Download 431-624 Computer Networks

Network Technology
CSE3020
Week 13
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Network Technology
 Basic Data Communications Theories
• Data transmission
• Coding & Modulation
• Multiplexing & Switching
• Transmission Media
 Local Area Networks
• Ethernet and Token Passing Networks
 Wide Area Networks
• ATM and ISDN
 Wireless Networks
• Cellular Networks and Wireless LAN
 Residential Area Networks
• ADSL, Cable TV
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Simplified Network Model
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OSI Model
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OSI Model
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TCP/IP Protocol Architecture
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OSI and TCP/IP
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Computer Networks
Router
WLAN
Bridge
Application
Presentation
Session
Transport
Network
Data link
Physical
Residential Area
Networks
Backbone
Ethernet
Token Ring, FDDI
PCM
Capacity
ATM
Encoding & Modulation
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Sine Wave
 General sine wave: s(t)=Asin(2 ft + ).
 Peak Amplitude (A) - maximum strength of signal,
generally in volts.
 Frequency (f) - rate of change of signal.
- Hertz (Hz) or cycles per second.
- Period = time for one repetition (T).
- T = 1/f
relative position in time.
 Phase ()  Wavelength () - Distance occupied by one cycle.
-  = vT where v is signal velocity.
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Frequency Domain Concepts

 Signal are usually made up of many frequencies.
 Components are sine waves.
 Fourier analysis:
• Any signal is made up of sine waves.
• Can plot frequency domain functions.
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Transmission Impairments
 Signal received may differ from signal transmitted.
 Analog - degradation of signal quality.
 Digital - bit errors
 Impairments: Attenuation, Delay distortion & Noise
Noise
Attenuation
Delay Distortion
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Channel Capacity
 Maximum rate at which data can be transmitted.
 Nyquist Theorem: Maximum bit rate on a noise-free channel.
C = 2 B log 2 M bits/sec
 Shannon Theorem: Maximum bit rate on a noisy channel.
C = B log 2 (1 + S/N) bits/sec
channel bandwidth
signal-to-noise ratio
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Data Encoding
Data and Signals:
 Digital data  digital signal (Encoding/Decoding)
 Digital data  analog signal (Modulation/Demodulation)
 Analog data  analog signal (Modulation /Demodulation)
 Analog data  digital signal (Digitization/Conversion)
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Signaling/Modulation Rate
 Data rate - Rate of data transmission in bits per second.
 Signaling/Modulation rate
– Rate at which the signal elements are transmitted.
– Measured in baud = signal elements per second.
– For binary signaling, bit rate = baud rate.
 Bit rate = Baud rate  Number of bits per signal element.
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Interpreting Signals
• Need to know: Timing of bits/signals and Signal levels.
• Factors affecting successful interpreting of signals:
– Signal to noise ratio, Data rate and Bandwidth
• An increase in data rate increases bit error rate (BER).
• An increase in SNR decreases bit error rate.
• An increase in bandwidth allows an increase in data rate.
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Encoding Schemes
 Signal Spectrum.
 Clocking.
 Signal interference and noise
immunity.
 Error detection.
 Cost and complexity.
 Nonreturn to Zero-Level (NRZ-L)
 Nonreturn to Zero Inverted (NRZI)
 Bipolar-Alternate Mark Inversion (Bipolar-AMI)
 Pseudoternary
 Manchester
 Differential Manchester
 Bipolar with 8-zeros substitution (B8ZS)
 High-density bipolar-3 zeros (HDB3)
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Digitization
 Analog to digital conversion: PCM & Delta Modulation.
 If a signal is sampled at regular intervals at a rate higher than twice
the highest signal frequency, the samples contain all the information
of the original signal.
 Voice data limited to below 4000Hz - Require 8000 sample/second.
 Samples are quantized: Quantizing error or noise.
 Each sample assigned digital value (4 bit system gives 16 levels).
 Equally spaced level: Uniform Quantization.
 Non-equally spaced level: Non-uniform Quantization
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Pulse Code Modulation(PCM)
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Modulation
 Why modulate analog/digital signals?
–
–
–
–
Higher frequency can give more efficient transmission.
Permits frequency division multiplexing.
Unguided Transmission needs high frequencies.
For practical antenna size.
 Analog modulation: - Amplitude Modulation (AM)
- Frequency Modulation (FM)
- Phase Modulation(PM)
 Digital modulation:
– Amplitude shift keying (ASK)
– Phase shift keying (PSK)
– Frequency shift keying (FSK)
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Spread Spectrum
 Spread data over wide bandwidth.
 Makes jamming and interception harder.
 Frequency hopping:
- Signal broadcast over seemingly random series of frequencies.
- Receiver hops between frequencies in synchronization with
transmitter.
 Direct Sequence:
- Each bit is represented by multiple bits in transmitted
signal by a chipping code.
- Chipping code spreads the signal across a wider frequencies.
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Transmission Media
• Guided Transmission:
– Twisted Pair
- Unshielded Twisted Pair (UTP)
- Shielded Twisted Pair (STP)
– Coaxial Cable
– Optical Fiber
• Unguided (wireless) Transmission:
– Terrestrial Microwave
– Satellite Microwave
– Broadcast Radio
– Infrared
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Transmission Media
• Electromagnetic waves.
• Characteristics and quality determined by medium and
the transmitted signal.
• Key concerns are data rate and distance.
• Design Factors:
– Bandwidth.
– Transmission impairments.
– Interference.
– Number of receivers.
• Each transmission media:
– Limitations & characteristics.
– Pros & Cons.
– Applications.
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Asynchronous and Synchronous
Transmission
• Transmission requires cooperation and agreement between the
two sides.
• Fundamental requirement is Synchronization: Receiver must
know the beginning and end of a bit/rate at which bits are
received.
– Asynchronous transmission
– Synchronous transmission
• Asynchronous transmission:
– Each character treated independently and begins with a start bit.
– Not good for long block of data.
• Synchronous transmission:
– Block of data is formatted as a frame with a starting and an ending flag.
– Good for block of data.
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Multiplexing
 Multiplexing.
 Demultiplexing.
 Different types:
 Frequency division multiplexing (FDM).
 Time division multiplexing (TDM).
 Synchronous TDM
 Statistical TDM
 Code division multiplexing (CDM).
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Switching
• Circuit switching & Packet switching.
• Circuit switching: designed for voice.
- Dedicated communication path between.
- Data rate is fixed. Both ends must operate at the same rate.
• Packet switching: designed for data networks.
– Data transmitted in small packets.
– Longer messages split into series of packets.
– Each packet contains a portion of user data plus some control
information: Routing (addressing).
– Packets handled in two ways.
– Datagram: No call setup phase and More flexible
– Virtual circuit: Sequencing and error control, Fast, Less reliable.
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Data Link Control
• Flow control: Preventing buffer overflow at the receiver.
- Stop-and-wait & Sliding window.
• Error control: Detecting and correcting transmission errors.
- Parity check & Cyclic Redundancy Check (CRC).
• Automatic Repeat Request (ARQ): Error & Flow Control.
- Error detection & Retransmission.
- ARQ schemes.
- Stop-and-Wait.
- Go-back-N (retransmission from error frame).
- Selective Repeat (selective retransmission).
- ARQ efficiency:
- Unnecessary waiting and sending unnecessary transmission.
• High Level Data Link Control (HDLC).
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Local Area Network (LAN)
• LAN applications.
• LAN Architecture:
- Protocol architecture.
- Topologies.
- Media Access Control.
- Logical Link Control.
• LAN devices:
- Repeaters
- Bridges
- Hubs & Switches.
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Local Area Networks (LANs)
random access
token passing
polling
MAC
protocols
FDDI
Ethernet
Token ring
Wireless LAN
products
topologies
LAN
standard
bodies
transmission
media
IEEE
ISO, ATM Forum
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star
ring
tree
fiber
twisted pair
coax
air (wireless)
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LAN Types
• Ethernet:
• Token ring network.
• FDDI
• ATM LANE.
• Backbone network.
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Wireless LAN (WLAN)
• WLAN advantages.
• WLAN design considerations.
• WLAN types/products.
• WLAN topology/architecture.
• WLAN MAC protocol (CSMA/CA).
• Hidden station & exposed station problem.
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Asynchronous Transfer Mode (ATM)
• ATM characteristics.
• ATM Protocol reference model.
• ATM logical connections: Virtual paths & circuits.
• ATM Cell.
• ATM Service characteristics.
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Management Plane
Control Plane
User Plane
Higher Layer
ATM Adaptation Layer (AAL)
ATM Layer
Layer Management
Plane Management
ATM Protocol Reference Model
Physical Layer
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Residential Area Networks
 PSTN:
 ISDN:
 ADSL:
 Cable modem:
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