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Data and Computer Communications
Seventh Editionby William Stallings
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Chapter 1 – Data Communications and Networks overview
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Types of information systems
Storage systemTransport information in time without altering the message.
Processing system.Process input information to generate different output.
Communication system.Transport information from one point in time and space to another point in time and space without altering the message.
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storage system
Information source
Recorder f
destination n
Playback device
Memory m
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Processing system
Information source
Input device
destination n
Output device
memory
Processor k
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Communication system
Information source
Input transducer
destination n
Output transducer
Comm. system
Transmitter Channel Receiver
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Comm. System cont.
Transmitterconsist of one or more of the following components: filters, amplifiers, A/D ,encoders, modulator, …..etc.Channeldegradation of transmitted signal during propagation due to distortion, noise, interference.
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Comm. System cont.
Receiverconsist of one or more of the following components: filters, amplifiers, D/A, decoders, demodulator, …..etc.
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Types of comm. systemsAnalog comm. system
Transport analog information using analog modulation techniques (AM,FM,PM).
Digital comm. system.Transport digital information using digital modulation techniques (ASK,FSK,PSK).
Hybrid comm. system.Transport digitized analog information using one of the following digital techniques:
1. Analog pulse modulation schemes (PAM,PDM,PPM). 2. digital modulation schemes (ASK,FSK,PSK).3. Pulse code modulation schemes (PCM,DPCM, δ).
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Analysis and Design of comm. system
AnalysisTransmission rate, quality of transmission,
robustness to noise.
DesignType of comm. System for given application,
performance requirements, resources, constraints ( Time-bandwidth, noise limitation, equipment limitation).
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Analysis and Design of comm. System cont.
Design efficient utilization of the two primary
resources of comm. System, namely: transmitted power (SNR) and channel bandwidth.
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Analysis and Design of comm. System cont.
Limitation imposed on the transmission rate by channel bandwidth B, and SNR is given by
C: channel capacity (maximum rate at no error)M: #of signaling levels
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2
log (1 ) bps (Shannon equation)2 log bps (Nyquist equation)
C B SNRC B M= +=
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Types of transmission
Base-band transmission:Short distance.No modulation is needed.
Band-pass transmission:long distance.Modulation is needed.
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Why modulation?
For ease of radiation.Modulation for multiplexing.For exchange of SNR with B.To over come equipment limitation.To match channel characteristics.
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Types of modulation
Continuous wave (CW) modulation.RF sinusoidal carrier wave.
Pulse modulation.RF pulse carrier wave.
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Digital versus analog transmission
Immunity to noise and distortion.Viability of regenerative repeaters.Digital hardware implementation is flexible and scalable.Digital signals can be encoded to yield low BER.Multiplexing is easier and more efficient.Realization of exchange SNR and B is more efficient.Digital storage easier and cheaper.cost of digital hardware is cheaper.
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A Communications Model
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Communications Tasks
Transmission system utilization Addressing
Interfacing Routing
Signal generation Recovery
Synchronization Message formatting
Exchange management Security
Error detection and correction Network management
Flow control
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Data communication system
Data Communications Model
Data communication : concern with exchange of information between two directly connected devices.
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Computer Networks
Computer Network: An interconnected collection of computers which are:Cooperative
Cooperative action is required between componentsNo master-slave relationships
AutonomousAll components are capable of independent actionAny resource is capable of refusing requests
Mutually Suspicious–Components verify requests
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Cont.Computer network: concern with the exchange of information among several devices (computers, serversrouters, data processing devices,...etc. )
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Cont.Role of Computers in Communication
As users - main sources and sinks for info and dataAs providers - used to implement switching nodes, controllers, concentrators, protocol translators, etc.
Three General Types of Computer Communication
Computer-to-computer - including intra-computer communication.Human-to-computer - user interface protocols, etc.Computer-aided human-to-human – electronic mail, bboard, publishing, etc.
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Cont.
Factors lead to fast growing of computer-communication networks:Hardware and software technologies of computerDigital transmissionFiber opticsDigital signal processingVLSI technologies, etc
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Cont.Network Goals
Resource (and Load) SharingReduced CostHigh Reliability
Applications of Computer NetworksReservation systemsElectronic mail systemsRemote teller banking systemsCredit verification systemsAccess to remote data systems
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Cont.
Trends in Computer Networks– Higher speed network > 100 Mbps– Wider geographic coverage– Integrated services: text, graphics,
voice, audio, image, video,...
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Types of comm. networks
two broad categories of communications networks:
Local Area Network (LAN)Wide Area Network (WAN)
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Wide Area Networks
span a large geographical areacross public right-of-waysrely in part on common carrier circuitsalternative technologies used include:
circuit switchingpacket switchingframe relayAsynchronous Transfer Mode (ATM)
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Circuit Switching
uses a dedicated communications path established for duration of conversationPath consists of a sequence of physical links.Each link has a dedicated logical channel.E.g. telephone network
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Packet Switching
data sent out of sequencesmall chunks (packets) of data at a timepackets passed from node to node between source and destination.used for terminal to computer and computer to computer communicationsData rate about 64kbps.
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Frame Relay
packet switching systems have large overheads to compensate for errorsmodern systems are more reliableerrors can be caught in end systemFrame Relay provides higher speeds up to 2 Mbps.with most error control overhead removed
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Asynchronous Transfer Mode
ATMevolution of frame relayfixed packet (called cell) lengthwith little overhead for error controlanything from 10Mbps to Gbpsconstant data rate using packet switching technique with multiple virtual circuits
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Local Area Networks
smaller scopeBuilding or small campus
usually owned by same organization as attached devicesdata rates much higherswitched LANs, eg Ethernetwireless LANs
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Metropolitan Area Networks
MANmiddle ground between LAN and WANprivate or public networkhigh speedlarge area
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Distance-Speed in Networks
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The Internet
Internet evolved from ARPANETfirst operational packet networkapplied to tactical radio & satellite nets alsohad a need for interoperabilityled to standardized TCP/IP protocols
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Internet Elements
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Internet Architecture
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Example: Network Configuration
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Summary
introduced data communications needscommunications modeldefined data communicationsoverview of networksintroduce Internet
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Topics to be covered in following chapters
Protocol architecture (ch2).Transmission and Transmission Media (ch3-4)Communication Techniques (ch5-6)Flow and Error control (ch7)Transmission efficiency ( ch8)Switching Techniques (ch10)