1. 7. Transmission Media

2. Transmission Media Transmission Medium and Physical Layer
Classes of Transmission Media

3. Twisted-Pair Cable
Consist of two conductors (normally copper), each with its own plastic insulation, twisted together
One is used to carry signal to the receiver
The other is used only as a ground reference
Reason for Twisting
Reduce noise caused by electromagnetic interference

4. Unshielded vs. Shielded TP Cables
Unshielded TP (UTP)
Most common TP cable used in communication
Shielded TP (STP)
Improve quality of cable by preventing noise or crosstalk
Bulky and more expensive

5. Categories of UTP Cables
Category
Bandwidth
Data Rate
Digital/Analog
Use 1
very low
< 100 kbps
Analog
Telephone 2
< 2 MHz
2 Mbps
Analog/digital
T-1 lines 3
16 MHz
10 Mbps
Digital
LANs 4
20 MHz
20 Mbps 5
100 MHz
100 Mbps
6 (draft)
200 MHz
200 Mbps
7 (draft)
600 MHz
600 Mbps

6. RJ45 – Most Common UTP Connector

7. Coaxial Cable Better shielding than twisted pairs Coaxial Cable
High bandwidth and excellent noise immunity
Longer distances at higher speeds
Coaxial Cable

8. Coaxial Cable (cont.) 75-Ohm Cable (Broadband) 50-Ohm cable (Baseband)
Analog transmission on standard CATV
“Broadband” means “cable using analog transmission”
Anything wider than 4 kHz
300MHz (or 450MHz) over 100km
Inferior to baseband for sending digital data
Superior for huge amount of cable in place
50-Ohm cable (Baseband)
Digital transmission
1 to 2 Gbps data rate for 1-km cable

9. Coaxial Cable Connectors
BNC Connectors

10. Optical Fiber Optical Fiber Refraction/Reflection
Made of glass or plastic and transmit signals in form of light
Refraction/Reflection

11. Optical Fiber (cont.) Optical Fiber
Use reflection to guide light through a channel

12. Propagation Modes

13. Propagation Modes (cont.)

14. Cable Composition
Fiber Construction

15. Cable Composition (cont.)
Light Sources for Optical Fiber
Light-Emitting Diode (LED)
Cheaper source
Provide unfocused light
Limited to short-distance use
Laser
Focused to a very narrow range
Preserve character of signal over considerable distance
Detector (Photodiode)
Generate electrical pulse when light falls on it

16. Characteristics of Optical Fiber
Advantage
Noise resistance
Less signal attenuation
Higher bandwidth
Disadvantage
Cost
Installation/maintenance
Unidirectional
Fragility

17. Unguided Media: Wireless
Transport electromagnetic waves without using a physical conductor
Signals are normally broadcast through air and thus are available to anyone who has a device capable of receiving them

18. Figure 7.17 Electromagnetic spectrum for wireless communication

19. Figure 7.18 Propagation methods

20. Radio Wave
3 KHz – 1 GHz
Omnidirectional – signal propagates in all directions
Sky transmission
Used for multicast communications, such as radio and television

21. Figure 7.20 Omnidirectional antenna

22. Figure 7.21 Unidirectional antennas

23. Microwave 1 GHz – 300 GHz Unidirectional Line-of-sight propagation
Used for unicast communication, such as cellular telephones, satellite networks, and wireless LANs

24. Infrared 300 GHz – 400 THz Line-of-sight propagation
Used for short-range communication

25. Table 7.4 Bands

26. 011-019 광고 https://www.youtube.com/watch?v=bgeKHBB_QhU