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
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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.
L13: (Meelis) - 20. nov, K 12-14 ?
19. Distributed Applications.
Sissejuhatus
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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, multiprocessor, 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
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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
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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
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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
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Large geographical area
Crossing public rights of way
Rely in part on common carrier circuits
Alternative technologies
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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
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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.
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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