Architectures de communication

Transcription

1 Architectures de commuicatio C. Pham RESO-LIP/INRIA Uiversité Lyo 1, basé sur les supports de Keshav, du livre: A Egieerig Approach to Computer Networkig et les supports de l UREC

2 Ce que ous allos voir Pourquoi avos ous besoi de défiir ue architecture de commuicatio? Quelle architecture? Les avatages et les icovéiets de ces architectures. Cours de C. Pham, Uiv. Lyo 1

3 Example Exchage a file over a etwork that corrupts packets but does t lose or reorder them A simple protocol sed file as a series of packets sed a checksum receiver seds OK or ot-ok message seder waits for OK message if o respose, reseds etire file Problems sigle bit corruptio requires retrasmissio of etire file what if lik goes dow? what if ot-ok message itself is corrupted? Cours de C. Pham, Uiv. Lyo 1

4 Défiir ue architecture de commuicatio Peut-o défiir ue architecture qui soit: Modulaire? Flexible? Performate? Portable? Même problématique que lorsque l o écrit u programme O cherche à idetifier les procédures de base (gééricité, modularité ) O découpe le programme e esemble foctioel, chaque esemble pouvat être iter-chageable. O va doc idetifier les services de base d u réseau et ce que doit fourir ue architecture de commuicatio Cours de C. Pham, Uiv. Lyo 1

5 Les services de base A vous de jouer! Cours de C. Pham, Uiv. Lyo 1

6 Protocols Key poit i etworkig: tells how to behave ad commuicate to be uderstood Sytax of a message what fields does it cotai? i what format? Sematics of a message what does a message mea? for example, ot-ok message meas receiver got a corrupted file Actios to take o receipt of a message for example, o receivig ot-ok message, retrasmit the etire file Cours de C. Pham, Uiv. Lyo 1

7 Aother way to view a protocol As providig a service The example protocol provides reliable file trasfer service Peer etities use a protocol to provide a service to a higher-level peer etity for example, postal workers use a protocol to preset customers with the abstractio of a ureliable letter trasfer service Cours de C. Pham, Uiv. Lyo 1

8 Protocol layerig A etwork that provides may services eeds may protocols Turs out that some services are idepedet But others deped o each other Protocol A may use protocol B as a step i its executio for example, packet trasfer is oe step i the executio of the example reliable file trasfer protocol This form of depedecy is called layerig reliable file trasfer is layered above packet trasfer protocol like a subroutie Cours de C. Pham, Uiv. Lyo 1

9 Protocol stack A set of protocol layers Each layer uses the layer below ad provides a service to the layer above Key idea oce we defie a service provided by a layer, we eed kow othig more about the details of how the layer actually implemets the service iformatio hidig decouples chages Cours de C. Pham, Uiv. Lyo 1

10 Some termiology Service access poit (SAP) iterface betwee a upper layer ad a lower layer Protocol data uits (PDUs) packets exchaged betwee peer etities Service data uits (SDUs) packets haded to a layer by a upper layer PDU = SDU + optioal header or trailer Example letter trasfer service protocol data uit betwee customers = letter service data uit for postal service = letter protocol data uit = mailbag (aggregatio of letters) (what is the SDU header?) Cours de C. Pham, Uiv. Lyo 1

11 SAP, SDU, PDU... Cours de C. Pham, Uiv. Lyo 1

12 The importace of beig layered Breaks up a complex problem ito smaller maageable pieces ca compose simple service to provide complex oes for example, WWW (HTTP) is Java layered over TCP over IP (ad uses DNS, ARP, DHCP, RIP, OSPF, BGP, PPP, ICMP) Abstractio of implemetatio details separatio of implemetatio ad specificatio ca chage implemetatio as log as service iterface is maitaied Ca reuse fuctioality upper layers ca share lower layer fuctioality example: WiSock o Microsoft Widows Cours de C. Pham, Uiv. Lyo 1

13 Layerig There is a tesio betwee iformatio-hidig (abstractio) ad achievig good performace Art of protocol desig is to leak eough iformatio to allow good performace but ot so much that small chages i oe layer eed chages to other layers Cours de C. Pham, Uiv. Lyo 1

14 ISO OSI referece model A set of protocols is ope if protocol details are publicly available chages are maaged by a orgaizatio whose membership ad trasactios are ope to the public A system that implemets ope protocols is called a ope system Iteratioal Orgaizatio for Stadards (ISO) prescribes a stadard to coect ope systems ope system itercoect (OSI) Has greatly iflueced thikig o protocol stacks Cours de C. Pham, Uiv. Lyo 1

15 ISO OSI Referece model formally defies what is meat by a layer, a service etc. Service architecture describes the services provided by each layer ad the service access poit Protocol architecture set of protocols that implemet the service architecture compliat service architectures may still use o-compliat protocol architectures Cours de C. Pham, Uiv. Lyo 1

16 Le modèle OSI Cours de C. Pham, Uiv. Lyo 1

17 La couche physique Moves bits betwee physically coected edsystems Stadard prescribes codig scheme to represet a bit shapes ad sizes of coectors bit-level sychroizatio Postal etwork techology for movig letters from oe poit to aother (trais, plaes, vas, bicycles, ships ) Iteret techology to move bits o a wire, wireless lik, satellite chael etc. Cours de C. Pham, Uiv. Lyo 1

18 La couche Liaiso Itroduit la otio de trame Esemble de bits faisat partie d ue iformatio a faire passer Ex: u From - Thu Ju 6 16:04: Retur-Path: <saissa@bat710.uiv-lyo1.fr> Received: from pluvier (pluvier.es-lyo.fr [ ]) by oceaite.es-lyo.fr (Postfix) with SMTP id 32AC for <Cogduc.Pham@es-lyo.fr>; Thu, 6 Ju :55: (CEST) Received: from bat710.uiv-lyo1.fr ([ ] idet=root) by pluvier with smtp (Exim 3.35 #1 (Debia)) id 17Fxjb-0002sg-00 for <Cogduc.Pham@es-lyo.fr>; Thu, 06 Ju :55: Received: from b710paa (b710paa.uiv-lyo1.fr [ ]) by bat710.uiv-lyo1.fr (8.9.3/8.9.3/Debia ) with SMTP id PAA17174 for <Cogduc.Pham@es-lyo.fr>; Thu, 6 Ju :55: X-Autheticatio-Warig: bat710.uiv-lyo1.fr: Host b710paa.uiv-lyo1.fr [ ] claimed to be b710paa Message-Id: < f670@bat710.uiv-lyo1.fr> X-Seder: saissa@bat710.uiv-lyo1.fr X-Mailer: Widows Eudora Pro Versio (32) [F] Date: Thu, 06 Ju :05: To: Cogduc.Pham@es-lyo.fr From: Saida AISSA <saissa@bat710.uiv-lyo1.fr> Subject: hello Mime-Versio: 1.0 Cotet-Type: text/plai; charset="iso " Cotet-Trasfer-Ecodig: quoted-pritable X-Mozilla-Status: 8001 X-Mozilla-Status2: X-UIDL: oceaite,S=1958 Cours de C. Pham, Uiv. Lyo 1

19 La couche Liaiso (co( co t) Idle markers tell us that a lik is ot carryig a frame Begi ad ed markers delimit a frame O a broadcast lik (such as Etheret) ed-system must receive oly bits meat for it eed datalik-layer address also eed to decide who gets to speak ext these fuctios are provided by Medium Access sublayer (MAC) Some data liks also retrasmit corrupted packets ad pace the rate at which frames are placed o a lik part of logical lik cotrol sublayer layered over MAC sublayer Cours de C. Pham, Uiv. Lyo 1

20 La couche Liaiso (co( co t.) Datalik layer protocols are the first layer of software Very depedet o uderlyig physical lik propeties Usually budle both physical ad datalik layer o host adaptor card example: Etheret Postal service mail bag frames letters Iteret a variety of datalik layer protocols most commo is Etheret others are FDDI, SONET, HDLC Cours de C. Pham, Uiv. Lyo 1

21 Network layer Logically cocateates a set of liks to form the abstractio of a ed-to-ed lik Allows a ed-system to commuicate with ay other ed-system by computig a route betwee them Hides idiosycrasies of datalik layer Provides uique etwork-wide addresses Foud both i ed-systems ad i itermediate systems At ed-systems primarily hides details of datalik layer segmetatio ad reassembly error detectio Cours de C. Pham, Uiv. Lyo 1

22 Network layer (cotd.) At itermediate systems participates i routig protocol to create routig tables resposigle for forwardig packets schedulig the trasmissio order of packets choosig which packets to drop Cours de C. Pham, Uiv. Lyo 1

23 Two types of etwork layers I datagram etworks provides both routig ad data forwardig I coectio-orieted etwork we distiguish betwee data plae ad cotrol plae data plae oly forwards ad schedules data (touches every byte) cotrol plae resposible for routig, call-establishmet, callteardow (does t touch data bytes) Cours de C. Pham, Uiv. Lyo 1

24 Network layer Postal etwork set up iteral routig tables forward letters from source to destiatio static routig multiple qualities of service Iteret etwork layer is provided by Iteret Protocol foud i all ed-systems ad itermediate systems provides abstractio of ed-to-ed lik segmetatio ad reassembly packet-forwardig, routig, schedulig uique IP addresses ca be layered over aythig, but oly best-effort service Cours de C. Pham, Uiv. Lyo 1

25 Couche OSI pour l itercoexio Cours de C. Pham, Uiv. Lyo 1

26 Trasport layer Network provides a raw ed-to-ed service Trasport layer creates the abstractio of a errorcotrolled, flow-cotrolled ad multiplexed ed-toed lik Error cotrol message will reach destiatio despite packet loss, corruptio ad duplicatio retrasmit lost packets; detect, discard, ad retrasmit corrupted packets; detect ad discard duplicated packets Flow cotrol match trasmissio rat to rate curretly sustaiable o the path to destiatio, ad at the destiatio itself Cours de C. Pham, Uiv. Lyo 1

27 Trasport layer (cotd.) Multiplexes multiple applicatios to the same ed-toed coectio adds a applicatio-specific idetifier (port umber) so that receivig ed-system ca had i icomig packet to the correct applicatio Some trasport layers provide fewer services e.g. simple error detectio, o flow cotrol, ad o retrasmissio lightweight trasport layer Cours de C. Pham, Uiv. Lyo 1

28 Trasport layer (cotd.) Postal system does t have a trasport layer implemeted, if at all, by customers detect lost letters (how?) ad retrasmit them Iteret two popular protocols are TCP ad UDP TCP provides error cotrol, flow cotrol, multiplexig UDP provides oly multiplexig Cours de C. Pham, Uiv. Lyo 1

29 Sessio layer Not commo Provides full-duplex service, expedited data delivery, ad sessio sychroizatio Duplex if trasport layer is simplex, cocateates two trasport edpoits togeter Expedited data delivery allows some messages to skip ahead i ed-system queues, by usig a separate low-delay trasport layer edpoit Sychroizatio allows users to place marks i data stream ad to roll back to a prespecified mark Cours de C. Pham, Uiv. Lyo 1

30 Example Postal etwork suppose a compay has separate shippig ad receivig clerks chief clerk ca maage both to provide abstractio of a duplex service chief clerk may also sed some messages usig a courier (expedited service) chief clerk ca arrage to have a set of messages either delivered all at oce, or ot at all Iteret does t have a stadard sessio layer Cours de C. Pham, Uiv. Lyo 1

31 Presetatio layer Ulike other layers which deal with headers presetatio layer touches the applicatio data Hides data represetatio differeces betwee applicatios e.g. edia-ess Ca also ecrypt data Usually ad hoc Postal etwork traslator traslates cotets before givig it to chief clerk Iteret o stadard presetatio layer oly defies etwork byte order for 2- ad 4-byte itegers Cours de C. Pham, Uiv. Lyo 1

32 Applicatio layer The set of applicatios that use the etwork Does t provide services to ay other layer Postal etwork the perso who uses the postal system suppose maager wats to sed a set of recall letters traslator traslates letters goig abroad chief clerk seds some priority mail, ad some by regular mail mail clerk seds a message, retrasmits if ot acked postal system computes a route ad forwards the letters datalik layer: letters carried by plaes, trais, automobiles physical layer: the letter itself Cours de C. Pham, Uiv. Lyo 1

33 Les primitives de services das OSI X peut être 'importe quelle primitives de services d'ue couche doée. Ex: T_CONNECT.request, N_DATA.idicatio Cours de C. Pham, Uiv. Lyo 1

34 Layerig We have broke a complex problem ito smaller, simpler pieces Provides the applicatio with sophisticated services Each layer provides a clea abstractio to the layer above Cours de C. Pham, Uiv. Lyo 1

35 Why seve layers? Need a top ad a bottom -- 2 Need to hide physical lik, so eed datalik -- 3 Need both ed-to-ed ad hop-by-hop actios; so eed at least the etwork ad trasport layers -- 5 Sessio ad presetatio layers are ot so importat, ad are ofte igored So, we eed at least 5, ad 7 seems to be excessive Note that we ca place fuctios i differet layers Cours de C. Pham, Uiv. Lyo 1

36 Le modèle TCP/IP par rapport à OSI Cours de C. Pham, Uiv. Lyo 1

37 Problems with layerig Layerig hides iformatio if it did t the chages to oe layer could require chages everywhere layerig violatio But sometimes hidde iformatio ca be used to improve performace for example, flow cotrol protocol may thik packet loss is always because of etwork cogestio if it is, istead, due to a lossy lik, the flow cotrol breaks this is because we hid iformatio about reaso of packet loss from flow cotrol protocol Cours de C. Pham, Uiv. Lyo 1

38 La ormalisatio 2 orgaismes de ormalisatio pour les réseaux L'ISO (Iteratioal Stadardizatio Orgaizatio) UIT-T (Uio Iteratioale des Télécommuicatio) ex CCITT L'ISO est dépedat de l'onu, les représetats atioaux sot les orgaismes atioaux de ormalisatio ANSI (USA) AFNOR (Frace) DIN (Allemage) BSI (Royaume Ui) HSC (Japo) L'UIT-T compred des idustriels et des opérateurs de télécommuicatio Cours de C. Pham, Uiv. Lyo 1