Kĩ thuật lập trình - The internet & the world wide web

1The Internet & the World Wide WebExploring CyberspaceConnecting to the InternetHow Does the Internet work?The World Wide WebEmail & Other Ways of Communicating over the NetTelephony, Multimedia, Webcasting, Blogs, E-CommerceSnooping, Spoofing, Phishing, Pharming, Cookies, & SpywareChapter2McGraw-Hill/Irwin© 2007 The McGraw-Hill Companies, Inc. All rights reserved.Connecting to the InternetInternet HistoryBegan with 1969’s ARPANET for US Dept. of Defense62 computers in 1974500 computers in 198328,000 computers in 1987Early 1990s, multimedia became available on internetTo connect you needAn access device (computer)A means of connection (phone line, cable hookup, or wireless)An Internet Service Provider (ISP)3Connecting to the InternetDefinition: Bandwidth is an expression of how much data – text, voice, video and so on – can be sent through a communications channel in a given amount of time.Definition: Baseband is a slow type of connection that allows only one signal to be transmitted at a time.Definition: Broadband is a high speed connection that allows several signals to be transmitted at once. 4Connecting to the InternetData Transmission SpeedsOriginally measured in bits per second (bps) 8 bits are needed to send one character, such as A or aCurrently measured in kilobits per second (Kbps)Kilo- stands for a thousandA 28.8 Kbps modem sends 28,800 bits per secondHow many characters per second would that be?Mbps connections send 1 million bits per secondGbps connections send 1 billion bits per second28,800 / 8 = 3600 characters per second5Connecting to the InternetModemsCan be either internal or external to your PCMost ISPs offer local access numbersNeed call waiting turned off; either manually or in WindowsHigh-speed phone linesISDN lineDSL lineCable ModemsSatelliteWi-Fi & 3G6Connecting to the InternetModemsHigh-speed phone linesISDN lineIntegrated Services Digital NetworkAllows voice, video, & data transmission over copper phone linesCan transmit 64 to 128 KbpsDSL lineUses regular phone lines, DSL modemReceives data at 1.5-9 Mbps; sends at 128Kbps – 1.5 MbpsIs always onCable ModemsSatelliteWi-Fi & 3G7Connecting to the InternetModems28.8 Kbps takes 4 3/4 hours to download 6 minute videoHigh-speed phone linesISDN line1 hour to download 6 minute videoDSL line11 minutes to download 6 minute videoCable ModemsConnects the PC to a cable-TV system2 minutes to download a 2 minute videoSatelliteWi-Fi & 3G8Connecting to the InternetModemsHigh-speed phone linesISDN lineDSL lineCable ModemsSatelliteAlways-on connection using satellite dish to satellite orbiting earthSend data at 56 – 500 Kbps; receive at 1.5 MbpsWi-Fi & 3G9Connecting to the InternetModemsHigh-speed phone linesISDN lineDSL lineCable ModemsSatelliteWi-Fi & 3GWi-Fi Name for a set of wireless standards set by IEEETypically used with laptops that have Wi-Fi hardware3GHigh-speed wireless that does not need access pointsUses cell phones10Connecting to the InternetInternet Access ProvidersInternet Service Providers (ISP)Local, regional, or national organization that provides internet accessExamples: AT&T Worldnet, EarthLinkCommercial Online ServiceA members-only company that provides specialized content and internet accessExamples: AOL, MSNWireless Internet Service Providers11Connecting to the InternetInternet Access ProvidersCommercial Online ServiceWireless Internet Service ProvidersInternet Access for laptops, notebooks, smartphones, PDA usersThese devices contain wireless modemsExamples: AT&T Wireless, Verizon Wireless, Earthlink Net Zero12How Does the Internet Work?The internet consists of thousands of smaller networksThese link educational, commercial, nonprofit, and military organizationsMost are Client/Server networksClient: a computer requesting data or servicesServer or Host: a central computer supplying data or services requested of it13How Does the Internet Work?Point of Presence (POP)A local access point to the internetA local gateway to the ISP’s networkNetwork Access Point (NAP)A routing computer at a point on the internet where several connections come togetherOwned by Network Service Providers (NAP)Four major NAPs established in 1993 when the internet was privatized Source of much internet congestion  PNAPS14How Does the Internet Work?Private/Peer NAPs (PNAP)Established in late 1990sProvide more backbone access locations than the original 4 NAPs in Chicago, Washington D.C., New Jersey and San Francisco>100 in U.S.A. at presentFacilitate more efficient routing since there are more backbone access locations15How Does the Internet Work?Internet BackboneHigh-capacity, high-speed data transmission lines Use the newest technologyProviders include AT&T, Cable & Wireless, Sprint, Teleglobe, UUNETInternet 2Cooperative university/business research projectNew standards for large-scale higher-speed data transmission Requires state-of-the-art infrastructure 16How Does the Internet Work?ProtocolsThe set of rules a computer follows to electronically transmit data.TCP/IP is the internet protocolDeveloped in 1978Used for all internet transactionsPacketsFixed-length blocks of data for transmissionData transmissions are broken up into packets17How Does the Internet Work?IP AddressesEvery device connected to the internet has an addressEach IP address uniquely identifies that deviceThe address is four sets of 3-digit numbers separated by periodsExample: 95.160.10.240Each number is between 0 and 255Static IP addresses don’t changeDynamic IP addresses don’t changeSince addresses are limited, and most PCs are not connected a lot of the time, dynamic addresses are common18How Does the Internet Work?The board of trustees of the Internet Society (ISOC) oversees the standardsInternet Corporation for Assigned Names and Numbers (ICANN) regulates domain namesAmerican Registry for Internet Numbers (ARINN) administers the unique IP addresses for North & South America, Caribbean, and sub-Saharan AfricaTwo other organizations administer the unique IP addresses for Europe and the Asia-Pacific region19The World Wide WebBrowsersSoftware for web-surfingExamples: Internet Explorer, Netscape Navigator, Mozilla FireFox, Opera, Apple Macintosh browserWebsiteThe location on a particular computer that has a unique addressExample: www.barnesandnoble.com, www.mcgraw-hill.comThe website could be anywhere – not necessarily at company headquarters20The World Wide WebWeb PagesThe documents and files on a company’s websiteCan include text, pictures, sound, and videoHome pageThe main entry point for the websiteContains links to other pages on the website21The World Wide WebUniform Resource Locator (URL)A character string that points to a specific piece of information anywhere on the webA website’s unique addressIt consists ofThe web protocol, httpThe domain name of the web serverThe directory or folder on that serverThe file within the directory, including optional extension namefile name . extensiondirectory22The World Wide WebDomain namesMust be uniqueIdentify the website, and the type of site it iswww.whitehouse.gov is NOT the same as www.whitehouse.org.gov means government.org means professional or nonprofit organizationDiscussion Question: Have you ever mistyped a URL and gone to a website you weren’t expecting? As we learn later in this chapter, some unscrupulous websites take advantage of this.23The World Wide WebHTTPThe internet protocol used to access the World Wide WebHTTPSThe secure version of HTTP Hypertext Markup Language (HTML)The language used in writing and publishing web pagesThe set of tags used to specify document structure, formatting, and links to other documents on the webHypertext links connect one web document to another24The World Wide WebWeb BrowsersYour tool for using the internetComes preinstalled on most PCs5 basic elementsMenu barToolbarURL barWorkspaceStatus bar25The World Wide WebHome PageThe page you see when you open your web browserYou can change the Home Page on your browserBack,Forward, Home & SearchUse the menu bar icons to move from one page to another26The World Wide WebNavigationHistory ListsA list of websites you visited since you opened up your browser for this sessionAllows you to easily return to a particular siteBookmarksAllows you to store the URL from a site on your PC so you can find it again in another browser sessionTo save the URL for a site, click on “Bookmark” in Internet Explorer or Mozilla FirefoxOr just type in the URL of the page you want to visit27The World Wide WebWeb portalsA gateway website that offers a broad array of resources and services, online shopping malls, email support, community forums, stock quotes, travel info, and links to other categories.Examples: Yahoo, AOL, Microsoft Network (MSN), Lycos, or GoogleMost require you to log in, so you canCheck the home page for general informationUse the subject guide to find a topic you wantUse a keyword to search for a topic28The World Wide WebSearch ServicesOrganizations that maintain databases accessible through websites to help you find information on the internetExamples: portals like Yahoo Search and MSN, and Google, Ask Jeeves, and GigablastDatabases are compiled using software programs called spidersSpiders crawl through the World Wide WebFollow links from one page to anotherIndex the words on that siteDiscussion Question: If you publish an embarrassing web page and then take it down, is it REALLY gone?29The World Wide Web4 web search toolsKeyword IndexesType one or more search keywords, and you see web pages “hits” that contain those wordsFor phrases with two or more words, put phrase in quotesExamples are Google, Gigablast, HotBot, MSN Search, TeomaSubject DirectoriesSearch by selecting lists of categories or topicsExample sites are Beaucoup, Galaxy, LookSmart, MSN Directory, Netscape, Open Directory Project, YahooMetasearch EnginesSpecialized Search Engines30The World Wide Web4 web search toolsKeyword IndexesSubject DirectoriesMetasearch EnginesAllows you to search several search engines simultaneouslyExamples are Dogpile, Ixquick, Mamma, MetaCrawler, ProFusion, Search, VivisimoSpecialized Search EnginesHelp locate specialized subject matter, like info on movies, health, jobs31The World Wide WebMultimedia Search ToolsAllow you to search for nontext resources Search Tool SiteA9 (Amazon.com) World Wide WebShould you trust information you find online?There is no central authority that verifies all internet sitesGuidelines to evaluate Web ResourcesDoes the information appear on a professional site maintained by a professional organization?Does the website authority appear to be legitimate?Is the website objective, complete, and current?33Email & Other Ways of Communicating over the NetEmail ProgramEnables you to send email by running email software on your computer that interacts with an email server at your ISPIncoming mail is stored on the server in an electronic mailboxUpon access, mail is sent to your client’s inboxExamples: Microsoft’s Outlook Express, Netscape’s Mail, Apple Computer’s Apple Mail, QualComm’s EudoraDiscussion Question: If your email is stored at the server and servers are backed up, when you delete an email is it gone for good?34Email & Other Ways of Communicating over the NetWeb-based EmailYou send and receive messages by interacting via a browser with a websiteAdvantage: You can easily send and receive messages while travelingExamples: Yahoo! Mail, Hotmail, Bluebottle, Sacmail35Email & Other Ways of Communicating over the NetUsing emailGet an email address, following the format Joe_Black@earthlink.net.usType addresses carefully, including capitalization, underscores, and periodsUse the reply command to avoid addressing mistakesUse the address-book feature to store email addressesSort your email into folders or use filtersUser NameDomain name36Email & Other Ways of Communicating over the NetEmail AttachmentsA copy of a file or document that you send attached to an email to one or more peopleBe careful about opening attachmentsMany viruses hide in themKnow who is sending it to you before you open itThe recipient must have compatible software to open the attachment. If they don’t have Excel, they probably can’t read the spreadsheet you sent them.37Email & Other Ways of Communicating over the NetInstant MessagingAny user on a given email system can send a message and have it pop up instantly on the screen of anyone logged into that systemExamples: AOL Instant Messenger, MSN Messenger, ICQ, AT&T IM Anywhere, Yahoo MessengerNot all IM systems interoperateTo get it, you:download the software connect to the internetregister with the service38Email & Other Ways of Communicating over the NetFTP – File Transfer ProtocolA software standard for transferring files between computers with different Operating SystemsMicrosoft Windows  Linux Unix  Macintosh OS, and so forthYou can transfer files from an FTP site on the internet to your PCKnow your FTP site! If the FTP site is offering copyrighted material such as music and movies for free, you are breaking US law if you download files!You may also get a virus or spyware on your PC from them39Email & Other Ways of Communicating over the NetNewsgroupsA giant electronic discussion boardThere are thousands of free internet newsgroupsUsenet is the worldwide public network of servers on the internet www.usenet.com To participate you need a newsreaderListservAn email-based discussion groupUses an automatic mailing-list server that sends email to subscribers on selected topics40Email & Other Ways of Communicating over the NetReal-Time Chat (RTC)Participants have a typed discussion while online at the same timeThis is not allowed in most college classroomsIM is one-on-one, but RTC has a list of participantsNetiquette – appropriate online behaviorBefore you ask a question, consult the FAQAvoid flamingDon’t SHOUT – use all capital lettersBe careful with jokesDon’t send huge file attachments unless requested41Telephony, Multimedia, Webcasting, Blogs, E-CommerceInternet TelephonyUses the internet to make phone callsLong-distance calls are either very inexpensive or freeWith no PC, dial a special phone number to packetize your callWith a PC that has a sound card, microphone, Internet connection, and internet telephone software such as Netscape Conference or Microsoft NetMeetingCurrently inferior in quality to normal phone connectionsAlso allows videoconferencing42Telephony, Multimedia, Webcasting, Blogs, E-CommerceMultimedia on the WebAllows you to get images, sound, video, and animationMay require a plug-in, player, or viewerA program that adds a specific feature to a browser so it can view certain filesExample: Adobe Acrobat Reader, RealPlayer, QuickTimeMultimedia AppletsSmall programs that can be quickly downloaded and run by most browsersJava is the most common Applet languageMicrosoft’s Visual Studio creates ActiveX and com objects 43Telephony, Multimedia, Webcasting, Blogs, E-CommerceMultimedia on the WebAnimationThe rapid sequencing of still images to create the appearance of motionUsed in video games and web images that seem to moveVideoStreaming video is process of transferring data in a continuous flow so you can begin viewing a file before it is all completely sentAudio may be transmitted either:Downloaded completely before the file can be played, orDownloaded as streaming audio44Telephony, Multimedia, Webcasting, Blogs, E-CommerceRSS newsreadersPrograms that scour the web and pull together “feeds” from several websites to one placeBlogShort for web log, a diary-style web pageHave become popular, both privately and in politicsPodcastingRecording internet radio or similar internet audio programsSome radio stations webcast their audio programs over the internet 45Telephony, Multimedia, Webcasting, Blogs, E-CommerceE-CommerceConducting business activities onlineB2B Commerce is business-to-business e-commerceOnline Finance now involves online banking, stock trading online, and e-money such as PayPalOnline auctions link buyers with sellerseBay is the most well-known example of person-to-person auctionsOnSale is a vendor-based auction that buys merchandise and sells it at a discountPriceline is an auction site for airline tickets and other items46Snooping, Spoofing, Phishing, Pharming, Cookies, & SpywareThe internet was founded as a collaborative tool based on trustNot everyone on the internet is honestSnoopingEmail is not privateCorporate management has the right to view employees’ emailEmail that travels over the internet may be captured and monitored and read by someone elseNot all ISPs protect their customers’ privacy47Snooping, Spoofing, Phishing, Pharming, Cookies, & SpywareSpam: Electronic Junk MailUnsolicited email that takes up your time and may carry viruses or spywareDelete it without opening the messageNever reply to a spam messageWhen you sign up for something, don’t give your email addressUse spam filtersFight back by reporting new spammers to www.abuse.net or www.spamhaus.org or www.rahul.net/falk 48Snooping, Spoofing, Phishing, Pharming, Cookies, & SpywareSpoofingUsing fake email sender names so the message appears to be from a different source, so you will trust it.If you don’t know the sender, don’t open it.PhishingUsing trusted institutional names to elicit confidential informationSome common schemes look like they are from your bank or from eBay and ask you to “update” your account. Don’t do it – the legitimate company already knows your account information!If you want to update your information, CALL the number in the phone book, not the number in the email!49Snooping, Spoofing, Phishing, Pharming, Cookies, & SpywarePharmingRedirecting you to an imposter web page.Thieves implant malicious software on your PCRedirects you to an imposter web page even when you type the correct URL!To foil it, type the URL with https first (for http secure) https://www.microsoft.com Use this one with https, not Since it has http, it could be spoofed50Snooping, Spoofing, Phishing, Pharming, Cookies, & SpywareCookiesLittle text files left on your hard disk by some websites you visitCan include your log-in name, password, and browser preferencesCan be convenientBut they can be used to gather information about you and your browsing habits51Snooping, Spoofing, Phishing, Pharming, Cookies, & SpywareSpywareApplications that download without your knowledgeThey hide on your PC and capture information about what is on the PC and what you are doingThat information is then transmitted to the spyware master’s website on the internetInformation may be used against you to steal your identity, get credit cards in your name, or for other crimes52Snooping, Spoofing, Phishing, Pharming, Cookies, & SpywareSpyware (continued)To prevent spyware, you must install and use “Antispyware software” at all timesExamples: Ad Aware, AntiSpyware, Spybot Search & Destroy, Pest Patrol, SpyCatcher, Yahoo toolbar with Anti-SpyBe careful about free and illegal downloads since they are a source of spywareDon’t say “I agree” when you are downloading something – read the fine printBeware of unsolicited downloads53