Transcript 7 장 Transmission media(전송매체)

7 장 Transmission media(전송매체)
7.1 Guided Media(유도매체)
7.2 Unguided media(비유도매체)
7.3 Performance(성능)
7.4 요약
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전송매체(cont’d)
~ Can be divided into two broad categories :
유도매체, 비유도매체
Classes of transmission media
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7.1 Guided Media(유도매체)
Categories of guided media
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유도매체(cont’d)
Twisted-Pair Cable
~ comes in two forms : unshielded(비차폐) and
shielded(차폐)
UTP(Unshielded Twisted-Pair) Cable
~ is the most common type of telecommunication
medium in use today.
Frequency range for twisted-pair cable
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유도매체(cont’d)
Twisted-Pair Cable
~ consists of two conductors (usually copper), each
with its own colored plastic insulation.
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유도매체(cont’d)
Effect of noise on parallel lines
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유도매체(cont’d)
Effect of noise on twisted-pair lines
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유도매체(cont’d)
Advantage of UTP
~ is cheap, flexible, and easy to install.
Cable with 5 unshielded twisted pairs of wires
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유도매체(cont’d)
UTP standards has developed to grade by
quality
Category 1 : basic twisted-pair cabling (telephone
systems)
Category 2 : suitable for voice and for digital data
transmission of up to 4 Mbps
Category 3 : ~ used for data transmission of up to
10 Mbps(now standard cable)
Category 4 : possible transmission rate to 16Mbps
Category 5 : ~ used for data transmission up to
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100Mbps
유도매체(cont’d)
UTP connectors
~ a type of snap-in plus like that used with telephone
jacks.
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유도매체(cont’d)
STP(Shielded Twisted-Pair) cable
~ has the same quality consideration as UTP (more
expensive, less susceptible to noise)
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유도매체(cont’d)
동축 케이블(Coaxial Cable)
~ carries signals of higher frequency ranges
Frequency range of coaxial cable
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유도매체(cont’d)
Coaxial cable
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유도매체(cont’d)
Coaxial Cable Standards
~ are categorized by RG(radio government)
RG-8 (used in Thick Ethernet)
RG-9 (used in Thick Ethernet)
RG-11 (used in Thick Ethernet)
RG-58 (used in Thin Ethernet)
RG-75 (used for TV)
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유도매체(cont’d)
Optical Fiber(광섬유)
~ is made of glass or plastic and transmits signals in
the form of light
Nature of Light
~ is a form of electromagnetic energy. It travels at its
fastest in a vacuum : 300,000km/s. This speed
decreases as the medium through which the light
travels become denser.
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유도매체(cont’d)
굴절(Refraction)
* Fiber-optic technology takes advantage of the
properties shown in Figure 7.13b to control the
propagation of light through the fiber channel.
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유도매체(cont’d)
임계각(critical angle)
As the angle of incidence(입사각) increase, it
moves away from vertical and closer to the
horizontal.
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유도매체(cont’d)
반사(Reflection)
When the angle of incidence becomes greater
than the critical angle, a new phenomenon occurs
called reflection
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유도매체(cont’d)
Propagation Model
current technology supports two models for
propagating light along optical channel.
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유도매체(cont’d)
Multimode
~ multiple beams from a light source move through
the core in different paths.
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유도매체(cont’d)
Multimode graded-index
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유도매체(cont’d)
Single Mode
~ uses step-index fiber and a highly focused source
of light that limits beams to a small range of
angles, all close to the horizontal.
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유도매체(cont’d)
Fiber sizes
~ are defined by the ratio of the diameter of their
core to the diameter of their cladding.
Fiber Type
62.5/125
50/125
100/140
8.3/125
Core(microns)
Cladding(microns)
62.5
50
100
8.3
125
125
140
125
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유도매체(cont’d)
Cable Composition
Fiber can be made of either glass or plastic
Inner core must be ultrapure and completely
regular in size and shape
Outer jacket can be made Teflon coating, plastic
coating, fibrous plastic, metal tubing, and metal
mesh
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유도매체(cont’d)
Light Sources for optical label
LED(Light-Emitting Diode) : Short distance
ILD(Injection Laser Diode) : Long distance
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유도매체(cont’d)
Fiber-Optic Connectors
~ must be as precise as the cable itself.
~ All of the popular connector are barrel(원통)
shaped and come in male and female versions.
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유도매체(cont’d)
Advantages of Optical Fiber
Noise resistance
Less signal attenuation
Higher bandwidth
Disadvantages of Optical Fiber
Cost
Installation/maintenance
Fragility
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7.2 비유도 매체(Unguided media)
wireless
signals are broadcast through air
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비유도 매체(cont’d)
Radio Frequency Allocation
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비유도 매체(cont’d)
Propagation of radio waves
Types of propagation
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비유도 매체(cont’d)
Type of propagation
Surface Propagation
~ Radio wave travel trough the lowest portion of the
atmosphere(대기권)
Troposphere(대류권) Propagation
~ can work two ways( signal can be directed in a
straight line from antenna to antenna.  It can be
broadcast at an angle into the upper layers of
troposphere where it is reflected back down to the
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earth’s surface
비유도 매체(cont’d)
Ionosphere(전리층) Propagation
~ High-frequency radio waves radiate upward into
the ionosphere where they are reflected back to
earth
Line-of-Sight Propagation
~ Very high frequency signals are transmitted in
straight lives directly from antenna to antenna
Space Propagation
~ utilizes satellite relays in place of atmospheric
retraction
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비유도 매체(cont’d)
Propagation of Specific Signals
~ The type of propagation used in radio transmission
depends on the frequency(speed) of the signal
VLF(Very Low Frequency)
~ are propagated as surface waves, usually through
air but sometimes through seawater
~ are used mostly for long-range radio navigation
and for submarine communication
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비유도 매체(cont’d)
LF(Low Frequency)
~ are also propagated as surface waves
~ are used for long-range radio navigation and for
radio beacons or navigation locators
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비유도 매체(cont’d)
MF(Middle Frequency)
are propagated in the troposphere(대류권)
are absorbed by the ionosphere
uses for MF transmissions include AM radio,
maritime radio, radio direction finding(RDF), and
emergency frequencies
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비유도 매체(cont’d)
HF(High-Frequency)
~ use ionospheric propagation
~ uses of for HF signals include amateur radio(ham
radio), CB(Citizen’s band) radio, international
broadcasting, military communication, longdistance aircraft and ship communication,
telephone, telegraph, and facsimile
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비유도 매체(cont’d)
VHF(Most Very High Frequency)
~ use line-of-sight propagation
~ uses for VHF include VHF television, FM radio,
aircraft AM radio, and aircraft navigational aid
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비유도 매체(cont’d)
UHF(UltraHigh Frequency)
~ always use line-of-sight propagation.
~ uses for UHF include UHF television, mobile
telephone, cellular radio, paging , and micro wave
links
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비유도 매체(cont’d)
SHF(SuperHigh Frequency)
~ are transmitted using mostly line-of-sight and
some space propagation.
~ uses for SHF include terrestrial and satellite
microwave, and radar communication
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비유도 매체(cont’d)
EHF(Externally High Frequency)
~ use space propagation
~ uses for EHF are radar, Satellite, and experimental
communication
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비유도 매체(cont’d)
Terrestrial microwave
~ require line-of-sight transmission and reception
equipment. The distance coverable by a line-ofsight signal depends to a large extent on the height
of the antenna : the taller the antenna, the longer
the sight distance
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비유도 매체(cont’d)
Repeaters
~ To increase the distance served by terrestrial
microwave, a system of repeaters can be installed
with each antenna.
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비유도 매체(cont’d)
Antennas
~ two types of antenna
Parabolic dish
~ is based on the geometry of a parabola
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비유도 매체(cont’d)
Horn antenna
~ looks like a gigantic scoop
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비유도 매체(cont’d)
Satellite Communication
~ is much like line of sight microwave transmission
in which one of the station is a satellite orbiting
the earth
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비유도 매체(cont’d)
Geosynchronous satellites
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비유도 매체(cont’d)
Frequency bands for satellite communication
Band
Downlink
Uplink
C
03.7 - 04.2 GHz
05.925 - 06.425 GHz
Ku
`
11.7 - 12.2 GHz
14.000 - 14.500 GHz
Ka
17.7 - 21.0 GHz
27.500 - 31.000 GHz
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비유도 매체(cont’d)
Cellular telephony
~ is designed to provide stable communications
connections between two moving device or
between one mobile unit and one stationary(land)
unit.
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비유도 매체(cont’d)
Cellular System
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비유도 매체(cont’d)
Cellular Bands
Tradition cellular transmission is analog.
The FCC has assigned two bands for cellular use.
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비유도 매체(cont’d)
Transmitting
The caller enter a code of 7 or 10 digits(phone
number)
Press the send button
The mobile phone then scans the band, seeking a
setup channel with a strong signal
Sends the data(phone number) to the closest cell
office
Cell office relays the data to the MOS0
MTS0 send data on to the telephone central office 51
비유도 매체(cont’d)
Receiving
Telephone central office sends the number to the
MTSO
MTSO search for the location of the mobile
phone
Mobile phone is found, the MTSO transmits a
ringing signal
When the mobile phone is answered, assigns a
voice channel to the call, allowing voice
communication to begin
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비유도 매체(cont’d)
Handoff
During a conversation, the mobile phone moves
from one cell to another
Signal may become weak
MTSO monitors the level of the signal every few
seconds
MTSO seeks a new cell that can accommodate the
communication better
Handoff one performed so smoothly that most of
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the time they are not observed by the users
비유도 매체(cont’d)
Digital
Integration with Satellites and PCs
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7.3 Performance
Cost
Speed
Attenuation
EMI(Electromagnetic Interference)
Security
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Performance(cont’d)
Transmission media performance
Medium
Cost
Speed
Attenuation
EMI
Security
UTP
Low
1 - 100 Mbps
High
High
Low
STP
Moderate
1 - 150 Mbps
High
Moderate
Low
Coax
Moderate
1 Mbps - 1 Gbps
Moderate
Moderate
Low
Optical fiber
High
10 Mbps - 2 Gbps
Low
Low
High
Radio
Moderate
1 - 10 Mbps
Low-high
High
Low
Microwave
High
1 Mbps - 10 Gbps
Variable
High
Moderate
Satellite
High
1 Mbps - 10 Gbps
Variable
High
Moderate
Cellular
High
9.6 - 19.2 Kbps
Low
Moderate
Low
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