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Datakommunikasjon Høsten 2001 Forelesning nr 2, 27. august 2001 Chapter 2, Protocols and Architecture, men med fordypning og eksempler.

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Presentasjon om: "Datakommunikasjon Høsten 2001 Forelesning nr 2, 27. august 2001 Chapter 2, Protocols and Architecture, men med fordypning og eksempler."— Utskrift av presentasjonen:

1 Datakommunikasjon Høsten 2001 Forelesning nr 2, 27. august 2001 Chapter 2, Protocols and Architecture, men med fordypning og eksempler.

2 Forelesning nr 2, høsten Praktiske opplysninger zØvingslærer Siv Hilde Houmb  Web side: z2 obligatoriske øvinger: ySlutten av september ySlutten av oktober

3 Forelesning nr 2, høsten Noen begreper zProtokoller yRegler som som benyttes i et nettverk for overføring av data mellom to parter. yProtokoller som går mellom over flere nett er rutbare. zMultiprotokoll nettverk yNettverk som bruker mer enn en protokoll

4 Forelesning nr 2, høsten Protokoller zTCP/IP - Transmission Control Protocol / Internet Protocol zSNA/SDLC - Systems Network Architecture/Synchronous Data Link Control zX.25 zFrame Relay zATM - Asynchronous Transfer Mode zISDN – Integrated Services Digital Network yQ.931 D-kanal signalering

5 Forelesning nr 2, høsten 20015

6 6

7 7 Internet Protocol (IP) zProvides information about how and where data should be delivered zSubprotocol enabling TCP/IP to internetwork zTraverse more than one LAN segment and more than one type of network through a router zSubnets zThe individual networks joined together by routers in an internetwork

8 Forelesning nr 2, høsten Andre protokoller zUser Datagram Protocol (UDP) yA connectionless transport service yBrukes f.eks. av SNMP, Simple Network Management Protocol zInternet Control Message Protocol (ICMP) yNotifies the sender that something has gone wrong in the transmission process and that packets were not delivered zAddress Resolution Protocol (ARP) yObtains the MAC address of a host or node yCreates a local database mapping the MAC address to the host’s IP address

9 Forelesning nr 2, høsten ICMP eksempel PC Internett Ruter GW = WEB-server ICMP redirect Intranett

10 Forelesning nr 2, høsten En protokoll kan være: zDirect or indirect zMonolithic or structured zSymmetric or asymmetric zStandard or nonstandard

11 Forelesning nr 2, høsten Direct or Indirect zDirect ySystems share a point to point link or ySystems share a multi-point link yData can pass without intervening active agent zIndirect ySwitched networks or yInternetworks or internets yData transfer depend on other entities

12 Forelesning nr 2, høsten Monolithic or Structured zCommunications is a complex task zTo complex for single unit zStructured design breaks down problem into smaller units zLayered structure

13 Forelesning nr 2, høsten Symmetric or Asymmetric zSymmetric yCommunication between peer entities zAsymmetric yClient/server

14 Forelesning nr 2, høsten Standard or Nonstandard zNonstandard protocols built for specific computers and tasks zK sources and L receivers leads to K*L protocols and 2*K*L implementations zIf common protocol used, K + L implementations needed

15 Forelesning nr 2, høsten Use of Standard Protocols

16 Forelesning nr 2, høsten Funsksjoner for en protokoll: zEncapsulation zSegmentation and reassmebly zConnection control zOrdered delivery zFlow control zError control zAddressing zMultiplexing zTransmission services

17 Forelesning nr 2, høsten Encapsulation zAddition of control information to data yAddress information yError-detecting code yProtocol control

18 Forelesning nr 2, høsten Segmentation (Fragmentation) zMeldinger/data (f.eks en fil) som skal overføres kan være på flere Mbyte zNettverket kan ikke håndtere så store mengder data på en gang zDet å splittte store blokker med data i mindre blokker kalles segmentering (TCP/IP kaller det fragmentering) yATM celler er 53 oktetter lange yEthernet rammer kan være opp til 1526 oktetter lange

19 Forelesning nr 2, høsten Hvorfor fragmentere? zFordeler ved å dele i mindre pakker: yMore efficient error control yShorter delays ySmaller buffers needed zUlemper ved å dele i mindre pakker: yOverheads yIncreased interrupts at receiver yMore processing time

20 Forelesning nr 2, høsten Connection Control zConnection Establishment zData transfer zConnection termination zSequence numbers used for yOrdered delivery yFlow control yError control

21 Forelesning nr 2, høsten Connection Oriented Data Transfer

22 Forelesning nr 2, høsten Eksempel TCP Maskin A Maskin B Tid SYN (SYNchronize sequence numbers) SYN, ACK ACK Kalles for: Three-way handshake

23 Forelesning nr 2, høsten Ordered Delivery zPDUs may traverse different paths through network zPDUs may arrive out of order zSequentially number PDUs to allow for ordering (PDU=Protocol Data Unit)

24 Forelesning nr 2, høsten Flow Control zDone by receiving entity zLimit amount or rate of data zStop and wait zSliding window zNeeded at application as well as network layers

25 Forelesning nr 2, høsten Sliding Windows Flow Control zAllow multiple frames to be in transit zReceiver has buffer W long zTransmitter can send up to W frames without ACK zEach frame is numbered zACK includes number of next frame expected

26 Forelesning nr 2, høsten Sliding Window Diagram

27 Forelesning nr 2, høsten Example Sliding Window

28 Forelesning nr 2, høsten Error Control zGuard against loss or damage zError detection ySender inserts error detecting bits yReceiver checks these bits yIf OK, acknowledge yIf error, discard packet zRetransmission yIf no acknowledge in given time, re-transmit

29 Forelesning nr 2, høsten Error detection zCyclic Redundancy Check – CRC yUt fra meldingen som skal sendes genereres det en FCS – Frame Check Sequence. yMeldingen + FCS sendes til mottaker yMottaker kan basert på dette sjekke om det er oppstått feil under sending av meldingen

30 Forelesning nr 2, høsten Error control mechanisms zRefereres til som ARQ - Automatic Repeat Request zTre versjoner av ARQ er standarisert: yStop-and-wait ARQ yGo-Back-N ARQ (sliding window) ySelective-reject ARQ

31 Forelesning nr 2, høsten Addressing level zLink address yMAC address yIdentifiserer nettverkskortet zNetwork level address yIP or internet address (TCP/IP) yNetwork service access point or NSAP (OSI) zProcess within the system yPort number (TCP/IP), eks. Telnet=port 23, SMTP=port 25 yService access point or SAP (OSI)

32 Forelesning nr 2, høsten Address Concepts

33 Forelesning nr 2, høsten IP Address (IPv4) zLogical address used in TCP/IP networking zUnique 32-bit number zDivided into four groups of octets (8-bit bytes) zSeparated by periods zEks angir nettverksid 8 angir maskin på nettet zIPv6 y128-bit address field

34 Forelesning nr 2, høsten IP-adresse klasser zClass A: til zClass B: til zClass C: til

35 Forelesning nr 2, høsten IP-adresse typer zUnicast – sending til en enkelt maskin zBroadcast – sender til alle maskiner på et nett zMulticast – sender til en gruppe maskiner på et nett

36 Forelesning nr 2, høsten Addressing in TCP/IP z8 bit gir 256 mulige kombinasjoner, men bare tallene fra 1 til 254 benyttes til å identifisere nettverk og maskiner z0 og 255 er reservert for broadcasts yDvs. Sendes alle maskiner på nettverket

37 Forelesning nr 2, høsten Addressing in TCP/IP zLoopback address yIP address reserved for communicating from a node to itself yValue of the loopback address is always zInterNIC yAuthority for Internet IP addressing and domain name registration

38 Forelesning nr 2, høsten Addressing in TCP/IP zStatic IP address yIP address manually assigned to a device zDynamic Host Configuration Protocol yApplication layer protocol yManages the distribution of IP addresses on a network yDHCP-server yDHCP lease time

39 Forelesning nr 2, høsten DHCP meldingssekvens

40 Forelesning nr 2, høsten Connection Identifiers zConnection oriented data transfer (virtual circuits) zAllocate a connection name during the transfer phase yReduced overhead as connection identifiers are shorter than global addresses yRouting may be fixed and identified by connection name yEntities may want multiple connections - multiplexing yState information

41 Forelesning nr 2, høsten Multiplexing zSupporting multiple connections on one machine zMapping of multiple connections at one level to a single connection at another yCarrying a number of connections on one fiber optic cable yEks. Sammenslåing av 2 ISDN B-kanaler, dvs 64 kbit/s x 2 = 128 kbit/s

42 Forelesning nr 2, høsten Transmission Services zPriority ye.g. control messages zQuality of service yMinimum acceptable throughput yMaximum acceptable delay zSecurity yAccess restrictions

43 Forelesning nr 2, høsten OSI - The Model zA layer model zEach layer performs a subset of the required communication functions zEach layer relies on the next lower layer to perform more primitive functions zEach layer provides services to the next higher layer zChanges in one layer should not require changes in other layers

44 Forelesning nr 2, høsten The OSI Environment

45 Forelesning nr 2, høsten OSI as Framework for Standardization

46 Forelesning nr 2, høsten Layer Specific Standards

47 Forelesning nr 2, høsten Elements of Standardization zProtocol specification yOperates between the same layer on two systems yMay involve different operating system yProtocol specification must be precise xFormat of data units xSemantics of all fields xallowable sequence of PDUs zService definition yFunctional description of what is provided zAddressing yReferenced by Service Access Points

48 Forelesning nr 2, høsten OSI Layers (1) zPhysical yPhysical interface between devices xMechanical xElectrical xFunctional xProcedural zData Link yMeans of activating, maintaining and deactivating a reliable link yError detection and control yHigher layers may assume error free transmission

49 Forelesning nr 2, høsten OSI Layers (2) zNetwork yTransport of information yHigher layers do not need to know about underlying technology yNot needed on direct links zTransport yExchange of data between end systems yError free yIn sequence yNo losses yNo duplicates yQuality of service

50 Forelesning nr 2, høsten OSI Layers (3) zSession yControl of dialogues between applications yDialogue discipline yGrouping yRecovery zPresentation yData formats and coding yData compression yEncryption zApplication yMeans for applications to access OSI environment

51 Forelesning nr 2, høsten Use of a Relay

52 Forelesning nr 2, høsten TCP/IP Protocol Suite zDominant commercial protocol architecture zSpecified and extensively used before OSI zDeveloped by research funded US Department of Defense zUsed by the Internet

53 Forelesning nr 2, høsten TCP/IP Protocol Architecture(1) zApplication Layer yCommunication between processes or applications zEnd to end or transport layer (TCP/UDP/…) yEnd to end transfer of data yMay include reliability mechanism (TCP) yHides detail of underlying network zInternet Layer (IP) yRouting of data

54 Forelesning nr 2, høsten TCP/IP Protocol Architecture(2) zNetwork Layer yLogical interface between end system and network zPhysical Layer yTransmission medium ySignal rate and encoding

55 Forelesning nr 2, høsten PDUs in TCP/IP

56 Forelesning nr 2, høsten TCP/IP Compared to the OSI Model zApplication layer roughly corresponds to Application and Presentation layers zTransport layer roughly corresponds to Session and Transport layers zInternet layer is equivalent to the Network layer zNetwork Interface layer roughly corresponds to Data Link and Physical layers

57 Forelesning nr 2, høsten Some Protocols in TCP/IP Suite

58 Forelesning nr 2, høsten TCP/IP Application Layer Protocols zTelnet is used to log on to remote hosts using TCP/IP Protocol zFile Transfer Protocol (FTP) is used to send and receive files via TCP/IP zSimple Mail Transfer Protocol (SMTP) is responsible for moving messages from one server to another, using the Internet and other TCP/IP-based networks zSimple Network Management Protocol (SNMP) manages devices on a TCP/IP network

59 Forelesning nr 2, høsten

60 Forelesning nr 2, høsten

61 Forelesning nr 2, høsten Ipconfig kommando N:\>ipconfig /all Windows 2000 IP Configuration Host Name : bak3 Primary DNS Suffix : Node Type : Broadcast IP Routing Enabled : No WINS Proxy Enabled : No DNS Suffix Search List : Ethernet adapter Local Area Connection: Connection-specific DNS Suffix. : Description : 3Com EtherLink XL 10/100 PCI For Complete PC Management NIC (3C905C-TX) Physical Address : DA-DD-2E-5E DHCP Enabled : No IP Address : Subnet Mask : Default Gateway : DNS Servers :

62 Forelesning nr 2, høsten netstat kommando N:\>netstat -rn Active Routes: Network Destination Netmask Gateway Interface Metric Default Gateway: Persistent Routes: None

63 Forelesning nr 2, høsten Ping kommando N:\>ping Pinging with 32 bytes of data: Reply from : bytes=32 time<10ms TTL=128 Reply from : bytes=32 time<10ms TTL=128 Ping statistics for : Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 0ms, Average = 0ms

64 Forelesning nr 2, høsten ARP kommando N:\>arp -a Interface: on Interface 0x2 Internet Address Physical Address Type af-0b-9f dynamic da-4f-31-8c dynamic a-48 dynamic c-8e dynamic fe-29 dynamic Kobling mellom IP-adresse og MAC-adresse

65 Forelesning nr 2, høsten Tracert kommando zTraceroute, lister opp hvilke rutere som passeres på vei til mottaker zBenytter TTL (Time To Live) feltet i ICMP Echo Request zFår svar i form av ICMP Time Exceeded melding zTTL settes til 1 for så å økes med 1 hver gang

66 Forelesning nr 2, høsten Tracert

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