Internet

Class-In charge: S.Sasirekha

COMPUTER NETWORK

• A computer network is a collection of two or more computers, which are connected together to share information and resources.

• Network Operating Systems (NOS) is an • Network Operating Systems (NOS) is an interconnected system of computing devices that provide shared and economical access to computer services.

• NOS are broadly divided into two types namely, client/server and peer-to-peer networks.

Today, when talking about networks, we are generally referring to three primarycategories:Local Area Network (LAN): LAN spans only a small geographical area such as anoffice, home, or building. In LAN one computer is designated as the file server, whichstores all the software that controls the network and other computers connected arecalled workstations.Metropolitan Area Network (MAN): MAN is a network of computers spread over ametropolitan area such as city and its suburbs. Operated by one organisation (acorporate with several offices in one city), or be shared resources used by severalorganisations in the same city.Wide Area Network (WAN): WAN is a system of interconnecting computers over alarge geographical area such as cities, states, countries, or even the world. Theselarge geographical area such as cities, states, countries, or even the world. Thesekinds of networks use telephone lines, satellite links, and other long-rangecommunications technologies to connect.

Stand-alone and Networked Environments

NETWORK TOPOLOGIES

• The term topology refers to the way a network is laid out, either physically or logically.

• It is the geometric representation of the relationship of all the links.

• There are five basic topologies: – Bus: Bus topology network uses a common backbone (a single cable) to connect all devices with terminators at both the ends.both the ends.

– Ring: In ring topology, every node has exactly two neighbours connected to form a ring for communication purposes.

– Star: In star topology, devices are not directly linked to each other but are connected through a hub forming the shape of a star.

Star Topology

• Tree: Tree topology consists of groups of star-configured workstations connected to a bus backbone cable.

• Mesh: In mesh topology, every node has a dedicated point-to-point link to every other node.other node.

Mesh Topology

COMMUNICATION PROTOCOL• A computer protocol is a set of rules that coordinates the exchange of information.

• Open Systems Interconnection (OSI) is a standard reference model for communication between two end users in a network.

• It consists of seven separate but related layers:– Physical Layer– Physical Layer– Data Link Layer– Network Layer– Transport Layer– Session Layer– Presentation Layer– Application Layer

NETWORK DEVICES• To communicate over a network, a particular set of network devicesinterconnect individual computers and ensure that they communicateefficiently.• The various types of networking devices available in the formation ofcomputer network are as follows:

•Network Interface Card•Hub•Repeater•Switch

Router

Network Interface CardGateway

•Switch•Bridge•Router•Gateway

The Internet• The Internet is the world' s largest computernetwork made up of thousands of networksworldwide, which allows the users to shareinformation.

• It enables the users to use applications such ase-mail and the world wide web.

EVOLUTION OF INTERNET

• In 1969, US DoD created a network known as ARPANET, which linkedUs scientific and academic researchers.

• By 1970s, ARPA helped in the development of a new protocol calledTCP/IP for transferring data between the networks.

• In 1980s, Usenet newsgroup and Electronic Mail (e-mail) came intopicture.

• Internet really became popular in the 1990s after the developmentof the World Wide Web (WWW).

• In 1991, CERN developed the protocol based on hypertext (HTTP) thatmakes it possible to connect content on the web with hyperlinks.

• Nowadays, an Internet user gets information on all sorts of activitiesranging from how to add to the design of a functional spaceship tochoosing a product for personal use.

BASIC INTERNET TERMS

• Web Page: It is an electronic document written in a computer language called HTML and are linked together through a system of connections (called hyperlinks), which enable the user to jump from one web page to another by clicking on a link.

• Website: It is a set of related (linked through hypertext links) web pages, published by an organisation or individual.organisation or individual.

• Home Page: It is the starting point or a doorway to the web site.

• Browser: It is a computer program used to access web pages and display them on the computer screen.

• Uniform Resource Locator (URL): It is a unique address assigned to a web page.

• Hypertext: It refers to the text that connects to other documents. These texts are known as hypertext link, hyperlink, hotlink, or simply links.

• Internet Service Provider (ISP): It is an organisation that provides the required software, which is used to connect to the Internet.

• Web Server: It is a computer equipped with a server software, which provides a specific kind of service to client software running on other computers.

• Download and Upload: Download refers to the activity of moving • Download and Upload: Download refers to the activity of moving or copying a document, program or other data from the Internet or other interconnected computer to one's own computer. Upload refers to the act of moving or copying data or program from one computer to another, usually to a server, remote computer.

• Online and Offline: Online is commonly referred to as 'connected to the World Wide Web via Internet‘ and Offline refers to the actions performed when the user is not connected, via telecommunications, to another computer or a network like the Internet.

GETTING CONNECTED TO INTERNET

• The basic requirements for getting online are:

• A TCP/IP enabled computer with a web browser

• An account with an ISP• A telephone line plugged to • A telephone line plugged to

a suitable socket• A modem to connect the

computer to the telephone line

Types of Internet Connections–Some common types of Internet access, available for the users are: •Dial-up, ISDN, Cable Modem, Leased Line, DSL, and Broadband.

Internet SoftwareInternet Software• To connect to the Internet, computer requires three kinds of software–TCP/IP, Dialler Software, and Browser.

INTERNET APPLICATIONS

Some of the important services provided by Internet are:

World Wide Web (WWW): It is a subset of the Internet and it presents text,images, animation, video, sound, and other multimedia in a single interface.The operation of the Web relies primarily on hypertext, as it is a means ofinformation retrieval.

Electronic Mail (E-Mail): It is the process of exchanging messageselectronically, via a communications network, using the computer.

File Transfer Protocol (FTP): It is a system of rules and a software programFile Transfer Protocol (FTP): It is a system of rules and a software programthat enables a user to log on to another computer and transfer informationbetween it and his/her computer.

Telnet: It connects one machine to another in such a way that a person mayinteract with another machine as if it is being used locally.

Internet Relay Chat (IRC): This service allows people to communicate in realtime and carry on conversations via the computer with one or more people. Itprovides the user with the facility to engage in simultaneous (synchronous)online 'conversations' with other users from anywhere in the world.

• Chatting and Instant Messaging: Chat programs allow users on the Internet to communicate with each other by typing in real time. Instant messaging allows a user on the Web to contact another user currently logged in and type a conversation.

• Internet Telephony: It refers to the use of the Internet rather than the traditional telephone company infrastructure, to exchange spoken or company infrastructure, to exchange spoken or other telephonic information.

• Video Conferencing: It uses the same technology as IRC, but also provides sound and video pictures. It enables direct face-to-face communication across networks via web cameras, microphones, and other communication tools.

Commerce through Internet: It refersto buying and selling goods and servicesonline.

Newsgroups (Usenet): It is aninternational discussion group that focuson a particular topic and helps ingathering information about that topic.

Mailing Lists (Listserver): It refers to alarge community of individuals who carryout active discussions, organised aroundtopic-oriented forums that are distributedvia e-mail and this method is known asmailing list.

Mailing List

DATA OVER INTERNET

• The data, in terms of Internet, primarily comprises the hypertext documents containing links that connects to other documents or files.

• These documents may even include animations, and multimedia components. We can divide the displayed data into two categories:

Static Component– Static component includes the information displayed on the browser that does not interact with the user.the browser that does not interact with the user.

Dynamic Component– Dynamic component imparts life to a web page. This component refers to a specification by which a user can interact with a web server. Some of the programming languages (often called scripts) used to provide dynamism to a web page are Perl, JavaScript and Jscript, VBScript, Active Server Pages (ASP), PHP, XML, Java, and so on.

Internet Tools

• Internet has become one of the most popular means ofcommunication and is probably the best solution that providesall kinds of information at a single place.

WEB BROWSER•A web browser (or simply browser) is a software application, whichprovides a graphical user interface (GUI) so that the user can navigate theprovides a graphical user interface (GUI) so that the user can navigate theInternet easily by clicking on menus, icons, or buttons instead of learningdifficult keyboard commands.•The two most popular web browsers are Netscape Navigator andMicrosoft Internet Explorer.

Internet Explorer Environment

• To open Internet Explorer, double-click the Internet Explorer icon located on the desktop or click Start, select All Programs, and select Internet Explorer. When Internet Explorer is opened, the main screen of the program appears. This main window has many parts to it; these parts are:

• Title bar• Title bar• Menu bar• Standard toolbar• Address bar• Link bar• Status bar• Content Area or Document View

BROWSING INTERNET USING INTERNET EXPLORER

• Browsing is an act of looking through information on the Internet by repeatedly scanning and selecting, usually with the help of hyperlinks. It is also known as navigating or surfing the web.

• Opening and Navigating a Website: In the Address box, enter the website’s address (URL) and press Enter to open the website. When the website opens, its home page is displayed.

• Saving Text and Images: If you wish to save any text from the Internet, first select the text on the web page. After selecting the desired text, right-click it to open a pop-up menu, which contains desired text, right-click it to open a pop-up menu, which contains options like Cut, Copy, Paste, Select All, and Print.

• Downloading Files from Links: Many web pages have links to files that are not natively displayed in the Internet Explorer content area. Such files have to be copied on the hard disk so that the user can use them later on.

• Add to Favorites: Internet Explorer uses a feature called Favorites to put websites one visits often within easy reach.

ELECTRONIC MAIL (E-MAIL)Electronic mail or e-mail can be defined as the process ofexchanging messages electronically, through acommunications network, using the computer. It providesinstant delivery of information and the ability to send fileattachments by using the Internet.E-mail Address Structure: A typical e-mail address wouldlook like: username@website.comLogin at Mail ServerLogin at Mail ServerChecking E-mails: One can read received e-mails byopening his/her e-mail account.Sending E-mails: One of the important functions of an e-mailservice is to provide a platform to send e-mails. A user canreply to the received e-mail or send a new e-mail.E-mail Attachments: To send or receive files likecompressed (.ZIP) files or any executable (.EXE) files youneed to ‘attach’ them in your e-mails.

• How E-mail Works: To send e-mail, one needs a connection to the Internet and access to a mail server, which forwards the mail. The standard protocol used for sending Internet e-mail is called SMTP (Simple Mail Transfer Protocol). It works in conjunction with POP (Post Office Protocol) and IMAP (Internet Mail Access Protocol) servers.

• Netiquette: Communicating online, whether by e-mail, chat rooms or message boards, is informal, quick, and easy. Netiquettes are rules that should be followed while communicating over the Internet. Disobeying netiquettes while sending e-mail can create trouble. Like e-mail and other online communication, the rules of netiquette are short and to the point.

Working of E-Mail System

E-MAIL CLIENT

• An e-mail client (also known as Mail User Agent) is a computer program that runs on a personal computer and enables the user to organise, filter, and sort all the sent and received e-mails. Some examples of e-mail clients include Microsoft Outlook Express, Eudora, and Pegasus Mail.

• Outlook Express Environment: To open Outlook Express, double-click the Outlook Express icon located on the desktop or click Start, select All Programs, and then select Outlook Express. When Outlook Express is opened, the desktop or click Start, select All Programs, and then select Outlook Express. When Outlook Express is opened, the main screen of the program appears, and it is divided into four panes: folder list, folder content, contact list, and preview pane.

• Creating an Account: Before you can send or receive e-mail using the Outlook Express, you need to configure it to communicate with incoming and outgoing mail servers.

• Sending E-mails Using Outlook Express:Sending mails using Outlook Express is similar to sending mail using any web-based mail accounts.

• Checking E-mails Using Outlook Express: To open the received e-mails in Outlook Express, there is no requirement to open a web browser. Instead, Outlook Express itself downloads the received e-mails. The e-mails sent to you are stored on the mail server of your ISP until you retrieve them.retrieve them.

• Creating Newsgroup Account: A newsgroup is a virtual place where people with common interests can ask questions and get answers on just about any imaginable topic ranging from sports to space. Newsgroups generate huge volumes of messages for which you need a newsreader to read.

SEARCH ENGINES

A search engine is a searchable database of Internet fileswhich allows the user to enter keywords relating to particulartopic and retrieve information about Internet sites containingthose keywords.Searching the Internet: Some of the well-known searchSearching the Internet: Some of the well-known searchengines are www.google.com, www.hotbot.com,www.lycos.com, and www.altavista.com.Refining the Search: The major search engines allow theuser to choose whether to search for the exact typed phrase,all the words in the phrase, any of the words in a phrase, andso on.

INSTANT MESSAGING

• Instant messaging is a web-based service to exchange messages in real time between two or more people over the Internet.

• It is a combination of e-mail and chat room. Usually, users send their messages in text format.

• However, while sending instant messages, a user can also communicate through web cam (video chatting) as well as through speakers and microphone (voice chatting).through speakers and microphone (voice chatting).

• Features of Messenger: The features of messenger that make it a favourite among Intenet users include Chatting, Emoticons/Smileys, Audibles, Games, and Address book.

• Getting Started with Yahoo Messenger: To use Yahoo Messenger, a unique Yahoo ID is required. When you start the messenger, it will display a screen asking you to enter your yahoo mail ID and password. If you are using the messenger for the first time, you may wish to add the e-mail addresses of all those known ones who also use Yahoo messenger. Once you and your friends are online, you can chat and send instant messages.chat and send instant messages.

• Sending Instant Messages: A message can be sent to a friend whose e-mail address you have stored in your Friend List.

• Sending Files: In addition to the messages, you can also send and receive text, image, audio, or graphical files using the messenger