Transmission Media & Codes © Prof. Aiman Hanna Department of Computer Science Concordia University...

Transmission Media & CodesTransmission Media & Codes

© Prof. Aiman Hanna© Prof. Aiman HannaDepartment of Computer Science Department of Computer Science

Concordia University Concordia University Montreal, CanadaMontreal, Canada

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C C onnect then onnect then Communicate!Communicate!

There are many factors that controls how devices should be There are many factors that controls how devices should be connected: connected: • CostCost• Capacity of the link / speedCapacity of the link / speed• Immunity to noiseImmunity to noise• Vulnerability to unauthorized listening (security)Vulnerability to unauthorized listening (security)• Logistics Logistics • MobilityMobility

• Once connected communication is guaranteed. Correct?Once connected communication is guaranteed. Correct?

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C C onnect then Communicate!onnect then Communicate! (continue...)(continue...)

DigitalDigital vs. vs. AnalogAnalog Signals Signals Different devices may represent or send information differentlyDifferent devices may represent or send information differently Many devices use digital signals (1 or 0 bit), while others use analog signals Many devices use digital signals (1 or 0 bit), while others use analog signals

(varying voltage)(varying voltage) Conversion between digital and analog is possible but complex Conversion between digital and analog is possible but complex

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C C onnect then Communicate!onnect then Communicate! (continue...)(continue...)

Signals travels from one place to another through a Signals travels from one place to another through a transmission mediatransmission media

There are 3 types of transmission media:There are 3 types of transmission media:• Conductive metalConductive metal

• Transparent glass strand (optical fiber)Transparent glass strand (optical fiber)

• Electromagnetic waves (no physical connection)Electromagnetic waves (no physical connection)

Which media to use depends on many factorsWhich media to use depends on many factors

Two important measures exist: Two important measures exist: bit ratebit rate and and bandwidthbandwidth

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C C onnect then Communicate!onnect then Communicate! (continue...)(continue...) Bit RateBit Rate

• How many How many bits per secondbits per second (bps) a link can (bps) a link can transmittransmit

• Rates range from 100s bps to billions of bps Rates range from 100s bps to billions of bps (gigabits) and now pushing for trillion bps (gigabits) and now pushing for trillion bps (terabit) (terabit)

BandwidthBandwidth• PeriodPeriod: Time needed for a signal to complete : Time needed for a signal to complete

one cycleone cycle• FrequencyFrequency: Number of cycles per second, : Number of cycles per second,

measured in measured in HertzHertz (Hz) (Hz) f = 1 / pf = 1 / p

• For example, if For example, if pp = 0.5 microseconds (μsec) = 0.5 microseconds (μsec) then then ff = 2 MHz = 2 MHz

• A given medium can accommodate a range of A given medium can accommodate a range of frequencyfrequency

• BandwidthBandwidth is the difference between the is the difference between the highest and the lowest possible frequency that highest and the lowest possible frequency that can be transmittedcan be transmitted

• For example, telephone signals can handle For example, telephone signals can handle frequencies between 300 Hz & 3300Hz; the frequencies between 300 Hz & 3300Hz; the bandwidth is hence 3000 Hzbandwidth is hence 3000 Hz

• In other words, very high or very low audible In other words, very high or very low audible sounds cannot pass though the telephonesounds cannot pass though the telephone

Figure 2.2 - Periodic Signal

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C C onductive Metal onductive Metal Made of metals such as copper or ironMade of metals such as copper or iron Examples include Examples include twisted wire pair twisted wire pair andand

coaxial cablecoaxial cable

Twisted Pair:Twisted Pair:• One of the oldest media; used for the One of the oldest media; used for the telegraphtelegraph• Basically a circuit of power source, switch & sensorBasically a circuit of power source, switch & sensor• Closing the switch allows current to run and the sensor Closing the switch allows current to run and the sensor

to clickto click

Information on 2-way telegraph can be found at: http://hypertextbook.com/facts/2005/telegraph.shtml

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C C onductive Metal onductive Metal (continue...)(continue...) Twisted Pair Twisted Pair (continue)(continue)::

• Copper is usually used due to its less resistance to Copper is usually used due to its less resistance to electricity, as well as high resistance to corrosionelectricity, as well as high resistance to corrosion

• Twisted wires use balanced signals; 180Twisted wires use balanced signals; 180oo out of phase out of phase

• More twists reduce More twists reduce crosstalkcrosstalk, the electromagnetic , the electromagnetic interference between adjacent pairsinterference between adjacent pairs

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C C onductive Metal onductive Metal (continue...)(continue...) Twisted Pair Twisted Pair (continue)(continue)::

• Although copper has less resistance to electricity, signal will Although copper has less resistance to electricity, signal will eventually die (eventually die (attenuateattenuate))

• RepeatersRepeaters are used to solve this problem are used to solve this problem• Two types of twisted pair wires exist: Unshielded & Shielded; they Two types of twisted pair wires exist: Unshielded & Shielded; they

have different cost & qualityhave different cost & quality

Figure 2.4 – Two Points Connected using a Repeater

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C C onductive Metal onductive Metal (continue...)(continue...) Coaxial Cable:Coaxial Cable:

• Typically transmits information in either Typically transmits information in either basebandbaseband or or broadbandbroadband modemode

• With baseband, the cable bandwidth is devoted to a single stream With baseband, the cable bandwidth is devoted to a single stream of data; this is typical in LANsof data; this is typical in LANs

• With broadband, the BW is divided into ranges; each range carries With broadband, the BW is divided into ranges; each range carries separate code informationseparate code information

• Cable TVs use broadband coaxial cableCable TVs use broadband coaxial cable

Figure 2.5 – Coaxial Cable

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C C onductive Metal onductive Metal (continue...)(continue...) Coaxial Cable Coaxial Cable (continue)(continue)::

• Two types of coaxial cable exist: Two types of coaxial cable exist: ThickNetThickNet and and ThinNetThinNet

• Coaxial cables accommodate a higher BW and better Coaxial cables accommodate a higher BW and better error rate than twisted pair, however it is more costlyerror rate than twisted pair, however it is more costly

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O O ptical Fiber ptical Fiber There are several problems with conductive There are several problems with conductive

metals:metals:• Electrical signals are susceptible to external Electrical signals are susceptible to external

interference, such as electric motors, lightening, …interference, such as electric motors, lightening, …

• Weight; cables are heavy and bulkyWeight; cables are heavy and bulky

Optical fiber is an alternative to conductive Optical fiber is an alternative to conductive metalmetal

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O O ptical Fiber ptical Fiber (continue...)(continue...) Optical fiber uses light, not electricity, to Optical fiber uses light, not electricity, to

transmit informationtransmit information Impervious to electrical noise and capable of Impervious to electrical noise and capable of

transmitting enormous amount of information transmitting enormous amount of information Very thin compared to cables; they can be Very thin compared to cables; they can be

bundled together bundled together

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O O ptical Fiber ptical Fiber (continue...)(continue...)

Figure 2.6 – Light Refraction & Reflection

Figure 2.7 – Step-Index Multimode fiber

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O O ptical Fiber ptical Fiber (continue...)(continue...)

Figure 2.8 – Graded-Index Multimode Fiber

Figure 2.9 – Single-Mode Fiber

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O O ptical Fiber ptical Fiber (continue...)(continue...) Optical fiber have many advantages Optical fiber have many advantages

of over conducting metal: of over conducting metal:

On the other hand, On the other hand, • They require that electrical signals They require that electrical signals

must be converted first to light and must be converted first to light and converted back at the other endconverted back at the other end

• Must be handled with great care; some Must be handled with great care; some of these fibers could be a thin as of these fibers could be a thin as human hairhuman hair

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W W ireless Communications ireless Communications Physical communication is acceptable in many, Physical communication is acceptable in many,

but not all, situationsbut not all, situations

Wireless communication is an alternativeWireless communication is an alternative

It involves the sending of It involves the sending of electromagnetic electromagnetic waveswaves

The signal is then received by a receiving The signal is then received by a receiving antennaantenna

Broadcast radio & TV transmit signal this wayBroadcast radio & TV transmit signal this way

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W W ireless Communications ireless Communications (continue...)(continue...)

Wavelength = Speed of Light / FrequencyWavelength = Speed of Light / Frequency

Low–frequency (high-wavelength) waves traverse very long distances without Low–frequency (high-wavelength) waves traverse very long distances without much lossmuch loss

They also require a very long antenna, which even today may represent a health They also require a very long antenna, which even today may represent a health hazardhazard

There are three important types of wireless communication: There are three important types of wireless communication: • Microwave Microwave • Satellite Satellite • InfraredInfrared

Figure 2.10 – Electromagnetic Wave Spectrum

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W W ireless Communications ireless Communications (continue...)(continue...) Microwave TransmissionsMicrowave Transmissions

• Typically occur between two ground towersTypically occur between two ground towers• Travel in a straight line – does not follow Travel in a straight line – does not follow

earth’s curvatureearth’s curvature• Cannot travel through solid objectsCannot travel through solid objects

Figure 2.11 – Parabolic Dish Receiving Signals

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W W ireless Communications ireless Communications (continue...)(continue...) Microwave TransmissionsMicrowave Transmissions

• Often through Horn AntennaOften through Horn Antenna

• Towers are used as repeaters to solve earth curvature’s Towers are used as repeaters to solve earth curvature’s and signal loss problemsand signal loss problems

Figure 2.13 – Horn Antenna Figure 2.14 – Microwave Towers as Repeaters

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W W ireless Communications ireless Communications (continue...)(continue...) Satellite TransmissionsSatellite Transmissions

• A science fiction in 1945; A common science today!A science fiction in 1945; A common science today!• Primarily, it is a microwave transmission in which one of the Primarily, it is a microwave transmission in which one of the

towers is a satellite towers is a satellite • In 1957, the Soviet Union launched the In 1957, the Soviet Union launched the SputnikSputnik

Figure 2.15 – Satellite Communications

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• Now, how can a satellite remain in a fixed position?Now, how can a satellite remain in a fixed position?

• Kepler’s lawKepler’s law is used: is used: P P 22= KD= KD3 3

where: where: - PP is time period needed to rotate around planetary body, is time period needed to rotate around planetary body,- DD is the distance between the satellite and the planet’s center. is the distance between the satellite and the planet’s center.

The higher The higher DD is the longer it takes for a full rotation is the longer it takes for a full rotation - KK is a constant is a constant - Now, at what height a satellite will have a 24h period (Now, at what height a satellite will have a 24h period (PP)?)?- According to Kepler’s Law, the answer is According to Kepler’s Law, the answer is KK = 22,300 miles = 22,300 miles

above the equator above the equator - Geosynchronous OrbitGeosynchronous Orbit- Three satellites can almost cover the entire earthThree satellites can almost cover the entire earth

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Satellite TransmissionsSatellite Transmissions

Figure 2.16 – Satellites in Geosynchronous Orbit

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Satellite TransmissionsSatellite Transmissions

Figure 2.17 – Atmospheric Interference as a function of angle of transmissionAtmospheric Interference as a function of angle of transmission

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• Satellites must be located apart from each other (with a minimal angel) Satellites must be located apart from each other (with a minimal angel) • Transmission should also be restricted to a specific angelTransmission should also be restricted to a specific angel

Figure 2.18 – Satellite receiving more than one signalSatellite receiving more than one signal

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• Now, there is no interference. Good! But what about Now, there is no interference. Good! But what about legality?legality?

Figure 2.19 – Satellites receivingSatellites receiving one signalone signal

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• Some applications, such as military surveillance, require Some applications, such as military surveillance, require that the satellite does that the satellite does notnot remain in a fixed position remain in a fixed position

• Low Earth OrbitLow Earth Orbit • Low Earth Orbit Satellites can still be used for Low Earth Orbit Satellites can still be used for

communication. How?communication. How?

Figure 2.20 – Ground station communicating with LEO satellitesGround station communicating with LEO satellites

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• Using many LEO that can directly communicate with each other would enable any two Using many LEO that can directly communicate with each other would enable any two locations in the planet to be connectedlocations in the planet to be connected

• This however has not fully been implemented yetThis however has not fully been implemented yet• The LLC project by MotorolaThe LLC project by Motorola• Another player is the Teledesic Corporation – 288 satellites (12 groups of 24) – reduced Another player is the Teledesic Corporation – 288 satellites (12 groups of 24) – reduced

lately to 30lately to 30

Figure 2.21 – Two stations communicating via LEO satellitesTwo stations communicating via LEO satellites

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Constellation of Teledesic SatellitesConstellation of Teledesic Satellites

Teledesic SatelliteTeledesic Satellite

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W W ireless Communications ireless Communications (continue...)(continue...) Wireless LANsWireless LANs

• Two technologies used by wireless LANs are Two technologies used by wireless LANs are InfraredInfrared and and Radio WavesRadio Waves. .

Figure 2.25 – Wireless LAN configurationWireless LAN configuration

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W W ireless Communications ireless Communications (continue...)(continue...) BluetoothBluetooth

• Allows devices that are not considered as Allows devices that are not considered as typical network devices, such as fridges, typical network devices, such as fridges, microwaves, coffeemakers, …etc., to microwaves, coffeemakers, …etc., to communicatecommunicate

• This communication can possibly be This communication can possibly be between such device and an Internet service between such device and an Internet service

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W W ireless Communications ireless Communications (continue...)(continue...) Free Space Optics Free Space Optics

• Wireless optical technology without the use of a fiber, Wireless optical technology without the use of a fiber, which is also called as which is also called as Tera-beam Tera-beam technologytechnology

• LifeSpan BioSciences, Merill Lynch, and others used LifeSpan BioSciences, Merill Lynch, and others used FSOFSO

• Advantage: Advantage:

• Disadvantage:Disadvantage:

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W W ireless Communications ireless Communications (continue...)(continue...) Does New Technologies obsolete Older ones?Does New Technologies obsolete Older ones?

• Twisted Pair, Coaxial Cable, Optical Fiber, Twisted Pair, Coaxial Cable, Optical Fiber, Microwave, Satellite, Infrared, FSO, .. all coexistMicrowave, Satellite, Infrared, FSO, .. all coexist

• Reasons?Reasons?

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C C odes odes CodesCodes

• How is information coded in a format suitable for How is information coded in a format suitable for

transmission?transmission? Different codes include: Different codes include:

• Morse CodeMorse Code• ASCIIASCII (American Standard Code for Information Interchange), (American Standard Code for Information Interchange),

7-bit code, control characteristics7-bit code, control characteristics• EBCDICEBCDIC (Extended Binary Coded Decimal Interchange Code), (Extended Binary Coded Decimal Interchange Code),

used for IBM mainframes and peripherals, 8-bit code, control used for IBM mainframes and peripherals, 8-bit code, control characterscharacters

• Baudot codeBaudot code: 5-bit code for each character. It was designed for : 5-bit code for each character. It was designed for the French Telegraphthe French Telegraph

• BCDBCD (Binary Coded Decimal), which was common in many (Binary Coded Decimal), which was common in many early IBM mainframesearly IBM mainframes

• Unicode:Unicode: New. 16-bit code independent of language or computer New. 16-bit code independent of language or computer platform. Supports many scripts and mathematical symbolsplatform. Supports many scripts and mathematical symbols

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C C odes odes (continue...)(continue...) CodesCodes

Figure 2.26 – Transmitting an ASCII Coded MessageTransmitting an ASCII Coded Message

Transmission Media & Codes © Prof. Aiman Hanna Department of Computer Science Concordia University...

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Transcript of Transmission Media & Codes © Prof. Aiman Hanna Department of Computer Science Concordia University...