1

Computer Communication & Networks

Lecture 8Physical Layer: Transmission Media

http://web.uettaxila.edu.pk/CMS/coeCCNbsSp09/index.asp

Waleed Ejazwaleed.ejaz@uettaxila.edu.pk

2

Physical Layer

3

Physical Layer Topics to CoverSignals

Digital TransmissionAnalog 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)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

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)

Pros: Low attenuation Large bandwidth

Cons: Relatively “new” technology “Expensive”

24

Comparing optical fiber to UTPPros: 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

Radio waves are used for multicast communications, such as radio and

television, and paging systems.

Note

32

Unidirectional Antennas

33

Microwaves are used for unicast communication such as cellular telephones, satellite networks,

and wireless LANs.

Note

34

Infrared signals can be used for short-range communication in a closed area

using line-of-sight propagation.

Note

35

Readings

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

36