the internet session 6

8/8/2019 The Internet Session 6

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The InternetHow it Works


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A Brief History

The Int e rne t b ega n way back in 1969 - but it w a s c alled t he ARPANE T t he n. It st a rt ed out a sa r e s ea rc h proj e ct, a nd w a s devel op ed by a nage ncy c alled ARPA (A dva nc ed R e s ea rc h

Proj e cts A ge ncy) wit hin t he US D efe ns e De p a rtm e nt, in conjunction wit h a numb e r o f uni ve rsiti e s a nd mi l it a ry contr a ctors.


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Its purpos e w a s to ex p l or e t he possibi l ity o f a communic a tion n e twork t ha t cou ld surv i ve an u cl e a r attack . Th is w a s a c hi eved by hav ing a ne twork w he r e da t a cou ld t a k e mu l tiple pa t hs

f rom its sourc e to its de stin a tion. I f pa rt o f t he ne twork w a s de stroy ed , communic a tions wou ld sti ll be possib le t hrou gh a d i ffer e nt p a t h.


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W hat is the Internet??

The Int e rne t is a wor ld -wi de syst e m o f int e rconn e ct ed comput e rs wit h mor e t ha n 2 bi ll ion us e rs t ha t a r e l ink ed f or t he ex c ha nge of da t a , n e ws, con ve rs a tion a nd comm e rc e .


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The I nt er n e t is a gl ob al syst e m o f int e rconn e ct ed comput e r n e tworks t ha t us e t he st a nda r d Int e rne t Protoco l Suit e ( TC P/IP) to s e r ve bi ll ions o f us e rswor ld wi de . It is a ne twork o f ne tworks t ha t consists o f mi ll ions o f pri va t e , pub l ic, a c ade mic, busin e ss, a nd g ove rnm e nt n e tworks o f l oc al to gl ob al scop e t ha t a r e l ink ed by a bro ad a rr a y o f ele ctronic a nd optic al ne tworkin g t e c hno l og i e s. The Int e rne t c a rri e s a va st a rr a y o f inf orm a tion r e sourc e s a nd s e r v ic e s, most not a bl y t he int e r-l ink ed hyp e rt ex t d ocum e nts o f t he Wor ld Wi de W e b (WWW) a nd t he inf r a structur e tosupport ele ctronic m a i l .


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S everal ways to look at what theInternet actually is.

At t he hi ghe st level , t he Int e rne t is t he peo p l et ha t us e it - t he gl ob al community o f us e rs.


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At a not he r level , t he Int e rne t is a s e t o f p ro t o c o l s t ha t def ine t he ru les o f how t he comput e rs wi ll tr a ns fe r inf orm a tion wit h on e a not he r.


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At t he l ow e st level , it is t he h a rd wa re beh ind t he comput e r n e tworks - t he comput e rs,mo de ms, p hon e l ine s a nd c a bles t ha t l ink toge t he r to f orm a huge ne twork.


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W hat is the W orld W ide W eb?

The off ici al def inition o f t he WWW is "wi de -a r ea hype rm ed i a inf orm a tion r e tri eval initi a ti ve a iming to g i ve uni ve rs al a cc e ss to a lar ge uni ve rs e of d ocum e nts."


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WWW (W orld W ide W eb)

The i dea f or t he Wor ld Wi de W e b c a me f romC ERN - (t he Europ ea n La bor a tory f or P a rtic le P hysics). The y n eeded a w a y to k ee p tr a ck o f t he ir inf orm a tion a nd d ocum e nt a tion so t ha t it

cou ld be ea si l y a cc e ss ed a nd up da t ed .S eve r al d i ffer e nt w a ys o f v i e wing Wor ld Wi de W e b d ocum e nts w e r e dev ised

N a tion al Ce ntr e f or Sup e rcomputin g App l ic a tionsdevel op ed a pro g r a m c alled M os aic' in 1993 t ha t s ha p ed t he WWW into w ha t w e know it a s to da y.


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M os a ic w a s t he f irst g r a ph ical W e b b ro w ser -it all ow ed t ex t, g r a p hics, soun d s a nd ot he r mu l timed i a to b e v i e w ed in on e d ocum e nt. Th isr ev ol utioniz ed t he W e b a nd brou gh t its pot e nti al

to t he a tt e ntion o f t he r e st o f t he wor ld .


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L ist of Browsers

N e tsc a p e N av i ga tor N e tsc a p e C ommunic a tor Int e rne t E x p l or e r M ozi lla App l ic a tion Suit eM ozi lla Fir ef o x


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L anguage of the Internet

W e b Pa g e : A sin gle W e b d ocum e nt. E ve ryt hing you c a n s ee in your brows e r win d ow a t on e time (inc l ud ing w ha t you c a n s ee by scro ll ing )ma k e s up on e W e b p age .

B ro w ser, W e b B ro w ser : The pi e c e of so f tw a r e t ha t runs on your comput e r a nd all ows you tov i e w W e b p age s. The most common brows e rs

a r e N e tsc a p e a nd Int e rne t E x p l or e r.


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W e b Sit e : A s e t o f W e b p age s t ha t a r e l og ic all y conn e ct ed . The y usu all y have a consist e nt l ook a nd feel , a nd a r e all r ela t ed to t he s a me t he me .H ome Pa g e : The st a rting , intro d uctory or

w el com e page f or a W e b sit e . A p e rson's ownhom e page is a W e b p age t ha t de scrib e s all a bout t he m.


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W e b server, W e b S erver : A W e bs e r ve r is a comput e r w hic h hold s a numb e r o f W e b p age s,a nd 's e r ve s' t he m out to comput e rs t ha t r eq ue st t he m. The r e is not hing ve ry sp e ci al a bout t he

a ctu al comput e r - it's just a n or d ina ry comput e r (t hou gh usu all y a fa ir l y pow e r f ul on e ) runnin g sp e ci al so f tw a r e .


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S urf : "Sur f ing t he W e b" m ea ns c a su all y usin g t he W e b - not r eall y hav ing a ny d ir e ction, just c l ickin g t he l inks t ha t l ook int e r e stin g to f ind yours elf in w e ir d a nd int e r e stin g plac e s.

C yb ers pac e : A conc e ptu al plac e t ha t d oe sn't a ctu all y p hysic all y ex ist - but you c a n ro a ma roun d in it, v isit p lac e s, m ee t ot he r p e op le t he r e , c ha t to t he m, g o s hoppin g ... C ybe rsp a c e is a r eal wor ld me t a p hor f or t he Int e rne t.


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P os t : W he n you s e nd a me ss age to a d iscussion f orum , you'r e postin g . Th is wor d c a nbe us ed a s a ve rb ("I post ed a me ss age ") or a noun ("t ha t w a s a nic e post").

Snail M ail : T r ad itional ma i l usin g pa p e r, p e n,e nvel op e a nd st a mp.Lo cal : On your own comput e r, or on a

comput e r conn e ct ed c l os el y wit h yours ( a l oc al ne twork).


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FAQ : St a nd s f or Fr eq ue nt l y Ask ed Qu e stions.The y ori g ina t e f rom on l ine d iscussion f orumsw he r e mor e ex p e ri e nc ed us e rs g ot sick o f a nsw e ring t he s a me que stions o ve r a nd ove r

aga in. So t he y st a rt ed writing l ists o f f r eq ue nt l y a sk ed que stions a nd t he ir a nsw e rs so n e wbi e scou ld r efe r to t hos e . The conc e pt ha s g rown,a nd now a FAQ is mor e ge ne r al - de si g ned a sa n intro d uction to a c e rt a in topic


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I SP : St a nd s f or Int e rne t S e r v ic e Pro v i de r. The y a r e comp a ni e s w ho pro v i de you wit h Int e rne t a cc e ss eg T S TT . Usu all y you us e your t ele p hon e conn e ct ed to a mo de m to d i al up a nd

conn e ct your comput e r to your ISP.


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How a UR L W orkshttp : // www. d om a inn a me

.com /p a t h /to/ f i le .html

Th is in d ic a t e sit's a w e b p age add r e ss. It isquit e commonto leave t his

p a rt o ff . Inmo de rnbrows e rs, t he http : // wi ll a utom a tic all y

ge t pr ef i xed toadd r e ss e s youtyp e in.

Th is p a rt is c alled t he ' host n a me '. It ind ic a t e s w ha t comput e r t he

p age r e si de s on. A.com add r e ss isusu all y a n

Am e ric a n sit e (t hou gh not al w a ys), w hi le a

.nz add r e ss is a N e w Z eala nd sit e .

Th is p a rt sp e ci f i e s t he 'p a t h ' to t he a ctu al page you w a nt tol ook a t. E a c h '/' s e p a r a t e st he na me of t he d ir e ctori e s (or

f olde rs).

Th is is t he a ctu al na me of t he f i le , or

p age you a r e l ookin g a t. M ost p age s have a su ff i x of .html or .htm. Ot he r su ff ic e scou ld be .c g i, .a sp,.g i f , .jp g . Som e time syou' ll f ind t ha t t he r e is no f i le na me a t all ,

a nd t he ur l e nd s wit h a '/'. Th is m ea ns t ha t t he defa ul t p age wi ll be fe tc hed (common l y index .html or hom e .html ).


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The trick is to st a rt strippin g t hing s o ff t he URL,st a rting f rom t he e nd .

http : //mon e y.cnn.com/2006/12/04/t e c hno l og y/ps3_ti ps/in dex .htm


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P rotocols

In computin g , a p ro t o c o l is a con ve ntion or st a nda r d t ha t contro l s or e na bles t he conn e ction, communic a tion , a nd da t a tr a ns fe r be tw ee n two computin g e nd points. In its

simp lest f orm, a protoco l c a n b e def ined a s t h e ru l es g over nin g t he synt ax , s e ma ntics , a nd sync hroniz a tion o f communic a tion. Protoco l sma y b e imp leme nt ed by ha r d w a r e , so f tw a r e , or a combin a tion o f t he two. At t he l ow e st level , a

protoco l def ine s t he behav ior o f a ha r d w a r e conn e ction.


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TC P/ IP

T r a nsmission C ontro l Protoco l /Int e rne t Protoco l E a c h comput e r conn e ct ed up to t he Int e rne t ha s so f tw a r e c alled TC P/IP w hic h isr e sponsib le f or r e c e i v ing , s e nd ing a nd c he ckin g

p a ck e ts. TC P/IP is t he ' gl ue ' o f t he Int e rne t.


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Common P rotocols of TC P/ IP

H TT P (Hyp e r Tex t T r a ns fe r Protoco l )POP3 (Post O ff ic e Protoco l 3).S M T P (Simp le M a i l T r a ns fe r Protoco l ).F T P (Fi le T r a ns fe r Protoco l ).IP (Int e rne t Protoco l ).DH C P (Dyn a mic Host C on f i g ur a tion Protoco l ).


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Hyper Text Transfer P rotocol (HTT P )

Th is is t he protoco l us ed to tr a ns fe r da t a ove r t he Wor ld Wi de W e b. Tha ts w hy all W e b sit e add r e ss e s b eg in wit h http : // W he neve r you typ e a URL into your brows e r

a nd hit Ent e r, your comput e r s e nd s a n H TT P r eq ue st to t he a ppropri a t e W e b S e r ve r, w hic h isde si g ned to ha ndle H TT P r eq ue sts, t he n s e nd sto you t he r eq ue st ed H T M L page


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P ost Office P rotocol Version 3 ( P O P 3)

Loc al e -m a i l c l i e nts us e t he P os t O ff ic e P ro t o c o l vers i o n 3 ( POP3 ), a n a pp l ic a tion-lay e r Int e rne t st a nda r d protoco l , to r e tri eve e -ma i l f rom a r e mot e s e r ve r ove r a TC P/IP

conn e ction. N ea r l y all subscrib e rs to in d i v i d ual Int e rne t s e r v ic e pro v i de r e -m a i l a ccountsa cc e ss t he ir e -m a i l wit h c l i e nt so f tw a r e t ha t us e s POP3.


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S imple Mail Transfer P rotocol ( S MT P )

Th is Protoco l is us ed f or s e nd ing e -m a i l ove r t he Int e rne t.Your e -ma i l c l i e nt (suc h a s Out l ook, Eu d or a )us e s S M T P to s e nd a me ss age to t he ma i l

s e r ve r, a nd t he ma i l s e r ve r us e s S M T P to r ela y t ha t m e ss age to t he corr e ct r e c e i v ing ma i l s e r ve r

Ba sic all y, S M

T P is a s e t o f comm a nd s t ha t a ut he ntic a t e a nd d ir e ct t he tr a ns fe r o f ele ctronic ma i l .


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Internet P rotocol (I P )

An I P a ddress ( I nt er n e t P ro t o c o l A ddress ) isa uni que add r e ss t ha t dev ic e s us e in or de r toi de nti f y a nd communic a t e wit h ea c h ot he r on a comput e r n e twork uti l izing t he Int e rne t Protoco l

st a nda r d ( I P ). In simp ler t e rms, a comput e r add r e ss . Any p a rticip a ting ne twork dev ic e inc l ud ing rout e rs , comput e rs , tim e -s e r ve rs,

print e rs , Int e rne t fax ma c hine s, a nd som e t ele p hon e s c a n have t he ir own uni que add r e ss.


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W hat Happens W hen a Message is sent over the Internet?

It is brok e n up into a w hole l ot o f s a me-s iz ed p i e c es (c alled pack e t s ). A h e a der is added to ea c h pa ck e t t ha t ex p la insw he r e it c a me f rom, w he r e it s hou ld e nd up a nd

how it f its in wit h t he r e st o f t he pa ck e ts.


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E a c h pa ck e t is se nt from c om pu t er t o c om pu t er unti l it f ind s its w a y to its de stin a tion.E a c h comput e r al on g t he w a y de ci de s w he r e nex t to s e nd t he pa ck e t. Th is cou ld de p e nd on

t hing s l ik e how busy t he ot he r comput e rs a r e w he n t he pa ck e t w a s r e c e i ved . The pa ck e tsma y not all t a k e t he s a me rout e .


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At t he de stin a tion, t he pack e t s a re ex a m in ed .I f t he r e a r e a ny p a ck e ts missin g or da maged , a me ss age is s e nt a skin g f or t hos e pa ck e ts to b e r e s e nt. Th is continu e s unti l all t he pa ck e ts have

bee n r e c e i ved int a ct.The pa ck e ts a r e re a ssem bl ed into t he ir ori g inal f orm.


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Q uestion

W ha t d o t he Fo ll owin g a bbr ev i a tions st a nd f or?H TT P ISP URLS M T P

E x p la in bri efl y t he ir us e , g i v ing exa mp les.3mks E a c h.

the internet session 6

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