1. A quick look at network fundamentals
Introduction
A quick look at network fundamentals
F. M. Marchetti, Ph.D.
CSE / Rm 353
SMU
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2. Introduction Transmission Fundamentals
Factors that determine the best way to connect
Cost of connection
Speed
Immunity to interference
Security
Logistics
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3. Purpose of a Network To deliver data from one entity to another
Factors to consider:
Need for reliable transmission
Quality of Service
Need for transmission of real-time data
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4. Types of Network Maximum intercomputer distance
Computer located in same …
Example
1 m
System
Multicomputer
10 m / 100 m / 1 km
Room / building / campus
Local area network (LAN)
10 km
City
Metropolitan area network
100 km / 1000 km
Country / Continent
Wide area netwok (WAN)
10000 km
Planet
The Internet
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5. LANs
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6. WANs
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7. The Internet
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8. Forms of Data Transmission
Data must be converted to a physical signal for transmission
Analog transmission (such as speech over telephone lines)
Suffers from degradation which cannot be reconstructed
Digital transmission (such as VoIP)
Suffers from all-or-none degradation
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9. Digital vs. Analog
Digital less susceptible to distortion and interference compared to Analog
Digital signals can be regenerated to extend the length of the cable
Extremely low error rate (BER)
Cheaper
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10. Data Encoding Techniques
Analog Signals  Digital Data
Amplitude shift keying (ASK)
Frequency shift keying (FSK)
Phase shift keying
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11. Digital Data, Digital Signals
Non-return-to-Zero Level (NRZ-L)
NRZ - I
Manchester Encoding
Differential Manchester encoding
Disadvantages of NRZ
Synchronization is difficult
DC component
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12. Digital Data, Digital Signal (cont’d)
Advantages of Differential encoding
Easy detection
Can keep track of the polarity
Advantages of bi-phase encoding
Synchronization
No dc component
Error detection
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13. Analog Data, Digital Signal
Based on the sampling theorem
Nyquist Limit
Pulse code modulation (PCM)
ADPCM (more compressed)
Delta modulation
Only the change of information is sent
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14. Parallel vs. Serial Transmission
Dedicated functions to the wires
Higher speed for short distance interconnections
Not feasible for long distances (more than 100m )
Reduction in performance
Cross talk in long cables
Cost
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15. Parallel vs. Serial Serial Serialize the data Add control characters
Format the data into frames
Two types of transmission:
asynchronous: transmitter and receiver clocks are independent
synchronous: transmitter and receiver are synchronized
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16. Direction of Transmission
Simplex
Transmission in one direction only
Half-Duplex
Transmission in one direction at a time
Full-Duplex
Transmission in both directions
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17. Synchronous vs. Asynchronous
One character at a time
One start bit – one or more stop bits
No clock – receiver resynchronizes after each stop code
Cheap but inefficient – large overhead (20% or more)
Relatively low data rates (up to kbps, in practice  38.4 kbps)
Uses:
suitable for data transmitted at random intervals (e.g. keyboard to computer)
simplicity and availability: UART and RS232 are present in any PC
used in the great majority of dial-up connections
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18. Synchronous vs. Asynchronous
Arrival time of each bit is predictable
To prevent timing drift the receiver and transmitter clock are synchronized
Preamble and Postamble SYNC characters
Character Oriented
Clock signal transmitted either:
over a separate line (see V.35, RS232 lines)
or encoded into the data (Manchester, differential Manchester encoding) to allow a single line for both data and clock
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19. Transmission Media Guided Media Unguided Media Twisted Pair of Cables
Coaxial Cables
Optical Fibers
Unguided Media
Radio
Microwave
Satellite
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20. Multiplexing Link Sharing For cost-effective transmission
The medium carries multiple signals simultaneously
Commonly used techniques:
FDM - Frequency Division Mux
TDM - Time Division Mux (STDM)
WDM - Wavelength Division Mux
CDM - Code Division Mux (frequency hopping and spread spectrum techniques)
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21. Statistical MUX Link is shared over time (like STDM)
Scan the buffer and create a variable-size frame
Transmission-on-demand
Also called Concentrator
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22. Communication Switching Techniques
Spectrum of Switching Techniques
Circuit switching
Multi-rate circuit switching
Cell relay
Frame relay
Packet switching
Dedicated
Virtual
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23. Circuit Switching Dedicated communication path between two stations
Three Phases
Check also whether the destination is ready to accept the request
Data transfer
Could be either digital or analog signaling
Generally full duplex
Circuit disconnect
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24. Packet Switching Greater line efficiency Data rate conversion
Connection request is always accepted irrespective of the traffic
Dynamic routing and priority assignment possible
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25. Packet Switching - Approaches
Datagram
Virtual Circuit
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26. Packet Switching - Approaches
Datagram
Each packet is treated independently
The packets may be received out of sequence
Some packets may be lost in the event of some node crashes
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27. Packet Switching - Approaches
Virtual Circuit
A preplanned route is established before the data is sent
At any time, each station can have more than one VC to any other station and can have VCs to more than one station
Provides sequencing, error control, and flow control
If an intermediate node fails, all virtual circuits going through that node may be lost - less reliable when compared to datagrams
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28. Frame relay Too much overhead built into packet switching
Frame relays take advantage of the low error rates of networking facilities
Cell Relay
ATM
Fixed length packets
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29. OSI Layers Application Presentation Session
provides electronic mail, file transfers etc.
Presentation
Translates data format, encrypts and decrypts data
Session
Synchronizes communicating users, recovers from errors
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30. OSI Layers (cont’d) Transport Network Data Link Physical
Determines network, may assemble and reassemble packets
Network
Determines routes, manages billing information
Data Link
Detects or correct errors, defines frames
Physical
Transmits physical data
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31. End of Class 1
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