Basic : Computer Network & Application of Internet

Computer Network

• A computer network is a set of computers or their devices which are connected by links or communication channels to share & communicate data or their resources.
• For example, when you are going to send any data/information to another person by e-mail, this is done by internet which is basically a computer network.

Types of Computer Network

A computer network can be categorized by their size. There are mainly four types of computer network. LAN, MAN, WAN, PAN

LAN : Local Area Network

• It is a group of computers that connects with each other in a small area such as office, building.
• It is used to connect two or more personal computers through a communication medium such as coaxial cable, twisted pair cable etc.
• It is less costly as it is built with inexpensive hardware such as hubs, network adapters, and ethernet cables.
• The data is transferred at an extremely faster rate in Local Area Network.
• Local Area Network provides higher security.

MAN : Metropolitan Area Network

• It is a group of computer that connects a larger geographic area as compared to LAN such as a whole city or a large campus.
• Government agencies use MAN to connect to the citizens and private industries.
• In MAN, various LANs are connected to each other through a telephone exchange line.
• Cable TV network is another example of MAN.
• It has a higher range than Local Area Network(LAN).

WAN : Wide Area Network

• It is a network that extends over a large geographical area such as states or countries.
• It is quite bigger network than the MAN.
• It is not limited to a single location, but it spans over a large geographical area through a telephone line, fiber optic cable or satellite links.
• The internet is one of the biggest WAN in the world.
• It is widely used in the field of Business, government, and education.

PAN : Personal Area Network

• It is a network that connects electronic devices within a user’s immediate area.
• The size of a PAN ranges from a few centimetres to a few meters.
• The most common examples of this network is the connection between a Bluetooth earphone and a smartphone.
• It can also connect laptops, tablets, printers, keyboards, and other computerized devices.
• It can either be wired or wireless.
• Wired connection methods include USB, etc.; wireless connection methods include Bluetooth, WiFi, etc.

Network Topology

• A network topology defines how devices in a network are arranged to communicate with each other. It is an arrangement of elements/devices in a network. Here we are discussing types of network topology : Bus Topology, Ring Topology, Tree Topology, Star Topology, Mesh Topology, Hybrid Topology

Bus Topology

• In a bus topology, all the devices are arranged on a network along a single cable running in a single direction from one end of the network to the other. That’s why it’s called a “line topology” or “backbone topology.” The configuration of a bus topology is quite simpler as compared to other topology.

Advantages

• It is cost-effective choice for smaller networks because the layout is simple.
• It allows all devices to be connected via a single coaxial or RJ45 cable.
• If needed, more nodes(computers) can be easily added to the network by joining additional cables.

Disadvantages

• Data transmission is only in a single direction (also known as Half Duplex), meaning it can’t be sent in two opposite directions at the same time, so this layout is not the ideal choice for networks with huge amounts of traffic.
• It uses a single cable to transmit data, they’re somewhat vulnerable. If the cable experiences a failure, the whole network goes down, which can be time-consuming and expensive to restore.

Ring Topology

• In the ring network topology, the node(computers)s are connected in a closed-loop configuration. The data can travel through the ring network in either one direction or both directions, with each device having exactly two neighbors. These bidirectional ring networks are more resilient than bus networks since traffic can reach a node by moving in either direction. 

Advantages

• Since each device is only connected to the ones on either side, when data is transmitted, the packets also travel along the circle, moving through each of the intermediate nodes until they arrive at their destination.
• Only one station on the network is permitted to send data at a time, which greatly reduces the risk of packet collisions, making ring topology efficient at transmitting data without errors.

Disadvantages

• Though it is popular, it is still vulnerable to failure without proper network management.
• Since the flow of data transmission moves one direction between nodes along each ring, if one node goes down, it can take the entire network with it. That’s why it is important for each of the nodes to be monitored.
• If the transmission line is broken, then entire network gets down.
• In a ring topology, all the devices on the network share bandwidth, so the addition of more devices can contribute to overall communication delays.
• The entire network must be taken offline to reconfigure, add, or remove nodes.

Tree Topology

• The tree network topology consists of one root node (Center Node), and all other nodes are connected in a hierarchy.

Advantages

• Combining elements of the star and bus topologies allows for the easy addition of nodes and network expansion.
• Troubleshooting errors on the network is also a straightforward process, as each of the branches can be individually assessed for performance issues.

Disadvantages

• If any fault occurs in the node, then it becomes difficult to troubleshoot the problem.
• It is expensive because of the complete amount of cabling required to connect each device to the next within the hierarchical layout.
• A tree topology mainly relies on main bus cable and failure in main bus cable will damage the overall network.  
• If new devices are added, then it becomes difficult to reconfigure.

Star Topology

• Star topology is an arrangement of the network in which every node is connected to the central hub, switch or a central computer. The central computer is known as a server, and the peripheral devices attached to the server are known as clients. Star topology is the most popular topology in network implementation.

Advantages

• Star topology is a familiar technology as its tools are cost-effective.  
• It is easily expandable as new stations can be added to the open ports on the hub.
• Star topology networks are cost-effective as it uses inexpensive coaxial cable.
• It has a high data speed. It supports a bandwidth of approx 100Mbps.

Disadvantages

• If the central hub or switch goes down, then all the connected nodes will not be able to communicate with each other.

Mesh Topology

• It is an arrangement of the network in which computers are interconnected with each other through various redundant connections.
• There are multiple paths from one computer to another computer.
• It does not contain the switch, hub or any central computer which acts as a central point of communication.
• The Internet is an example of the mesh topology.
• Mesh topology is mainly used for WAN implementations where communication failures are a critical concern.
• Mesh topology can be formed by using the formula: Number of cables = (n*(n-1))/2; Where n is the number of nodes that represents the network

Advantages

• The mesh topology networks are very reliable as if any link breakdown will not affect the communication between connected computers.
• Adding new devices would not disrupt the communication between other devices.

Disadvantages

• A mesh topology contains a large number of connected devices such as a router and more transmission media than other topologies.
• Mesh topology networks are very large and very difficult to maintain and manage. If the network is not monitored carefully, then the communication link failure goes undetected.

Hybrid Topology

• The combination of various different topology is known as Hybrid topology.
• It is a connection between different links and nodes to transfer the data.
• When two or more different topology are combined together is termed as Hybrid topology. For example, if there exist a ring topology in one branch of bank A and bus topology in another branch of bank A, connecting these two topology will result in Hybrid topology.

Advantages

• If a fault occurs in any part of the network will not affect the functioning of the rest of the network.
• Size of the network can be easily expanded by adding new devices without affecting the functionality of the existing network.
• This topology is very flexible as it can be designed according to the requirements of the organization.
• Hybrid topology is very effective as it can be designed in such a way that the strength of the network is maximized and weakness of the network is minimized.

Disadvantages

• The design of the Hybrid network is very complex. It is very difficult to design the architecture of the Hybrid network.
• The Hubs used in the Hybrid topology are very expensive as these hubs are different from usual Hubs used in other topologies.

OSI Reference Model

• OSI – Open System Interconnection model is a standard model to describe how data/information from a software application of one device/computer moves through a physical medium to a software application in another device/computer.

• OSI model has seven layers which performs their own functions.
• OSI model was developed by the ISO – International Organization for Standardization in 1984.
• These layers are Application Layer, Presentation Layer, Session Layer, Transport Layer, Network Layer, Data Link Layer, Physical Layer respectively.
• The sequence of the layer must be maintained.
• The data passes through each layer of OSI model – from Application to Physical, where each layer performs its functionality independently.

Let’s start each layer’s function

• Application Layer : It is a User interface or a kind of software application that provides an access to use resources on a network and share their data/information among other devices/computers. For example, if a user wants to send a document via e-mail from his/her computer to other device, then a web browser(chrome, Firefox, internet explorer) which he/she uses to send an e-mail, works as an Application Layer.

• Presentation Layer : This layer ensures that the data is in a usable format which is known as Translation. It performs encryption at sender side to convert confidential data into a format which can not be readable by hackers/crackers and a same way it performs decryption at receiver side to convert data in an original form. It also performs compression to reduce the size of files have a huge size.

• Session Layer : It establishes, manages & terminates the session between the devices of sender & receiver. It creates communication channels, called sessions, between devices. It is responsible for opening sessions, ensuring they remain open and functional while data is being transferred, and closing them when communication ends.

• Transport Layer : It takes data transferred in the session layer and breaks it into segments (process divides in a smaller parts) on the transmitting end. It uses the Transmission Control Protocol(TCP) & User Datagram Protocol(UDP) to carry out its tasks. It is responsible for reassembling the segments on the receiving end, turning it back into data that can be used by the session layer. The transport layer carries out flow control, sending data at a rate that matches the connection speed of the receiving device, and error control, checking if data was received incorrectly and if not, requesting it again.

• Network Layer : It is responsible for moving the packets(small parts of large messages) from source to destination. It breaks up segments into network packets, and reassembling the packets on the receiving end. It routs packets by discovering the best path across a physical network. The network layer uses network addresses (IP address) to route packets to a destination node.

• Data Link Layer : It provides a reliable and efficient communication between two or more devices. It converts packets into frames which transfers error free to destination. It is mainly responsible for the unique identification of each device that resides on a local network. The Data link layer adds the header and trailer to the frame. The header which is added to the frame contains the hardware destination and source address. It also maintains the rate of data at both the sides.

• Physical Layer :  It defines the way how two or more devices can be connected physically. It also defines the way how network devices are arranged. It determines the type of the signal used for transmitting the information. It transmits an individual bit from one node to another node by physical medium.

TCP/IP

• TCP/IP, or Transmission Control Protocol/Internet Protocol, is the foundational suite of communication protocols used for the internet and other networks. It enables devices to communicate with each other and facilitates data exchange across diverse networks.

TCP : Transmission Control Protocol

• TCP is one of the main protocols used in the Internet Protocol Suite. It ensures reliable communication between devices over a network.
• TCP is connection-oriented protocol. That means it establishes a connection before data is sent, ensuring that packets are delivered reliably.
• TCP verifies that data packets are received accurately and in the correct order. If packets are lost or corrupted, it requests retransmission.
• TCP (Transmission Control Protocol) regulates how quickly data is sent to ensure that the device receiving the data can handle it without becoming overloaded.
• By controlling the speed of data transmission, it helps maintain smooth communication and prevents data loss or errors due to the receiving device being unable to process the incoming information quickly enough.

IP: Internet Protocol

• The Internet Protocol (IP) is the method for sending data from one device to another across the internet.
• Every device has an IP address that uniquely identifies it and enables it to communicate with and exchange data with other devices connected to the internet.
• IP determines the best path for data packets to travel from the source to the destination, often through multiple intermediate devices.

ISP – Internet Service Provider

• An Internet Service Provider (ISP) is a company such as Airtel, Vodafone, Jio, BSNL, MTNL and many more that provides Internet access to companies, families, and even an individual. ISPs use fiber-optics, satellite, copper wire, and other forms to provide Internet access to its customers.
• Internet service providers connect your personal or business computer, laptop, mobile device etc to the internet. ISPs may be commercial, non-profit, privately owned or community owned companies.
• Most providers offer the same types of internet services to customers, including:
  • Internet Access
  • E-mail Access
  • Domain Name Registration
  • Web hosting

Intranet

• An intranet is a private network contained within an enterprise/company that is used to securely share company information and computing resources among employees.
• Usually each company or organization has their own Intranet network and members/employees of that company can access the computers in their intranet.
• It can not be used outside or other than the area at which it is provided.

VSAT – Very Small Aperture Terminal

•  VSAT is a small-sized earth station used in the transmit/receive of data, voice and video signals over a satellite communication network.
• A VSAT consists of two parts: a transceiver placed outdoors in direct line of sight to the satellite, and a device that is placed indoors to interface the transceiver with the end user’s communications device, such as PC.
• The transceiver receives or sends a signal to a satellite transponder.
• The satellite sends and receives signals from a ground station computer that acts as a hub for the system.
• Each end user is interconnected with the hub station via the satellite, forming a star topology.
• The hub controls the entire operation of the network.
• For one end user to communicate with another, each transmission must first go to the hub station, which then re transmits it via the satellite to the other end user’s VSAT.

DNS – Domain Name Server

• DNS convert URLs and domain names(www.example.com) into IP addresses that computers can understand and use.
• They translate what a user types into a browser into something the machine can use to find a webpage.
• DNS (Domain Name Server) is mainly used to convert human meaningful name (domain name) to computer meaningful name (IP address) in Internet.
• It allows you to use internet more easily by allowing you to specify a meaningful name on your web browser instead of using IP address.

WWW – World Wide Web

• The World Wide Web commonly known as the Web, is an information system where documents and other web resources are identified by Uniform Resource Locators, which may be interconnected by hyperlinks, and are accessible over the Internet.
• We can also describe it as a collection of websites/web pages stored in web servers and connected to local computers through the internet.
• These websites contain text pages, digital images, audios, videos, etc.
• Users can access the content of these sites from any part of the world over the internet using their devices such as computers, laptops, cell phones, etc.
• With WWW & internet, we can access & display different websites or text/media etc. in our devices.

Search Engine

• A search engine is a software system that is designed to carry out web searches.
• They search the World Wide Web in a systematic way for particular information specified in a textual web search query that user want to know.
• For example, if anyone wants to know the places to visit in Jamnagar, he or she just need to write in Google “Places to visit in Jamnagar” and he/she gets the list of websites, images, videos, maps and many more related to the query. This is the task of search engine.
• There are so many search engine available: Google, Bing, MSN, Alta Vista, AoL, Duck Duck Go, Yahoo!, ASK, Yandex and many more.
• Among all these search engines, Google is known as the Best as It gives the information at its best.

Remote Login

• It refers to any method that controls or access to remote device/computer from host/own computer.
• Software applications that allow remote login/administration are becoming increasingly common as it provides the way to access from that device where we can con available physically.
• For example, TeamViewer. With this software you can access remote computer from your computer at your location & its resources too.
• It is very continent & time saving as well.

E-mail – Electronic Mail

• Electronic Mail, commonly known as E-mail is a method of exchanging data/messages via internet from one device(computer, mobile, etc.) to another device (computer, mobile, etc) using some special application software or normally web based application.
• Like normal mail, E-mail contains main three parts : sender address, receiver address & the message to send.
• This can be a simple text, multimedia (video,audio, photos, etc.).
• A sender can send an e-mail to one or more than one receiver. This is one of the easiest and convenient way to communicate.

E-Commerce

• Electronic Commerce, most commonly known as E-Commerce allows an individual & companies to buy & sell goods & services over the internet.
• E-commerce has focused on some of the major segments: Computers, Tablets, Smart Phones & other smart devices.
• For example, amazon, flipkart, Ajio, Myntra, etc. are some of the major E-Commerce websites that serve not only goods but other services like, book a cab, book tickets of airline, bus or train, online payment of electricity bill, mobile bill, etc.
• Now a days, e-commerce is very popular to buy or sell as it is a convenient for customer to do so.

E-Business

• Electronic Business or E-Business refers to all the business transaction that make online via an internet.
• Electronic business differs from electronic commerce as it does not only deal with online transactions of selling and buying of a product and/or service but also enables to conduct of business processes such as, manufacturing & operations, marketing and sales, customer service etc.
• There are several types of e-business models. In the business-to-consumer (B2C) model, sellers offer products and services directly to consumers online, and the buyer purchases them via the internet.
• Under the business-to-business (B2B) model, companies use the internet to conduct transactions with one another.
• The consumer-to-business (C2B) model defines a type of e-business where consumers create their own value and demand for goods and services. Reverse online auctions are examples of C2B e-business models.
• In consumer-to-consumer (C2C) model, consumers are both buyers and sellers via third-party-facilitated online marketplaces, such as eBay. For example, OLX , where consumers can sell/buy their own goods & get their own price.

E-Governance

• Electronic Governance is the application of Information and Communication Technologies (ICTs) for delivering government services to citizens & business in a convenient & efficient manner.
• These services include Digital India initiative, National Portal of India, Prime Minister of India portal, Aadhaar, filing and payment of taxes online, digital land management systems, Common Entrance Test etc. 

Mobile Commerce

•  Mobile commerce involves using wireless handheld devices like cellphones and tablets to conduct commercial transactions online, including the purchase and sale of products, online banking, and paying bills.
• With m-commerce, users can transact anywhere provided there’s a wireless internet provider available in that area.
• Mobile commerce has increased rapidly as security issues have been resolved.
• Companies like Apple and Google have introduced their own mobile commerce services.

HTTP – Hyper Text Transfer Protocol

• Hyper Text Transfer Protocol is used to send the request from client (web browser) to server & it also receive the response from server to client as well.
• It is the data communication protocol used to establish communication between client and server.
• That is why it is also known as “Request Response Protocol”.
• HTTP is TCP/IP based communication protocol, which is used to deliver the data like image files, query results, HTML files etc.. on the World Wide Web (WWW) with the default port is TCP 80.
• It provides the standardized way for computers to communicate with each other.

FTP – File Transfer Protocol

• FTP – File Transfer Protocol allows the process of file downloading and uploading on different computers from the internet.
• It also does file management.
  • Users can list files and directories on the server.
  • It allows users to delete files on the server.
  • Users can rename files stored on the server.
  • Users can create or remove directories on the server.

TELNET

• TELNET stands for TErminaL NETwork.
• It is a type of protocol that allows one computer to connect to remote computer.
• It provides access to virtual terminals of remote systems on local area networks or the Internet. 
• Computer which starts connection is known as the client/local computer.
• Computer which is being connected by client computer is known as Remote computer.
• Client computer uses telnet client program and the remote computers uses telnet server program.
• Telnet is used to edit files, checking mails, running various programs on remote computer.

Domain Names

• It refers to string of text that maps to numeric IP address, used to access a website from client software.
• It is a unique address where your website can be found online. For example, google.com, amazon.in, etc are domain names.

URL – Uniform Resource Locator

• URL – Uniform Resource Locator is a unique identifier used to locate a resource on the internet. It is also referred as Web Address.
• Example of URL, https://swatilathia.wordpress.com/javascript-events/index.php indicates a protocol(HTTP), a host name (swatilathia.wordpress.com) & a file name (index.php)

Web Page

• Web page is a document available on internet.
• Web pages are stored in web servers and are displayed on browser when a user writes a specified URL in a browser.
• Web pages are normally created in HTML . Each web page is associated with its unique URL.

Web Site

• A set of related web pages interconnected with each other located under a single domain name is known as web site.
• Google.com, Wikipedia.org, etc are example of web site.
• Websites are typically dedicated to a particular subject area, such as education, commerce, entertainment, news or social networking. 
• The main page of web site is known as home page from where the web site starts.
• Users can access websites on number of devices, such as desktops, laptops, tablets, and smartphones. 

Types of Website

• The main three types of website : Static, Dynamic & Responsive

• Static Web Site : It contains web pages with fixed content which is something like a printed page that can not be change until & unless we change its code/script. It shows the same information to every visitor. Static websites are the most basic type of web sites & it is very easy to create as it uses HTML, CSS & JavaScript to design & develop the websites.
• Dynamic Web Site : Dynamic websites are those websites that changes the content or layout with every request to the web server. These web sites have their own database to store & retrieve information. These websites have the capability of producing different content for different users from the same source code file. For example, login & signup pages, application & submission forms, inquiry and shopping cart all are the content which are different as per user. To create dynamic websites, mostly server-side scripting language are used like PHP, ASP, JSP, etc. pages.
• Responsive Web Site : Responsive web sites are the sites that display well on variety of devices & windows or screen size from minimum to maximum display size to ensure user satisfaction & usability. These web sites are suitable to every smart device that can display the web page properly according to the size of their screen so that every user can access the content.

Web Browser

• Web browser is a software application used to access the information on the World Wide Web. When a user requests some information, the web browser fetches the data from a web server and then displays the web page/web site on the user’s screen. For example, Google Chrome, Mozilla Fire fox, opera, Apple safari, Microsoft internet explorer all are web browsers.

Web Server

• Web server is a dedicated computer that stores the content of the web site. In simple term, it serves the information to the web client (browser). It is a software & hardware that responds to the client’s(browser) request with the use of HTTP & other protocols. Apache, IIS and many more are examples of web server which are most commonly used.

Web Hosting

• Web hosting is a type of Internet Hosting that provides a facility to host a website for a client. It allows the website to publish on the internet so that everyone can visit & access it.
• A web hosting service provider is a business that provides the technologies and services needed for the website to be viewed in the Internet. Websites are hosted or stored on called servers. When Internet users want to view your website, all they need to do is type your website address or domain name into their browser. Their computer will then connect to your server and your webpages/website will be delivered to them through the browser.
• Most hosting companies require that you own your domain in order to host with them. If you do not have a domain, the hosting companies will help you purchase one.

Network Security Concept

• Cyber Law : Cyber law also known as Internet Law, is the part of the legal system that is related to legal informatics and supervises the digital circulation of information, e-commerce, software and information security. It focuses many areas, such as Internet Access, freedom of expression, and online privacy.
• Cyber laws help to reduce or prevent people from cyber criminal activities with the help of protecting information access from unauthorized people, freedom of speech related to the use of the Internet, privacy, communications, email, websites, intellectual property(copyright issues), hardware and software.
• As usage of Internet increases day by day, it leads to a huge percentage of legal issues worldwide. This is the reason to include cyber laws.
• Cyber law offers legal protections for people who are using the Internet as well as running an online business. It is most important for Internet users to know about the local area and cyber law of their country by which they could know what activities are legal or not on the network.
• Also, they can prevent ourselves from unauthorized activities.

Firewall :

• A firewall is a network security device that monitors incoming and outgoing network traffic and decides whether to allow or block specific traffic based on a defined set of security rules.
• Firewalls have been a first line of defense in network security for over 25 years.
• They establish a barrier between secured and controlled internal networks that can be trusted and untrusted outside networks, such as the Internet. 
• A firewall can be hardware, software, or both.

Cookies

• Cookies are text files with small pieces of data — like a username, contact number, email address, etc. — that are used to identify your computer as you use a computer network.
• Specific cookies known as HTTP cookies are used to identify specific users and improve your web browsing experience.
• Data stored in a cookie is created by the server upon your connection. This data is labeled with an ID unique to you and your computer.
• When the cookie is exchanged between your computer and the network server, the server reads the ID and identifies what information to specifically serve to you.
• Cookies let websites recognize users and recall their individual login information and preferences, such as Entertainment & News
• Customized advertising is the main way cookies are used to personalize your sessions. You may view certain items or parts of a site, and cookies use this data to help build targeted ads that you might enjoy.
• Shopping sites use cookies to track items users previously viewed, allowing the sites to suggest other goods they might like and keep items in shopping carts while they continue shopping.

Hackers

• Hackers are the people who hack devices and systems with good intentions.
• They may hack a system for a specified purpose or to gain more knowledge out of it.
• They work by finding loopholes(an error) in a given system and by covering these loopholes.
• Hackers are basically programmers who gather extensive knowledge regarding programming languages and operating systems (OS).
• They never intend to harm, compromise, or damage any system data.

Crackers

• Crackers are people who hack a system by breaking into it and violating it with some bad intentions.
• They may hack a system to steal the data/information or to harm it permanently.
• Crackers destroy the data and information contained in a system by getting unauthorized access to its concerned network.
• They keep their works hidden because what they do is illegal and mostly prohibited or forbidden.
• A cracker can easily bypass your device’s passwords, company websites, social media, personal bank details and can use those details for directly transferring money from your bank.

Types of Payment System

• Digital Cash : Digital Cash is a form of electronic currency that exists only in cyberspace and has no real physical properties, but offers the ability to use real currency in an electronic format. For example, cryptocurrency like bitcoin can accepted by some of the countries.

• Electronic Cheque : An electronic cheque or e-cheque, is a form of payment made via the Internet, or another data network, designed to perform the same function as a conventional paper cheque. Since the cheque is in an electronic format, it can be processed in fewer steps. The costs associated with issuing an electronic cheque are comparatively lower than those associated with paper cheque. Electronic cheque also come with a lower risk of the associated funds being stolen, as there is no tangible item to intercept. There are multiple levels of authentication to help ensure funds are routed properly.

• Smart Card : A smart card is a physical card that has an embedded integrated chip that acts as a security token. Smart cards are typically the same size as a driver’s license and can be made out of metal or plastic

• Debit Card / Credit Card : A debit card is a payment card that can be used in place of cash to make purchases. The money debits directly from consumer’s bank account. A credit card is a payment card issued by banks with a pre-set credit limit, helping you make cashless transactions.  Credit cards has put the condition that cardholders pay back the borrowed money, plus any applicable interest, as well as any additional agreed-upon charges, either in full by the billing date or over time.