Chapter 7
Transmission
Media
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Figure 7.1
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Transmission medium and physical layer
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Figure 7.2
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Classes of transmission media
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7.1 Guided Media
Twisted-Pair Cable
Coaxial Cable
Fiber-Optic Cable
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Figure 7.3
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Twisted-pair cable
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Cable
Twisted Pair Cable
•Twisted pair cable implies the use of
balanced signaling
•Twisted pair is used in telephony as
well as local area networking
•The shield can be wrapped around a
single pair or over an entire group of
pairs
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Figure 7.4
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UTP and STP
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Table 7.1 Categories of unshielded twisted-pair cables
Category
Bandwidth
Data Rate
Digital/Analog
Use
1
very low
< 100 kbps
Analog
Telephone
2
< 2 MHz
2 Mbps
Analog/digital
T-1 lines
3
16 MHz
10 Mbps
Digital
LANs
4
20 MHz
20 Mbps
Digital
LANs
5
100 MHz
100 Mbps
Digital
LANs
6 (draft)
200 MHz
200 Mbps
Digital
LANs
7 (draft)
600 MHz
600 Mbps
Digital
LANs
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Figure 7.5
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UTP connector
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UTP Cable and Connectors
PALO ALTO, Calif., and PISCATAWAY, NJ,- June 28, 1999 - Members of
the IEEE and the Gigabit Ethernet Alliance today announced that the
final milestone in the IEEE standards approval process was reached last
week when the 1000BASE-T specification for Gigabit Ethernet over copper
(also known as IEEE Std 802.3ab) was unanimously approved as an IEEE
standard by the IEEE Standards Association (IEEE-SA) Standards Board.
The standard defines Gigabit Ethernet operation over distances of up to
100 meters using four pairs of CAT-5 balanced copper cabling…
…1000BASE-T is important for three reasons," commented Colin Mick,
technical editor of the IEEE 802.3ab Task Force. "First, most of the cabling
installed inside buildings today is CAT-5 UTP, and 1000BASE-T will enable
Gigabit Ethernet operation over this installed base. Second, 1000BASE-T,
on a per-connection basis, is expected to be very cost-effective which will
stimulate market demand. Finally, 1000BASE-T allows auto-negotiation
between 100 and 1000 Mb/s which eases the migration path for
customers."
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Figure 7.6
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UTP performance
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Figure 7.7
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Coaxial cable
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Table 7.2 Categories of coaxial cables
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Category
Impedance
Use
RG-59
75 W
Cable TV
RG-58
50 W
Thin Ethernet
RG-11
50 W
Thick Ethernet
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Figure 7.8
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BNC connectors
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Figure 7.9
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Coaxial cable performance
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Bending of light ray
Think of a mirage. You look along a road surface on
a hot day and see the reflected sky, looking for all
the world like a pool of water.
Think of window glass on the front of a department
store. As you walk down the sidewalk you can’t
see what’s inside. Once you’re in front of the
window it’s easy to see inside.
These effects are related to the “Critical Angle”
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Figure 7.10
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Bending of light ray
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Figure 7.11 Optical fiber
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Figure 7.12
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Propagation modes
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Figure 7.13
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Modes
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Table 7.3 Fiber types
Type
Core
Cladding
Mode
50/125
50
125
Multimode, graded-index
62.5/125
62.5
125
Multimode, graded-index
100/125
100
125
Multimode, graded-index
7
125
Single-mode
7/125
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Figure 7.14
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Fiber construction
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Figure 7.15
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Fiber-optic cable connectors
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Figure 7.16
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Optical fiber performance
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7.2 Unguided Media: Wireless
Radio Waves
Microwaves
Infrared
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Figure 7.17
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Electromagnetic spectrum for wireless communication
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Figure 7.18
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Propagation methods
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Table 7.4 Bands
Band
Range
Propagation
Application
VLF
3–30 KHz
Ground
Long-range radio navigation
LF
30–300 KHz
Ground
Radio beacons and
navigational locators
MF
300 KHz–3 MHz
Sky
AM radio
HF
3–30 MHz
Sky
Citizens band (CB),
ship/aircraft communication
VHF
30–300 MHz
Sky and
line-of-sight
VHF TV,
FM radio
UHF
300 MHz–3 GHz
Line-of-sight
UHF TV, cellular phones,
paging, satellite
SHF
3–30 GHz
Line-of-sight
Satellite communication
EHF
30–300 GHz
Line-of-sight
Long-range radio navigation
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Figure 7.19
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Wireless transmission waves
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•Radio waves are used for multicast
communications, such as radio and
television, and paging systems.
•They use a frequency spectrum from
3KHz to 300 MHz
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Figure 7.20
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Omnidirectional antennas
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Omnidirectional
antenna
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•Microwaves are used for unicast
communication such as cellular
telephones, satellite networks, and
wireless LANs.
•They use the frequency spectrum
from 300 MHz to 300 GHz
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Figure 7.21
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Unidirectional antennas
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Dish antennas
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Horn antenna
Note the Cell antenna below
the horns
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Cell Telephone antennas
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Infrared
•Infrared signals can be used for shortrange communication in a closed area
using line-of-sight propagation.
•Not used commercially for LANs
•Used commercially for short links
•Infrared starts at 300 GHz
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