Applikasjoner. System arkitektur. Network applications:som e jargon. Client-serverparadigm

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1 Applikasjoner Network applications:som e jargon Disposisjon overføringsproblem atikk navnetjener world wide w eb epost 4/14/2008 Slide 1 A processis a program thatis running within a host. W ithin the sam e host,two processes com m unicate with interprocess com m unication defined by the OS. Processes running in differenthosts com m unicate with an application-layerprotocol A useragentis an interface betw een the userand the network application. W eb:brow ser mailreader stream ing audio/video: media player 4/14/2008 Slide 2 Tjener LAN Disk Komm. Prog. vare System arkitektur Navne tjener Internett Disk Komm. Prog. vare Klient LAN 4/14/2008 Slide 3 B r u k e r Typicalnetwork app has two pieces: clientand Client-paradigm Client: initiates contactwith ( speaks first ) typically requests service from, forweb,clientis implem ented in browser;fore-m ail,in m ailreader Server: provides requested service to client e.g.,w eb sends requested Web page,maildelivers e- mail application transport network data link physical request reply application transport network data link physical 4/14/2008 Slide 4 1

2 Overføringsproblem er Data representeres på ulik måte iulike m askinerpå grunn av forskjelli: hardw are Sm all-endians og Big-endians m askiner 1-kom plem entog 2-kom plem entlogikk ordstørrelse 32-bitmaskin til64-bitmaskin komm. operativsystem program m eringsspråk og kom pilere forskjellig lokalrepresentasjon EBCDIC (IBM )tilasciielleria5 (standard) Applik.data Overføringssyntaks Presentasjons koding Pakke 1 Pakke 2 Pakke 3 Applik.data Presentasjons dekoding Data m åoverføres ien overføringssyntaks som begge sideroppfatterpåsam m e m åte 4/14/2008 Slide 5 4/14/2008 Slide 6 Abstraktsyntaks/overføringssyntaks Sam taleunivers Abstraktsyntaks kom pilator Lokal repr. Applik.pros. Koding og innpakking (marshalling) Abstraktkontekst Felles sam taleunivers Datastrukturer Operasjoner Abstraktsyntaks Overføringssyntaks Lokal repr. Applik.pros. Dekoding og utpakking (marshalling) fellesoppfatning av hvade to prosessene kan sam arbeideom en merformellbeskrivelse: etsettav datastrukturer(residentdel) operasjonersom kan utførespådissestrukturene (kom m unisertovernettet) 4/14/2008 Slide 7 4/14/2008 Slide 8 2

3 Eksem pelpåsam taleunivers <Fligth> :: <Carrier>>Flight-no> <Origin><Departure-time> <Destination><Arrival-time> <Available-seats-class-1> <Available-seats-class-2> <O perations>::<type> < C arrier><fligth-no> <Class><No-of-seats> <Type>::Inquire Book-seats C ancel-seats residentdel kom m uniseres overnettet 4/14/2008 Slide 9 Marshalling/serialisering Serialisering Applikasjonens datastruktur Marshalling konvertering serialisering innpakking 4/14/2008 Slide 10 ASN.1 eksem pler W hattransportservice does an app need? Integer> bits maskin;representertiet32-bits ord 16-bits m askin;representertito 16-bits ord Hverdatatype kodes ved overføring: Type Lengde Verdi Type lengde type lengde verdi type lengde verdi INT 4 B1 B2 B3 B4 Primitive typer: Bolean Integer Bitstreng Oktettstreng Null ObjektID Objektdeskrip. R eal Strukturtyper Data loss some apps (e.g.,audio)can tolerate som e loss otherapps (e.g.,file transfer, telnet)require 100% reliable data transfer Bandwidth some apps (e.g.,multimedia) require minimum am ountof bandwidth to be effective otherapps ( elastic apps )make use ofwhateverbandw idth they get Timing some apps (e.g.,internet telephony,interactive gam es) require low delay to be effective 4/14/2008 Slide 11 4/14/2008 Slide 12 3

4 Navnetjener K onvertere fra navn tiladresser navn erbrukervennlig adresserernødvendig forfrem sending av pakker husk;etendepunktforen forbindelse er identifisertved tripletten: IP-adresse;IP-SA P (Protocol);T-SA P (T-Port) Service (foreks.mail) vel-kjentport Organisering av navnetjenesten Organiserthierarkisk idom ener, reflekteres inavnekonvensjonen foreks. baugi.ifi.uio.no hvertdom ene eransvarlig forsittnavneom råde fleksibeltog forenkleradm inistrasjonen 4/14/2008 Slide 13 4/14/2008 Slide 14 Navnehierarkietog soner Hierarkiav navnetjenere Generisk Land com edu m il gov org uk no se Rot-sone adm.nic Rot navnetjener princeton berkeley arpa uio no navnetjener ifi baugi m jolnir skibladnir hver sone korresponderer med to eller flere navnetjenere en navnetjener kan implem entere en eller flere soner fys uio navnetjener ifi navnetjener 4/14/2008 Slide 15 4/14/2008 Slide 16 4

5 The W eb:som e jargon W eb page: consists of objects addressed by a URL M ostweb pages consist of: base HTM L page,and severalreferenced objects. URL has two com ponents: hostnam e and path nam e: UseragentforWeb is called a brow ser: M S InternetExplorer Netscape Com m unicator ServerforWeb is called Web : Apache (public dom ain) M S Internet Inform ation Server 4/14/2008 Slide 17 The W eb:the http protocol W eb s application layer protocol client/m odel client:brow serthat requests,receives, displays W eb objects :Web sends objects in response to requests http1.0:rfc 1945 http1.1:rfc 2068 PC running Explorer Mac running Navigator Server running NCSA Web Port80 is default for http. 4/14/2008 Slide 18 The http protocol:more http is stateless maintains no information aboutpastclientrequests 4/14/2008 Slide 19 http m essage form at:request two types ofhttp m essages:request,response m essage: ASCII(hum an-readable format) request line (GET, POST, HEAD commands) header lines Carriage return, line feed indicates end of message GET /somedir/page.html HTTP/1.0 User-agent: Mozilla/4.0 Accept: text/html, image/gif,image/jpeg Accept-language:fr (extra carriage return,line feed) 4/14/2008 Slide 20 5

6 http m essage form at:response Trying outhttp (clientside)foryourself status line (protocol status code status phrase) data, e.g., requested html file header lines HTTP/ OK Date: Thu, 06 Aug :00:15 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Mon, 22 Jun Content-Length: 6821 Content-Type: text/html data data data data data... 1.Telnetto yourfavorite Web : telnet 80 Opens TCP connection to port 80 (default http port) at Anything typed in sent to port 80 at 2.Type in a GET : GET /~ross/index.html HTTP/1.0 By typing this in (hit carriage return twice), you send this minimal (but complete) GET request to http 3.Look atresponse m essage sentby http! 4/14/2008 Slide 21 4/14/2008 Slide 22 User-interaction:cookies sends cookie to clientin response m sg Set-cookie: clientpresents cookie in laterrequests cookie: matches presented-cookie with -stored info authentication rem em bering user preferences,previous choices client usual msg usual + Set-cookie: # usual msg cookie: # usual msg usual msg cookie: # usual msg cookiespectific action cookiespecific action 4/14/2008 Slide 23 Web Caches (proxy ) Goal:satisfy clientrequestwithoutinvolving origin usersets brow ser: Web accesses via web cache Proxy clientsends allhttp client requests to web cache ifobjectatweb cache, web cache immediately returns objectin else requests object client from origin, then returns http response to client origin origin 4/14/2008 Slide 24 6

7 Electronic Mail Form atofan em ail Sending/Receiving Mail A ddresses User Agent MIME MailTransfer Agent MailA ccess Protocols 4/14/2008 Slide 25 4/14/2008 Slide 26 Em ailaddress U ser agent 4/14/2008 Slide 27 4/14/2008 Slide 28 7

8 MIME MIME header 4/14/2008 Slide 29 4/14/2008 Slide 30 Data types and subtypes in M IM E Type Text Multiport M essage Im age Video A udio Plain JPE G GIF MPEG Basic Subtype Mixed Parallel Digest Alternative RFC822 Partial Ext.Body Unform atted text Body contains ordered parts ofdifferentdata types Sam e as above,butno order Sim ilar to m ixed,butthe defaultis m essage/rfc822 Parts are differentversions ofthe sam e m essage Body is an encapsulated m essage Body is a fragm entofa bigger m essage Body is a reference to another m essage Im age is in JPEG Video is in GIF form at Video is in M PEG form at D escription Single-channelencoding ofvoice at8 K H z PostScript Adobe PostScript A pplication 4/14/2008 Slide 31 Octet-Stream G eneralbinary data (8-bitbytes) Category Type 7bit 8bit Binary Base64 Content-transfer transfer encoding D escription ASCII characters and shortlines Non-ASCII characters and shortlines Non-ASCII characters with unlimited-length lines 6-bitblocks ofdata are encoded into 8-bitASCII characters Non-ASCII characters are encoded as an equalsign follow ed by an ASCII code 4/14/2008 Slide 32 8

9 C om m ands and responses Em aildelivery 4/14/2008 Slide 33 4/14/2008 Slide 34 9