7 장 Transmission media(전송매체) 7.1 Guided Media(유도매체) 7.2 Unguided media(비유도매체) 7.3 Performance(성능) 7.4 요약

전송매체(cont’d) ~ Can be divided into two broad categories : 유도매체, 비유도매체 Classes of transmission media

7.1 Guided Media(유도매체) Categories of guided media

유도매체(cont’d) Twisted-Pair Cable UDP(Unshielded Twisted-Pair) Cable ~ comes in two forms : unshielded(비차폐) and shielded(차폐) UDP(Unshielded Twisted-Pair) Cable ~ is the most common type of telecommunication medium in use today. Frequency range for twisted-pair cable

유도매체(cont’d) Twisted-Pair Cable ~ consists of two conductors (usually copper), each with its own colored plastic insulation.

유도매체(cont’d) Effect of noise on parallel lines

유도매체(cont’d) Effect of noise on twisted-pair lines

유도매체(cont’d) Advantage of UTP ~ is cheap, flexible, and easy to install. Cable with 5 unshielded twisted pairs of wires

유도매체(cont’d) UDP 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

유도매체(cont’d) UTP connectors ~ a type of snap-in plus like that used with telephone jacks.

유도매체(cont’d) STP(Shielded Twisted-Pair) cable ~ has the same quality consideration as UTP (more expensive, less susceptible to noise)

유도매체(cont’d) 동축 케이블(Coaxial Cable) Frequency range of coaxial cable ~ carries signals of higher frequency ranges Frequency range of coaxial cable

유도매체(cont’d) Coaxial cable

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)

유도매체(cont’d) Optical Fiber(광섬유) Nature of Light ~ 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.

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.

유도매체(cont’d) 임계각(critical angle) As the angle of incidence(입사각) increase, it moves away from vertical and closer to the horizontal.

유도매체(cont’d) 반사(Reflection) When the angle of incidence becomes greater than the critical angle, a new phenomenon occurs called reflection

유도매체(cont’d) Propagation Model current technology supports two models for propagating light along optical channel.

유도매체(cont’d) Multimode ~ multiple beams from a light source move through the core in different paths.

유도매체(cont’d) Multimode graded-index

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.

유도매체(cont’d) Fiber sizes Fiber Type Core(microns) Cladding(microns) ~ 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 8.3 125 140

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

유도매체(cont’d) Light Sources for optical label LED(Light-Emitting Diode) : Short distance ILD(Injection Laser Diode) : Long distance

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.

유도매체(cont’d) Advantages of Optical Fiber Noise resistance Less signal attenuation Higher bandwidth Disadvantages of Optical Fiber Cost Installation/maintenance Fragility

7.2 비유도 매체(Unguided media) wireless signals are broadcast through air

비유도 매체(cont’d) Radio Frequency Allocation

비유도 매체(cont’d) Propagation of radio waves Types of propagation

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 earth’s surface

비유도 매체(cont’d) Ionosphere(전리층) Propagation Line-of-Sight 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

비유도 매체(cont’d) Propagation of Specific Signals VLF(Very Low Frequency) ~ 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

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

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

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

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

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

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

비유도 매체(cont’d) EHF(Externally High Frequency) ~ use space propagation ~ uses for EHF are radar, Satellite, and experimental communication

비유도 매체(cont’d) Terrestrial microwave ~ require line-of-sight transmission and reception equipment. 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

비유도 매체(cont’d) Repeaters ~ To increase the distance served by terrestrial microwave, a system of repeaters can be installed with each antenna.

비유도 매체(cont’d) Antennas Parabolic dish ~ two types of antenna ~ is based on the geometry of a parabola

비유도 매체(cont’d) Horn antenna ~ looks like a gigantic scoop

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

비유도 매체(cont’d) Geosynchronous satellites

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

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.

비유도 매체(cont’d) Cellular System

비유도 매체(cont’d) Cellular Bands Tradition cellular transmission is analog. The FCC has assigned two bands for cellular use.

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

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

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

비유도 매체(cont’d) Digital Integration with Satellites and PCs

7.3 Performance Cost Speed Attenuation EMI(Electromagnetic Interference) Security

Performance(cont’d) Transmission media performance Medium Cost Speed Attenuation EMI Security UTP STP Coax Optical fiber Radio Microwave Satellite Cellular Low Moderate High 1 - 100 Mbps 1 - 150 Mbps 1 Mbps - 1 Gbps 10 Mbps - 2 Gbps 1 - 10 Mbps 1 Mbps - 10 Gbps 9.6 - 19.2 Kbps High Moderate Low Low-high Variable High Moderate Low Low High Moderate

7.4 요약