Transcript Data Communication & Network

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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Note
Radio waves are used for multicast
communications, such as radio and
television, and paging systems.
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Unidirectional Antennas
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Note
Microwaves are used for unicast
communication such as cellular
telephones, satellite networks,
and wireless LANs.
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Note
Infrared signals can be used for shortrange communication in a closed area
using line-of-sight propagation.
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Readings

Chapter 7 (B.A Forouzan)

Section 7.1, 7.2
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