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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( 비 차 폐 ) 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 100Mbps
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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 Core(microns) Cladding(microns)
62.5/125
50/125
100/140
8.3/125
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 regul
ar in size and shape Outer jacket can be made Teflon coating, plastic c
oating, 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( 원 통 ) 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)
wirelesssignals 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 propagationSurface 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 earth’s surface
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비유도 매체 (cont’d)
Ionosphere( 전리층 ) Propagation~ High-frequency radio waves radiate upward into the io
nosphere 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 retractio
n
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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, long-distance 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 som
e 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 eq
uipment. The distance coverable by a line-of-sight 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
Ku
Ka
03.7 - 04.2 GHz
11.7 - 12.2 GHz
17.7 - 21.0 GHz
05.925 - 06.425 GHz
14.000 - 14.500 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
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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 the time they
are not observed by the users
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비유도 매체 (cont’d)
DigitalIntegration with Satellites and PCs
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7.3 Performance
CostSpeedAttenuationEMI(Electromagnetic Interference)Security
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Performance(cont’d)
Transmission media performanceMedium Cost Speed Attenuation EMI Security
UTP
STP
Coax
Optical fiber
Radio
Microwave
Satellite
Cellular
Low
Moderate
Moderate
High
Moderate
High
High
High
Low
Low
Low
High
Low
Moderate
Moderate
Low
High
Moderate
Moderate
Low
High
High
High
Moderate
High
High
Moderate
Low
Low-high
Variable
Variable
Low
1 - 100 Mbps
1 - 150 Mbps
1 Mbps - 1 Gbps
10 Mbps - 2 Gbps
1 - 10 Mbps
1 Mbps - 10 Gbps
1 Mbps - 10 Gbps
9.6 - 19.2 Kbps