1. Physical Layer Theoretical basis for data communications
Fourier analysis
distortion
by different attenuation rates of different frequency components
by different transmission speeds of different frequency components
by limited bandwidth

2. Physical Layer (cont’d)
Theoretical basis for data communications (cont’d)
baud rate vs. bit rate
Nyquist’s result
finite bandwidth H Hz
noiseless
number of discrete signal levels V
maximum data rate = 2H log2V

3. Physical Layer (cont’d)
Theoretical basis for data communications (cont’d)
Shannon’s result
finite bandwidth H Hz
with signal-to-noise ratio S/N
maximum data rate = H log2(1+S/N)
If H=3000 (3K) Hz and S/N=1000 (30dB), then the corresponding maximum data rate is around 30Kbps.

4. Physical Layer (cont’d)
Transmission media
twisted pair
low cost
few Mbps capacity
widely used in telephone networks (loops)
UTP (unshielded twisted pair)
category 3
category 5
STP (shielded twisted pair)

5. Physical Layer (cont’d)
Transmission media (cont’d)
coaxial cable
two transmission modes
baseband: 50 ohms, digital, 10Mbps over 1 Km
broadband: 75 ohms, analog, a few hundred Mbps over 100 Km
Fig. 2-4 (p. 86)

6. Physical Layer (cont’d)
Transmission media (cont’d)
coaxial cable (cont’d)
the most versatile
higher cost
higher noise immunity
higher capacity

7. Physical Layer (cont’d)
Transmission media (cont’d)
fiber optics
extremely high capacity (tens of Tbps)
based upon total internal reflection
Fig. 2-5 (p. 88)

8. Physical Layer (cont’d)
Transmission media (cont’d)
fiber optics (cont’d)
single mode versus multimode
Fig. 2-7 (p. 90)

9. Physical Layer (cont’d)
Transmission media (cont’d)
fiber optics (cont’d)
operating wavelength
Fig. 2-6 (p. 89)

10. Physical Layer (cont’d)
Transmission media (cont’d)
fiber optics (cont’d)
LED/laser -- transmission media -- photodiode
Fig. 2-8 (p. 91)

11. Physical Layer (cont’d)
Transmission media (cont’d)
fiber optics (cont’d)
extremely high noise immunity
thin and light
difficult to splice and tap (good and bad)
interfaces
passive interface: simple, cheap, reliable, limited no. of nodes
active interface: less reliable, longer links, no limit on the no. of nodes

12. Physical Layer (cont’d)
Wireless transmission
the electromagnetic spectrum
wavelength times frequency = speed of light
Fig (p. 95)

13. Physical Layer (cont’d)
Wireless transmission (cont’d)
radio transmission
air/free space as media
easy to generate
can travel long distance (also cause interference)
high penetration capability
omnidirectional

14. Physical Layer (cont’d)
Wireless transmission (cont’d)
radio transmission (cont’d)
frequency-dependent transmission properties
Fig (p. 98)

15. Physical Layer (cont’d)
Wireless transmission (cont’d)
microwave transmission
air/free space as media
line-of-sight transmission
directional transmission (with parabolic antenna)
repeaters needed periodically (spaced 80Km apart with 100-m high towers)
low penetration capability
multipath fading problem
sensitive to weather condition
no right of way needed

16. Physical Layer (cont’d)
Wireless transmission (cont’d)
microwave transmission
air/free space as media
line-of-sight transmission
directional transmission (with parabolic antenna)
repeaters needed periodically (spaced 80Km apart with 100-m high towers)
low penetration capability
multipath fading problem
sensitive to weather condition
no right of way needed

17. Physical Layer (cont’d)
Wireless transmission (cont’d)
infrared and millimeter waves
air/free space as media
line-of-sight transmission
for short range communication, e.g. TV remote control, wireless LANs
directional, cheap and easy to build
no government license required
very low penetration capability (also low interference)
indoor use only

18. Physical Layer (cont’d)
Wireless transmission (cont’d)
lightwave transmission
air/free space as media
line-of-sight transmission
laser is usually used
directional, high bandwidth, cheap and easy to build
no government license required
sensitive to weather condition
aiming problem

19. Physical Layer (cont’d)
Wireless transmission (cont’d)
lightwave transmission (cont’d)
deflection problem
Fig (p. 101)

20. Physical Layer (cont’d)
Wireless transmission (cont’d)
satellites
air/free space as media
big microwave repeater/frequency converter in the air
broadcasting mode
500 MHz bandwidth
significant propagation delay
expensive
large geographic coverage
geosynchronous satellites