Week2 Data&Media Transmission

Data CommunicationData Communication 11

Data Transmission Data Transmission andand

Media TransmissionMedia Transmission


Element of communicationsElement of communications

• TransmitterTransmitter

• ReceiverReceiver

• MediumMedium– Guided mediumGuided medium

•e.g. twisted pair, optical fibere.g. twisted pair, optical fiber

– Unguided mediumUnguided medium•e.g. air, water, vacuume.g. air, water, vacuum


Basic TopologyBasic Topology

• Direct linkDirect link– No intermediate devicesNo intermediate devices

• Point-to-pointPoint-to-point– Direct link Direct link – Only 2 devices share linkOnly 2 devices share link

• Multi-pointMulti-point– More than two devices share the linkMore than two devices share the link


Direction of communicationDirection of communication

• SimplexSimplex– One directionOne direction

• e.g. Radio, Televisione.g. Radio, Television

• Half duplexHalf duplex– Either direction, but only one way at a timeEither direction, but only one way at a time

• e.g. police radio, HT, Walkie-Talkiee.g. police radio, HT, Walkie-Talkie

• Full duplexFull duplex– Both directions at the same timeBoth directions at the same time

• e.g. telephonee.g. telephone


Data Flow: SimplexData Flow: Simplex

• only transmit in one directiononly transmit in one direction

• rarely used in data communicationsrarely used in data communications

• e.g., receiving signals from the radio e.g., receiving signals from the radio station, TV station or CATVstation, TV station or CATV

• the sending station has only one the sending station has only one transmitter the receiving station has transmitter the receiving station has only one receiveronly one receiver


host computer terminal

one w ay only

Simplex IllustrationSimplex Illustration


Data Flow: Half DuplexData Flow: Half Duplex• data may travel in both directions, but only data may travel in both directions, but only

in one direction at a timein one direction at a time

• provides non-simultaneous two-way provides non-simultaneous two-way communicationcommunication

• computers use control signals to negotiate computers use control signals to negotiate when to send and when to receivewhen to send and when to receive

• the time it takes to switch between sending the time it takes to switch between sending and receiving is called turnaround timeand receiving is called turnaround time



first one w ay....

terminal

...then the other

Half Duplex IllustrationHalf Duplex Illustration


Data Flow: Full DuplexData Flow: Full Duplex

• complete two-way simultaneous complete two-way simultaneous transmissiontransmission

• faster than half-duplex faster than half-duplex communication because no communication because no turnaround time is neededturnaround time is needed



both w aysat the same time

Full Duplex IllustrationFull Duplex Illustration


Electromagnetic SignalsElectromagnetic Signals

• Function of timeFunction of time– Analog (varies smoothly over time)Analog (varies smoothly over time)– Digital (constant level over time, Digital (constant level over time,

followed by a change to another level)followed by a change to another level)

• Function of frequencyFunction of frequency– Spectrum (range of frequencies)Spectrum (range of frequencies)– Bandwidth (width of the spectrum)Bandwidth (width of the spectrum)


Periodic Signal Periodic Signal CharacteristicsCharacteristics

– Amplitude (A): signal value, measured in Amplitude (A): signal value, measured in voltsvolts

– Frequency (Frequency (ff): repetition rate, cycles per ): repetition rate, cycles per second or Hertzsecond or Hertz

– Period (T): amount of time it takes for Period (T): amount of time it takes for one repetition, T=1/one repetition, T=1/ff

– Phase (Φ): relative position in time, Phase (Φ): relative position in time, measured in degrees measured in degrees


time(sec)

amp

litu

de

(vo

lts)

1 cycle

frequency (hertz)= cycles per second

phase difference

Analog SignalingAnalog Signaling

• represented by sine waves represented by sine waves


Conversion of Voice Input into Conversion of Voice Input into Analog SignalAnalog Signal


Digital SignalingDigital Signaling

• represented by square waves or represented by square waves or pulsespulses

time(sec)

amp

litu

de

(vo

lts)

1 cycle

frequency (hertz)= cycles per second


Conversion of PC Input to Conversion of PC Input to Digital SignalDigital Signal


Digital Text SignalingDigital Text Signaling• Transmission of electronic pulses Transmission of electronic pulses

representing the binary digits 1 and 0representing the binary digits 1 and 0• How do we represent letters, How do we represent letters,

numbers, characters in binary form?numbers, characters in binary form?• Earliest example: Morse code (dots Earliest example: Morse code (dots

and dashes)and dashes)• Most common current form: ASCIIMost common current form: ASCII

““A” = 41 Hexadecimal = 65 Decimal = 01000001A” = 41 Hexadecimal = 65 Decimal = 01000001

““B” = 42 Hexadecimal = 66 Decimal = 01000010B” = 42 Hexadecimal = 66 Decimal = 01000010


ASCII Character CodesASCII Character Codes

• Use 8 bits of data (1 byte) to Use 8 bits of data (1 byte) to transmit one charactertransmit one character

• 8 binary bits has 256 possible 8 binary bits has 256 possible outcomes (0 to 255)outcomes (0 to 255)

• Represents alphanumeric characters, Represents alphanumeric characters, as well as “special” charactersas well as “special” characters


Digital Image SignalingDigital Image Signaling

• Pixelization and binary Pixelization and binary representationrepresentation

Code: 0000000000111100011101100111111001111000011111100011110000000000


Why Study Analog?Why Study Analog?

• Telephone system is primarily analog Telephone system is primarily analog rather than digital (designed to carry rather than digital (designed to carry voice signals)voice signals)

• Low-cost, ubiquitous transmission Low-cost, ubiquitous transmission mediummedium

• If we can convert digital information (1s If we can convert digital information (1s and 0s) to analog form (audible tone), and 0s) to analog form (audible tone), it can be transmitted inexpensivelyit can be transmitted inexpensively


Voice SignalsVoice Signals

• Easily converted from sound frequencies Easily converted from sound frequencies (measured in loudness/db) to (measured in loudness/db) to electromagnetic frequencies, measured in electromagnetic frequencies, measured in voltagevoltage

• Human voice has frequency components Human voice has frequency components ranging from 20Hz to 20kHzranging from 20Hz to 20kHz

• For practical purposes, the telephone For practical purposes, the telephone system has a narrower bandwidth than system has a narrower bandwidth than human voice, from 300 to 3400Hzhuman voice, from 300 to 3400Hz


BandwidthBandwidth

• Width of the spectrum of frequencies that Width of the spectrum of frequencies that can be transmittedcan be transmitted– if spectrum=300 to 3400Hz, bandwidth=3100Hzif spectrum=300 to 3400Hz, bandwidth=3100Hz

• Greater bandwidth leads to greater costsGreater bandwidth leads to greater costs

• Limited bandwidth leads to distortionLimited bandwidth leads to distortion

• Analog communication measured in Hertz, Analog communication measured in Hertz,

• Digital communication measured in bpsDigital communication measured in bps


BPS vs. BaudBPS vs. Baud

• BPS=bits per secondBPS=bits per second

• Baud=# of signal changes per Baud=# of signal changes per secondsecond

• Each signal change can represent Each signal change can represent more than one bit, through variations more than one bit, through variations on amplitude, frequency, and/or on amplitude, frequency, and/or phasephase


Bandwidth Pipe AnalogyBandwidth Pipe Analogy


Bandwidth Highway AnalogyBandwidth Highway Analogy


Transmission MediaTransmission Media

• the physical path between the physical path between transmitter and receivertransmitter and receiver

• design factorsdesign factors– bandwidthbandwidth– attenuation: weakening of signal over attenuation: weakening of signal over

distancesdistances– interference: interference: – number of receiversnumber of receivers


Impairments and CapacityImpairments and Capacity

• Impairments exist in all forms of data Impairments exist in all forms of data transmissiontransmission

• Analog signal impairments result in Analog signal impairments result in random modifications that impair random modifications that impair signal qualitysignal quality

• Digital signal impairments result in Digital signal impairments result in bit errors (1s and 0s transposed)bit errors (1s and 0s transposed)


Transmission ImpairmentsTransmission Impairments

• AttenuationAttenuation– loss of signal strength over distanceloss of signal strength over distance

• Attenuation DistortionAttenuation Distortion– different losses at different frequenciesdifferent losses at different frequencies

• Delay DistortionDelay Distortion– different speeds for different frequenciesdifferent speeds for different frequencies

• NoiseNoise


Types of NoiseTypes of Noise

• Thermal (aka “white noise”)Thermal (aka “white noise”)– Uniformly distributed, cannot be Uniformly distributed, cannot be

eliminatedeliminated

• IntermodulationIntermodulation– when different frequencieswhen different frequencies

• CrosstalkCrosstalk

• Impulse noiseImpulse noise– Less predictableLess predictable


Transmission MediaTransmission Media

• two major classestwo major classes– conducted or guided mediaconducted or guided media

•use a conductor such as a wire or a fiber use a conductor such as a wire or a fiber optic cable to move the signal from sender optic cable to move the signal from sender to receiverto receiver

– wireless or unguided mediawireless or unguided media•use radio waves of different frequencies and use radio waves of different frequencies and

do not need a wire or cable conductor to do not need a wire or cable conductor to transmit signalstransmit signals


Electromagnetic SpectrumElectromagnetic Spectrum


Guided Transmission MediaGuided Transmission Media

• the transmission capacity depends the transmission capacity depends on the distance and on whether the on the distance and on whether the medium is point-to-point or medium is point-to-point or multipointmultipoint

• e.g.,e.g.,– twisted pair wirestwisted pair wires– coaxial cablescoaxial cables– optical fiberoptical fiber


Twisted Pair WiresTwisted Pair Wires

• consists of two insulated copper wires consists of two insulated copper wires arranged in a regular spiral pattern to arranged in a regular spiral pattern to minimize the electromagnetic minimize the electromagnetic interference between adjacent pairsinterference between adjacent pairs

• often used at customer facilities and often used at customer facilities and also over distances to carry voice as also over distances to carry voice as well as data communicationswell as data communications

• low frequency transmission mediumlow frequency transmission medium



• two varietiestwo varieties– STP (shielded twisted pair)STP (shielded twisted pair)

•the pair is wrapped with metallic foil or braid the pair is wrapped with metallic foil or braid to insulate the pair from electromagnetic to insulate the pair from electromagnetic interferenceinterference

– UTP (unshielded twisted pair)UTP (unshielded twisted pair)•each wire is insulated with plastic wrap, but each wire is insulated with plastic wrap, but

the pair is encased in an outer coveringthe pair is encased in an outer covering


Shielded Twisted-Pair CableShielded Twisted-Pair Cable


Unshielded Twisted Pair Unshielded Twisted Pair (UTP)(UTP)



• Category 3 UTPCategory 3 UTP– data rates of up to 16mbps are achievabledata rates of up to 16mbps are achievable

• Category 5 UTPCategory 5 UTP– data rates of up to 100mbps are achievabledata rates of up to 100mbps are achievable– more tightly twisted than Category 3 cablesmore tightly twisted than Category 3 cables– more expensive, but better performancemore expensive, but better performance

• STPSTP– More expensive, harder to work withMore expensive, harder to work with


Bad and Good Connector Bad and Good Connector


Twisted Pair AdvantagesTwisted Pair Advantages

• inexpensive and readily availableinexpensive and readily available

• flexible and light weight flexible and light weight

• easy to work with and installeasy to work with and install


Twisted Pair DisadvantagesTwisted Pair Disadvantages

• susceptibility to interference and susceptibility to interference and noisenoise

• attenuation problemattenuation problem– For analog, repeaters needed every 5-For analog, repeaters needed every 5-

6km6km– For digital, repeaters needed every 2-For digital, repeaters needed every 2-

3km3km

• relatively low bandwidth (3000Hz)relatively low bandwidth (3000Hz)


Coaxial Cable (or Coax)Coaxial Cable (or Coax)

• bandwidth of up to 400 MHzbandwidth of up to 400 MHz

• has an inner conductor surrounded has an inner conductor surrounded by a braided meshby a braided mesh

• both conductors share a common both conductors share a common center axial, hence the term “co-center axial, hence the term “co-axial”axial”


Coax LayersCoax Layers

copper or aluminum conductor

insulating material

shield(braided wire)

outer jacket(polyethylene)


Coax AdvantagesCoax Advantages

• higher bandwidthhigher bandwidth– 400 to 600Mhz400 to 600Mhz– up to 10,800 voice conversationsup to 10,800 voice conversations

• can be tapped easily (pros and cons)can be tapped easily (pros and cons)

• much less susceptible to interference much less susceptible to interference than twisted pairthan twisted pair


Coax DisadvantagesCoax Disadvantages

• high attenuation rate makes it high attenuation rate makes it expensive over long distanceexpensive over long distance

• bulky bulky


Fiber Optic CableFiber Optic Cable

• relatively new transmission medium used relatively new transmission medium used by telephone companies in place of long-by telephone companies in place of long-distance trunk linesdistance trunk lines

• also used by private companies in also used by private companies in implementing local data communications implementing local data communications networksnetworks

• require a light source with injection laser require a light source with injection laser diode (ILD) or light-emitting diodes (LED)diode (ILD) or light-emitting diodes (LED)


plastic jacket glass or plasticcladding

fiber core

Fiber Optic LayersFiber Optic Layers

• consists of three concentric sectionsconsists of three concentric sections


Fiber Optic ModeFiber Optic Mode


Multimode FiberMultimode Fiber


Fiber Optic TypesFiber Optic Types

• multimode step-index fibermultimode step-index fiber– the reflective walls of the fiber move the the reflective walls of the fiber move the

light pulses to the receiverlight pulses to the receiver

• multimode graded-index fibermultimode graded-index fiber– acts to refract the light toward the center of acts to refract the light toward the center of

the fiber by variations in the densitythe fiber by variations in the density

• single mode fibersingle mode fiber– the light is guided down the center of an the light is guided down the center of an

extremely narrow coreextremely narrow core


fiber optic multimodestep-index

fiber optic multimodegraded-index

fiber optic single mode

Fiber Optic SignalsFiber Optic Signals


Fiber End Face Polishing Fiber End Face Polishing TechniquesTechniques


Fiber Optic AdvantagesFiber Optic Advantages

• greater capacity (bandwidth of up to greater capacity (bandwidth of up to 2 Gbps)2 Gbps)

• smaller size and lighter weightsmaller size and lighter weight• lower attenuationlower attenuation• immunity to environmental immunity to environmental

interferenceinterference• highly secure due to tap difficulty highly secure due to tap difficulty

and lack of signal radiationand lack of signal radiation


Fiber Optic DisadvantagesFiber Optic Disadvantages

• expensive over short distanceexpensive over short distance• requires highly skilled installersrequires highly skilled installers• adding additional nodes is difficultadding additional nodes is difficult


Wireless (Unguided Media) Wireless (Unguided Media) TransmissionTransmission• transmission and reception are achieved transmission and reception are achieved

by means of an antennaby means of an antenna

• directionaldirectional– transmitting antenna puts out focused beamtransmitting antenna puts out focused beam– transmitter and receiver must be alignedtransmitter and receiver must be aligned

• omnidirectionalomnidirectional– signal spreads out in all directionssignal spreads out in all directions– can be received by many antennascan be received by many antennas


Omni Directional AntennaOmni Directional Antenna


Wireless ExamplesWireless Examples

• terrestrial microwave transmissionterrestrial microwave transmission

• satellite transmissionsatellite transmission

• broadcast radiobroadcast radio

• infraredinfrared


Terrestrial Terrestrial Microwave TransmissionMicrowave Transmission• uses the radio frequency spectrum, commonly uses the radio frequency spectrum, commonly

from 2 to 40 Ghzfrom 2 to 40 Ghz

• transmitter is a parabolic dish, mounted as transmitter is a parabolic dish, mounted as high as possiblehigh as possible

• used by common carriers as well as by private used by common carriers as well as by private networksnetworks

• requires unobstructed line of sight between requires unobstructed line of sight between source and receiversource and receiver

• curvature of the earth requires stations (called curvature of the earth requires stations (called repeaters) to be ~30 miles apartrepeaters) to be ~30 miles apart


Wireless NetworkWireless Network


Microwave Transmission Microwave Transmission ApplicationsApplications

• long-haul telecommunications long-haul telecommunications service for both voice and television service for both voice and television transmissiontransmission

• short point-to-point links between short point-to-point links between buildings for closed-circuit TV or a buildings for closed-circuit TV or a data link between LANsdata link between LANs


Microwave Transmission Microwave Transmission AdvantagesAdvantages• no cabling needed between sitesno cabling needed between sites

• wide bandwidth wide bandwidth

• multichannel transmissionsmultichannel transmissions


Microwave Transmission Microwave Transmission DisadvantagesDisadvantages

• line of sight requirementline of sight requirement

• expensive towers and repeatersexpensive towers and repeaters

• subject to interference such as subject to interference such as passing airplanes and rainpassing airplanes and rain


Satellite Satellite Microwave TransmissionMicrowave Transmission

• a microwave relay station in spacea microwave relay station in space

• can relay signals over long distancescan relay signals over long distances

• geostationary satellites geostationary satellites – remain above the equator at a height of remain above the equator at a height of

22,300 miles (geosynchronous orbit)22,300 miles (geosynchronous orbit)– travel around the earth in exactly the travel around the earth in exactly the

time the earth takes to rotatetime the earth takes to rotate


Satellite Transmission LinksSatellite Transmission Links

• earth stations communicate by sending earth stations communicate by sending signals to the satellite on an uplinksignals to the satellite on an uplink

• the satellite then repeats those signals the satellite then repeats those signals on a downlinkon a downlink

• the broadcast nature of the downlink the broadcast nature of the downlink makes it attractive for services such as makes it attractive for services such as the distribution of television the distribution of television programmingprogramming


dish dish

uplink station downlink station

satellitetransponder

22,300 miles

Satellite Transmission Satellite Transmission ProcessProcess


Satellite Transmission Satellite Transmission ApplicationsApplications

• television distributiontelevision distribution– a network provides programming from a a network provides programming from a

central locationcentral location– direct broadcast satellite (DBS)direct broadcast satellite (DBS)

• long-distance telephone transmissionlong-distance telephone transmission– high-usage international trunkshigh-usage international trunks

• private business networksprivate business networks


Principal Satellite Principal Satellite Transmission BandsTransmission Bands• C band: 4(downlink) - 6(uplink) GHzC band: 4(downlink) - 6(uplink) GHz

– the first to be designated the first to be designated

• Ku band: 12(downlink) -14(uplink) GHzKu band: 12(downlink) -14(uplink) GHz– rain interference is the major problemrain interference is the major problem

• Ka band: 19(downlink) - 29(uplink) GHzKa band: 19(downlink) - 29(uplink) GHz– equipment needed to use the band is still equipment needed to use the band is still

very expensivevery expensive


Satellite AdvantagesSatellite Advantages

• can reach a large geographical areacan reach a large geographical area

• high bandwidthhigh bandwidth

• cheaper over long distancescheaper over long distances


Satellite DisadvantagesSatellite Disadvantages

• high initial costhigh initial cost

• susceptible to noise and interferencesusceptible to noise and interference

• propagation delaypropagation delay


InfraredInfrared

• Line of sight (or reflection)Line of sight (or reflection)

• Blocked by wallsBlocked by walls

• e.g. TV remote controle.g. TV remote control


Broadcast RadioBroadcast Radio

• OmnidirectionalOmnidirectional

• FM radioFM radio

• UHF and VHF televisionUHF and VHF television

• Line of sightLine of sight


Radio WaveRadio Wave


RoamingRoaming


Common CarriersCommon Carriers

• a government-regulated private company a government-regulated private company

• involved in the sale of infrastructure involved in the sale of infrastructure services in transportation and services in transportation and communicationscommunications

• required to serve all clients required to serve all clients indiscriminatelyindiscriminately

• services and prices from common carriers services and prices from common carriers are described in tariffsare described in tariffs


Leased (or Dedicated) LinesLeased (or Dedicated) Lines

• permanently or semi-permanently permanently or semi-permanently connect between two pointsconnect between two points

• economical in high volume calls economical in high volume calls between two pointbetween two point

• no delay associated with switching no delay associated with switching timestimes

• can assure consistently high-quality can assure consistently high-quality connectionsconnections


Leased (or Dedicated) LinesLeased (or Dedicated) Lines

• voice grade channelsvoice grade channels– normal telephone lines normal telephone lines – in the range of 300 Hertz to 3300 Hertzin the range of 300 Hertz to 3300 Hertz

• conditioning or equalizingconditioning or equalizing– reduces the amount of noise on the line, reduces the amount of noise on the line,

providing lower error rates and providing lower error rates and increased speed for data increased speed for data communicationscommunications


End of End of PresentationPresentation

Week2 Data&Media Transmission

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