related to computer networking

2. Transmission
mediaTransmission media
are located below the
physical layer
Computers use
signals to represent
data.
Signals are
ransmitted in form
of electromagnetic
energy.

3. Transmission
MediaTransmission Media and Physical
Layer

4. Transmission
Media Guided Media (Wired)
 Twisted-Pair Cable
 Coaxial Cable
 Fiber-Optic Cable
 Unguided Media (Wireless)
 Radio Waves
 Microwaves
 Infrared

5. Classes of transmission
media

6. GUIDED MEDIA
Guided media, which are those that provide a medium from one device to another, include
twisted-pair cable, coaxial cable, and fiber-optic cable.

7. Overvie
w
 The transmission media that are used to convey information can be
classified as guided or unguided. Guided media provide a physical
path along which the signals are propagated; these include twisted
pair, coaxial cable, and optical fiber. Unguided media employ an
antenna for transmitting through air, vacuum, or water.
 The characteristics and quality of a data transmission are
determined both by the characteristics of the medium and the
characteristics of the signal. In the case of guided media, the
medium itself is more important in determining the limitations of
transmission.
 For unguided media, the bandwidth of the signal produced by the
transmitting antenna is more important than the medium in
determining transmission characteristics. One key property of signals
transmitted by antenna is directionality. In general, signals at lower
frequencies are omnidirectional; that is, the signal propagates in all
directions from the antenna. At higher frequencies, it is possible to
focus the signal into a directional beam. In considering the design of
data transmission systems, key concerns are data rate and distance:
the greater the data rate and distance the better.

8. Data Rate and
BandwidthAny transmission system has a limited band
of frequencies
This limits the data rate that can be carried

9. Design
Factors
Bandwidth
 higher bandwidth gives higher data rate
Transmission impairments
 eg. attenuation
Interference
Number of receivers in guided media
 more receivers introduces more
attenuation

10. Guided Media – Twisted-pair
Cable
Twisted-pair
cable

11. Twisted
Pair

12. Twisted
pair One of the wires carries signal, the other is used only as a
ground reference.
 The receiver uses the difference b/w the two levels.
 Twisting increases the probability that both wires are effected
by the noise in the same manner, thus the difference at the
receiver remains same.
 Therefore, number of twists per unit length determines the
quality of the cable.

13. Twisted Pair -
Transmission
Characteristicsanalog
 needs amplifiers every 5km to 6km
digital
 can use either analog or digital signals
 needs a repeater every 2-3km
limited distance
limited bandwidth (1MHz)
limited data rate (100MHz)
susceptible to interference and
noise

14. Unshielded Versus Shielded Twisted-Pair
Cable
UTP and STP cables

15. Unshielded Twisted Pair
(UTP)Ordinary telephone
wire
Cheapest
Easiest to install
Suffers from
external EM
interference

16. Shielded Twisted Pair
(STP)Metal braid or
sheathing that
reduces interference
More expensive
Harder to handle
(thick, heavy)

17. Near End
Crosstalkcoupling of signal from one pair to another
occurs when transmit signal entering the link
couples back to receiving pair
ie. near transmitted signal is picked up by near
receiving pair

18. Categories of unshielded twisted-pair
cables

19. UTP
Categories

20. Guided Media –
UTP
UTP Connector

21. Guided Media -
UTP Applications:
 Telephone lines connecting subscribers
to the central office
 DSL lines
 LAN – 10Base-T and 100Base-T

22. Twisted Pair -
ApplicationsMost common medium
Telephone network
Within buildings
For local area networks
(LAN)

23. Twisted Pair - Pros and
ConsCheap
Easy to work
with
Low data rate
Short range

24. Guided Media – Coaxial
Cable Coaxial
Cable

25. Coaxial
Cable

26. Coaxial
cableInner conductor is a
solid wire outer
conductor serves
both as a shield
against noise and a
second conductor

27. Coaxial Cable
ApplicationsMost versatile medium
Television distribution
Long distance telephone transmission
Can carry 10,000 voice calls
simultaneously
Short distance computer systems links
Local area networks

28. Coaxial Cable -
TransmissionCharacteristi
cs
superior frequency characteristics to TP
performance limited by attenuation &
noise
analog signals
 amplifiers every few km
 closer if higher frequency
 up to 500MHz
digital signals
 repeater every 1km
 closer for higher data rates

29. Guided Media – Coaxial
Cable Categories of coaxial
cables

30. Guided Media – Coaxial
Cable BNC
Connectors

31. BNC
connectors BNC = Bayone-Neill-
Concelman
 BNC Connector is used to
connect the end of the
cable to a device
 BNC T is used in
networks to branch out a
cable for connection to a
computer or other device
 BNC Terminator is used
at the end of the cable to
prevent the reflection of
signal.

32. Coaxial cable
performance

33. Guided Media – Coaxial
Cable Applications:
 Analog telephone networks
 Cable TV networks
 Traditional Ethernet LAN – 10Base2,
10Base5

34. Bending of light
ray
Guided Media – Fiber-Optic Cable
Fiber-optic cable transmit signals in the form of light.

35. Guided Media – Fiber-Optic
Cable Optic
Fiber

36. Optical
fiberUses reflection to
guide light through a
channel
Core is of glass or
plastic surrounded
by Cladding
Cladding is of less
dense glass or plastic

37. Optical
Fiber

38. 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

39. Optical Fiber -
Benefits The following characteristics distinguish optical fiber from twisted pair or coaxial cable:
 Greater capacity: The potential bandwidth, and hence data rate, of optical fiber is
immense; data rates of hundreds of Gbps over tens of kilometers have been
demonstrated. Compare this to the practical maximum of hundreds of Mbps over
about 1 km for coaxial cable and just a few Mbps over 1 km or up to 100 Mbps to 10
Gbps over a few tens of meters for twisted pair.
 Smaller size and lighter weight: Optical fibers are considerably thinner than coaxial
cable or bundled twisted-pair cable. For cramped conduits in buildings and
underground along public rights-of-way, the advantage of small size is considerable.
The corresponding reduction in weight reduces structural support requirements.
 Lower attenuation: Attenuation is significantly lower for optical fiber than for coaxial
cable or twisted pair, and is constant over a wide range.
 Electromagnetic isolation: Optical fiber systems are not affected by external
electromagnetic fields. Thus the system is not vulnerable to interference, impulse
noise, or crosstalk. By the same token, fibers do not radiate energy, so there is little
interference with other equipment and there is a high degree of security from
eavesdropping. In addition, fiber is inherently difficult to tap.
 Greater repeater spacing: Fewer repeaters mean lower cost and fewer sources of
error. The performance of optical fiber systems from this point of view has been
steadily improving. Repeater spacing in the tens of kilometers for optical fiber is
common, and repeater spacings of hundreds of kilometers have been demonstrated.

40. Optical Fiber -
TransmissionCharacteristi
cs
uses total internal reflection to transmit
light
 effectively acts as wave guide for 1014 to 1015
Hz
can use several different light sources
 Light Emitting Diode (LED)
 cheaper, wider operating temp range, lasts
longer
 Injection Laser Diode (ILD)
 more efficient, has greater data rate
relation of wavelength, type & data rate

41. Guided Media – Fiber-Optic
Cable Propagation
Modes

42. Guided Media – Fiber-Optic
Cable
Propagation
Modes

43. Optical Fiber Transmission
Modes

44. Guided Media – Fiber-Optic
Cable
Fiber Construction

45. Guided Media – Fiber-Optic Cable
Fiber-optic Cable Connectors

46. Guided Media – Optical Fiber
Cable Applications:
 Backbone networks – SONET
 Cable TV – backbone
 LAN
 100Base-FX network (Fast Ethernet)
 100Base-X

47. Transmission
Characteristics of Guided
MediaFrequency
Range
Typical
Attenuation
Typical
Delay
Repeater
Spacing
Twisted pair
(with loading)
0 to 3.5 kHz 0.2 dB/km @ 1
kHz
50 µs/km 2 km
Twisted pairs
(multi-pair
cables)
0 to 1 MHz 0.7 dB/km @
1 kHz
5 µs/km 2 km
Coaxial cable 0 to 500 MHz 7 dB/km @ 10
MHz
4 µs/km 1 to 9 km
Optical fiber 186 to 370
THz
0.2 to 0.5
dB/km
5 µs/km 40 km

48. Comparison of Physical
Media

49. Electromagnetic
Spectrum

50. Wireless Transmission
Frequencies2GHz to 40GHz
 microwave
 highly
directional
 point to point
 satellite
30MHz to 1GHz
 omnidirectional
 broadcast radio
 3 x 1011 to 2 x
1014
 infrared
 local

51. Unguided Media
Propagation Methods

52. Band
s

53. Unguided
Media Wireless transmission
waves

54. Broadcast
Radioradio is 3kHz to 300GHz
use broadcast radio, 30MHz - 1GHz,
for:
 FM radio
 UHF and VHF television
is omnidirectional
still need line of sight
suffers from multipath interference
 reflections from land, water, other
objects

55. Unguided Media – Radio
WavesOmnidirectional Antenna
Frequencies between 3 KHz and 1 GHz.
are used for multicasts communications, such as radio
and television, and paging system.

56. Terrestrial
Microwave
used for long haul telecommunications
and short point-to-point links
requires fewer repeaters but line of sight
use a parabolic dish to focus a narrow beam onto
a receiver antenna
1-40GHz frequencies
higher frequencies give higher data rates
main source of loss is attenuation
 distance, rainfall
also interference

57. Unguided Media –
Microwaves Frequencies between 1 and 300 GHz.
 Used for unicast communication such as cellular phones,
satellite networks and wireless LANs.
Unidirectional Antenna

58. Satellite
Microwavesatellite is relay station
typically requires geo-stationary
orbit
 height of 35,784km
 spaced at least 3-4° apart
typical uses
 television
 long distance telephone
 private business networks
 global positioning

59. Unguided Media –
Infrared
Frequencies between 300 GHz to 400 THz.
Can not penetrate walls.
Used for short-range communication in a
closed area using line-of-sight propagation.

60. Infrare
dare blocked by walls
no licenses required
typical uses
 TV remote control
 IRD port