Transmission Media

Guided Transmission Media zTransmission capacity depends on the distance and on whether the medium is point-to-point or multipoint zExamples ytwisted pair wires ycoaxial cables yoptical fiber

Design Factors zBandwidth yHigher bandwidth gives higher data rate zTransmission impairments yAttenuation zInterference zNumber of receivers yIn guided media yMore receivers (multi-point) introduce more attenuation

Electromagnetic Spectrum

Guided Transmission Media zTwisted Pair zCoaxial cable zOptical fiber

Twisted Pair

Twisted Pair - Applications zMost common medium zTelephone network yBetween house and local exchange (subscriber loop) zWithin buildings yTo private branch exchange (PBX) zFor local area networks (LAN) y10Mbps or 100Mbps

Twisted Pair Wires zConsists of two insulated copper wires arranged in a regular spiral pattern to minimize the electromagnetic interference between adjacent pairs zOften used at customer facilities and also over distances to carry voice as well as data communications zLow frequency transmission medium

Types of Twisted Pair zSTP (shielded twisted pair) ythe pair is wrapped with metallic foil or braid to insulate the pair from electromagnetic interference zUTP (unshielded twisted pair) yeach wire is insulated with plastic wrap, but the pair is encased in an outer covering

Ratings of Twisted Pair zCategory 3 UTP ydata rates of up to 16mbps are achievable zCategory 5 UTP ydata rates of up to 100mbps are achievable ymore tightly twisted than Category 3 cables ymore expensive, but better performance zCategory 6, 6E, 7 STP (250, 550, 1Ghz yMore expensive, harder to work with

Twisted Pair Advantages zInexpensive and readily available zFlexible and light weight zEasy to work with and install

Twisted Pair Disadvantages zSusceptibility to interference and noise zAttenuation problem yFor analog, repeaters needed every 5-6km yFor digital, repeaters needed every 2-3km zRelatively low bandwidth (3000Hz)

Twisted Pair - Pros and Cons zCheap zEasy to work with zLow data rate zShort range

Twisted Pair - Transmission Characteristics zAnalog yAmplifiers every 5km to 6km zDigital yUse either analog or digital signals yrepeater every 2km or 3km zLimited distance zLimited bandwidth (1MHz) zLimited data rate (100MHz) zSusceptible to interference and noise

Unshielded and Shielded TP zUnshielded Twisted Pair (UTP) yOrdinary telephone wire yCheapest yEasiest to install ySuffers from external EM interference zShielded Twisted Pair (STP) yMetal braid or sheathing that reduces interference yMore expensive yHarder to handle (thick, heavy)

UTP Categories zCat 3 yup to 16MHz yVoice grade found in most offices yTwist length of 7.5 cm to 10 cm zCat 4 yup to 20 MHz zCat 5 yup to 100MHz yCommonly pre-installed in new office buildings yTwist length 0.6 cm to 0.85 cm

Near End Crosstalk zCoupling of signal from one pair to another zCoupling takes place when transmit signal entering the link couples back to receiving pair zi.e. near transmitted signal is picked up by near receiving pair

Coaxial Cable

Coaxial Cable Applications zMost versatile medium zTelevision distribution yAriel to TV yCable TV zLong distance telephone transmission yCan carry 10,000 voice calls simultaneously yBeing replaced by fiber optic zShort distance computer systems links zLocal area networks

Coaxial Cable - Transmission Characteristics zAnalog yAmplifiers every few km yCloser if higher frequency yUp to 500MHz zDigital yRepeater every 1km yCloser for higher data rates

Coaxial Cable (or Coax) zUsed for cable television, LANs, telephony zHas an inner conductor surrounded by a braided mesh zBoth conductors share a common center axial, hence the term “co-axial”

Coax Layers copper or aluminum conductor insulating material shield (braided wire) outer jacket (polyethylene)

Coax Advantages zHigher bandwidth y400 to 600Mhz yup to 10,800 voice conversations zCan be tapped easily (pros and cons) zMuch less susceptible to interference than twisted pair

Coax Disadvantages zHigh attenuation rate makes it expensive over long distance zBulky

Evolution of Fiber z1880 – Alexander Graham Bell z1930 – Patents on tubing z1950 – Patent for two-layer glass wave-guide z1960 – Laser first used as light source z1965 – High loss of light discovered z1970s – Refining of manufacturing process z1980s – OF technology becomes backbone of long distance telephone networks in NA.

Advantages of Optical Fibre zThinner zLess Expensive zHigher Carrying Capacity zLess Signal Degradation& Digital Signals zLight Signals zNon-Flammable zLight Weight

Fiber Optic Disadvantages zexpensive over short distance zrequires highly skilled installers zadding additional nodes is difficult

Type of Fibers Optical fibers come in two types: zSingle-mode fibers – used to transmit one signal per fiber (used in telephone and cable TV). They have small cores(9 microns in diameter) and transmit infra-red light from laser. zMulti-mode fibers – used to transmit many signals per fiber (used in computer networks). They have larger cores(62.5 microns in diameter) and transmit infra-red light from LED.

© 2006, VDV Works LLC Fiber Types

© 2006, VDV Works LLC Fiber Attenuation

© 2006, VDV Works LLC Fiber Optic Applications zOutside Plant vs Premises

Fiber Optic Cable zRelatively new transmission medium used by telephone companies in place of long-distance trunk lines zAlso used by private companies in implementing local data communications networks zRequire a light source with injection laser diode (ILD) or light-emitting diodes (LED)

plastic jacketglass or plastic cladding fiber core Fiber Optic Layers zconsists of three concentric sections

Fiber Optic Types zmultimode step-index fiber ythe reflective walls of the fiber move the light pulses to the receiver zmultimode graded-index fiber yacts to refract the light toward the center of the fiber by variations in the density zsingle mode fiber ythe light is guided down the center of an extremely narrow core

fiber optic multimode step-index fiber optic multimode graded-index fiber optic single mode Fiber Optic Signals

Optical Fiber

Optical Fiber - Benefits zGreater capacity yData rates of hundreds of Gbps zSmaller size & weight zLower attenuation zElectromagnetic isolation zGreater repeater spacing y10s of km at least

Optical Fiber - Applications zLong-haul trunks zMetropolitan trunks zRural exchange trunks zSubscriber loops zLANs

Optical Fiber - Transmission Characteristics zAct as wave guide for to Hz yPortions of infrared and visible spectrum zLight Emitting Diode (LED) yCheaper yWider operating temp range yLast longer zInjection Laser Diode (ILD) yMore efficient yGreater data rate zWavelength Division Multiplexing

Optical Fiber Transmission Modes

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Wireless Transmission zUnguided media zTransmission and reception via antenna zDirectional yFocused beam yCareful alignment required z Omnidirectional ySignal spreads in all directions yCan be received by many antennae

Frequencies z2GHz to 40GHz yMicrowave yHighly directional yPoint to point ySatellite z30MHz to 1GHz yOmnidirectional yBroadcast radio z3 x to 2 x yInfrared yLocal

Wireless Examples zterrestrial microwave zsatellite microwave zbroadcast radio zinfrared

Terrestrial Microwave zused for long-distance telephone service zuses radio frequency spectrum, from 2 to 40 Ghz zparabolic dish transmitter, mounted high zused by common carriers as well as private networks zrequires unobstructed line of sight between source and receiver zcurvature of the earth requires stations (repeaters) ~30 miles apart

Terrestrial Microwave zParabolic dish zFocused beam zLine of sight zLong haul telecommunications zHigher frequencies give higher data rates

Satellite Microwave Applications zTelevision distribution zLong-distance telephone transmission zPrivate business networks

Microwave Transmission Disadvantages zline of sight requirement zexpensive towers and repeaters zsubject to interference such as passing airplanes and rain

Satellite Microwave Transmission za microwave relay station in space zcan relay signals over long distances zgeostationary satellites yremain above the equator at a height of 22,300 miles (geosynchronous orbit) ytravel around the earth in exactly the time the earth takes to rotate

Satellite Transmission Links zearth stations communicate by sending signals to the satellite on an uplink zthe satellite then repeats those signals on a downlink zthe broadcast nature of the downlink makes it attractive for services such as the distribution of television programming

dish uplink stationdownlink station satellite transponder 22,300 miles Satellite Transmission Process

Satellite Transmission Applications ztelevision distribution ya network provides programming from a central location ydirect broadcast satellite (DBS) zlong-distance telephone transmission yhigh-usage international trunks zprivate business networks

Principal Satellite Transmission Bands zC band: 4(downlink) - 6(uplink) GHz ythe first to be designated zKu band: 12(downlink) -14(uplink) GHz yrain interference is the major problem zKa band: 19(downlink) - 29(uplink) GHz yequipment needed to use the band is still very expensive

Fiber vs Satellite

Broadcast Radio zOmnidirectional zFM radio zUHF and VHF television zLine of sight zSuffers from multipath interference yReflections

Radio zradio is omnidirectional and microwave is directional zRadio is a general term often used to encompass frequencies in the range 3 kHz to 300 GHz. zMobile telephony occupies several frequency bands just under 1 GHz.

Infrared zUses transmitters/receivers (transceivers) that modulate noncoherent infrared light. zTransceivers must be within line of sight of each other (directly or via reflection ). zUnlike microwaves, infrared does not penetrate walls.

Satellite Microwave zSatellite is relay station zSatellite receives on one frequency, amplifies or repeats signal and transmits on another frequency zRequires geo-stationary orbit yHeight of 35,784km/22235 miles zTelevision zLong distance telephone zPrivate business networks