1. Switching & Data Networks
Lecture ID: ET-IDA-067
Lecture 6
Media and Data Transmission
Chapter 3 and 4 from textbook Data and Computer Communications
by W. Stallings
, v03
Prof. W. Adi

2. Chapter 4- from Textbook Data and Computer Communications
Transmission Media
Chapter 4- from Textbook
Data and Computer Communications
by W. Stallings

3. Overview Guided - wire Unguided - wireless
Characteristics and quality determined by medium and signal
For guided, the medium is more important
For unguided, the bandwidth produced by the antenna is more important
Key concerns are data rate and distance

4. Design Factors Bandwidth Transmission impairments Interference
Higher bandwidth gives higher data rate
Transmission impairments
Attenuation
Interference
Many signals at the same time
Number of receivers
In guided media
More receivers (multi-point) introduce more attenuation and distortion

5. Electromagnetic Spectrum

6. Guided Transmission Media
Twisted Pair
Coaxial cable
Optical fiber

7. Twisted Pair
Two categories:
Unshielded
Shielded

8. Twisted Pair - Applications
Most common medium
Telephone network
Between house and local exchange (subscriber loop)
Within buildings
To private branch exchange (PBX)
For local area networks (LAN)
10Mbps or 100Mbps

9. Twisted Pair - Pros and Cons
Cheap
Easy to work with
Low data rate MHz
Short range Attenuation !
2.6 dB/100m at 1MHz
21.4 dB/100m at 300 MHz

10. Twisted Pair - Transmission Characteristics
Analog
Amplifiers (repeaters) every 5km to 6km
Digital
Use either analog or digital signals
repeater every 2km or 3km
Limited distance
Limited bandwidth
Limited data rate
Susceptible to interference and noise

11. Unshielded and Shielded TP
Unshielded Twisted Pair (UTP)
Ordinary telephone wire
Cheapest
Easiest to install
Suffers from external EM interference
Shielded Twisted Pair (STP)
Metal shield that reduces interference
More expensive
Harder to handle (thick, heavy)

12. UTP Categories Cat 3 Cat 4 Cat 5 up to 16MHz
Voice grade found in most offices
Twist length of 7.5 cm to 10 cm
Cat 4
up to 20 MHz
Cat 5
up to 100MHz
Commonly pre-installed in new office buildings
Twist length 0.6 cm to 0.85 cm

13. Near End Crosstalk Coupling of signal from one pair to another
Coupling takes place when transmit signal entering the link couples back to receiving pair
i.e. near transmitted signal is picked up by near receiving pair

14. Coaxial Cable

15. Coaxial Cable Applications
Most versatile medium
Television distribution
Arial to TV
Cable TV
Long distance telephone transmission
Can carry 10,000 voice calls simultaneously
Being replaced by fiber optic
Short distance computer systems links
Local area networks

16. Coaxial Cable - Transmission Characteristics
Analog
Amplifiers every few km
Closer if higher frequency is used
Up to 500MHz
Digital
Repeater every 1km
Closer for higher data rates

17. Optical Fiber

18. Optical Fiber - Benefits
Greater capacity
Data rates of hundreds of Gbps
Smaller size & weight
Lower attenuation
Electromagnetic isolation
Greater repeater spacing
10s of km at least

19. Optical Fiber - Applications
Long-haul trunks
Metropolitan trunks
Rural exchange trunks
Subscriber loops
LANs

20. Optical Fiber - Transmission Characteristics
Act as wave guide for 1014 to 1015 Hz
Portions of infrared and visible spectrum
Light Emitting Diode (LED)
Cheaper
Wider operating temp range
Last longer
Injection Laser Diode (ILD)
More efficient
Greater data rate
Wavelength Division Multiplexing ‘WDM’
(1000Gbps=1 Terabit/sec Bell-labs 1997)

21. Optical Fiber Transmission Modes

22. Wireless Transmission
Unguided media
Transmission and reception via antenna
Directional
Focused beam
Careful alignment required
Omnidirectional
Signal spreads in all directions
Can be received by many antennae

23. Frequencies 2GHz to 40GHz 30MHz to 1GHz 3 x 1011 to 2 x 1014 Microwave
Highly directional
Point to point
Satellite
30MHz to 1GHz
Omnidirectional
Broadcast radio
3 x 1011 to 2 x 1014
Infrared
Local

24. Terrestrial Microwave
Parabolic dish
Focused beam
Line of sight
Long haul telecommunications
Higher frequencies give higher data rates
propagation
source

25. Satellite Microwave Satellite is relay station
Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency
Requires geo-stationary orbit to stay still relative to a location on the earth
Height of 35,784km
Television
Long distance telephone
Private business networks

26. Broadcast Radio Omnidirectional, sends to all directions FM radio
UHF and VHF television
Line of sight
Suffers from multipath interference
Reflections

27. Infrared Modulate noncoherent infrared light
Line of sight (or reflection)
Blocked by walls
e.g. TV remote control, IRD port

28. Chapter 3- from Textbook Data and Computer Communications
Data Transmission
Chapter 3- from Textbook
Data and Computer Communications
by W. Stallings

29. Basic Components Transmitter Receiver Medium
Guided medium, e.g. twisted pair, optical fiber
Unguided medium, e.g. air, water, vacuum
Transmitter
Medium
Receiver Z0 Z0 Z0
Example: typical twisted pair connection

30. Art of Transmissions Simplex Half duplex Full duplex One direction
e.g. Television
Half duplex
Either direction, but only one way at a time
e.g. police radio
Full duplex
Both directions at the same time
e.g. telephone

31. Transmitted Signals: Continuous & Discrete Signals

32. Wavelength Distance occupied by one cycle
Or distance between two points of corresponding phase in two consecutive cycles
 : Wavelength
Assuming signal velocity v
 = v T
 f = v
c = 3*108 ms-1 (speed of light in free space)

33. Signal Spectrum & Bandwidth
The range of frequencies contained in a signal
Absolute bandwidth
width of spectrum
Effective bandwidth
Often just bandwidth: Narrow band of
frequencies containing most of the energy
DC Component
Component of zero frequency

34. Addition of Frequency Components
Fundamental frequency
3rd Harmonic frequency
Simplified square wave

35. Signal with DC Component

36. Analog and Digital Data Transmission
Definitions
Data
Entities that convey meaning
Signals
Electric or electromagnetic representations of data
Transmission
Communication of data by propagation and processing of signals

37. Data Analog Digital Continuous values within some interval
e.g. sound, video
Digital
Discrete values
e.g. text, integers

38. Acoustic Spectrum (Analog)
Voice: 300 – 3400 Hz

39. Data and Signals Representation
Usually use digital signals for digital data and analog signals for analog data
Can use analog signal to carry digital data
Example: Modem
Can use digital signal to carry analog data
Example: Compact Disc audio

40. Analog Signals Carrying Analog and Digital Data

41. Digital Signals Carrying Analog and Digital Data

42. Transmission Impairments
Signal received may differ from signal transmitted (distortion)
Analog --> degradation of signal quality
Digital --> bit errors
Caused by
Attenuation and attenuation distortion
Delay distortion
Noise

43. Attenuation Signal strength falls off with distance
Depends on transmission medium
Attenuation is an increasing function of frequency
Received signal strength:
must be enough to be detected
must be sufficiently higher than noise to be received without error

44. Delay Distortion Only in guided media
Propagation velocity varies with frequency

45. Noise (1) Additional signals inserted between transmitter and receiver
Thermal
Due to thermal agitation of electrons
Uniformly distributed
White noise
Thermal Noise power is : N = K T B
K: Boltzmann‘s constant J/oK
T: teprature, degrees kelvin (273 + oC)
B: Bandwidth in Hz
Intermodulation
Signals that are the sum and difference of original frequencies sharing a medium (due to nonlinearity)

46. Noise (2) Crosstalk Impulse
A signal from one line is picked up by another
Impulse
Irregular pulses or spikes
e.g. External electromagnetic interference
Short duration
High amplitude

47. Channel Capacity Data rate Question: Given - Channel Bandwidth
Measured in bits per second bps
Rate at which data can be communicated
Question: Given
- Channel Bandwidth
- Channel quality (noise)
What is the channel capacity ?

48. Nyquist Bandwidth and Channel Capacity
Nyquist Formula: Given a noisless channel with
bandwidth B Hz, the highest bit rate
C that can be carried is:
C = 2B log2 M
Where M is the number of discrete signalling levels
Example: A Modem operating at a telephone channel with
a bandwidth of 3100 Hz. The number of different
signal levels is 8.
The Nyquist capacity is: C = 2 x 3100 log2 8 = bps

49. Shannon Capacity
(Maximum error-free Channel Transmission Rate)
Shannon Formula: Given a channel with a signal-to-noise
ratio of SNR, the theoretical error-free transmission rate is:
C = B log2 (1 + SNR)
Where C is the channel capacity in bits per second pbs
(still no techniques are known today to reach this limit) !
Example: A Modem operating at a telephone channel with
a bandwidth of 3100 Hz. The channel signal-to-
noise ratio is 7.
The maximum theoretical error-free transmission rate is:
C = 3100 log2 (1+7) = 9300 bps