Internet and Web Chapter Notes | Informatics Practices for Class 12 - Humanities/Arts PDF Download

Introduction to Computer Networks

• We live in a connected world where information is produced, exchanged, and traced globally in real time.
• Interconnectivity in the digital world enables almost everyone and everything to be linked through various means.
• A network is a group of two or more similar entities (things or people) interconnected with each other.
• Examples of networks in everyday life include social networks, mobile networks, computer networks, and networks of airlines, railways, banks, and hospitals.
• A computer network is an interconnection among two or more computers or computing devices to share data and resources.
• A basic computer network may connect a few computers in a single room, while larger networks can connect numerous devices.
• Network size varies depending on the number of connected computers or devices.
• Computer networks can include various hosts (nodes) such as servers, desktops, laptops, and cellular phones.
• Networks incorporate networking devices like switches, routers, and modems to facilitate connectivity.
• Data in a network is divided into smaller chunks called packets for communication.
• Devices in a network can be connected via wired media (e.g., cables) or wireless media (e.g., air).
• In a communication network, a node is any device that can receive, create, store, or send data to different network routes.
• Examples of nodes include modems, hubs, bridges, switches, routers, digital telephone handsets, printers, computers, or servers.
• Network interconnectivity allows simultaneous information exchange through email, websites, audio/video calls, etc.
• Networks enable resource sharing, such as making a printer or networked storage accessible to multiple computers.
• Personal networks, like those formed through mobile hotspots, allow users to connect their devices.

Types of Networks

• Computer networks vary from small networks of handheld devices connected via Wi-Fi or Bluetooth to global networks connecting millions of computers.
• Networks can be wired or wireless, depending on the connection medium.
• Based on geographical area covered and data transfer rate, networks are categorized as Local Area Network (LAN), Metropolitan Area Network (MAN), and Wide Area Network (WAN).

Local Area Network (LAN)

• A LAN connects devices like computers, mobile phones, tablets, mice, and printers within a limited distance.
• The geographical area covered by a LAN can include a single room, a floor, an office, a building, a laboratory, a school, a college, or a university campus.
• Connectivity in a LAN is achieved through wires, Ethernet cables, fiber optics, or Wi-Fi.
• LANs are relatively secure, allowing only authenticated users to access other computers or shared resources.
• Users in a LAN can print documents, upload/download documents, and access software from a local server.
• LANs provide short-range communication with high-speed data transfer rates, typically ranging from 10 Mbps (Ethernet) to 1000 Mbps (Gigabit Ethernet).
• LANs can be extended up to 1 km in distance.
• Ethernet is a set of rules governing how devices connect through cables in a LAN.

Metropolitan Area Network (MAN)

• A MAN is an extended form of LAN, covering a larger geographical area such as a city or town.
• Data transfer rates in a MAN are in the Mbps range but are lower compared to LANs.
• Examples of MANs include cable TV networks and cable-based broadband internet services.
• MANs can extend up to 30–40 km.
• A MAN can be formed by connecting multiple LANs together.

Wide Area Network (WAN)

• A WAN connects computers, LANs, and MANs across different geographical locations, such as countries or continents.
• WANs are formed by connecting LANs to other LANs via wired or wireless media.
• Large businesses, educational institutions, and government organizations use WANs to connect branches in different locations worldwide.
• The Internet is the largest WAN, connecting billions of computers, smartphones, and millions of LANs across continents.

Network Devices

• Network devices like modems, hubs, switches, repeaters, routers, and gateways are essential for data communication and network configuration.
• These devices enable connectivity and functionality across different network settings.

Modem

• A modem (Modulator Demodulator) converts between analog signals and digital bits.
• Computers process data in binary (0s and 1s), but data transmission over media requires analog signals.
• At the sender’s end, the modem modulates digital data into analog signals for transmission.
• At the receiver’s end, the modem demodulates analog signals back into digital data.
• Modems are connected to both source and destination nodes to facilitate data transmission.

Ethernet Card

• An Ethernet card, or Network Interface Card (NIC), is a network adapter used to establish a wired network connection.
• It serves as an interface between a computer and the network.
• The NIC is a circuit board mounted on a computer’s motherboard.
• An Ethernet cable connects the computer to the network via the NIC.
• Ethernet cards support data transfer rates from 10 Mbps to 1 Gbps (1000 Mbps).
• Each NIC has a unique MAC address to identify the computer on the network.

Repeater

• A repeater is an analog device that regenerates weakened signals on a cable.
• Signals weaken after traveling a certain distance (approximately 100 meters).
• The repeater receives a weak signal, regenerates it, and retransmits it on the cable.

Hub

• An Ethernet hub is a network device that connects multiple devices through wires.
• Data arriving at the hub is sent out to all connected devices.
• A limitation of hubs is that simultaneous data from multiple devices can cause collisions.

Switch

• A switch is a networking device that plays a central role in a LAN.
• Like a hub, a switch connects multiple computers or devices but filters network traffic.
• When data arrives, the switch extracts the destination address and forwards the packet to the intended device only.
• Switches can forward multiple packets simultaneously and do not forward noisy or corrupted signals.
• If a signal is corrupted, the switch drops it and requests the sender to resend.
• Ethernet switches are commonly used in homes and offices to create LANs or access the Internet.

Router

• A router receives, analyzes, and transmits data to other networks.
• It connects a LAN to the Internet and can handle data across different network types.
• Routers can repackage data (e.g., breaking large packets into smaller ones) for compatibility with other networks.
• Routers can be wired or wireless, with wireless routers providing Wi-Fi access to devices like smartphones.
• Modern home Wi-Fi routers often combine the functions of a router, modem, or switch.
• Routers connect to broadband lines from an Internet Service Provider (ISP) and convert signals to digital data.

Gateway

• A gateway is a key access point between an organization’s network and the external Internet.
• It serves as the entry and exit point for all data entering or leaving the network.
• Gateways route data packets and maintain information about internal and external network paths.
• When a node communicates with a foreign network, the gateway routes the data packet to the destination via the best possible route.
• For home Internet connectivity, the Internet Service Provider (ISP) typically acts as the gateway.
• A router is often configured as a gateway in computer networks.
• Gateways can be implemented as software, hardware, or a combination of both.
• Gateways are typically placed at the network’s edge, often integrated with a firewall.

Networking Topologies

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

Mesh Topology

• In a mesh topology, each device is connected to every other device in the network.
• This topology supports large amounts of traffic as multiple nodes can transmit data simultaneously.
• Mesh networks are reliable; if one node fails, data transmission between other nodes continues unaffected.
• Each cable between nodes carries different data, enhancing security.
• However, mesh topology involves complex wiring, high cabling costs, and many redundant connections.

Ring Topology

• In a ring topology, each node is connected to two other devices, forming a circular network.
• Data transmission is unidirectional, moving either clockwise or counterclockwise.
• Ring topologies are considered less secure and less reliable compared to other topologies.

Bus Topology

• In a bus topology, each device connects to a common transmission medium called a bus.
• Data sent from a node is transmitted along the bus in both directions, accessible to all connected nodes.
• A single backbone wire (bus) is shared among nodes, making it cost-effective and easy to maintain.
• Bus topologies are considered less secure and less reliable compared to other topologies.

Star Topology

• In a star topology, each device is connected to a central node (e.g., a hub or switch) via separate cables.
• The central node can be a broadcasting device (transmitting data to all nodes) or a unicast device (forwarding data to a specific node).

Tree or Hybrid Topology

• A tree topology is hierarchical, with multiple branches, each potentially using star, ring, or bus topologies.
• It is commonly used in WANs where multiple LANs are connected.
• Data from a source reaches the centralized device and is then distributed through branches to other nodes.

The Internet

• The Internet is a global network of computing devices, including desktops, laptops, servers, tablets, mobile phones, and peripherals like printers and scanners.
• It also includes networking devices such as routers, switches, and gateways.
• Smart electronic appliances (e.g., TVs, ACs, refrigerators, fans, lights, drones, vehicles, door locks, security cameras) can connect to the Internet.
• Devices connect to the Internet via modems (wired or wireless), which link to a local ISP, then to national and regional networks, forming the Internet backbone.
• The Internet’s influence extends beyond technical fields, impacting education, creativity, entertainment, socialization, and e-commerce.

Applications of Internet

The World Wide Web (WWW)

• The WWW, or web, is a vast collection of interlinked web pages and resources accessible via the Internet.
• Previously, accessing files on different computers required individual logins, and file formats often varied, causing compatibility issues.
• Sir Tim Berners-Lee invented the WWW in 1990, introducing three fundamental technologies: HTML, URI, and HTTP.
• HTML (HyperText Markup Language) is used to design standardized web pages readable across different computers globally.
• HTML uses tags to define how content is displayed in a web browser.
• URI (Uniform Resource Identifier) uniquely identifies resources on the web by location, name, or both.
• URL (Uniform Resource Locator), a type of URI, specifies the location and protocol (e.g., http, https) to access a resource.
• Examples of URLs include https://www.mhrd.gov.in, http://www.ncert.nic.in, and http://www.airindia.in.
• A URL includes the protocol (e.g., http), subdomain (e.g., www), domain name (e.g., ncert.nic.in), and additional path information.
• Modern browsers automatically prefix the protocol and subdomain if omitted.
• HTTP (HyperText Transfer Protocol) is a set of rules for retrieving linked web pages, with HTTPS being its secure version.
• The web is distinct from the Internet; the Internet is the global network, while the web is the collection of interlinked web pages accessible over it.
• The WWW is the most popular information retrieval system, providing access to a vast array of global information.

Electronic Mail (Email)

• Email (electronic mail) is a method of sending and receiving messages over the Internet.
• Emails can be sent anytime to multiple recipients worldwide.
• Messages can include text typed directly or attached files (text, images, audio, videos) stored on secondary storage.
• To use email, users must register with an email service provider (free or paid) to create an account.
• Popular email providers include Google (Gmail), Yahoo (Yahoo Mail), and Microsoft (Outlook).
• Organizations often use customized business email addresses (e.g., username@companyname.com).
• Email features include composing emails, attaching files, saving drafts, sending/receiving emails, and sending copies (cc or bcc).
• Users can forward emails, filter spam, organize emails in folders, manage contacts, set signatures, print emails, and search emails by address or subject.

Chat

• Chatting, or Instant Messaging (IM), involves real-time text communication over the Internet.
• It enables discussions among individuals or groups across different geographic locations.
• Messages are sent and received instantly, simulating a conversation as if participants were in the same location.
• Both communicating parties must be online and use the same chat application for a successful session.
• With increased Internet speeds, instant messengers support sending images, documents, audio, and video.
• Users can engage in audio calls, video calls, group chats, or group calls.
• Examples of instant messaging applications include WhatsApp, Slack, Skype, Yahoo Messenger, Google Talk, Facebook Messenger, and Google Hangout.
• Some applications support text, audio, and video messaging modes.

VoIP

• Voice over Internet Protocol (VoIP) enables voice calls over the Internet instead of traditional telephone networks.
• It is also known as Internet Telephony or Broadband Telephony.
• VoIP requires a reasonably fast Internet connection.
• It converts analog voice signals into digital data and transmits them over broadband lines.
• VoIP services are often free or economical, making them popular for international calls.
• VoIP calls can be made or received from any location with Internet access, enhancing portability.
• Incoming calls can be automatically routed to a VoIP phone when connected to the Internet.
• The call quality of VoIP depends on Internet connection speed; slow connections result in poor voice quality.

Website

• A website is a collection of interlinked web pages stored on a web server, accessible under a single domain name.
• Websites typically contain information about an organization, a specific purpose, theme, or service.
• Pages within a website are linked through hyperlinks, allowing navigation by clicking on links.
• All pages share a common theme and template design.
• For example, the NCERT website includes pages on textbooks, syllabi, events, and resources under one domain with a consistent design.
• To access a website, users type its URL into a browser’s address bar and press enter to display the home page.

Purpose of a Website

• Websites make information accessible to a global audience in a connected world.
• They serve purposes like advertising/selling products, publishing circulars, floating tenders, inviting applications, or gathering feedback.
• Websites facilitate specific, transparent, and user-friendly communication with people.
• Website development starts with defining its purpose and designing pages to meet that purpose.
• Websites should be user-friendly, providing information with minimal effort for diverse users.
• Common purposes include selling products/services, sharing/finding information, communication, entertainment, and disseminating content/software.

Web Page

• A web page is a document on the WWW viewed in a web browser.
• Its basic structure is created using HTML (HyperText Markup Language) and CSS (Cascaded Style Sheet).
• Web pages may contain text (paragraphs, lists, tables), images, audio, video, software applications, or interactive content.
• Styling and formatting enhance the attractiveness and organization of web pages.
• Scripts (program codes) define interactive behaviors, with JavaScript being the most popular scripting language, alongside Python and PHP.
• The home page, the first page of a website, typically includes information and links to related pages.
• Each web page has a unique address visible in the browser’s address bar.
• Web pages within a website share a common domain name.
• For example, https://swayam.gov.in/ is a website with multiple pages linking to online course information.

Static and Dynamic Web Pages

• Web pages can be static or dynamic based on content behavior.
• A static web page displays the same content for all users and does not change unless manually updated.
• When a browser requests a static page, the web server retrieves and sends it without additional processing.
• Static pages are typically written in HTML, JavaScript, and/or CSS and have .htm or .html extensions.
• A dynamic web page displays different content for different users based on their choices or other factors.
• When a dynamic page is requested, the server processes additional tasks (e.g., retrieving database data, updating date/time, or weather information) before sending the page.
• Dynamic pages are more complex, take longer to load, and often change frequently.
• They are created using languages like JavaScript, PHP, ASP.NET, Python, Java, or Ruby.
• Dynamic pages are often linked to databases to retrieve and update content on each load.
• Examples include pages displaying real-time date, time, weather, or e-commerce applications.

Web Server

• A web server stores and delivers website content (HTML pages, images, CSS, JavaScript files) to clients, such as browsers, upon request.
• It can be hardware (a computer storing web server software and website content) or software (a program handling URL requests).
• Hardware web servers must be Internet-connected to make content accessible.
• Software web servers understand and respond to browser requests using a unique domain name.
• To develop/test a website locally, a web server software must be installed on the computer.
• The browser sends an HTTP request for a page, and the server accepts, interprets, searches, and responds with the requested page or an error (e.g., Error 404 if the page is not found).

Hosting of a Website

• Web hosting is a service that makes a website or web page accessible on the Internet, integrating it into the WWW.
• After creating a website on a local server, it must be connected to the Internet for global access.
• Alternatively, server resources (CPU, RAM, storage) can be rented from a cloud service provider to host the website.
• Hosting involves uploading website files (HTML, CSS, JavaScript, images, databases) from a local computer to the allocated server space.
• Web hosting services, which provide resources like RAM, storage, and bandwidth, are typically paid and can be scaled based on website load.
• A web server (local or cloud) is assigned a unique IP address, which is mapped to a textual domain name for user convenience.
• Domain names must be registered (purchased) through an authorized agency.
• Steps to host a website include selecting a hosting provider, registering a domain name, creating logins, uploading files to organized folders, and mapping the domain to the server’s IP address.
• The Domain Name System (DNS) maps domain names to IP addresses, directing browser requests to the correct server.

Browser

• A browser is a software application that displays web pages by retrieving data from web servers on the Internet.
• Common browsers include Google Chrome, Internet Explorer, Mozilla Firefox, Opera, and Apple Safari.
• Browsers render HTML documents containing text, images, audio, video, and hyperlinks for navigation.
• Early browsers like Mosaic supported only static HTML text, while modern browsers handle interactive and dynamic websites.
• Modern browsers support visual effects, encryption for security, and cookies to store settings and data.

Browser Settings

• Browser settings define how a browser behaves, covering privacy, search engine preferences, download options, auto-signatures, autofill, autocomplete, and themes.
• Settings can be customized in a user-friendly manner.
• In Mozilla Firefox, settings are accessed by clicking the Menu button (top right) and selecting Options.
• The Preferences and Options window includes panels for General, Home, Search, Privacy and Security, and Sync.
• The General panel allows setting the default browser, language, text appearance, download settings, Firefox updates, and browsing/network settings.
• The Home panel configures the home page, browser window, and tab settings.
• The Search panel adjusts search engine settings.
• The Privacy and Security panel includes options for enhanced tracking protection, forms/passwords, history, address bar, cookies, site data, pop-up permissions, and add-on installations.
• The Sync panel manages Firefox account settings for accessing Mozilla services.
• Changes to settings are applied after closing the settings window.

Add-Ons and Plug-ins

• Add-ons and plug-ins are tools that extend and modify browser functionality.
• Plug-ins are complete programs or third-party software (e.g., Flash, Java) installed on the host computer.
• Plug-ins, like Flash Player for video playback, can be used by browsers and other applications for multiple functionalities.
• Add-ons (also called extensions) add specific functionalities to a browser and are not complete programs.
• An example of an add-on is adding sound or graphics card functionality.
• In Mozilla Firefox, add-ons are managed by clicking the Options button, selecting Add-ons, and choosing the Extensions panel.
• The Extensions panel displays enabled, disabled, and recommended extensions for user selection.
• Plug-ins are managed similarly via the Plug-ins panel, where users can enable or disable them.

Cookies

• A cookie is a text file containing information transferred by a website to the browser during browsing.
• Cookies are stored on the browser and retransmitted to the server to recognize the user.
• They track visited pages, user choices, language preferences, auto-login settings, shopping preferences, and advertisement interests.
• Cookies are generally harmless, unable to access hard disk data or transmit viruses/malware.
• However, viruses can be disguised as cookies, posing potential risks.
• Browsers store and manage cookies, and users can disable them via Privacy and Security settings.
• The first cookie software was created in 1994 by Netscape to identify first-time or returning visitors.