Arvutikommunikatsiooni alused

Computer Networks Technology

Andi Hektor, andi@ut.eeMeelis Roos, mroos@ut.eeTõnis Eenmäe, tonis@ut.eeUrmas Tamm, urmast@ut.eeAndero Belov, belov@ut.eeVeiko Hani, weiko@ut.ee

Sügis 2002

Loengu kava

1. Sissejuhatus

2. Andmeside

3. Kaugvõrgud

4. Lokaalvõrgud

5. Andmeside arhitektuur ja protokollid

6. Andmeside turve

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/

Loengu kavaL1: (Andi) - 9. okt, K 12-14I. OVERVIEW. 1. Introduction.2. Protocols and Architecture.

L2: (Andi) - 10. okt, N 8-10II. DATA COMMUNICATIONS.3. Data Transmission.4. Transmission Media.

L3: (Andi) - 16. okt, K 12-145. Data Encoding.6. The Datacommunication Interface.

L4: (Andi) - 17. okt, N 8-107. Data Link Control.8. Multiplexing.

Loengu kavaL5: (Urmas) - 23. okt, K 12-14III. WIDE-AREA NETWORKS.9. Circuit Switching.10. Packet Switching.

L6: (Urmas) - 24. okt, N 8-1011. ATM and Frame Relay.12. Congestion Control in Data Networks.

L7: (Andero) - 30. okt, K 12-14IV. LOCAL AREA NETWORKS.13. LAN Technology.

L8: (Andero) - 31. okt, N 8-1014. LAN Systems.

Loengu kavaL9: (Veiko) - 6. nov, K 12-14V. COMMUNICATIONS ARCHITECTURE AND PROTOCOLS.15. Internet Protocols.

L10: (Veiko) - 7. nov, N 8-1016. Internetwork Operation.

L11: (Andi) - 13. nov, K 12-1417. Transport Protocols.

L12: (Meelis) - 14. nov, N 8-10 ?18. Network Security.

L13: (Meelis) - 20. nov, K 12-14 ?19. Distributed Applications.

Sissejuhatus

• Andmeside üldine mudel• Andmeside• Andmesidevõrgud• Andmesideprotokollid ja nende

arhidektuur• Standardid

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

Alapeatükk 1.1

Andmeside üldine mudel

Mis on kõige selle iva?

Milleks on meile üldse vaja andmesidet ja arvutikommunikatsiooni?

Lihtne vastus: et vahetada infot kahe (või rohkema) osapoole vahel.

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

Lihtne andmeside mudel (F1.1)

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

Alapeatükk 1.2

Andmeside

Andmeside (F1.2)

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

Alapeatükk 1.3

Andmesidevõrgud

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

Lihtne andmesidevõrgu mudel

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)

KanalkommunikatsioonCircuit Switching

• Dedicated communications path established for the duration of the conversation

• e.g. telephone network

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

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

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

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

Alapeatükk 1.4

Andmeside protokollid ja protokollide arhidektuur

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

Protokolli tähtsamad osad• Syntax

Data formats Signal levels

• Semantics Control information Error handling

• Timing Speed matching Sequencing

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

Lihtne näide failiülekandest andmesideprotokolli korral

Kolmekihiline mudelA Three Layer Model

• Võrgukiht (Network Access Layer)• Transpordikiht (Transport Layer)• Rakenduskiht (Application Layer)

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.)

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

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

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

Protokolli arhitektuur ja andmesidevõrk

Protokoll ja võrk

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

Võrgu PDU• Adds network header

network address for destination computer Facilities requests

Kuidas reaalselt protokoll töötab?

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

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.

Võrguühenduse kihtNetwork Access Layer

• Exchange of data between end system and network

• Destination address provision• Invoking services like priority

Interneti kiht (IP) Internet Layer

• Systems may be attached to different networks

• Routing functions across multiple networks

• Implemented in end systems and routers

Transpordi koht (TCP) Transport Layer

• Reliable delivery of data• Ordering of delivery

RakenduskihtApplication Layer

• Support for user applications• e.g. http, SMPT

TCP/IP protokolli arhitektuur

OSI v TCP/IP