The World Wide Web. http: //www. hw. ac. uk/libwww/irn/irn. html UNIT 13. Study this URL (Uniform Resource Locator).

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1 UNIT 13 The World Wide We STARTER Study this URL (Uniform Resource Loctor). http: //www. hw. c. uk/liwww/irn/irn. html Fig 1 Uniform Resource Loctor protocol prefix We domin domin nme extension country code directory pth document Which prt of the ddress tells you: 1 the compny is in the UK 2 this is the wepge 3 the type of trnsmission stndrd your rowser must use to ccess the dt 4 this points to the computer where the wepge is stored 5 this is where the wepge is stored in the computer 6 this is compny 7 this is We file Study these pproved domin nme extensions nd their menings. Then mtch these suggestions for new extensions to their menings. Extension. ero. iz. com (. co in UK). coop. edu(. c in UK). gov. info. int. mil. museum. nme. net. org. pro Mening vition industry usinesses commercil coopertives eductionl nd reserch government generl use interntionl orgnistion militry gency museums individuls gtewy or host non-profit orgnistion professionls

2 Suggested extension firm. store. we. rts. rec. info. nom Mening informtive culturl or entertinment c personl d firm or gency e online retil shop f We-relted g recretionl LISTENING Study this digrm which illustrtes how your rowser finds the wepge you wnt. Lel these items: c d e f Router Domin Nme System (DNS) server Remote We server Browser PC URL Internet Protocol ddress Fig 2 How your rowser finds the pge you wnt

3 90 UNIT 13 The World Wide We Now listen to this recording which explins how the process works nd tke rief notes on ech stge. For exmple: Stge 1 Click on wepge hyperlink or URL. The rowser sends the URL to DNS server. LANGUAGE WORK Time cluses Wht is the reltionship etween ech of these pirs of ctions? 1 You click on URL. Your rowser sends it to DNS server. 2 The pckets re pssed from router to router. They rech the We server. 3 The pckets my trvel y different routes. They rech the We server. 4 The individul pckets rech the We server. They re put ck together gin. Ech pir of ctions is linked in time. We cn show how ctions re linked in time y using time cluses. For exmple: We cn use when to show tht one ction hppens immeditely fter nother ction: 1 When you click on URL, your rowser sends it to DNS server. We cn use once in plce of when to emphsise the completion of the first ction. It often occurs with the Present perfect. For exmple: Once the DNS server hs found the IP ddress, it sends the ddress ck to the rowser. We cn use until to link n ction nd the limit of tht ction: 2 The pckets re pssed from router to router until they rech the We server. We cn use efore to show tht one ction precedes nother: 3 The pckets my trvel y different routes efore they rech the We server. If the sujects re the sme in oth ctions, we cn use prticiple: The pckets my trvel y different routes efore reching the We server. We cn use s to link two connected ctions hppening t the sme time: 4 As the individul pckets rech the We server, they re put ck together gin. Link ech pir of ctions using time cluse. You use serch engine. It provides set of links relted to your serch. With POP3, emil is stored on the server. You check your emil ccount. You hve clicked on hyperlink. You hve to wit for the wepge to e copied to your computer.

4 UNIT 13 The World Wide We 91 4 You listen to the first prt of stremed udio file. The next prt is downloding. 5 The grphics cn e displyed grdully. The wepge is downloded. 6 You receive n emil messge. You cn forwrd it to nother ddress. 7 You click on hyperlink. The rowser checks to see if the linked wepge is stored in the cche. 8 You cn ookmrk wepge to mke it esier to find in the future. You find wepge you like. 9 You type in We ddress. You should press the Enter key. 10 You click on the Home utton. The rowser displys your strting wepge. Fill in the gps in this description of uffering, wy of ensuring tht We video runs smoothly. The plyer feeds udio or video dt into the uffer. When connection slowdowns or interruptions occur, the mount of dt in the uffer decreses, ut s long s some remins, plyck is uninterrupted. Dt goes out to the plyer's decompression nd plyck routines. Streming is wy of deling with ndwidth prolems 1 you downlod video from the Internet. One key to successful streming is the process of uffering 2 you downlod movie, the video plyer stores prt of the 3 movie in memory plying it. Imgine the uffer s continer filled from the top s shown in Fig 3 4 the continer is full, the plyer sends dt on for plyck from the ottom. Dt keeps coming in 5 clip plys. The user cn view the eginning of the movie 6 the rest of the clip downlods. 7 connection slowdowns or interruptions occur, the mount of dt in the uffer decreses ut s long s some remins, plyck is uninterrupted. Plyck continues t stedy rte 8 the uffer is empty. Fig 3 Video uffering

5 92 UNIT 13 The World Wide We PROBLEM-SOLVING Serch engines Study these tips for conducting serches using AltVist. Then decide wht you would type into the serch ox to find this dt. Compre your nswers with others in your group nd together decide wht would e the est serch. Restrict sites to English lnguge. Don't use simple keywords. Typing in the word footll is unlikely to help you to find informtion on your fvourite footll tem. Unless specil opertors re included, AltVist ssumes the defult opertor is OR. If, for exmple, the serch query is Americn footll, AltVist will look for documents contining either Americn or footll lthough it will list higher those documents which contin oth. AltVist is specificlly cse sensitive. If you specify pple s your serch term, AltVist will return mtches for pple, Apple nd APPLE. However, if you use Apple or pple, AltVist will only mtch Apple nd pple respectively. AltVist supports nturl lnguge queries. If you relly ren't sure where to strt looking, try typing nturl lnguge query in the serch ox. The question Where cn I find pges out digitl cmers? will find numer of nswers ut t lest it will give you some ide of where to strt.

6 UNIT 13 The World Wide We 93 Try using phrse serching. This is where you plce quottion mrks round your serch term, e. g. 'lterntive medicine'. This will serch for ll documents where these two words pper s phrse. Attching + to word is wy of nrrowing your serch. It mens tht word must e included in your serch. For exmple, if you were looking for informtion on cncer reserch, use +cncer +reserch insted of just cncer. Attching - to word or using NOT is nother wy of nrrowing your serch. This excludes the serch item following the word NOT or the - sign. For exmple, science NOT fiction or science -fiction will exclude sites in which these two words occur together. Use rckets to group complex serches, for exmple: (ckes AND recipes) AND (chocolte OR ginger) will find pges including ckes nd recipes nd either chocolte or ginger or oth. You cn refine your serch y doing field serch. Put the field, then colon nd then wht you re looking for. For exmple, URL: UK +universities will find only British universities. title: 'English lnguge' will find only sites which contin this phrse in their titles. AltVist supports the use of wildcrd serches. If you insert * to the right of prtil word, sy hydro*, it will find mtches for ll words eginning with hydro such s hydrocron nd hydrofoil. Wildcrds cn lso e used to serch for pges contining plurls of the serch terms s well s to ctch possile spelling vritions, for exmple lumin*m will ctch oth luminium (UK) nd luminum (US). If you re looking for multimedi files then sve yourself time y selecting imges, udio or video with the rdio uttons on AltVist's serch ox nd then entering your serch street mp of Edinurgh, Scotlnd trin times etween London nd Pris the exchnge rte of your currency ginst the US dollr recipe for chocolte chip or hzelnut rownies video clips of the Betles sumo wrestler competitions in Jpn this yer the wether in New York city tomorrow hert disese mongst women New Zelnd universities which offer courses in computing Sir Isc Newton's lws of motion Test your nswers using AltVist. WRITING Write your own description of how your rowser finds the pge you wnt. Use Fig 2 to help you. When you hve finished, compre your nswer with the listening script to Tsk 4 on pge 198.

7 94 UNIT 13 The World Wide We Find the nswers to these questions in the following text. Nme three different emil protocols mentioned in the text. Which emil protocol is used to trnsfer messges etween server computers? Why is SMTP unsuitle for delivering messges to desktop PCs? Nme two host-sed mil systems mentioned in the text. Where re emil messges stored in n SMTP system? Wht hppens when you use your We mil ccount to ccess POP3 milox? Give n dvntge nd disdvntge of hving n option to leve POP3 messges on the server. Wht re the dvntges of using the IMAP4 protocol? We mil systems use some of the sme protocols s client/server mil. Some cn ccess n ISP-sed POP3 milox, llowing you to red your mil nywhere you cn find rowser. Emil Protocols Although the formt of mil messge, s trnsmitted from one mchine to nother, is rigidly defined, different mil protocols trnsfer nd store messges in slightly different wys. The mil system you're proly used to employs comintion of SMTP nd POP3 to send nd receive mil respectively. Others my use IMAP4 to retrieve mil, especilly where ndwidth is limited or expensive. SMTP is used to trnsfer messges etween one mil server nd nother. It's lso used y emil progrms on PCs to send mil to the server. SMTP is very strightforwrd, providing only fcilities to deliver messges to one or more recipients in tch mode. Once messge hs een delivered, it cn't e reclled or cncelled. It's lso deleted from the sending server once it's een delivered. SMTP uses 'push' opertion, mening tht the connection is initited y the sending server rther thn the receiver. This mkes it unsuitle for delivering messges to desktop PCs, which ren't gurnteed to e switched on t ll times.

8 UNIT 13 The World Wide We 95 In host-sed mil systems, such s Unix nd We mil, SMTP is the only protocol the server uses. Received messges re stored loclly nd retrieved from the locl file system y the mil progrm. In the cse of We mil, the messge is then trnslted into HTML nd trnsmitted to your rowser. SMTP is the only protocol for trnsferring messges etween servers. How they're then stored vries from system to system. Post Office Protocol POP is messge-retrievl protocol used y mny PC mil clients to get messges from server, typiclly your ISP's mil server. It only llows you to downlod ll messges in your milox t once. It works in 'pull' mode, the receiving PC inititing the connection. PC-sed POP3 mil clients cn do this utomticlly t preset intervl. When you use your We mil ccount to ccess POP3 milox, the mil server opens connection to the POP3 server just s PC-sed ppliction would. The messges re then copied into your We milox nd red vi rowser. Since POP3 downlods ll the messges in your milox, there's n option to leve messges on the server, so tht they cn e picked up from different mchines without losing ny. This does men tht you'll get every messge downloded every time you connect to the server. If you don't clen out your milox regulrly, this could men long downlods. When using We mil ccount to retrieve POP3 mil, e creful out leving messges on the server - if too mny uild up. ech downlod will tke long time nd fill up your inox. Mny We mil systems won't recognise messges you've lredy downloded, so you'll get duplictes of ones you hven't deleted. Internet Mil Access Protocol IMAP is similr in opertion to POP, ut llows you more choice over wht messges you downlod. Initilly, only messge heders re retrieved, giving informtion out the sender nd suject. You cn then downlod just those messges you wnt to red. You cn lso delete individul messges from the server, nd some IMAP4 servers let you orgnise your mil into folders. This mkes downlod times shorter nd there's no dnger of losing messges. 0 Re-red the text to find the nswers to these questions. 1 Mrk the following sttements s True or Flse: c d e f g Different mil systems trnsfer emils in different wys. IMAP4 requires more ndwidth thn the other emil protocols. SMTP is used for sending emils from PC to server. SMTP delivers messges one t time. SMTP does not llow delivered messge to e cncelled. SMTP is only one of mny protocols used to send mil etween servers. POP protocol llows the user to downlod one messge t time. 2 Mtch the terms in Tle A with the sttements in Tle B. Tle A c SMTP 'Push' opertion POP d 'Pull' opertion e IMAP Tle B i An emil trnsfer process in which the connection is initited y the sending computer rther thn the receiving computer. ii A mil trnsfer protocol tht initilly only retrieves the messge heders. iii An emil trnsfer process in which the receiving computer initites the connection. iv A simple mil trnsfer protocol tht is used to send messges etween servers. v A messge-retrievl protocol tht downlods ll emil messges t the sme time. [Adpted from 'Using We-sed Emil' y Jonthn Bennett, PC Mgzine, Novemer 1999]