (WANs) to connect multiple LANs together.

• The World Wide Web (WWW): An ocean of information stored in the form of trillions of interlinked web pages and web resources.
• Electronic Mail (Email): A fast, reliable method of sending and receiving digital messages over the Internet.
• Chat: Real-time \text-based communication (Instant Messaging) between users at different locations.
• Voice Over Internet Protocol (VoIP): Allows voice calls (telephone service) to be transmitted over a computer network rather than traditional telephone lines.

Invented by Sir Tim Berners-Lee in 1990, the WWW relies on three fundamental technologies:

1. HTML (HyperText Markup Language): Used to design standardized web pages so that content can be read and displayed by any web browser.
2. URI (Uniform Resource Identifier): A unique identifier to identify a resource on the web. A URL (Uniform Resource Locator) is a specific type of URI that provides the location and mechanism (protocol) to access the resource.
3. HTTP (HyperText Transfer Protocol): A set of rules used to retrieve linked web pages across the web. Its secure version is HTTPS .

Consider the URL: http://www.ncert.nic.in/textbook/textbook.htm

• Protocol: http (can also be https , ftp , etc.)
• Subdomain: www
• Domain Name: ncert.nic.in
• Path/File: textbook/textbook.htm

A website is a collection of related web pages integrated under a single domain name, sharing a common theme and template. A web page is a document on the WWW viewed in a web browser, created using HTML, CSS, and scripting languages like JavaScript.

A web server is used to store and deliver website contents to client browsers upon request.

• Hardware Web Server: A physical computer that stores web server software and website files (HTML, CSS, JS, images).
• Software Web Server: A specialized program that understands URLs, processes HTTP requests from browsers, and returns HTTP responses.

Web hosting is a service that allows individuals or organizations to post a website or web page onto the Internet.

1. Select a web hosting service provider (to rent server space, bandwidth, and database support).
2. Identify and register a unique domain name through a domain registrar.
3. Upload website files (HTML, CSS, JS, databases) to the allocated server space.
4. Map the domain name to the server's unique IP address using the Domain Name System (DNS) .

A browser is a software application that retrieves and displays web pages from web servers.

• History: Mosaic was the first web browser, developed by the National Centre for Supercomputing Applications (NCSA).
• Common Browsers: Google Chrome, Mozilla Firefox, Microsoft Edge, Apple Safari, Opera.
• Add-ons vs Plug-ins:
  • Plug-in: A complete, third-party program installed on the host computer to add broad capabilities (e.g., Flash Player, Java).
  • Add-on (Extension): A lightweight tool used to add specific, custom functionalities directly to the browser interface (e.g., ad blockers, grammar checkers).
• Cookies: Small \text files stored on the user's computer by the browser to save user preferences, login states, and browsing history.