1. Computer Communication & Networks
Lecture 8
Physical Layer: Transmission Media

2. Physical Layer

3. Physical Layer Topics to Cover
Signals
Digital Transmission
Analog Transmission
Multiplexing
Transmission Media

4. Transmission Medium and Physical Layer

5. Twisted-pair Cable

6. Categories of unshielded twisted-pair cables

7. Twisted Pair Cable
(a) Category 3 UTP
(b) Category 5 UTP

8. UTP connector

9. Twisted Pair Cables (Example)
ADSL
Ethernet networks
- 10BASE-T
- 100BASE-TX
- 1000BASE-T
- 1000BASE-TX (Cat5e (enhanced))

10. UTP Performance

11. Twisted Pair Cable (Pros & Cons)
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

12. Coaxial cable

13. BNC connectors

14. Performance Coaxial Cable

15. Bending of light ray

16. Optical fiber

17. Propagation Modes

18. Modes

19. Fiber types

20. Fiber construction

21. Fiber-optic Cable Connectors

22. Performance Optical Fiber

23. Optical Fiber (Pros & Cons)
Low attenuation
Large bandwidth
Cons:
Relatively “new” technology
“Expensive”

24. 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

25. Unguided Media: Wireless
Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication.

26. Wireless
Modern wireless digital communication began in the Hawaiian Islands
What is “the best” frequency to use for communication?

27. Propagation Methods

28. Bands

29. Wireless Transmission Waves

30. Omni directional Antenna

31. Note
Radio waves are used for multicast communications, such as radio and television, and paging systems.

32. Unidirectional Antennas

33. Note
Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.

34. Note
Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.

35. Readings
Chapter 7 (B.A Forouzan)
Section 7.1, 7.2