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8/3/2019 MSIS 4523 Ch7.Transmission Media
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Data Communications SystemsCh 7: Transmission Media
JinKyu Lee, Ph.D.
Include the course code (MSIS4523) in every email subject!!
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Topics
Transmission Media
Guided
Twisted Pair
Coaxial Fiber-optic
Unguided
Air / Space
Wireless Transmission Electromagnetic spectrum
Categories of wireless Transmission
Propagation Methods
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Transmission medium and physical layer
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Classes of Transmission Media
Medium sets signal characteristics and quality Key concerns are data rate and distance
Conducted (guided) media
use a conductor such as a wire or a fiber optic cable to move thesignal from sender to receiver
The medium is more important
Wireless (unguided) media
use radio waves of different frequencies and do not need a wireor cable conductor to transmit signals
Bandwidth produced by the antenna is more important
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Design Factors for Transmission Media
Bandwidth All other factors remaining constant, the greater the bandwidth of
a signal, the higher the data rate that can be achieved
Transmission impairments Attenuation limits the distance a signal can travel
Interference Competing signals in overlapping frequency bands can distort or
wipe out a signal
Number of receivers & splices Each attachment introduces some attenuation and distortion,
limiting distance and/or data rate
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Guided Media - Twisted Pair Wires
Consists of two insulated copper wires arranged in a
regular spiral pattern to minimize the electro-magneticinterference between adjacent pairs Often "bundled" into cables
Often used at customer facilities and also over distances
to carry voice as well as data communications Limited distance
Analog requires an amplifier every 5km to 6km
Digital requires a repeater every 2km or 3km
Limited bandwidth (1MHz)
Limited data rate (100MHz)
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Types of Twisted Pair
UTP (unshielded twisted pair)
Most common, least expensive medium
Suffers from external EM interference
Very easy to install
STP (shielded twisted pair)
the pair is wrapped with metallic foil or braid to insulate the pairfrom electromagnetic interference
More expensive and harder to handle (thick, heavy)
Used for local area networks (LAN)
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Twisted-pair cable
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Ratings of Twisted Pair
Traditional UTP
2 & 3 pairs of wires
Core of telephone service
Used by 80-90% of businessand 99+% of existingresidences
Up to 2500 pair cables used bytelephone companies
Category 3 UTP
4 pr of wires - 8 conductors
Twist length of 7.5 to 10 cm
Data rates of up to 16Mbps Provides voice to offices
Category 5, 5E UTP
4 pr of wires - 8 conductors
Twist length 0.6 to 0.85 cm
Data rates of up to 100Mbps
More expensive, but betterperformance
Installed in star config. in allnew buildings by FCC rule
STP
More expensive, harder towork with
Can go to 1Gbps over shortdistances
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RJ-45 Ethernet UTP Connector
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UTP performance
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Guided Media - Coaxial Cable (or Coax)
Solid inner conductor covered by a braided mesh
Separated by insulating material
Inner conductor is wire
Both conductors share a common center axis
Hence the term co-axial
Transmission Characteristics of Coax
Up to 750MHz
Analog requires amplifiers every few km
Digital requires repeaters every 1km
Closer for higher data rates
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Coaxial Cable & Connectors
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Categories of Coaxial Cables
Category Impedance Use
RG-59 75 Cable TV
RG-58 50 Thin Ethernet
RG-11 50 Thick Ethernet
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Coaxial cable performance
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Coax Advantages & Disadvantages
Advantages
Higher bandwidth
400 to 750Mhz
up to 10,800 voiceconversations
Can be tapped easily(pros and cons)
Much less susceptible tointerference than twisted
pair
Disadvantages
High attenuation ratemakes it expensive overlong distance
Bulky and somewhat
harder to work with
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Coaxial Cable Applications
Television distribution
From Antenna to TV
Cable TV
Long distance telephone transmission
Can carry 10,000 voice calls simultaneously Being replaced by fiber optic
Short distance computer systems links
Local area networks
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Guided Media - Fiber Optic Cable
Relatively new (late 1960s) transmission medium used by telephone
companies in long-distance trunk lines Now standard feeder for new commercial buildings
Common in feeder plant to neighborhood service points
Fiber to the Home (FTTH) or Premise (FTTP) being installed selectivelytoday expensive
Also used by private companies in implementing local datacommunications networks
Require a light source with injection laser diode (ILD) or light-emitting diodes (LED)
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Bending of light ray
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Fiber Optic Types
Multimode step-index fiber
The reflective walls of the fiber move the light pulsesto the receiver
Multimode graded-index fiber
Acts to refract the light toward the center of the fiberby variations in the density
Single mode fiber
The light is guided down the center of an extremely
narrow core
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Optical Fiber Modes
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Categories of Fiber
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 7 125 Single-mode
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Fiber Optic Cable (cont.)
http://www.tigerdirect.com/applications/category/category_slc.asp?CatId=429&Nav=|c:74|&Sort=0&Recs=108/3/2019 MSIS 4523 Ch7.Transmission Media
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Fiber Construction
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Fiber-Optic Cable Connectors
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Transmission Characteristics of OpticalFiber
Act as wave guide for 1014 to 1015 Hz light
Portions of infrared and visible spectrum
Transmitters
Light Emitting Diode (LED) Injection Laser Diode (ILD)
Multiple channels with Wavelength DivisionMultiplexing (WDM)
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Optical fiber Performance
m
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Fiber Optic Advantages
Greater capacity (bandwidth up to 2 Tbps)
Existing systems can deliver 40 Gbps/wavelength
Dense Wave-division multiplexing (DWM) systems can multiplexup to 160 wavelengths per fiber
Smaller size and lighter weight
Lower attenuation Repeater spacing 10s of km at least
Immunity to environmental interference
Electromagnetic isolation
Highly secure due to tap difficulty and lack of signalradiation
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Fiber Optic Disadvantages
Expensive over short distance
Requires highly skilled installers
More susceptible to vibration and physicaldamage
Adding additional nodes is difficult
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Conducted Media
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Unguided Media - Wireless transmission
Categories:
Electromagnetic spectrum for communication:
Infrared signals can be used for short-range communicationin a closed area using line-of-sight propagation
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Propagation methods
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Wireless Frequency Bands
Band Range Propagation Application
VLF 330 KHz Ground Long-range radio navigation
LF 30300 KHz GroundRadio beacons andnavigational locators
MF 300 KHz3 MHz Sky AM radio
HF 330 MHz SkyCitizens band (CB),
ship/aircraft communication
VHF 30300 MHzSky and
line-of-sightVHF TV, FM radio
UHF 300 MHz3 GHz Line-of-sight UHF TV, cellular phones,paging, satellite
SHF 330 GHz Line-of-sight Satellite communication
EHF 30300 GHz Line-of-sight Long-range radio navigation
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Useful Electromagnetic Spectrum
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Wireless Media
Radio, satellite transmissions, and infrared light are all different
forms of electromagnetic waves
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Wireless transmission Categories
Infrared signals can be used for short-range communication in a closed area
using line-of-sight propagation
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Radios Use Omnidirectional Antennas
Radio waves are usedfor multicast
communications, such
as radio and television,and paging systems
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Microwave Radios Use UnidirectionalAntennas
Microwaves are used for unicastcommunication such as cellular telephones,
satellite networks, and wireless LANs