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3 / $ #;! $13 #? ;! $,!6 ;! ;! / $ #;! A ;!# $ # # $# APPLICATION VIEWPOINT / $6!,! / $ #;!! # $!! # $ "!! B9 1Stdin36 $1ServOut 3 $ 6$ 6 $ 1ServIn %Stdout3! # $% 3

4 / $ #;! / $ ;! keyboard! screen!! Server running on hostid) create socket, port=x, for incoming request: socket); bind) wait for incoming connection request: ConnSock = accept) Client create socket, connect to hostid, port=x: ClientSock = socket); connect)! &! % & % read request from ConnSock write reply to ConnSock close ConnSock write request to ClientSock read reply from ClientSock close ClientSock " / $ #'! / $ '! '! C D #E $ 9,! 9,!6 '! 6 APPLICATION VIEWPOINT ' Server running on hostid) create datagram socket, port=x, for incoming request: ServSock = socket); bind) read request from ServSock write reply to ServSock, specifying host and port number Client create datagram socket, ClientSock = socket) Create, address hostid, port=x) datagram request, send using ClientSock read reply from ClientSock close ClientSock 0 4

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6 ' /,;9 > * *: /4, B /! //>:;>/ ; IJ ; I ' ' I@@KJ ; ' I #J *# ' I # CDJ Application file transfer Web documents realtime audio/video streamed audio/video interactive games financial apps Data loss no loss no loss losstolerant losstolerant losstolerant losstolerant no loss Bandwidth elastic elastic elastic audio: 5Kb1Mb video:10kb5mb same as above few Kbps up elastic Time Sensitive no no no yes, 100 s msec yes, few secs yes, 100 s msec yes and no " 6

7 ,;! I# 6 # # #? # ## $ 6#,'! # 66 # 6 66 # L# J A'!J 0 ; Application remote terminal access Web file transfer streaming multimedia remote file server Internet telephony Application layer protocol smtp [RFC 81] telnet [RFC 854] http [RFC 068] ftp [RFC 959] proprietary eg RealNetworks) NFS H33 / SIP RTP etc Underlying transport protocol TCP TCP TCP TCP TCP or UDP TCP or UDP TCP and UDP / ' $ / '>$>H #!"#$" : $ #1 $3 / CD / 8 7

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9 ; ;! ;! 6 8@ ;! 9 # #13 A13 ;! CD I! CD 9P 13 :6 # CD 6 9 contains text, / > references to 10 jpeg images) ;! 1 3 wwwsomeschooledu! 8@ I1 >3 ;! $ wwwsomeschooledu # ;! 8@ CD 6 I6 I F 1someDepartment/indexhtml 36 $ " 91 3! 0 F F " ;! 4 :@ I6 6 ;! ;; F ;! FI: ;!? # #! : ;! I6 6# I6= I F Q; > #;;6 # 0 9

10 I I # I6 I /,1 3 :)&! ; )# GET /somedir/pagehtml HTTP/10 Useragent: Mozilla/40 Accept: text/html, image/gif,image/jpeg Acceptlanguage:fr extra carriage return, line feed) ' < 1 1 ; 8 Q;;! // HTTP/10 00 OK Date: Thu, 06 Aug :00:15 GMT Server: Apache/130 Unix) LastModified: Mon, Jun 1998 ContentLength: 681 ContentType: text/html data data data data data 99, 99 "99 "@ & "@"4 099/ 0@/ 7 "@ 10

11 ! ; A ###I8@ ;! 8@1 3###I ;)B;I )B;:<:9Q;;!:@ Q#6 )B;I > $ P " & 6# 501>/ WWW authenticate: & I = Authorization: <cred> authorization: I authorization 6 Authorization: <cred> 6 WWW authenticate: " $$CD )B; R6 R6 : C $D Setcookie: $ I cookie: = Setcookie: # cookie: # cookie: # " )? F I Ifmodifiedsince: <date> F HTTP/ Not Modified Ifmodifiedsince: <date> HTTP/ Not Modified Ifmodifiedsince: <date> HTTP/11 00 OK <data>?? "" 11

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18 ,!9,! C: A81 CREATE foo S: A81 OK CREATE completed C: A8 LIST "" * S: * LIST ) "" art S: * LIST ) "" foo S: * LIST ) "" foobar S: A8 OK LIST completed C: A83 DELETE art S: A83 OK DELETE completed H 4H *'H $ # '! /,9 / % ; ;! >% B 4*' /9/, /*! 1% 3%/ # / 7708@@# 9 '# B # / # 18

19 6 3 3 : : 3 1 : ;! # ;! 9 6 #6 C D CD " 6 ;!'; / /,9 USER username PASS password LIST RETR filename 13 STOR filename 13 / Username OK, password required 15 data connection already open; transfer starting 45 Can t open data connection 45 Error writing file /;B *>6!B//B' B ' 6!/G

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