Unit 4: Computer Networks PDF

**Unit 4** **Syllabus:** Concept of Internet; Applications of Internet; Internet Service Provider; Basics of Internet connectivity related troubleshooting. World Wide Web, Search Engines; Understanding URL, Domain name. Basics of electronic mail. **Network:** A group of two or more similar things...

**Unit 4** **Syllabus:** Concept of Internet; Applications of Internet; Internet Service Provider; Basics of Internet connectivity related troubleshooting. World Wide Web, Search Engines; Understanding URL, Domain name. Basics of electronic mail. **Network:** A group of two or more similar things or people interconnected with each other is called network. Some of the examples of network in our everyday life include: - Social Network - Mobile network - Network of computers - Airlines, railway, banks, hospitals networks. **Computer network:** A computer network is an interconnection among two or more computers or computing devices. Such interconnection allows computers to share data and resources among each other. A basic network may connect a few computers placed in a room.  The network size may vary from small to large depending on the number of computers it connects. A computer network can include different types of **hosts (also called nodes)** like **server, desktop, laptop, cellular phones.** - Apart from computers, networks include **networking devices like switch, router, modem, etc**. Networking devices are used to connect multiple computers in different settings. - For communication, **data in a network is divided into smaller chunks called packets.** These packets are then carried over a network. - Devices in a network can be connected either through wired media like cables or wireless media like air. - 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.** - In the context of data communication, **a node can be a device such as a modem, hub, bridge, switch, router, digital telephone handset, a printer, a computer or a server**. - Interconnectivity of computing devices in a network allows us to exchange information simultaneously with many parties through email, websites, audio/video calls, etc. Network allows sharing of resources. - For example, a printer can be made available to multiple computers through a network; a networked storage can be accessed by multiple computers. People often connect their devices through hotspot, thus forming a small personal network. **Types of Networks** There are various types of computer networks ranging from network of handheld devices (like mobile phones or tablets) connected through Wi-Fi or Bluetooth within a single room to the millions of computers spread across the globe. Some are connected wireless while others are connected through wires. Based on the geographical area covered and data transfer rate, computer networks are broadly categorised as: LAN (Local Area Network) MAN (Metropolitan Area Network) 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, an office having one or more buildings in the same premise, laboratory, a school, college, or university campus.** - The connectivity is done by means of wires, Ethernet cables, fibre optics, or Wi-Fi. - LAN is comparatively secure as only authentic users in the network can access other computers or shared resources. - Users can print documents using a connected printer, upload or download documents and software to and from the local server. Such LANs provide the short range communication with the high speed data transfer rates. - These types of networks **can be extended up to 1 km. Data transfer in LAN is quite high, and usually varies from 10 Mbps (called Ethernet) to 1000 Mbps (called Gigabit Ethernet)**, where Mbps stands for Megabits per second. - Ethernet is a set of rules that decides how computers and other devices connect with each other through cables in a local area network or LAN. **Metropolitan Area Network (MAN):** - Metropolitan Area Network (MAN) **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 kind of network can be extended up to 30--40 km. Sometimes, many LANs are connected together to form MAN.  **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. Large business, educational and government organisations connect their different branches in different locations across the world through WAN. - **The Internet is the largest WAN that connects billions of computers, smartphones and millions of LANs from different continents.** **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 as shown in Figure. - Such a network can handle large amounts of traffic since multiple nodes can transmit data simultaneously. - Also, such networks are more reliable in the sense that even if a node gets down, it does not cause any break in the transmission of data between other nodes. - This topology is also more secure as compared to other topologies because each cable between two nodes carries different data. - However, wiring is complex and cabling cost is high in creating such networks, and there are many redundant or unutilised connections.  **Ring Topology** In ring topology, each node is connected to two other devices, one each on either side, as shown in Figure. 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 counter clockwise). **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 are transmitted to the length of the bus in both directions. That means 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. Both ring and bus topologies are considered to be less secure and less reliable.  **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, as shown in Figure. - Star topology is considered very effective, efficient and fast as each device is directly connected with the central device. - Although 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. - The central node can be either a broadcasting device means data will be transmitted to all the nodes in the network, or a unicast device means the node can identify the destination and forward data to that node only. **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. - Those LANs may be in the form of ring, bus or star. In Figure, a hybrid topology is shown connecting 4 star topologies in bus. In this type of network, data transmitted from source first reaches the centralised device and from there the data passes through every branch where each branch can have link for more nodes. **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. - In addition, it also consists of networking devices such as routers, switches, gateways, etc. - Today, smart electronic appliances like TV, AC, refrigerator, fan, light, etc., can also communicate through the Internet. The list of such smart devices are always increasing e.g., drones, vehicles, door lock, security camera, etc. - The Internet is evolving everyday. - Computers are either connected to a modem through a cable or wirelessly (Wi-Fi). A modem, be it wired or wireless, is connected to a local Internet Service Provider (ISP) who then connects to a national network. Many such ISPs connect together forming a regional network and regional networks connect together forming a national network, and such country-wise networks form the Internet backbone. - The Internet today is a widespread network, and its influence is no longer limited to the technical fields of computer communications. 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:** - The World Wide Web (WWW) - Electronic mail (Email) - Chat - Voice Over Internet Protocol (VoIP) **The World Wide Web (WWW):** - The World Wide Web (WWW) or web in short, is an ocean of information, stored in the form of trillions of interlinked web pages and web resources. - The resources on the web can be shared or accessed through the Internet. - Earlier, to access files residing in different computers, one had to login individually to each computer through the Internet. Besides, files in different computers were sometimes in different formats, and it was difficult to understand each other's files and documents. - 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: - 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. It uses tags to define the way page content should be displayed by the web browser. Basic structure of every webpage is designed using HTML. - 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: https://www.mhrd.gov. in, http://www.ncert.nic.in, http://www.airindia. in, etc. - URL is sometimes also called a web address. However, it is not only the domain name, but contains other information that completes a web address, as depicted below: - In the above URL, http is the protocol name, it can be https, http, FTP, Telnet, etc. www is a subdomain. ncert.nic.in is the domain name. Note: These days it is not mandatory to mention protocol and subdomain while entering a URL. The browser automatically prefixes it. - 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. Many people confuse the web with the Internet. The Internet as we know is the huge global network of interconnected computers, which may or may not have any file or webpage to share with the world. The web on the other hand is the interlinking of a collection of WebPages on these computers which are accessible over the Internet. WWW today gives users access to a vast collection of information created and shared by people across the world. It is today the most popular information retrieval system. **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. The message can be either text entered directly onto the email application or an attached file (text, image audio, video, etc.) stored on a secondary storage. - An existing file can be sent as an attachment with the email, so no need to type it again. - To use email service, one needs to register with an email service provider by creating a mail account. These services may be free or paid. - Some of the popular email service providers are Google (gmail), Yahoo (yahoo mail), Microsoft (outlook), etc. However, many organisations nowadays get customised business email addresses for their staff using their own domain name. - For example, username\@companyname.com. Following are some of the common facilities available for an email user: 1\. Creating an email, attaching files with an email, saving an email as draft for mailing later. Creating email is also termed as composing. 2\. Sending and receiving mail. Same email can be sent to multiple email addresses, simultaneously. 3\. Sending the copy of mail, as carbon copy (cc) or blind carbon copy (bcc). 4\. Forwarding a received email to other user(s) 5\. Filtering spam emails 6\. Organising email in folders and sub folders 7\. Creating and managing email ids of the people you know. 8\. Setting signature/footer to be inserted automatically at the end of each email 9\. Printing emails using a printer or saving as files. 10\. Searching emails using email address or email subject text **Chat** - 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. Two individuals can also send messages instantly. - The sender types a message and sends it; the receiver immediately receives the message and can read and revert through text message. - All this happens in real time, as if the sender and receiver were sitting in the same place. For a successful chat session, the communicating parties should be online simultaneously, and use the same chat application. With ever increasing internet speed, it is now possible to send image, document, audio, video as well through instant messengers. It means, the communicating parties can talk to each other through an audio call or through a video call. - Moreover, it is also possible to chat through text, audio and video in a group. Thus, we can have group chat or group calls. Applications such as WhatsApp, Slack, Skype, Yahoo Messenger, Google Talk, Facebook Messenger, Google Hangout, etc., are examples of instant messengers. Some of these applications support instant messaging through all the modes --- text, audio and video. **VoIP** - Voice over Internet Protocol or VoIP, allows us to have voice call (telephone service) over the Internet, i.e., the voice transmission over a computer network rather than through the regular telephone network. - It is also known as Internet Telephony or Broadband Telephony. - But to avail the phone service over the Internet, we need to have an Internet connection with reasonably good speed. - 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--- - These services are either free or very economical, so people use them to save on cost. That is why these days even international calls are being made using VoIP. - 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. Incoming phone calls can be automatically routed to the VoIP phone as soon as it is connected to the Internet. - 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. **Website:** - A website in general contains information organised in multiple pages about an organisation. A website can also be created for a particular purpose, theme or to provide a service. - A website (usually referred to as a site in short) 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. Also, all the pages of a website are integrated under one domain name and have a common theme and template. For example, the website of DIT-ERP will have all the pages related to DIT, under one domain name and having a common design theme. 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 We are living in an Internet era where the whole world is connected. A website's purpose is to make the information available to people at large. For example, a company might like to advertise or sell its products, a government organisation may like to publish circulars, float tenders, invite applications or get feedback from various stakeholders. A website is a means that helps to communicate with people in a specific, transparent and user friendly manner. Therefore, while developing a website, the first question to ask is why the website is being created, and what should be its pages so that it serves the required purpose. Basically, a website should be user friendly and provide information to users with minimum efforts. A website should be designed keeping in mind different categories of people that will be visiting the site. Some of the common purposes for which websites are designed are listed below: - Selling products and delivering services - Posting and finding information on the internet - Communicating with each other - Entertainment purposes - Disseminating contents and software **Web Page** - A web page (also referred to as a 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: Additionally, various styling and formatting are applied on a web page to make it attractive and organised. - Further, program codes called scripts are used to define the manner in which the page will behave on different actions. - Scripts make a web page interactive. - JavaScript is the most popular and commonly used scripting language. However, Python and PHP are also used to apply scripting on a web page. - The first page of the website is called a home page. It generally contains information and links to all the related web pages. - Each web page has a unique address that is visible on the address bar. Hence if we want to view a particular web page, its address has to be typed in the address bar of the browser. - The web pages that are linked to form a website share a unique domain name. For example, https://swayam.gov.in/ is a website by the Government of India to deliver online courses for School, College and University students and teachers. It is a collection of multiple web pages that link to different courses related information. **Static and Dynamic Web :** - A web page can be static or dynamic. A static webpage is one whose content always remains static, i.e., does not change for person to person. When a web server receives a request (from browser) for a static web page, it just locates the page on its storage media and sends it to the browser of the client. No additional processing is performed on the page.  Hence, a static web page remains the same for all users until someone changes its code manually. Static web pages are generally written in HTML, JavaScript and/or CSS and have the extension.htm or.html. - On the other hand, a dynamic web page is one in which the content of the web page can be different for different users. - The difference in content may be because of different choices made by the user. - When a request for a dynamic web page is made to the web server, it does not simply retrieve the page and send. Before sending the requested web page, the server may perform some additional processes like getting information from the database, updating date and time, updating weather information, etc. - The content of such pages changes frequently. They are more complex and thus take more time to load than static web pages. - Dynamic web pages can be created using various languages such as JavaScript, PHP, ASP.NET, Python, Java, Ruby, etc. - These are complex to construct and design, as the code to perform the additional operations has to be added. Such server side code allows the server to change its content each time the page is loaded. Further, most dynamic pages are linked to databases so that each time the page is uploaded, the required information from the databases is retrieved to update the web page. Few common examples of dynamic web pages are those web pages displaying the date, time, and weather report or having e-commerce applications. **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. When talking about a web server as computer hardware, it stores web server software and a website\'s contents (HTML pages, images, CSS stylesheets, and JavaScript files). - The server needs to be connected to the Internet so that its contents can be made accessible to others. - When talking about a web server as a software, it is a specialised program that understands URLs or web addresses coming as requests from browsers, and responds to those requests. - The server is assigned a unique domain name so that it can be accessed from anywhere using the domain name. To develop and test a website using a personal computer, we need to first install a web server on that computer. - The web browser from the client computer sends a request (HTTP request) for a page containing the desired data or service. The web server then accepts, interprets, searches and responds (HTTP response) to the request made by the web browser. The requested web page is then displayed in the browser of the client. 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. **Browser** A browser is a software application that helps us to view the web page(s). In other words, it helps us to view the data or information that is retrieved from various web servers on the Internet. 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. The initial web browsers like Mosaic used to support HTML documents containing plain text (static website) only, but nowadays with the advancement of technology, modern web browsers allow us to view interactive and dynamic websites. In addition to this, most modern browsers allow a wide range of visual effects, use encryption for advanced security and also have cookies that can store the browser settings and data. **Search engines** Search engines are programs that allow users to search and retrieve information from the vast amount of content available on the internet. They use algorithms to index and rank web pages based on relevance to a user's query, providing a list of results for users to explore. Popular search engines include Google, Bing, and Yahoo. **How do Search Engines Work?** Since we know "What are Search Engine?" Now let's have a closer look at the elements involved in its working:  How Search Engine Works Search engines are generally work on three parts that are Crawling, Indexing, and Ranking - **[Crawling](https://www.geeksforgeeks.org/how-the-google-search-works-crawling-indexing-ranking-and-serving/):** Search engines have a number of computer programs that are responsible for finding information that is publicly available on the internet. The crawler scans the web and creates a list of all available websites. Then they visit each website and by reading HTML code they try to understand the structure of the page, the type of the content, the meaning of the content, and when it was created or updated. - Why crawling is important? Your first concern when optimizing your website for search engines is to make sure that they can access it correctly. If crawler cannot find your content you won't get any ranking or search engine traffic. - **[Indexing](https://www.geeksforgeeks.org/indexing-in-seo-definition-uses-steps-and-working/):** Information identified by the crawler needs to be organized, Sorted, and Stored so that it can be processed later by the ranking algorithm. Search engines don't store all the information in your index, but they keep things like the Title and description of the page, The type of content, Associated keywords Number of incoming and outgoing links, and a lot of other parameters that are needed by the ranking algorithm. - Why indexing is important? Because if your website is not in their index it will not appear for any searches this also means that if you have any pages indexed you have more chances of appearing in the search results for a related query. - **[Ranking](https://www.geeksforgeeks.org/search-engines-and-page-ranking/):** Ranking is the position by which your website is listed in any Search Engine. There is following three steps in which how ranking works. Components of Search Engine --------------------------- There three components in search engine. **They are web crawler, data base, and search interface:** - - - Usage of Search Engine ---------------------- Search engines have so many usages and some of them are: - - - - - - - References: 1. GeeksforGeeks. (2024, September 16). *The internet and the web*. GeeksforGeeks. https://www.geeksforgeeks.org/the-internet-and-the-web/ 2.