1. Computer Communication & Networks
Lecture # 07
Physical Layer: Transmission Media
Course Instructor:
Engr. Sana Ziafat

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

3. Transmission Media
Anything that carry information from source to destination.
Physical path between transmitter and receiver in data communication .

4. Media Issues Frequency range
Some media support higher frequencies than others
Impairments
Different media deform signals differently
Some are more susceptible to noise and distortion
Cost
We’re in the real world…
Number of receivers
Broadcast vs. point-to-point

5. Transmission Medium and Physical Layer

6. Types of transmission media
Transmission media is divided in to two: Wired or Wireless
Wired Media (Guided Media) , Is most common and is further divided in to three different types of cabling: Coaxial, Twisted pairs and fiber optic cables.
Wireless Media (Unguided Media), which is , in a sense, no media at all, is gaining popularity. Wireless transmission use radio waves or infrared light to transmit data

8. Guided Media Waves are guided along solid medium.
Guided media is also known as bounded media, since the data signals are bounded system.
Cabling technology is not limited to copper wire only. Cables can be any physical or conductive media like wires, coaxial cables or fiber optics.

9. Twisted-pair Cable

10. Categories of unshielded twisted-pair cables

11. Twisted Pair Cable (a) Category 3 UTP (16MHz)
(b) Category 5 UTP (100MHz)

12. UTP connector

13. Types of Twisted Pair Cable
Two types:
Shielded twisted pair
Unshielded twisted pair (most commonly used)

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

15. UTP Performance

16. 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

17. Coaxial Cable
It carries high frequency signals than in twisted pair cable.
Less susceptible to interference or crosstalk.

18. Coaxial cable

19. BNC connectors

20. Performance Coaxial Cable
Coaxial cable has much higher bandwidth, the signals weakens rapidly and requires the frequent use of repeaters.

21. Applications
Cable- TV
Long distance telephone transmission.

22. Optical Fiber
Made of glass or plastic and transmits signal in form of light.
Signal is sent using internal reflection.
Relies on total internal reflection
Light waves bounce of edge of fiber
Channels waves to destination
A glass or plastic core is surrounded by a cladding of less dense glass or plastic.

23. Bending of light ray

24. Optical fiber

25. Propagation Modes

26. Multimode
Multiple signals, multiple rays will pass and reflected with different angles
Light waves bounce off at different angles.
Two types:
Step Index
Graded Index

27. Modes

28. Fiber Types
Defined by the ratio of diameter of their core to the diameter of their cladding.
Fiber types

29. Fiber construction

30. Fiber-optic Cable Connectors

31. Performance Optical Fiber

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

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…
Lighter than copper cables
Corrosion resistant
Cons:
Optical components have higher cost
Expensive deploying protocols

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

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

36. Propagation Methods

37. Bands

38. Wireless Transmission Waves

39. Radio Waves
Electromagnetic waves ranging in frequencies between 3 kHz and 1 GHz are normally called radio waves.
They are omnidirectional (sends signal in all directions).
Radio waves are used for multicast communications, such as radio and television, and paging systems.

40. Omni directional Antenna

41. Microwaves Having range from 1 to 300 GHz. They are unidirectional.
Microwave propagation is line-of-sight.
Very high frequency microwaves can not penetrate walls.
Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.

42. Unidirectional Antennas

43. Infrared waves Range from frequencies 300 GHz to 400 THz.
Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.

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

45. Q & A