1. 2IC10 Computer Networks Physical layer Igor Radovanović Thanks to
B. A. Forouzan
A. Tanenbaum
Igor Radovanovic,
18/12/2019
18/12/2019
18/12/2019 1 1
TU/e Computer Science, System Architecture and Networking

2. Physical layer
18/12/2019

3. Analog versus digital signals
18/12/2019

4. Fourier Coefficients
18/12/2019

5. Fourier transformation
18/12/2019

6. Fourier transformation (cnt’d)
18/12/2019

7. Bandwidth
18/12/2019

8. Signal impairments
18/12/2019

9. Signal distortion
attenuation
distortion
noise
18/12/2019

10. What is the bandwidth of this signal?
Digital signal
QUESTION:
What is the bandwidth of this signal?
18/12/2019

11. Throughput
18/12/2019

12. Propagation time
18/12/2019

13. Wavelength
18/12/2019

14. Transmission media
Magnetic tapes?
18/12/2019

15. Twisted pair
18/12/2019

16. Twisted pair (cnt’d) - bandwidth issue -
(a) Category 3 UTP
(b) Category 5 UTP
18/12/2019

17. Using twisted pair cables in a network
Cat 3
Cat 3 or Cat 5
18/12/2019

18. Using twisted pair cables in a network (cnt’d)
18/12/2019

19. Twisted pair networks -example - ADSL Ethernet networks - 10BASE-T
- 100BASE-TX
- 1000BASE-T
- 1000BASE-TX (Cat5e (enhanced))
18/12/2019

20. Twisted pair - pros and cons - Pros: easy to understand
mass production - low cost
most widely used medium
Cons:
prone to electromagnetic interference
in power plants, airport buildings, military facilities, cars…
Note:
In-building networks at our university are almost all twisted pair
18/12/2019

21. Transmission media
18/12/2019

22. Coax cable Category Impedance Use RG-59 75 W Cable TV RG-58 50 W
Longer distances, higher bit-rates
Category
Impedance
Use
RG-59
75 W
Cable TV
RG-58
50 W
Thin Ethernet
RG-11
Thick Ethernet
18/12/2019

23. Coax cable network - example - 10Base2 Ethernet Note: Almost obsolete
18/12/2019

24. Coax cable network
- example 2-
cable modem
18/12/2019

25. Transmission media
18/12/2019

26. Optical fiber fundamentals
Banding the light ray
18/12/2019

27. Optical fiber fundamentals
18/12/2019

28. Optical fiber fundamentals (cnt’d)
50 microns
5-10 microns
18/12/2019

29. Optical fiber fundamentals (cnt’d)
18/12/2019

30. Optical fiber network
- example 1-
18/12/2019

31. Optical fiber network -example 2-
18/12/2019

32. Optical fiber - pros and cons - Pros: Low attenuation Large bandwidth
Relatively “new” technology
“Expensive”
18/12/2019

33. Comparing optical fiber to UTP
Pros:
Immune to electro-magnetic interference
no crosstalk
Reduced need for error detection and correction
Enables longer link distances
Attenuation unaffected by transmission rate
Easier network upgrade
Can combine different services: telephony, TV, internet…
Cons:
Optical components have higher cost
Expensive deploying protocols
18/12/2019

34. Comparing optical fiber to UTP
Unrepeated signal can travel larger distances
18/12/2019

35. Comparing coax to UTP coax cable performance UTP performance
18/12/2019

36. 18/12/2019

37. Wireless
Modern wireless digital communication began in the Hawaiian Islands
What is “the best” frequency to use for communication?
18/12/2019

38. Politics of the electromagnetic spectrum
IEEE b (11Mb), (22Mb) IEEE g (54 Mb) Bluetooth
IEEE a (100 Mbps)
Industrial Scientific and Medical band (ISM)
Government regulated
Transmission power is limited so as to limit interference
18/12/2019

39. Bandwidth delivery capability by technology
18/12/2019

40. Multiplexing
18/12/2019

41. Frequency Division Multiplexing
18/12/2019

42. Wavelength Division Multiplexing
18/12/2019

43. Time Division Multiplexing
18/12/2019

44. Inverse Time Division Multiplexing
Example: High-speed Ethernet networks
18/12/2019

45. TDM network -example- T1
high-speed digital network (1.544 Mbps) developed by AT&T in 1957 and implemented in the early 1960's
supports long-haul voice transmission
digitally representing analog telephone system
18/12/2019

46. TDM/FDM network -example-
GSM phones
uplink
downlink
890MHz
915MHz
935MHz
960MHz
124
124
18/12/2019

47. Code Division Multiplexing
Direct Sequence Spread Spectrum
Frequency Hopping Spread Spectrum
18/12/2019

48. Comparing different techniques
frequency
time
time
time
frequency
frequency
TDM
CDM
FDM
TDM: CSMA/CA
TDM/FDM: GSM
CDM: UMTS
18/12/2019

49. home
Dial-up
ADLS
Cable modem
Fiber-to-the-Home?
18/12/2019

50. Modems (a) A binary signal (c) Frequency modulation
(b) Amplitude modulation
(c) Frequency modulation
(d) Phase modulation
18/12/2019

51. Asynchronous data transmission
Bit encoding (1)
Asynchronous data transmission
Used for
character oriented devices
large indeterminate intervals between characters
receiver resynchronizes with sender on start and stop bits
polarity of stop bit different from polarity of start bit
Start
bit
Stop
bit(s)
18/12/2019

52. Bit encoding (2)
(a) Binary encoding, (b) Manchester encoding, (c) Differential Manchester encoding.
18/12/2019

53. Modems (2)
(a) QPSK.
(b) QAM-16.
(c) QAM-64.
18/12/2019

54. ADSL TDM/FDM Asymmetric – higher bit-rate for downloading
Use local loops (1.1 Mbps)
Adapted data rate based on the conditions on the line
18/12/2019

55. ADSL (cnt’d)
18/12/2019

56. Cable modem
Hybrid Coax-Fiber system
18/12/2019

57. Cable modem (cnt’d)
Theoretical downstream data rate 30 Mbps, upstream - 12 Mbps
18/12/2019

58. Cable modem (cnt’d)
18/12/2019

59. TDM in combination with WDM
Fiber-to-the-Home
TDM in combination with WDM
18/12/2019

60. Fiber-to-the-Home (cnt’d)
Passive fiber networks
Easy to upgrade
No electrical powering
Immune to lightening, EMI
What will happen to FTTH?
Cost?
Lifetime of telephone lines?
18/12/2019

61. Conclusions Physical layer is the basis of all networks
limitations: attenuation, dispersion, noise, interference.
aims: provide
as much bandwidth and as larger span as possible,
security,
low cost & protect investments, and
facilitate reconstruction of the transmitted signal.
Transmission media: guided & unguided
Multiplexing techniques introduced to increase bandwidth
TDM; FDM; (WDM); CDM
Broadband access: ADSL; Cable modem; FTTH
18/12/2019