notes_Lectuere42342342sdfwsf2r2234re 8.ppt

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Computer Communication &
Networks
Lecture 8
Physical Layer: Transmission Media
http://web.uettaxila.edu.pk/CMS/coeCCNbsSp09/index.asp
Waleed Ejaz
[email protected]

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Physical Layer

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

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Transmission Medium and Physical Layer

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Twisted-pair Cable

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Categories of unshielded twisted-pair cables

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

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UTP connector

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

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UTP Performance

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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

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Coaxial cable

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BNC connectors

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Performance Coaxial Cable

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Bending of light ray

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Optical fiber

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Propagation Modes

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Modes

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Fiber types

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Fiber construction

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Fiber-optic Cable Connectors

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Performance Optical Fiber

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

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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

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

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

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Propagation Methods

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Bands

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Wireless Transmission Waves

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Omni directional Antenna

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

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Unidirectional Antennas

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

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

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

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