Unit 6b - Internet.pdf

THE COPPERBELT UNIVERSITY SCHOOL OF INFORMATION AND COMMUNICATION TECHNOLOGY DEPARTMENT OF COMPUTER SCIENCE UNIT 6b: Internet Services INTRODUCTION In the past two decades, computers have played a significant role in our ev...

THE COPPERBELT UNIVERSITY SCHOOL OF INFORMATION AND COMMUNICATION TECHNOLOGY DEPARTMENT OF COMPUTER SCIENCE UNIT 6b: Internet Services INTRODUCTION In the past two decades, computers have played a significant role in our everyday life. With the growth in popularity and networking of computers, intercommunication between different computers became easier, which led to evolution of Internet. It is the most talked about computer technology in recent years. For a majority of people, who are unaware of computer technology, Internet depicts some enigmatic computer gizmo, which has something to do with games, music and generally entertainment. However, Internet is a much broader concept than mere entertainment and recreational activities. It is revolutionizing and enhancing the ways of human interaction and communication. The term 'Internet' is derived from two words—interconnection and networks. Also referred to as 'the Net', Internet is a worldwide system of computer networks, that is, a network of networks, which allows the participants (users) to share information. It consists of thousands of separately administered networks of various sizes and types. Each of these networks comprises tens of thousands of computers. Moreover, the total number of users of the Internet is known to be in millions. This high level of connectivity encourages an unparalleled degree of communication, resource sharing and information access. It is probably the most powerful and important technological advancement since the introduction of the desktop computer. To benefit from what the net has to offer, a basic understanding of what it is and how it works is helpful. EVOLUTION OF INTERNET The foundation of Internet was laid in 1969 by the Department of Defense (DOD) of United States of America. They wanted to create a computer network that could continue to function in the event 1 of a disaster such as a nuclear war. Even if a part of the network was damaged or destroyed, the rest of the system would continue to work. That network was known as ARPANET (Advanced Research Projects Agency Network), which linked US scientific and academic researchers. It was the forerunner of today's Internet. Later in 1980, another agency, the National Science Foundation (NSF) created a new network of computers based on ARPANET, called NSFNET, which turned out to be more efficient and capable. Initially, NSFNET was designed to link five super computers situated at the major universities of NSF and allowed only academic research. Over the time, this network expanded to include sites for business, universities, government and so on, and finally becoming a network consisting of millions of computers, now known as the Internet. In the 1980s, Usenet newsgroups and electronic mail (e-mail) came into picture. To keep track of the information on the Internet, indices such as Archie and the wide area information server (WAIS) were also created in this decade. To give users an easy-to-use interface to work with, the University of Minnesota created Gopher, a simple menu-driven system for accessing files. The Internet really became popular in the 1990s after the development of the World Wide Web (WWW). Before that, it was open for a handful of sites only. It is amazing that as recently as June 1993, there were only 130 websites, but now there are millions. With the growth of the Internet, the quality, quantity and variety of information also grew. The Internet today is a repository of every type of information. Nowadays, an Internet user can get all sorts of information ranging from how to add to the design of a functional spaceship to choosing a product for personal use. Internet Organizations and Committees Now that you are aware of how the Internet evolved, you may ask that who owns the Internet. Well the answer is 'nobody'. The Internet is a loosely organized international collaboration of autonomous, interconnected networks, which supports host-to-host communication through voluntary adherence to open protocols and procedures defined by Internet standards. Nobody really owns or controls the Internet. However, there are some governing bodies overseeing the technical aspects of the Internet. They define how the Internet works and how new technology is to be implemented. Some of the important governing bodies of Internet are as follows:  Internet Society (ISOC): It is concerned with the growth and evolution of the Internet and the way in which the Internet is and can be used.  Internet Architecture Board (IAB): It is a technical advisory group of the ISOC and is chartered to provide oversight of the architecture of the Internet and its protocols.  Internet Engineering Task Force (IETF): It is a self-organized group of people who provides technical and other contributions to the engineering and evolution of the Internet and its technologies. 2   Internet Engineering Steering Group (IESG): This group is responsible for the technical management of IETF activities and the Internet standards' development process.  Internet Research Task Force (IRTF): Its main purpose is to create research groups that focus on Internet protocols, applications, architecture and technology.  Internet Assigned Number Authority (IANA): The task of IANA is to assign protocol parameters such as Internet addresses, domain names and protocol numbers for the Internet.  Internet Network Information Center (InterNIC): It is a collaborative activity of AT&T, Network Solutions Inc. and National Science Foundation (NSF). It provides directory and database services, the Internet white pages and domain name registration.  World Wide Web Consortium (W3C): It was founded in 1994 to develop common protocols for the evolution of the World Wide Web. GETTING CONNECTED TO INTERNET Now, you are aware of the basic Internet terms, and let us shift our focus on how to connect to the Internet. The basic requirements for getting connected to the Internet are discussed in this section. The Computer The computer must have at least 386-microprocessor chip with a minimum of 16 MB of RAM. For a good browsing experience, use a faster chip (Pentium III/Pentium IV) with more RAM (128/256 MB). In addition, a color monitor, with at least 640 × 480 resolution and a capability of displaying a minimum of 256 colors, is also vital. The system should also possess a hard disk, with at least 200 MB of free space to store Internet software and temporary Internet files. Since the web is a multimedia, you can also enjoy sound on your system with a sound card and a pair of speakers. Modem Apart from the previously mentioned configuration, a computer system must have a device called modem, which enables a computer to transmit data over telephone lines. A modem (i.e. modulator- demodulator) is a hardware, which converts digital data into analog signals (i.e. modulation) that can be sent over an analog telephone line and convert the analog signal back into digital data (i.e. demodulation). Thus, when the modem receives the data from a web server via phone system, it reconstitutes the analog signal into digital form so that the computer can understand it. The most critical aspect of the modem is its speed of operation. The speed of modem is measured in kilobits per second (Kbps). Modern modem supports 28–56 Kbps speeds. Modems are of two types:  Internal Modem is a card, which is fitted inside the computer with a lead running directly from the computer to the phone socket.  External Modem is a small external box wired between the computer and the phone socket. 3 Internet Connection Before connecting to the Internet, you need to buy an Internet connection from an authorized Internet Service Provider (ISP). The speed of accessing the Internet entirely depends upon the type of connection you bought from the ISP. Some of connections available for the users these days are briefed as follows:  Dial-up: A dial-up connection is the access method that uses telephone lines to connect to the Internet. It is the most common way for the individuals who use home computers to connect to the Internet. To connect to the Internet by using dial up, the user needs to specify a username, a password and a telephone number. After the connection is established, the user can start browsing sites on the Internet.  ISDN: It stands for Integrated Services Digital Network and is more common in business and commercial use. It was the first high-speed alternative to regular analog phone modems. ISDN involves the digitization of telephone network so that voice, graphics, text and other data can be provided to users from a single terminal over existing telephone wiring. Digital connections have fewer errors in transmission, which means speed of downloading graphics, web pages, sound and so on is increased to four times faster than with dial-up modems.  Cable Modem: A cable modem connects the user to the Internet through a cable television line. Nowadays, many cable companies offer Internet along with television accessibility. A cable modem will typically have two connections, one to the television outlet and the other to the computer. Cable modems not only provide a faster Internet access (10–100 times as fast as the dial-up modem), but interactivity to the television also.  Leased Line: This facility provides reliable, high-speed Internet access ranging from 2.4 Kbps to 45 Mbps. A leased line connection is an affordable way to link two or more sites for a fixed monthly charge. Usually, leased lines facility can be provided via fibre optics or copper lines. Leased line service provides a consistent amount of bandwidth and is an excellent way to provide data, voice and video links between the sites.  DSL: Digital Subscriber Line (DSL) service is provided through an existing phone line, but it works differently than regular analog modem dial-up access. DSL operates over normal telephone lines and it can be used simultaneously with the telephone. DSL can increase the connection speed by as much as tenfold from a standard dial-up modem.  Broadband: This type of access is good for remote locations, where ISDN, cable or DSL are not available. It gives a decent download speed, but to upload data, the user still needs a regular analog modem to dial in, via a phone line. Satellite connection can be either a two-way service or a one-way service. In case of two-way satellite service, the data are transmitted via satellite to a dish antenna at the user's house. In one-way system, the user needs a conventional modem and telephone link to an ISP. Satellite connection is expensive, but sometimes is the only fast option for people who are beyond the service area of cable and DSL providers. 4 Before deciding the type of Internet connectivity, one should first decide the requirements. If the user wants the Internet mainly for sending e-mail, occasional chats infrequent browsing, then one should work with regular modem dial-up access. In this case, user should invest in a good quality 56 Kbps modem and a good ISP. If the user is using the Internet frequently for research, downloading or uploading a fair amount of data, to play multiplayer games or to use the multimedia capabilities of the Internet like live audio or video streaming, then one should look into other high-speed accesses such as cable modem or ISDN. Internet Software To connect to the Internet, a computer requires mainly three different kinds of software.  TCP/IP: TCP/IP, or Transmission Control Protocol/Internet Protocol, is the basic communication protocol of the Internet. It allows programs on the user's computer to communicate over the Internet. Usually, when you are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP. Similarly, every other computer that you may send messages to or get information from also has a copy of TCP/IP.  Dialer Software: This software is provided by the ISP to instruct the modem to dial the phone number and to identify the user's machine to the access provider's system for access to the network.  Browser: To use the Internet, a web browser is essential, which allows the user to view the information available on the World Wide Web. INTERNET APPLICATIONS Today, the Internet has grown from a small network to biggest network of computers. Due to this colossal growth, the Internet has become the biggest domain of information. Nowadays, an Internet user has access to a wide variety of services such as electronic mail, file transfer, vast information resources, interest group membership, interactive collaboration, multimedia displays, real-time broadcasting, shopping opportunities and much more. Some of the important services provided by the Internet are briefed in the following few sections. 5 Electronic Mail Electronic mail (e-mail) is a fast, easy and inexpensive way of communicating with other Internet users around the world. It is one of the basic and earliest services of the Internet and the most used application on the Internet too. E- Mail overcomes most of the problems and delays of getting a physical document from one person to another. Rather, it has the dual advantage of not only being faster, but also cheaper. Each user of e-mail has a mailbox address to which messages are sent and the mailbox can be accessed from anywhere and at anytime. It does not matter what type of connectivity the user is having, he will always be able to use this service. One can receive and send e-mails from all systems whether it is a Windows PC or a UNIX machine. Besides, e-mail can also be used to send documents, images, audio, and video and so on as an attachment along with the mail. File Transfer Protocol The file transfer protocol FTP is a set of rules that enables a user to transfer files from one system to another. It was the first service developed for the Internet so that government and educational institutions could easily exchange files. It allows the user to get access to the files stored in the directory of a remote computer that is connected to the Internet. Using FTP, one can upload and download files from the remote computer (known as FTP servers), if one has access permission on the remote machine. Although files can be transferred using e-mail, this is not a good choice if the file size is large or when there are many files. FTP sites consists of hundreds to thousands of files with information on books, music, software, games, images, sounds, multimedia, course ware and so on. Telnet The term 'telnet' is derived from 'telecommunications and network' and is a protocol that allows a user to log on to a remote computer. Telnet is also known as remote login, which means connecting one machine to another in such a way that a person may interact with another machine as if it is being used locally. It means that someone in New Delhi could connect to a computer in the CBU Library and search the card catalogue the same way as someone located at a terminal in the library. Once connected, the user's computer emulates the remote computer. When the user types in commands, they are executed on the remote computer. The user's monitor displays what is taking place on the remote computer during the telnet session. The user's computer, which initiates the connection, is referred to as the local computer or telnet client, and the machine being connected to, which accepts the connection, is referred to as the remote computer or telnet server. Note that the telnet client computer must run a telnet client application and the telnet server must run a telnet server application. Moreover, the user's machine has to be connected to the Internet or to a network to use telnet. In addition, to transmit information between the telnet client and the telnet server, the TCP/IP protocol is used. 6 Internet Relay Chat Internet Relay Chat (IRC) is a service on the Internet that allows people to communicate in real time and carry on conversations via the computer with one or more people. It provides the user with the facility to engage in simultaneous (synchronous) online 'conversations' with other users from anywhere in the world. Unlike other forms of group communication on the Internet, chat is an instant communication. However, both parties must be connected to the Internet and that too at the same time, running the right software and actively participating to chat. Generally, the user runs a program (called 'client') to connect to an IRC server. The server relays information to and from other servers on the same network. Popular IRC client applications are mIRC, Virc and LeafChat. Once connected to an IRC server on an IRC network, the user will usually join one or more 'channels' (also known as chat rooms) and converse with others there. Each channel is devoted to a different topic. Conversations may be public (where everyone in a channel can see what the user types) or private (messages between only two people, who may or may not be on the same channel). Chatting and Instant Messaging Chat programs allow users on the Internet to communicate with each other by typing in real time. They are sometimes included as a feature of a website, where the users can log into chat rooms to exchange comments and information about the topics addressed on the site. For example, America Online is well known for sponsoring a number of topical chat rooms. Chatting has become one of the 'killer applications' of the Internet and has become quite popular with all kinds of Internet users. It is quite cheap to chat online. E-mail is also a cheap source of communication, but it is not done on 'real time' and the response to the message solely depends on the recipient. Note that even though chatting is based on standardized IRC system, but unlike IRC, the user does not need to have any special software to connect to any chat rooms. A variation of chat is instant messaging where a user on the Web can contact another user currently logged in and type a conversation. To avail this Internet service, the user must have software called instant messenger installed on the system. Instant messaging is like making a text-only phone call over the Internet, that is, the user is 'talking' to the other person (possibly more) instantly. There are various instant messaging products such as MSN Messenger and Yahoo Messenger. Internet Telephony Internet telephony is the use of the Internet rather than the traditional telephone company infrastructure, to exchange spoken or other telephonic information. It consists of hardware and software that enable people to use the Internet as a transmission medium for telephone calls. There are many Internet telephony applications available. Some applications such as CoolTalk and NetMeeting come bundled with popular web browsers. The required hardware for the Internet telephony generally consists of end devices (either traditional telephones or audio-equipped personal computers) and gatekeepers that provide call 7 admission control, bandwidth management, addresses translation, authentication and user location. They communicate with each other using the voice over Internet Protocol (VoIP). For the cost of a local connection to their service providers, users can call anywhere in the world. Note that there is no single Internet phone standard at this time. Therefore, participants need to use the same software at each end of the connection. Video Conferencing Video conferencing uses the same technology as IRC, but also provides sound and video pictures. It enables direct face-to-face communication across the networks. A video conferencing system has two or more parties in different locations, which have the ability to communicate using a combination of video, audio and data. A video conference can be person to person (referred to as point-to-point) or can involve more than two people (referred to as multipoint) and the video conferencing terminals are often referred to as endpoints. In this form of meeting, participants in remote locations can view each other and carry on discussions via web cameras, microphones and other communication tools. The following five elements are common to all video conferencing endpoints:  Web Camera: It captures live images to send across the network.  Visual Display: It displays the images of the people taking part in the video conference.  Audio System: It includes microphones to capture audio from the endpoint and loudspeakers to play back the audio received from other endpoints across the network connection.  Compression: Videos are highly bandwidth-intensive and they take a long time to load. Therefore, video systems include technologies, often referred to as codecs, to compress and decompress video and audio data, allowing transmission across a network connection in near-real time.  User Interface and Control System: The user interface allows the users to control interactions, for example, placing calls, storing and locating numbers, and adjusting environment settings such as volume. The control system handles the underlying communication that takes place between the endpoints. Video conferencing has many benefits, as a tool for both teaching and learning. A key factor is that it provides real-time, visual communication, unlike other communication methods such as e- mail. Video conferencing technology is still in its infancy, and one of its major limitations is the bandwidth (the volume of information per unit time that a computer or transmission medium can handle) available on the Internet. As the protocols and applications for video conferencing develop higher resolution and improved speed, participation will increase. Commerce through Internet Today, business is taking place through electronic telecommunication media. Nowadays, various organizations offer the facility of shopping online. This type of business model is known as 8 electronic commerce or E-commerce. E-commerce refers to buying and selling goods and services online. It integrates communication, data management and security capabilities, which allow organizations to exchange information about the sales of goods and services. Essentially, it is the end-to-end digital exchange of information needed to conduct business including electronic data interchange (EDI) and electronic funds transfer (EFT). EDI is the computer-to-computer exchange of routine business transactions including payments, information exchange and purchase-order requests. EFT is a technology that allows the transfer of funds from the bank account of one person or organization to that of another. While discussing about e-commerce, we normally talk about virtual shopping malls, up-front stores where the user virtually visits and selects the product(s) of his/her choice. After selecting the desired product(s), the payment for the purchase is done. Online payment can be done through credit card. Techniques for cash transactions have also been developed in the form of Internet money such as Cyber cash and Digital money. After transfer of money, the items are received at the doorstep, which means delivery of the product is done at the address desired by the buyer. Through the development of e-commerce, the Internet has established an electronic global worldwide market that operates 24 hours and 365 days a year. Organizations and individuals are able to market goods and services, while purchasing is supported by secure facilities such as digital signatures (the process that operates on a message to assure message source authenticity and integrity) and encryption (a method of ensuring data secrecy). Developments in software mean that an increased number of facilities are becoming available all the time. Some of the well-known e- commerce sites are www.amazon.com and www.ebay.com. A Simple E-commerce Structure The increased use of mobile devices such as personal digital assistants (PDAs) and mobile phones has opened a new horizon of proliferation in the electronic market and has coined a new term 'mobile commerce'. Mobile commerce or M-commerce refers to transactions through a mobile phone network and data connection that result in the transfer of value (monetary or otherwise) in exchange for goods and services. Mobile commerce has evolved as a new and simpler concept to operate financial transaction through mobile phones and it includes services such as banking, payment and ticketing. M-commerce users may view and interact with information that appears through SMS (Short Message Service), WAP (Wireless Application Protocol) or a standard HTML browser on a PDA, web-enabled mobile phone or laptop computer connected to a mobile phone on a wireless network. Newsgroups (Usenet) Newsgroups are international discussion groups that focus on a particular topic and helps in gathering information about that topic. The topics discussed here cover all the fields such as politics, computers, technology and many more. The information or articles that make up the 'news' are written by people interested in a specific topic. These articles are posted to the newsgroup so 9 that others can read, reply and comment on them. To read and post articles in a newsgroup, newsreader software such as Microsoft Outlook Express or Netscape News is required. Some newsgroups are devoted to current events and headlines. However, newsgroups usually describe topical discussion groups, not 'the news' in the traditional sense. Most newsgroups exist on a network known as Usenet, which contains thousands of newsgroups. Reading News with Newsreader Newsgroups provide a source of information and a medium through which the users can ask questions from the Internet community. They provide a forum for users to discuss topics of mutual interest. It is normal to post the rules, restrictions and subject matter for the newsgroup in a message called frequently asked questions (FAQ). To simplify the selection of suitable newsgroups, they are divided into subject classifications known as top-level categories. These top- level categories are then further subdivided and this continues down the hierarchy. Mailing Lists (List server) The Internet is home to a large community who carry out active discussions, organized around topic-oriented forums that are distributed via e-mail. This method of Internet communication is known as mailing list and it enables people with similar interests from all over the world to communicate and share information with each other. The mailing list groups are administered by a software program known as listserver. There are varieties of programs available such as Listserv and Majordomo. A listserver watches for incoming mail on a certain mailbox continuously and forwards any message to a list of other addresses. Such a mailing list can bring people together with a common interest. There are hundreds of mailing lists, each for a different subject. Subscribers can send special messages to a separate address to retrieve files from the archive or to get other information about the mailing list. When the user subscribes to a listserver, messages from the other subscribers are automatically sent to their electronic mailbox (e-mail address). Note that to participate in a listserver discussion, the user must have an e-mail account. To subscribe to a listserver, the user has to send an E-mail message to the desired listserver located on the computer networks throughout the world. ELECTRONIC MAIL: AN INTRODUCTION The Internet was developed mainly to communicate and interchange knowledge irrespective of the distance limitation. Hence, from the very beginning, users used the Internet primarily for sending and receiving messages. Even today, communicating through the Internet is the main application of the Internet. Since these messages are communicated electronically, they are known as electronic mail or E-mail. Thus, electronic mail can be defined as the process of exchanging messages electronically, via a communications network, using the computer. E-mails allow users to communicate with each other in less time and at nominal cost as compared to traditional phone 10 or mail services. Apart from a textual message, e-mails can also consist of other data formats such as pictures, sound and video. E- mails can be sent anywhere in the world using a computer and a modem. Its delivery is almost instant and is very economical to use especially for international messages, costing only the price of the telephone connection to the ISP. You may send many messages at one time or just one to a designated location. E-mail Address Structure To use e-mail, one must have access to the Internet and an e-mail account. An e-mail account is a service that allows the user to send and receive e- mails through the Internet. Usually, e-mail accounts are provided as part of ISP's monthly packages. One can also obtain free e-mail accounts such as Yahoo and Hotmail on the Web. An e-mail account provides a unique e-mail address and a mailbox where the user can save all the mails. Generally, there are two parts of an e-mail address: the logon identity and the identity of the e- mail server. These are separated by the symbol @ (pronounced as ‘at’). For example, a typical e- mail address would look like: The first part of the address indicates the identifiable name of the user. It is just like a home address (and it is unique) so that the mails could be sent to that address. The user name is a name, which is assigned to or desired by the user, while signing up for e-mail address. For example, [email protected]. The @ symbol in the address is used to separate the user name from the rest of the address. Next comes the host name (yahoo), also called the domain name. This refers to the mail server, the computer where the recipient has an electronic mailbox. It is usually the name of a company or organization. The end of the domain name consists of a dot (.) followed by three or more letters (such as.com or.net). This part of the domain name indicates the type of organization or the country where the host server is located. Note that you may find variations in e-mail addresses, but these common elements will always remain the same. NOTE: There are no spaces in an e-mail address and it is usually (but not always) in lower case letters. Sending and Receiving E-mail To send and receive an e-mail, the user must have an e-mail account. In case, you do not have a mail account, you must sign up with e-mail provider. Let us assume that you have an e-mail account. Now, follow the steps given below to check the received e-mails. 1. Open Internet Explorer and type the address of the website on which you have an e-mail account. For example, type www.rediff.com in the address bar and press the Enter key. The home page of the website appears. 2. Click Sign In. A dialog box, which allows the existing users to log on, appears on the home page. 11  3. Type your email ID and password in the specified fields and click the Go button. By default, the Inbox page of your e-mail account appears which shows the received e-mails. Note that you can view the Inbox page any time by clicking the Check mails. 4. Click on the mail you want to read. 5. After reading the mail, you can reply to the mail or forward the same mail to other persons by clicking the Reply or Forward button, respectively. In case, you do not want to keep the mail in the mailbox, click the Delete button to delete it. One of the important functions of an e-mail service is to provide a platform to send e-mails. A user can reply to the received e-mail or send a new e-mail. To send an e-mail, follow the steps given below. 1. Click on the Write Mail link so that you can create and send e-mail to the desired address. A webpage will be displayed. The key elements of the Write Mail page are listed as follows:  To: It denotes to whom the mail is to be sent. The user has to write the recipient's e-mail address.  Cc: Cc or carbon copy is used to specify the addresses of all the recipients who will also receive copies of the same mail. It is used to send the same message to several people (all the addresses are separated with commas).  Bcc: Bcc or blind carbon copy is used to send message to several addresses without showing everyone all the addresses.  Subject: It denotes the subject of the message as specified by the sender.  Attachments: Clicking this link opens another page where the user can attach files (created with programs like MS Word or Zip files) that are to be sent with the e-mail. 2. Type the addresses of the recipients and subject of mail in the corresponding fields and the contents in the text area. 3. Click the Send button. How E-mail Works The electronic mailing system works in a similar fashion as the postal service. Just as the postal service uses letters in envelopes with addresses on them, mailboxes and post offices, electronic mailing system completes the same operation with the help of computers (clients and servers). 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 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. 12 When an e-mail is sent to a person, who has an e-mail address like [email protected], it is broken down into two parts: someonelse (the recipient's account name) and theirdomain.com (the recipient's domain name). The SMTP server contacts a domain name service (DNS) server and asks for the location of theirdomain.com. The DNS server sends the address back to the SMTP server. The SMTP server then sends the e-mail message to the SMTP server where theirdomain.com is located. This SMTP server delivers the e-mail message to 'someonelse's' account on the POP or IMAP server. Finally, when 'someonelse' logs on to the computer and opens the e-mail client, the e-mail client requests the POP or IMAP server to send all mails from the account to 'someonelse's' computer. Note that if you are sending mail to somebody whose account resides on the same mail server, the SMTP server will simply direct the mail to the local POP or IMAP server, where it will be delivered to the appropriate account. Advantages and Disadvantages of E-mail  E-mail can be sent anywhere in the world to anyone who has an e-mail address. It can take days to send a letter across the country and weeks to go around the world. To save time and money, more and more people are using e-mail. However, the slightest error in the address can deliver the mail to the wrong address. Hence, like there are two faces of a coin, e-mail also comes with its own share of benefits and limitations.  Multiple copies of the same message can be sent to a group of people at the same time and can be sent as easily to a single person. Since e-mail passes through a network, it may be intercepted in between.  Pictures, documents and other files can also be attached to messages.  Electronic mailing system depends on the electricity and telephone system. Thus, failure of any one of them can prevent the user from sending or receiving e-mails. Netiquette Communicating online, whether by e-mail, chat rooms or message boards, is informal, quick and easy. However, there are certain unsaid rules that one should follow. On the Web, you are what you write, so take some pride in your work and do it correctly. The standard rules of a polite Internet behavior are called netiquette. Like e-mail and other online communication, the rules of netiquette are short and to the point. Some of these rules are briefed below:  Never do anything online that you would not do in real life. Even while communicating online, you are dealing with real people. Therefore, do not say anything over the Internet that you would not say on their faces.  Good discussion should always be welcomed, but do not waste other's time with useless queries. For example, if you respond to a listserver to send a private message to one person, you have wasted a lot of other's time. Moreover, before participating in a newsgroup discussion, one should read the FAQs (frequently asked questions).  Do not use all upper case letters because using all caps equates to yelling. A single word in uppercase (to emphasize) is acceptable, but use upper case words sparingly. 13   Never send unsolicited junk mail and do not forward junk mails or chain letters.  Respect other people's privacy and copyrights. Treat the mails that you receive as confidential unless the sender permits you to share it with others. Moreover, if you are quoting something from an online book or paper, always mention the source.  When posting a message to a public bulletin board, forum or newsgroup, stick to the topic. Posting unrelated comments to a newsgroup is known as spamming, which leads to another unpleasant Internet practice, known as flaming. Flaming is the practice of attacking people on a personal level.  Respect other people's time and bandwidth. While mailing or posting to a discussion group, you are taking up other's time. So, it is your responsibility to ensure that the time they spend reading your posting is not wasted. Hence, be concise and brief while mailing and posting information online.  When someone makes a mistake, whether it is a spelling error, an unnecessarily long answer, be kind about it. If it is a minor error, try to avoid it and even if you feel strongly about it, be polite and point it preferably by private e-mail rather than in public. SEARCHING THE WEB (SEARCH ENGINES) The Internet provides access to a wealth of information on countless topics contributed by people throughout the world. However, the Internet is not a library in which all its available items are identified and can be retrieved by a single catalogue. In fact, no one knows how many individual files (could be in billions) reside on the Internet. Hence, to conduct a search on the Internet, a special search tool known as search engines is used. A search engine searches a database of Internet files collected by a computer program called a wanderer, crawler or spider. It allows the user to enter keywords relating to particular topics and retrieve information about the Internet sites containing those keywords. As such, a search engine consists of four components:  Spider: Program that traverses the Web from link to link, identifying and reading pages.  Indexing Software: Program that analyses web pages that are downloaded by spiders.  Database: Warehouse of the web pages downloaded and processed.  Search Engine Mechanism: Software that enables the users to query the index and that usually returns results in relevancy ranked order. With most search engines, the user fills out a form with the search terms and then asks the search engine to find web pages relevant to those search terms. Some of the well-known search engines are www.google.com, www.altavista.com, www.lycos.com and www.hotbot.com. Let us assume that you want to search the Web to get information regarding World Wide Web. To do this, first open the search engine's website (such as www.google.com). Now type your keyword(s) in the search box and click the Google Search button or press Enter. 14 The engine searches its index and generates a page with links to those resources containing some or all of the search terms. Clicking on any link opens a website or web page in which the searched keyword appears. Refining the Search The major search engines allow the user to choose whether to search for the exact typed phrase, all the words in the phrase, any of the words in a phrase and so on. However, a few search engines do not provide such options. In this case, the user can refine the search by adding one or more words or symbols to the search topic.  AND: It is used to search for two or more terms on the same page. Type the word AND between the terms (e.g. poverty AND crime) or put a plus sign right before the second term (e.g. poverty+crime).  OR: It is used to search for either of two (or more) terms on the same page. Type the word OR between the terms (e.g. college OR university).  NOT: It is used to search for pages that include the first term but not the second. Type the word NOT between the terms (e.g. cats NOT dogs) or put a minus sign right before the second term (e.g. cats−dogs).  "": Double quotes are used to search for an exact phrase, for example, 'desktop wallpapers'.  (): Parentheses are used to group parts of the search phrase, for example, type desktop AND (themes OR wallpapers). This returns pages with the words desktop and themes or both the words themes and wallpapers.  *: Asterisk is used to search for various forms of a word, for example, prior* returns pages with the words prior, prioritize, priority and so on. 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. Depending upon how information is displayed in the browser, the displayed data can be classified into two categories—static component and dynamic component. Static Component Static component includes the information displayed on the browser that does not interact with the user. For example, the text written in the form of a paragraph on the web page is a static component. Producing static component for the web page is accomplished by creating documents in HTML. 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. For example, when a user fills a form on the web page, the texts filled in various fields are sent back to the originating point of the web page. This way a user 15 is able to interact with the server hosting that web page. To impart dynamism, a special program (often called scripts) is written in any programming language, including Perl, VBScript, JavaScript and so on. Some of the programming languages used to provide dynamism to a web page include  Perl  JavaScript and Jscript  VBScript  Active Server Pages  PHP  eXtensible Markup Language (XML)  Java INTERNET AND VIRUSES With the use of the Internet and communications between the computers, viruses are spreading faster than ever. Virus (stands for Vital Information Resources Under Seize) is a program or small code of segment, which is written with a malicious intent. It has the capability to attach itself to existing programs or files and infect them as well as replicate itself without the user's knowledge or permission. The virus instructs the computer to perform a specific task, which is often destructive, for example, deleting important information or crashing the hard drive. However, other kinds of viruses also exist that may only be slightly irritating. It enters into the computer system from external sources like CD, pen drive or e-mail and executes when an infected program is executed. Further, as an infected computer gets in contact with an uninfected computer (e.g. through computer networks), virus may pass on to the uninfected system and destroy the files. Types of Computer Viruses There are many kinds of viruses. The level of destructiveness of viruses varies widely. Some viruses display pictures or messages on the screen periodically. Others erase or destroy programs and data. They can also inflict havoc at different speeds. Some viruses spread through the computer system quickly, but some may take days or even months to activate. Various categories of viruses are:  Boot Sector Virus: Boot sector virus infects the master boot record of a computer system. This virus either moves the boot record to another sector on the disk or replaces it with the infected one. It then marks that sector as a bad spot on the disk. This type of virus is very difficult to detect since the boot sector is the first program that is loaded when a computer starts. In effect, the boot sector virus takes full control of the infected computer.  File Infecting Virus: File infecting virus infects files with extensions.com and.exe. This type of virus usually resides inside the memory and infects most of the executable files on a system. The virus replicates by attaching a copy of itself to an uninfected executable 16  program. It then modifies the host programs and subsequently, when the program is executed, it executes along with it. File-infecting virus can only gain control of the computer if the user or the operating system executes a file infected with the virus.  Stealth Virus: Stealth virus attempts to conceal its presence from the user. It reads system files or system sectors and when some other program requests for information from portions of the disk, it changes back into the correct (unchanged) form. Use of stealth virus is the major reason why most antivirus programs operate best when the system is started (booted) from a known-clean floppy disk. When this happens, the virus does not gain control over the system and is immediately available to be seen and dealt with. The Stoned Monkey virus is an example of stealth virus. This virus uses 'read stealth' capability and if a user executes a disk-editing utility to examine the main boot record, the user would not find any evidence of infection.  Multipartite Virus: Multipartite virus infects both boot sectors and executable files, and uses both mechanisms to spread. It is the worst virus of all because it can combine some or all of the stealth techniques along with polymorphism to prevent detection. For example, if a user runs an application infected with a multipartite virus, the virus activates and infects the master boot record of the hard disk. Moreover, the next time the computer starts; the virus gets activated again and starts infecting every program that the user runs. One-half virus is an example of a multipartite virus, which exhibits both stealth and polymorphic behavior.  Polymorphic Virus: Polymorphic virus, unlike other viruses, consists of static virus program that gets copied from file to file as it propagates. Such virus is difficult to detect because each copy it generates, appears different from the other one. It uses encryption algorithm to multiply new copies of the program. For an encrypted virus to execute, it must decrypt the encrypted portion of itself. When an infected program launches, the virus decryption routine gains control of the computer and decrypts the rest of the virus body so that it can execute normally.  Worm: It is by far the most quickly spreading and sophisticated viruses. Internet worms exploit e-mail programs and network software to multiply their numbers. Once a system is infected, the worm may look for an address book and mail itself to everyone listed in the book.  Trojan horse: It is a kind of virus that hides its true intention. It was named after the famous hollow wooden horse used by the Greek hero Ulysses to sneak soldiers into the ancient city of Troy. It can be a threat to the computer software. They are often encountered as e-mail attachments with tempting or intriguing names that compel people to open them. Ill-effects of Viruses As already discussed, viruses are computer programs, which can virtually do anything like any normal program. This includes deleting files, formatting a user's hard drive, overwriting the system BIOS and completely disabling the computer. Some ill-effects that can be caused by viruses are as follows: 17  i. Corrupting the data ii. Increasing the file size iii. Formatting the hard disk iv. Slowing down the system v. Manipulating the directory contents vi. Renaming all files with different names Remedy of Viruses Different organizations have different styles of operation. This fact extends to the way they set up their computer networks and operating procedures. If computer operations consist of one or two personal computers used by fewer people, then the need for an elaborate defence system is not of utmost importance. However, if system is large enough to include the worldwide networks used by large corporations, then a detailed and systematic defense system is required. Using Antivirus Software In the early days of computer networking, computers were not networked very well, and computer viruses spread extremely slowly. Files were transmitted by means of bulletin board systems (BBSs) or on diskette. As a result, the transmission of infected files was not that fast and easy. However, as the connectivity improved, mostly by the use of computers in the workplace, the scope of virus threat widened. First, there was LAN, and then there was WAN and now the Internet. The extensive use of e-mail has also contributed to the significant rise in the number of virus incidents. As a result, probability of getting infected by a virus today is more than it was a few years ago. Until the preventive measures for virus were not invented, the only option to get rid of them was to get rid of that valuable file, which was infected. This proved very costly to the companies whose valuable work was destroyed due to viruses. As the computer technology gained heights, these viruses also advanced in causing destruction. Then came a software utility called Antivirus to the rescue. Antivirus is a software utility, which (upon installing on a computer) scans the hard disk for viruses and tries to remove them, if found. Most Antivirus programs include an auto-update feature that enables the program to download profiles of new viruses so that it can check for the new viruses as soon as they are discovered. The most popular Antivirus software available include Norton Antivirus, McAfee Antivirus and Avira AntiVir. Antivirus software has normally a built-in scanner, which scans all files on the computer hard disk. It looks for changes and activities in computers typical in case of a virus attack. Scanner look for particular types of codes within the programs. The software generally relies on having prior knowledge of the virus. As a result, frequent update to the tools is necessary. The important thing is to be aware of the possibility of an attack to possess a good virus checking software and to have data backups. 18