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Datakommunikasjon høsten 2001

Datakommunikasjon høsten 2001. Forelesning 1. Generell introduksjon. Om foreleser: Bjørn-Arild Kydland, sivilingeniør fra NTH 1984 Ansatt hos Scandpower som assisterende direktør. Tidligere Telenor og IBM.

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Datakommunikasjon høsten 2001

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  1. Datakommunikasjon høsten 2001 Forelesning 1

  2. Generell introduksjon • Om foreleser: • Bjørn-Arild Kydland, sivilingeniør fra NTH 1984 • Ansatt hos Scandpower som assisterende direktør. • Tidligere Telenor og IBM. • Arbeider 50% teknisk og 50 % administrativt. Teknisk primært med sikkerhet i tilknytning til telekommunikasjonssystemer. • Om kurset • 12 forelesninger á 3 timer. Siste forelesning 19.11. Ingen forelesninger 20.08 og 08.10) • 2 obligatoriske oppgaver • En del notater vil stilles til rådighet • Hjelpelærer: Ikke bestemt ennå. • Pensum • Data & Computer Communications (Sixth Edition), William Stallings, ISBN 0-13-086388-2 • Deler av boka + forelesning om DNS. • Forelesningsnotater

  3. Generell intro forts. • Informasjonsutveksling • epost bak@scandpower.com • www ref hjemmeside • news ref hjemmeside • Krav til studentene • Hold mobiltelefoner avslått • Still spørsmål - gode spørsmål og dumme spørsmål • 3 vekttall er mer enn en full arbeidsdag per uke. • Målsetning • Bygge opp et begrepsapparat rundt datakommunikasjon. • Vekt på praktiske eksempler • Generell introduksjon - med harelabb ....

  4. Foreløpig pensumliste • Chapter 1       Introduction • Chapter 2       Protocols and Architecture • Chapter 6       The Data Communication Interface • Chapter 7       Data Link Control • Chapter 8       Multiplexing • Chapter 10      Packet Switching • Chapter 11      ATM and Frame Relay • Chapter 13/14 LAN Technology/Systems • Chapter 15      Internet Protocols • Chapter 17      Transport Protocols • Chapter 18 Network Security • Chapter 19      Distributed Systems • + Domain Name System (DNS)

  5. Hva skal dere lære? • Nettverkskort • Protokoller • Adressering • Applikasjoner • ISDN • LAN • WAN • ISP • ASP • Ethernet • ARP • TCP/IP • Bro • Svitsj • Ruter • FW • DNS

  6. A Communications Model • Source • Generates data to be transmitted • Transmitter • Converts data into transmittable signals • Transmission System • Carries data • Receiver • Converts received signal into data • Destination • Takes incoming data

  7. Simplified Communications Model - Diagram

  8. Key Communications Tasks • Utnyttelse av transmisjonsmedium • Interface (V.24, RJ 45, V.35 osv) • Signalgenerering • Synkronisering (mellom avsender og mottaker) • Feil deteksjon og korreksjon (av mottaker) • Adressering og ruting • Recovery • Meldingsformatering • Sikkerhet (Konfidensialitet, Integritet og Tilgjengelighet) • Drift og vedlikehold (konfigurering, monitorering)

  9. Simplified Data Communications Model

  10. Networking • Point to point communication not usually practical • Devices are too far apart • Large set of devices would need impractical number of connections • Solution is a communications network

  11. Simplified Network Model

  12. WAN - Wide Area Networks • Store geografiske områder • Består av en rekke noder • Alternative teknologier • Linesvitsjing (Circuit switching) • Pakkesvitsjing (Packet switching) • Frame relay • Asynchronous Transfer Mode (ATM)

  13. Circuit Switching • Dedikert kommunikasjonsvei mellom partene så lenge kommunikasjonen pågår. • Eksempel: Telefonnettet

  14. Packet Switching • Datapakker sendes enkeltvis • Datapakkene behøver ikke ta samme vei gjennom nettet • Datapakkene sendes fra node til node mellom avsender og mottaker • Brukes mellom datamaskiner • Eksempel: Datapak basert på X.25

  15. Frame Relay • Pakksvitsjing systemer har stor overhead for å kompensere for feil • Moderne systemer er mer pålitlige • Feil kan håndteres i endesysteme • Det meste av overhead for feilkontroll er tatt vekk • Hastigheter fra 64 kbit/s til 2 Mbit/s

  16. Asynchronous Transfer Mode • ATM • Videreutvikling av Frame relay • Little overhead for error control • Fixed packet (called cell) length • Anything from 10Mbps to Gbps • Constant data rate using packet switching technique

  17. Integrated Services Digital Network • ISDN • Laget for å erstatte PSTN, dvs analog telefoni • Prøveprosjekt i Norge høsten 1989 • Ble først populært når det kunne benyttes for å koble seg mot Internett • Utvidet aksess • 30 tale/datakanaler, hver på 64 kbit/s • 1 signaleringskanal på 64 kbit/s • Grunnaksess • 2 tale/datakanaler, hver på 64 kbit/s • 1 signaleringskanal på 16 kbit/s

  18. ADSL – Assymetric Digital Subscriber Line • Telenor tilbyr (hastighet inn/ut): • 384 / 128 Kb/slaste ned lyd og bilde, samt gjøre flere ting på en gang (kostnad pr. måned 450,- kr) •  704 / 128 Kb/slaste ned filmklipp, programvare og andre store filer (kostnad pr. måned 550,- kr) •  1024 / 256 Kb/slaste ned og sende ut store filer raskt og effektivt (kostnad pr. måned 750,- kr)

  19. LAN - Local Area Networks • En eller fler bygninger • Eies vanligvis av den som henger utstyr på lokalnettet • Høyere datahastigheter enn WAN • Ethernet 10 eller 100 Mbit/s • Tidligere kun kringasting, dvs alle kan lytte på nettet • Nå mer og mer svitsjede systemer + noe bruk av ATM

  20. Protocols • Used for communications between entities in a system • Must speak the same language • Entities • User applications • e-mail facilities • terminals • Systems • Computer • Terminal • Remote sensor

  21. Key Elements of a Protocol • Syntax • Data formats • Signal levels • Semantics • Control information • Error handling • Timing • Speed matching • Sequencing

  22. Protocol Architecture • Task of communication broken up into modules • For example file transfer could use three modules • File transfer application • Communication service module • Network access module

  23. Simplified File Transfer Architecture

  24. A Three Layer Model • Network Access Layer • Transport Layer • Application Layer

  25. Network Access Layer • Exchange of data between the computer and the network • Sending computer provides address of destination • May invoke levels of service • Dependent on type of network used (LAN, packet switched etc.)

  26. Transport Layer • Reliable data exchange • Independent of network being used • Independent of application

  27. Application Layer • Support for different user applications • e.g. e-mail, file transfer

  28. Addressing Requirements • Two levels of addressing required • Each computer needs unique network address • IP-address • Each application on a (multi-tasking) computer needs a unique address within the computer • The service access point or SAP • TCP/UDP port nummer: • SNMP port 25 • DNS port 53 • Telnet port 23

  29. Protocol Architectures and Networks

  30. Protocols in Simplified Architecture

  31. Operation of a Protocol Architecture

  32. TCP/IP Protocol Architecture • Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET) • Used by the global Internet • No official model but a working one. • Application layer • Transport layer (host to host) • Internet layer • Network access layer • Physical layer

  33. Physical Layer • Physical interface between data transmission device (e.g. computer) and transmission medium or network • Characteristics of transmission medium • Signal levels • Data rates • etc.

  34. Network Access Layer • Exchange of data between end system and network • Destination address provision • IP-address (193.69.136.8) • http address (www.vg.no) • Invoking services like priority • Real time application

  35. Internet Layer (IP) • Systems may be attached to different networks • Routing functions across multiple networks • Implemented in end systems and routers

  36. Transport Layer • Reliable delivery of data • Ordering of delivery • TCP or UDP • TCP is connection oriented • UDP is connectionless

  37. Application Layer • Support for user applications • e.g. http, SMPT, FTP, SNMP

  38. Internetworking Protocols

  39. TCP/IP Protocol Architecture Model

  40. OSI Model • Open Systems Interconnection • Developed by the International Organization for Standardization (ISO) • Seven layers • A theoretical system delivered too late! • TCP/IP is the de facto standard

  41. OSI Layers • Application • Presentation • Session • Transport • Network • Data Link • Physical

  42. OSI Layers (1) • Physical • Physical interface between devices • Mechanical • Electrical • Functional • Procedural • Data Link • Means of activating, maintaining and deactivating a reliable link • Error detection and control • Higher layers may assume error free transmission

  43. OSI Layers (2) • Network • Transport of information • Higher layers do not need to know about underlying technology • Not needed on direct links • Transport • Exchange of data between end systems • Error free • In sequence • No losses • No duplicates • Quality of service

  44. OSI Layers (3) • Session • Control of dialogues between applications • Dialogue discipline • Grouping • Recovery • Presentation • Data formats and coding • Data compression • Encryption • Application • Means for applications to access OSI environment

  45. OSI v TCP/IP

  46. Standards • Required to allow for interoperability between equipment • Advantages • Ensures a large market for equipment and software • Allows products from different vendors to communicate • Disadvantages • Freeze technology • May be multiple standards for the same thing

  47. Standards Organizations • Internet Society • Internet Architecture Board (IAB) • Internet Engineering Task Force (IETF) • Internet Engineering Steering Group (IESG) • ISO - International Standard for Organization • JTC – Joint Technical Committee • ITU-T (tidligere CCITT) • ITU- International Telecommunication Union • 14 study groups • ATM forum

  48. Further Reading • Stallings, W. Data and Computer Communications (6th edition), Prentice Hall 1999 chapter 1 • Web site for Stallings book • www.shore.net/~ws/DCC6e.html • Web sites for IETF, IEEE, ITU-T, ISO • Internet Requests for Comment (RFCs) • Usenet News groups • comp.dcom.* • comp.protocols.tcp-ip

  49. Informasjon om IP på maskin ipconfig -all Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : halden.scandpower.noDescription . . . . . . . . . . . : 3Com EtherLink XL 10/100 PCI or Complete PC Management NIC (3C905C-TX) Physical Address. . . . . . . . . : 00-50-DA-DD-2E-5E DHCP Enabled. . . . . . . . . . . : NoIP Address. . . . . . . . . . . . : 193.69.136.78Subnet Mask . . . . . . . . . . . : 255.255.255.0Default Gateway . . . . . . . . . : 193.69.136.54DNS Servers . . . . . . . . . . . : 193.69.136.53

  50. ARP - Address Resolution Protocol arp -a Interface: 193.69.136.78 on Interface 0x2 Internet Address Physical Address Type 193.69.136.34 00-60-b0-3d-82-74 dynamic 193.69.136.54 00-10-5a-66-21-78 dynamic 193.69.136.60 00-50-da-4f-31-8c dynamic 193.69.136.61 00-60-97-17-2a-48 dynamic 193.69.136.91 00-60-08-49-2a-fe dynamic 193.69.136.115 08-00-09-70-2c-8e dynamic 193.69.136.133 08-00-09-87-fe-29 dynamic

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