Transcript William Stallings Data and Computer Communications
Arvutikommunikatsiooni alused Computer Networks Technology Andi Hektor, [email protected]
Meelis Roos, [email protected]
Tõnis Eenmäe, [email protected]
Urmas Tamm, [email protected]
Andero Belov, [email protected]
Veiko Hani, [email protected]
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 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.
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.
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.
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L13: (Meelis) - 20. nov, K 12-14 19. Distributed Applications.
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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)
Kanalkommunikatsioon Circuit Switching
• • Dedicated communications path established for the duration of the conversation e.g. telephone network
Pakettkommunikatsioon Packet 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
Kaaderedastus Frame 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 edastus Asynchronous 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
Lokaalvõrgud Local 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
Protokollid 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
Protokolli tähtsamad osad
• • • Syntax Data formats Signal levels Semantics Control information Error handling Timing Speed matching Sequencing
Protokolli arhitektuur 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
Lihtne näide failiülekandest andmesideprotokolli korral
Kolmekihiline mudel A 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 kiht 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.
Võrguühenduse kiht Network 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
Rakenduskiht Application Layer
• • Support for user applications e.g. http, SMPT
TCP/IP protokolli arhitektuur
OSI v TCP/IP