Arvutikommunikatsiooni alused Computer Networks Technology

1. Arvutikommunikatsiooni alusedComputer Networks Technology Andi Hektor, andi@ut.ee Meelis Roos, mroos@ut.ee Tõnis Eenmäe, tonis@ut.ee Urmas Tamm, urmast@ut.ee Andero Belov, belov@ut.ee Veiko Hani, weiko@ut.ee Sügis 2002

2. Loengu kava • Sissejuhatus • Andmeside • Kaugvõrgud • Lokaalvõrgud • Andmeside arhitektuur ja protokollid • Andmeside turve

3. Loengu kava • 13 loengut • 1 praks • 2 seminari • 1 eriseminar • kodutöö • 3 kodukntr + kirjalik test / 25 lk ref + ettekanne William Stalling, Data and Computer Communications http://www.physic.ut.ee/~andi/andmeside/

4. Loengu kava L1: (Andi) - 9. okt, K 12-14 I. OVERVIEW. 1. Introduction. 2. Protocols and Architecture. L2: (Andi) - 10. okt, N 8-10 II. DATA COMMUNICATIONS. 3. Data Transmission. 4. Transmission Media. L3: (Andi) - 16. okt, K 12-14 5. Data Encoding. 6. The Datacommunication Interface. L4: (Andi) - 17. okt, N 8-10 7. Data Link Control. 8. Multiplexing.

5. Loengu kava L5: (Urmas) - 23. okt, K 12-14 III. WIDE-AREA NETWORKS. 9. Circuit Switching. 10. Packet Switching. L6: (Urmas) - 24. okt, N 8-10 11. ATM and Frame Relay. 12. Congestion Control in Data Networks. L7: (Andero) - 30. okt, K 12-14 IV. LOCAL AREA NETWORKS. 13. LAN Technology. L8: (Andero) - 31. okt, N 8-10 14. LAN Systems.

6. Loengu kava L9: (Veiko) - 6. nov, K 12-14 V. COMMUNICATIONS ARCHITECTURE AND PROTOCOLS. 15. Internet Protocols. L10: (Veiko) - 7. nov, N 8-10 16. Internetwork Operation. L11: (Andi) - 13. nov, K 12-14 17. Transport Protocols. L12: (Meelis) - 14. nov, N 8-10? 18. Network Security. L13: (Meelis) - 20. nov, K 12-14? 19. Distributed Applications.

7. Sissejuhatus • Andmeside üldine mudel • Andmeside • Andmesidevõrgud • Andmesideprotokollid ja nende arhidektuur • Standardid

8. Ajalugu • 70-80 arendus, 90 massiline kasutuselevõtt • 90 on muutunud nii tehnoloogia, firmade struktuur, kui ka ühiskond tervikuna • Arenenud on arvutid, elektroonika jne • Detaile: • No real difference between data processing (computers) and data communications (transmission and switching equipment) • No real difference in data voice and video • Blurred distinction between single processor, multi-processor, LAN, MAN and long-haul network

9. Alapeatükk 1.1 Andmeside üldine mudel

10. Mis on kõige selle iva? Milleks on meile üldse vaja andmesidet ja arvutikommunikatsiooni? Lihtne vastus: et vahetada infot kahe (või rohkema) osapoole vahel.

11. Elementaarsed põhimõisted • Allikas (Source) • Generates data to be transmitted • Saatja (Transmitter) • Converts data into transmittable signals • Ülekande- e sidesüsteem (Transmission System) • Carries data • Vastuvõtja (Receiver) • Converts received signal into data • Sihtpunkt (Destination) • Takes incoming data

12. Lihtne andmeside mudel (F1.1)

13. Veel mõisteid ja seletusi • Transmission System Utilization – efficient use • Interfacing – how ‘hooked up’ • Signal Generation – propagated and interpreted • Synchronization – know start and stop of message • Exchange Management – cooperation of parties • Error detection and correction – where errors cannot be tolerated • Addressing and routing – destination defined and assurance of correct delivery • Recovery – restoration after fault interruption • Message formatting – character set used • Security – assurance that only intended recipients read • Network Management – status monitoring, config., etc

14. Alapeatükk 1.2 Andmeside

15. Andmeside (F1.2)

16. Mõned näited • Two PCs connected over Internet • m(t) – keystrokes in email package • g(t) – bits in PC buffer (memory) • s(t) – modem signal representation of bits • r(t) – received signal with possible impairments • g’(t) – sequence of bits; exchange may occur to be error-free • m’(t) – message viewed by user; exact copy of original • Telephone call between two people • m(t) – sound waves • g(t) = s(t) – electrical signals of same frequency • r(t) – received electrical signal with some distortion possible • g’(t) – return to sound with some audible distortion • m’(t) – sound heard by user; not exact copy of original

17. Alapeatükk 1.3 Andmesidevõrgud

18. Võrk • 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

19. Lihtne andmesidevõrgu mudel

20. Kaugvõrgud • Large geographical area • Crossing public rights of way • Rely in part on common carrier circuits • Alternative technologies • Circuit switching • Packet switching • Frame relay • Asynchronous Transfer Mode (ATM)

21. KanalkommunikatsioonCircuit Switching • Dedicated communications path established for the duration of the conversation • e.g. telephone network

22. PakettkommunikatsioonPacket Switching • Data sent out of sequence • Small chunks (packets) of data at a time • Packets passed from node to node between source and destination • Used for terminal to computer and computer to computer communications

23. KaaderedastusFrame Relay • Packet switching systems have large overheads to compensate for errors • Modern systems are more reliable • Errors can be caught in end system • Most overhead for error control is stripped out

24. Asünkroonne edastusAsynchronous Transfer Mode • ATM • Evolution of frame relay • Little overhead for error control • Fixed packet (called cell) length • Anything from 10Mbps to Gbps • Constant data rate using packet switching technique

25. LokaalvõrgudLocal Area Networks • Smaller scope • Building or small campus • Usually owned by same organization as attached devices • Data rates much higher • Usually broadcast systems • Now some switched systems and ATM are being introduced

26. Alapeatükk 1.4 Andmeside protokollid ja protokollide arhidektuur

27. ProtokollidProtocols • 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

28. Protokolli tähtsamad osad • Syntax • Data formats • Signal levels • Semantics • Control information • Error handling • Timing • Speed matching • Sequencing

29. Protokolli arhitektuurProtocol 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

30. Lihtne näide failiülekandest andmesideprotokolli korral

31. Kolmekihiline mudelA Three Layer Model • Võrgukiht (Network Access Layer) • Transpordikiht (Transport Layer) • Rakenduskiht (Application Layer)

32. Võrgukiht • 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.)

33. Transpordikiht • Reliable data exchange • Independent of network being used • Independent of application

34. Rakenduskiht • Support for different user applications • e.g. e-mail, file transfer

35. Adresseerimine • Two levels of addressing required • Each computer needs unique network address • Each application on a (multi-tasking) computer needs a unique address within the computer • The service access point or SAP

36. Protokolli arhitektuur ja andmesidevõrk

37. Protokoll ja võrk

38. Protokolli andmepakett (PDU) • At each layer, protocols are used to communicate • Control information is added to user data at each layer • Transport layer may fragment user data • Each fragment has a transport header added • Destination SAP • Sequence number • Error detection code • This gives a transport protocol data unit

39. Võrgu PDU • Adds network header • network address for destination computer • Facilities requests

40. Kuidas reaalselt protokoll töötab?

41. TCP/IP protokolli arhitektuur • 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 • Host to host or transport layer • Internet layer • Network access layer • Physical layer

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

43. Võrguühenduse kihtNetwork Access Layer • Exchange of data between end system and network • Destination address provision • Invoking services like priority

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

45. Transpordi koht (TCP) Transport Layer • Reliable delivery of data • Ordering of delivery

46. RakenduskihtApplication Layer • Support for user applications • e.g. http, SMPT

47. TCP/IP protokolli arhitektuur

48. OSI v TCP/IP