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Lecture #9: Wireless Lecture #9: Wireless Transmission. Telephone Transmission. Telephone

System.System.C o n t e n t s C o n t e n t s Physical basics of wireless signalingPhysical basics of wireless signaling

radio wavesradio waves microwaves microwaves infraredinfrared lightlight

Telephone system:Telephone system:

StructureStructure

MultiplexingMultiplexing

Switching methodsSwitching methods

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Physical Basics in Physical Basics in Wireless SignalingWireless Signaling

Electromagnetic waves, frequency Electromagnetic waves, frequency ((ff) ) Hz Hz and and length length (() ) m m

Broadcasting and receiving of the Broadcasting and receiving of the electromagnetic waves - antennas electromagnetic waves - antennas

Vacuum speed of the electromagnetic waves Vacuum speed of the electromagnetic waves ((cc). Speeds of the electrical and light pulses in ). Speeds of the electrical and light pulses in conductors. Main relation:conductors. Main relation:

ff = = cc (i.e.: (i.e.:[m] [m] 101044 1km1km 100100 1010 1m1m 1dm1dm 1cm1cm 1mm 1mm ff[Hz][Hz] 30k30k 300k300k 3M3M 30M30M 300M300M 3G3G 30G30G 300G)300G)

Differential form of Differential form of ff(() = c/) = c/ is: is:

ff==cc// || d/d d/d d df f = -(= -(cc//22)d)d i.e. for finite differences i.e. for finite differences

ff = ( = (cc//22))

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Physical Basics in Physical Basics in Wireless SignalingWireless Signaling

Since Since ff = ( = (cc//22))it is possible to calculate from it is possible to calculate from

the physical diagrams the frequency bandwidth of the physical diagrams the frequency bandwidth of

given material or media: on given material or media: on (2/6)(2/6) for for one has: one has:

0.85 0.85 mm 1.3 1.3 mm 1.55 1.55 mm

0.08 0.08 mm 0.17 0.17 mm 0.185 0.185 mm

ff 33.22 THz33.22 THz 30.18 THz30.18 THz 23.1 THz23.1 THz

Data rateData rate[b] [b] ff[Hz] and vary from 1b/Hz[Hz] and vary from 1b/HzLFLF

to 30-50b/Hz to 30-50b/Hz >UHF>UHF

FrequencyFrequencybandwidthbandwidth

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Electromagnetic SpectrumElectromagnetic Spectrum

Electromagnetic spectrumElectromagnetic spectrum: :

RadioRadioMicrowave Microwave Infrared Infrared Light Light UV UV X X Gamma Gamma.. ITU standard “radio” bandsITU standard “radio” bands Application of bands and correspondence to the Application of bands and correspondence to the

transmission mediatransmission media

Spectrum allocationSpectrum allocation: ITU-R/WARC and FCC: ITU-R/WARC and FCC Narrow frequency band (Narrow frequency band (f f << << ff) ) Spread spectrum (military but also business Spread spectrum (military but also business

applications; regular hops between frequencies applications; regular hops between frequencies in wide band for higher security/privacy)in wide band for higher security/privacy)

International Telecommunication International Telecommunication Union - Radio Communication Sector/Union - Radio Communication Sector/World Agency for Radio CommunicationsWorld Agency for Radio Communications

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Radio TransmissionRadio Transmission Radio-frequency waves are:Radio-frequency waves are: easy to generateeasy to generate with high penetration (buildings, with high penetration (buildings,

forest, but not hills/mountains)forest, but not hills/mountains) omnidirectionalomnidirectional with mutual interference with mutual interference with frequency-dependant with frequency-dependant

properties: properties: – power losses with the distancepower losses with the distance

– absorption and reflection (by LF/MF and absorption and reflection (by LF/MF and HF/VHF) HF/VHF) 2/12

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Microwave Microwave TransmissionTransmission

Microwaves have:Microwaves have: straight spreading (require straight line connection straight spreading (require straight line connection

between the transmitter and receiver: on the Earth between the transmitter and receiver: on the Earth surface they need repeaters on each 100 km)surface they need repeaters on each 100 km)

possibility of ray concentration (focusing) possibility of ray concentration (focusing) no interference between non-collinear transmissionsno interference between non-collinear transmissions low penetration (buildings and even rain are non low penetration (buildings and even rain are non

transparent) transparent) possible refraction in the dense atmosphere layers possible refraction in the dense atmosphere layers

multipath fading (phase shifting)multipath fading (phase shifting) frequency-dependant properties: frequency-dependant properties:

–power losses with the distancepower losses with the distance–absorption by water (absorption by water (ff above 8Ghz/ above 8Ghz/ 40cm and 40cm and

less )less )

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Microwave Microwave TransmissionTransmission

Microwave applications:Microwave applications: long-distance phone transmissions long-distance phone transmissions (incl. (incl.

POTS and cellular phones): POTS and cellular phones): W compete in W compete in this area with fiber optic. this area with fiber optic. – Advantages: cheap, non-wired communication Advantages: cheap, non-wired communication – Drawbacks: crowded spectrum, possible Drawbacks: crowded spectrum, possible

interference with other devices, low level of interference with other devices, low level of security, possible atmospheric disturbance security, possible atmospheric disturbance

non licensed free bandsnon licensed free bands – 902 902 928 MHz - industrial use (cordless home 928 MHz - industrial use (cordless home

devices and distanced controllers); devices and distanced controllers); cheapestcheapest transceivers (transmitters or receivers) and transceivers (transmitters or receivers) and lower level of interference lower level of interference

– 2400 2400 2484 MHz 2484 MHz – 5725 5725 5859 MHz 5859 MHz

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Infrared WavesInfrared Waves 10101212 10 101414 Hz band Hz band

(invisible light with thermal impact).(invisible light with thermal impact). PropertiesProperties::

– do not pass solid or non-transparent objectsdo not pass solid or non-transparent objects– strong attenuation in relatively short strong attenuation in relatively short

distance of airdistance of air– can be focused in a ray but also dispersed can be focused in a ray but also dispersed

in omnidirectional wayin omnidirectional way ApplicationApplication

– house remote control deviceshouse remote control devices– implementation of indoor wireless LANs (of implementation of indoor wireless LANs (of

portable computers) and communicationsportable computers) and communications..

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Light WavesLight Waves Visible light is called opticVisible light is called opticss.. Optic signals are transmitteOptic signals are transmitted usually ind usually in

form of coherent directed ligform of coherent directed lightht rayrayss (transmitters called (transmitters called LASERLASERs). s).

Unidirectional transmission needs very Unidirectional transmission needs very precise alignment between the precise alignment between the transmitter and receiver (photodetector); transmitter and receiver (photodetector); often application of defocusing lensesoften application of defocusing lenses

Same Properties like Same Properties like infrared raysinfrared rays Atmosphere distortions Atmosphere distortions

Light Amplification by Stimulated Emis-sion of Radiation

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Telephone SystemTelephone System Public Switched Telephone NetworkPublic Switched Telephone Network ( (PSTNPSTN) )

- used to for communication media - used to for communication media between computers that cannot share one between computers that cannot share one common LAN because they are:common LAN because they are:– of large number;of large number;– too distanced;too distanced;– separated by other property.separated by other property.

Communication properties of switched Communication properties of switched phone lines:phone lines:– low data rate - 10low data rate - 1044 b/S (10 b/S (1088 b/S for direct wire) b/S for direct wire)– high error rate - 10high error rate - 10-5-5 Err/b (10 Err/b (10-12-12 Err/b for Err/b for

direct wires)direct wires)

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Telephone System - Telephone System - StructureStructure

Development of the Telephone system Development of the Telephone system from non-switched fully interconnected from non-switched fully interconnected graph to centralized switching system and graph to centralized switching system and then to hierarchical system of [routable] then to hierarchical system of [routable] switches switches

Structure of the connectivity of the Structure of the connectivity of the hierarchical switched telephone system:hierarchical switched telephone system:– local loopslocal loops twisted pair twisted pair analog analog

– toll connecting trunkstoll connecting trunks coax, coax, W, fiber W, fiber analog, digital analog, digital

– intertoll trunksintertoll trunks coax, coax, W, fiber W, fiber digital, digital, analoganalog

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Telephone System - Telephone System - Transmission Transmission TechnologiesTechnologies

all electric optical transmissionelectric switching

all optical

• The transmission and switching are shifting towards fully optical systems:

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Analog TransmissionAnalog TransmissionIn In analog transmissionanalog transmission the physical the physical

quantity of the signal carrying the quantity of the signal carrying the information (amplitude, frequency, information (amplitude, frequency, phase) varies in a direct relationship to phase) varies in a direct relationship to the information to be transmitted.the information to be transmitted.

The nature of information transfer is The nature of information transfer is continuous.continuous.

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Digital TransmissionDigital Transmission In digital transmission the continuous signal is In digital transmission the continuous signal is

first first sampledsampled by slicing the signal at regular by slicing the signal at regular intervals into discrete values.intervals into discrete values.

Signal samples are then Signal samples are then quantifiedquantified, their , their amplitudes are approximated to the nearest pre-amplitudes are approximated to the nearest pre-defined value.defined value.

Quantified samples are Quantified samples are codedcoded into binary words. into binary words. After this, the binary words are transmitted.After this, the binary words are transmitted. The length of a coded binary sample depends on The length of a coded binary sample depends on

that how accurate the quantization must be.that how accurate the quantization must be. For example, if the signals are presented with For example, if the signals are presented with

256 different (voltage) levels, the coded binary 256 different (voltage) levels, the coded binary word is 8 bits long (2word is 8 bits long (28 8 = 256).= 256).

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Digital TransmissionDigital Transmission

Samples

Quantization

011 100 010Binary words

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Telephone System - Telephone System - Digital vs. Analog Digital vs. Analog

SignalingSignaling Digital vs. Analog signaling in Telephone Digital vs. Analog signaling in Telephone system:system:– stronger attenuation stronger attenuation butbut– possibility for multiple consecutive signal possibility for multiple consecutive signal

regenerationregeneration– possibility congestion of data rates on the linespossibility congestion of data rates on the lines– possibility for 1:1 data transmission (incl. image, possibility for 1:1 data transmission (incl. image,

voice, stored data) between two points (i.e. high voice, stored data) between two points (i.e. high QoSQoS))

– easier equipment implementationeasier equipment implementation– possibility for automation of maintenancepossibility for automation of maintenance– the ability to add redundant information (e.g. for the ability to add redundant information (e.g. for

error detection and correcting purposes) to the true error detection and correcting purposes) to the true information stream …information stream …

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Telephone System - Telephone System - Digital vs. Analog Digital vs. Analog

SignalingSignaling Digital vs. Analog signaling in Telephone Digital vs. Analog signaling in Telephone system - continue:system - continue:– not so sensitive for interference as the not so sensitive for interference as the

analogue transmission.analogue transmission.– the binary representation of the signal the binary representation of the signal

can be transmitted, for example, by can be transmitted, for example, by frequency modulation when a frequency frequency modulation when a frequency F1 represents the binary digit ‘0’ and a F1 represents the binary digit ‘0’ and a frequency F2 is associated with the frequency F2 is associated with the binary ‘1’.binary ‘1’.

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Local Loops by Inter-Local Loops by Inter-computer Communication computer Communication

Doubled digital-to/from-analog conversion in Doubled digital-to/from-analog conversion in

local loops of switched lineslocal loops of switched lines Main distortions:Main distortions:

attenuation attenuation AA(log(log1010dd, , ff) ) dB/km - signal power dB/km - signal power

losses and signal shape wrapping losses and signal shape wrapping

delay - different for the signal frequency delay - different for the signal frequency

components components overlapping of the components of overlapping of the components of

different consecutive bits different consecutive bits

noise - caused by line/relay commutations and noise - caused by line/relay commutations and

junctions, signal inductive interference or random junctions, signal inductive interference or random

energy sourcesenergy sources

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Local Loops - Local Loops - Modulation/DemodulatiModulation/Demodulati

onon ModemsModems: Digital-to-analog-and-analog-to-: Digital-to-analog-and-analog-to-digital converters. Analog coding is called digital converters. Analog coding is called modulation. Digital [de]coding is called modulation. Digital [de]coding is called demodulation. demodulation.

Analog signal is transmitted by sine carrier ofAnalog signal is transmitted by sine carrier of f f = 1= 12kHz2kHz. Modulation (i.e. analog coding) . Modulation (i.e. analog coding) can be performed by carrier tension amplitude, can be performed by carrier tension amplitude, by carrier frequency shifting or by carrier by carrier frequency shifting or by carrier phase shifting. phase shifting. Nyquist’s TheoremNyquist’s Theorem boundary: boundary: 3kHz local loop bandwidth transmits up to 6kHz 3kHz local loop bandwidth transmits up to 6kHz carriercarrier

Advanced modulation techniques transmit Advanced modulation techniques transmit multiple (3-4) bits per baud by combination of multiple (3-4) bits per baud by combination of amplitude and phase shifting (amplitude and phase shifting (QAMQAM - - Quadrature Amplitude Modulation). Quadrature Amplitude Modulation).

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Local Loops - Circuitry Local Loops - Circuitry Electrical Modem/Computer interfacesElectrical Modem/Computer interfaces

(DCE/DTE interface):(DCE/DTE interface):– RS232C (CCITT: V.24 standard): serial interface, RS232C (CCITT: V.24 standard): serial interface,

25 pin connectors including lines for in/out bit 25 pin connectors including lines for in/out bit stream, control, synchronization, clock. Null stream, control, synchronization, clock. Null modem - crossed transmit/receive data lines for modem - crossed transmit/receive data lines for computer/computer (no modem) interface.computer/computer (no modem) interface.

– RS232 variations ( RS422, RS423, RS 449 - RS232 variations ( RS422, RS423, RS 449 - difference in ground lines for the signals)difference in ground lines for the signals)

Optical interfacesOptical interfaces - for arising new telecom - for arising new telecom services services

FTTHFTTH (Fiber To The Home) - straight but expensive (Fiber To The Home) - straight but expensive

FTTCFTTC (Fiber To The Curb) - fiber to junction box (for (Fiber To The Curb) - fiber to junction box (for group of users); end connection[s] is twisted pair or group of users); end connection[s] is twisted pair or coax. coax.

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MultiplexingMultiplexing Multiplexing by Physical layer means splitting off Multiplexing by Physical layer means splitting off

(and thus sharing) the media transmission (and thus sharing) the media transmission capacity between multiple capacity between multiple users/processes/channelsusers/processes/channels

2 methods:2 methods:– multiplexing by frequencymultiplexing by frequency - FDM. Frequency spectrum - FDM. Frequency spectrum

is divided into smaller bands which are assigned to is divided into smaller bands which are assigned to each active user. Example: Radio broadcasting each active user. Example: Radio broadcasting stations over fixed frequency channel (static stations over fixed frequency channel (static assignment/multiplexing)assignment/multiplexing)

– multiplexing by timemultiplexing by time - TDM. The channel time is split - TDM. The channel time is split into [small] even periods, that are repeatedly assigned into [small] even periods, that are repeatedly assigned to a fixed (for given instant) list of active to a fixed (for given instant) list of active users/channels - in round-robin mannerusers/channels - in round-robin manner

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Frequency Division Frequency Division MultiplexingMultiplexing

Single phone voice-grade channel seizes 3kHz Single phone voice-grade channel seizes 3kHz band (sound transmission in band 50/3000 Hz) band (sound transmission in band 50/3000 Hz)

By FDM 4kHz band is allocated for each channel By FDM 4kHz band is allocated for each channel (3kHz signal + 2*500Hz separation bands)(3kHz signal + 2*500Hz separation bands)

The standard FDM: The standard FDM: groupgroup of 12 channel bands * of 12 channel bands * 4kHz placed in band 604kHz placed in band 60108kHz (60 + 12*4 = 108kHz (60 + 12*4 = 108) - . Option: second group in the band 108) - . Option: second group in the band 121260kHz.60kHz.

Overlapping between the adjacent channels Overlapping between the adjacent channels (although the separation bands) because of (although the separation bands) because of nonperfect filtration. nonperfect filtration.

MastergroupMastergroup = 5 = 5 supergroupssupergroups = 25 = 25 groupsgroups = = 300 vice-grade channels. 300 vice-grade channels.

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Frequency Division Frequency Division MultiplexingMultiplexing

FDM variation used in fiber optics: WDM - Wavelength FDM variation used in fiber optics: WDM - Wavelength Division Mux.Division Mux.

Same physical principle: junction of two light Same physical principle: junction of two light transmitting fiber by a diffraction grid (e.g. optic transmitting fiber by a diffraction grid (e.g. optic prism) in one fiber transmitting the combined (two prism) in one fiber transmitting the combined (two wavelengths/frequencies) signal to a common end wavelengths/frequencies) signal to a common end point. The signal separation at the end point by point. The signal separation at the end point by diffraction grid. diffraction grid.

WDM properties: WDM properties: – passive system (no frequency/wavelength shifting)passive system (no frequency/wavelength shifting)– reliabilityreliability

WDM based switches - light switching is harder then WDM based switches - light switching is harder then electricity switching. 1:electricity switching. 1:nn light switches are either of light switches are either of type type “Passive star”“Passive star” (for (for nn~10~1022) or some kind of ) or some kind of optical tunable filters like interferometrs (for optical tunable filters like interferometrs (for nn~10~1066) )

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[Interferometers][Interferometers] Interferometers isolate a specific portion of the Interferometers isolate a specific portion of the

electromagnetic spectrum. Unlike prism or grid electromagnetic spectrum. Unlike prism or grid monochromators, interferometers are not dispersive monochromators, interferometers are not dispersive instruments, but use interference to selectively instruments, but use interference to selectively transmit a certain wavelength. Two interferometer transmit a certain wavelength. Two interferometer designs:designs:

Schematic of a Mach-Zender interferometer

Schematic of a Fabry-Perot etalon

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WDMWDM WDMWDM is the technique for fiber optics that uses a is the technique for fiber optics that uses a

similar principle than FDM, except the channel similar principle than FDM, except the channel discriminator is a wavelength instead of time. discriminator is a wavelength instead of time.

Each input data stream is converted into separate Each input data stream is converted into separate wavelength. Each application creates a channel that wavelength. Each application creates a channel that operates at a separate wavelength. After that, the operates at a separate wavelength. After that, the WDM system combines and at the same time WDM system combines and at the same time transmits the channels through the same optical transmits the channels through the same optical fiber. Since each wavelength is completely isolated fiber. Since each wavelength is completely isolated from the other, protocols can be mixed within the from the other, protocols can be mixed within the same link. same link.

This is a great benefit to WDM, since FDM creates This is a great benefit to WDM, since FDM creates high-speed time slots in the form of frames or cells, high-speed time slots in the form of frames or cells, which allow multiple applications to share the which allow multiple applications to share the channel only if all applications are of the same channel only if all applications are of the same platform.platform.

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WDMWDM Stable WDM systems today multiplex just a few Stable WDM systems today multiplex just a few

wavelengths over fiber to extend capacity. However, wavelengths over fiber to extend capacity. However, some systems can now increase a fiber's capacity by some systems can now increase a fiber's capacity by multiplexing 32 wavelengths and more. Still newer multiplexing 32 wavelengths and more. Still newer multiplexers entering the market this year promise multiplexers entering the market this year promise 40 to 80 discrete optical channels. 40 to 80 discrete optical channels.

WDM is a WDM is a costly solutioncostly solution, although it works with the , although it works with the existing fiber infrastructure, since it requires existing fiber infrastructure, since it requires additional equipment like transmitters and optical additional equipment like transmitters and optical amplifiers for each wavelength. That equipment is amplifiers for each wavelength. That equipment is quite expensive nowadays.quite expensive nowadays.

The WDM market is predicted to increase The WDM market is predicted to increase dramatically over the next ten years as telephone dramatically over the next ten years as telephone companies, cable television and other carriers companies, cable television and other carriers maximize their optical-fiber network capacity.maximize their optical-fiber network capacity.

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WDMWDM Besides the telephone system trunks WDM is suitable for Besides the telephone system trunks WDM is suitable for

future LAN network environment:future LAN network environment:

WDMWDMWDMWDM

...

ATM

ETHERNET

TOKENRING

FIBERCHANNEL

FDDI

ETHERNET

TOKENRING

FIBERCHANNEL

...

ATM

FDDI

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Time Division Time Division MultiplexingMultiplexing

Applicable only in digital electronics Applicable only in digital electronics (while FDM is applicable only for analog (while FDM is applicable only for analog data) - i.e. TDM condenses just digital data) - i.e. TDM condenses just digital data for the telephone company trunks. data for the telephone company trunks.

Digitizing the analog signal by codec Digitizing the analog signal by codec ((Coder-DECoderCoder-DECoder). ).

PCMPCM - Pulse Code Modulation - Pulse Code Modulation In the telephone systems PCM is In the telephone systems PCM is performed with rate 8000Sperformed with rate 8000S-1-1 samples in samples in periods (i.e. 8kHz) of 125periods (i.e. 8kHz) of 125S. According S. According Niquist’s theorem 8kHz = 2*4kHz Niquist’s theorem 8kHz = 2*4kHz (telephone channel bandwidth - for (telephone channel bandwidth - for avoiding information losses and avoiding information losses and information overload). information overload).

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Pulse Code ModulationPulse Code Modulation T1-carrier MethodT1-carrier Method (USA, Japan): multiplexes (USA, Japan): multiplexes

24 voice channels in Round-robin for each 24 voice channels in Round-robin for each 125125S period [By data communication the S period [By data communication the 2424thth channel is reserved for a synchronization channel is reserved for a synchronization pattern]. pattern]. – The instant state of each channel is coded by 7b + The instant state of each channel is coded by 7b +

1b control. 1b control. – Transmission rate per each channel is 64kb/S Transmission rate per each channel is 64kb/S

(=8000*8b; 56kb/S data + 8kb/S control)(=8000*8b; 56kb/S data + 8kb/S control)– Frame size 193b (=24*8b + 1b framing code)Frame size 193b (=24*8b + 1b framing code)– Transmission rate per multiplexed channel Transmission rate per multiplexed channel

1.544Mb/S1.544Mb/S (=193b*8000) (=193b*8000) E1-carrier MethodE1-carrier Method: multiplexes 32 channels : multiplexes 32 channels

(30 data + 2 control/synchronization) in (30 data + 2 control/synchronization) in Round-robin for each 125Round-robin for each 125S period . S period . – Transmission rate per multiplexed channel Transmission rate per multiplexed channel

2.048Mb/S2.048Mb/S (=32ch*8b*8000) (=32ch*8b*8000)

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Pulse Code ModulationPulse Code Modulation Differential PCM - codes not the amplitude Differential PCM - codes not the amplitude

but the difference between the two latest but the difference between the two latest amplitudes. Differences of 7b-coded amplitudes. Differences of 7b-coded magnitude (0magnitude (0127) can be coded with less 127) can be coded with less bits (i.e. bits (i.e. 5b5b code difference 0 code difference 0 32 - 25% 32 - 25% of the maximum of the magnitude for of the maximum of the magnitude for single sampling step).single sampling step).

Delta PCM - Differential PCM modification -Delta PCM - Differential PCM modification - 1b1b code for the difference: “0” means code for the difference: “0” means magnitude[t] = magnitude[t-1]-1; “1” magnitude[t] = magnitude[t-1]-1; “1” means magnitude[t] = magnitude[t-1]+1. means magnitude[t] = magnitude[t-1]+1. – Possibility for delay of the modulated signal to Possibility for delay of the modulated signal to

the analog original.the analog original. Predictive PCM - Delta PCM modification - Predictive PCM - Delta PCM modification -

magnitude[t] = magnitude[t-1, t-2,...]magnitude[t] = magnitude[t-1, t-2,...]

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Hierarchy of the Time Hierarchy of the Time Division MultiplexingDivision Multiplexing

Higher order multiplexing of the Higher order multiplexing of the

sequential bits of T1 channels - sequential bits of T1 channels -

Round-robin for several T1 channelsRound-robin for several T1 channels

USA standard hierarcUSA standard hierarchy:hy: 2424ch ch T1 T1 44*T1*T1T2T2 66*T2*T2T3T3 77*T3*T3T4T4

1.544Mb/S1.544Mb/S 6.312Mb/S6.312Mb/S 37.400Mb/S37.400Mb/S260.500Mb/S260.500Mb/S

CCITT (ITU-T) standard hierarchy:CCITT (ITU-T) standard hierarchy:3232ch ch T1 T1 44*T1*T1T2T2 44*T2*T2T3T3 44*T3*T3T4T4 44*T4*T4T5T5

2.048Mb/S2.048Mb/S 8.848Mb/S8.848Mb/S 34.304Mb/S34.304Mb/S139.264Mb/S139.264Mb/S 565.148Mb/S565.148Mb/S

2/28Known as PDH (PlesiochronousDigital Hierarchy). Coax, fiber and radio links are applied in PDH connections over 2 Mbps

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SONET StandardSONET Standard SONETSONET (Synchronous Optical NETwork) - (Synchronous Optical NETwork) -

standard for optical long-distance telephone standard for optical long-distance telephone traffic (CCITT [ITU-T] equivalent: SDH - traffic (CCITT [ITU-T] equivalent: SDH - Synchronous Digital Hierarchy) Synchronous Digital Hierarchy)

SONET is the North American standard SONET is the North American standard for synchronous multiplexing that for synchronous multiplexing that corresponds to SDHcorresponds to SDH

ITU-T has based the standardization ITU-T has based the standardization work of SDH on SONET standardswork of SDH on SONET standards

In principle, SDH is an international In principle, SDH is an international extension of SONETextension of SONET

The terminology in SDH and SONET is The terminology in SDH and SONET is similar and in some cases identicalsimilar and in some cases identical

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SDHSDH Synchronous Digital HierarchySynchronous Digital Hierarchy (SDH) (SDH)

standardized by ITU-T has several standardized by ITU-T has several improvements compared to the PDH:improvements compared to the PDH:– Direct pointer based access to data without need of Direct pointer based access to data without need of

layers of hierarchical branching equipmentlayers of hierarchical branching equipment– Centralized remote control of network elementsCentralized remote control of network elements– Increased use of the physical networkIncreased use of the physical network– Shorter delivery time for leased linesShorter delivery time for leased lines

SDH is a standardized multiplexing hierarchy for SDH is a standardized multiplexing hierarchy for both plesiochronous and synchronous purposes.both plesiochronous and synchronous purposes.

The multiplexing levels in the SDH can be The multiplexing levels in the SDH can be divided into two groups:divided into two groups:– multiplexing levels (virtual containers, VC) and line multiplexing levels (virtual containers, VC) and line

signal levelssignal levels– (synchronous transport modules, STM).(synchronous transport modules, STM).

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SONET StandardSONET Standard SONET defines SONET defines

– internetworking parameters: wavelength / internetworking parameters: wavelength / frequen-cies, timing and framingfrequen-cies, timing and framing

– Operations, Administrations and Maintenance Operations, Administrations and Maintenance (OAM) support - tools and procedures.(OAM) support - tools and procedures.

SONET is synchronous system with one SONET is synchronous system with one master clock and TDM data congestion master clock and TDM data congestion method (i.e. one carrier frequency in method (i.e. one carrier frequency in entire bandwidth) standard bit lasting entire bandwidth) standard bit lasting varies 10varies 10-7-7%.%.

SONET is channel switching model. [ATM SONET is channel switching model. [ATM is cell switching model with asynchronous is cell switching model with asynchronous arrivals of cells].arrivals of cells].

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SONET System ModelSONET System Model SONET system structure: fiber-connected SONET system structure: fiber-connected

multiplexers, switches and repeaters.multiplexers, switches and repeaters. Sections, lines and paths.Sections, lines and paths. Physical topology is mesh; logical Physical topology is mesh; logical

topology is ring (any path).topology is ring (any path). SONET frame: 810B/6480b frame, frame SONET frame: 810B/6480b frame, frame

interval 125interval 125S i.e. 8000frames/S = S i.e. 8000frames/S = 6.48MB/S = 51.84Mb/S channel speed - 6.48MB/S = 51.84Mb/S channel speed - STS-1 (Synchronous Transport Signal-1).STS-1 (Synchronous Transport Signal-1).

Each SONET frame contains:Each SONET frame contains:– HeaderHeader of of Section overheadSection overhead followed byfollowed by Line Line

overheadoverhead andand Path overheadPath overhead. . – PayloadPayload [SPE (Synchronous Payload Envelope)] - user [SPE (Synchronous Payload Envelope)] - user

data (might be empty!) pointed by the 3 leading bytes data (might be empty!) pointed by the 3 leading bytes of the Line overhead. (SPE contains 9B of Path of the Line overhead. (SPE contains 9B of Path overload spread by each 87B intervals).overload spread by each 87B intervals).

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generated and read at the start/end of the section

generated and read at the start/end of the line

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?Why Path overload is aligned with SPE

and Section/Line overloads are aligned

with the frames

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SONET MultiplexingSONET Multiplexing 11stst stage: The standard T1, 2, 3 input streams are stage: The standard T1, 2, 3 input streams are

converted to standard STS-1 channel (rounded to converted to standard STS-1 channel (rounded to the STS-1 rate of 51.84 Mb/S). The input channels the STS-1 rate of 51.84 Mb/S). The input channels to a multiplexer are called tributaries. Multiplexing to a multiplexer are called tributaries. Multiplexing is Byte-level Round-robin of all the tributaries. is Byte-level Round-robin of all the tributaries. Further steps of multiplexing:Further steps of multiplexing:

– 3 of STS-1 tributaries are multiplexed to STS-3 155.52 Mb/S 3 of STS-1 tributaries are multiplexed to STS-3 155.52 Mb/S channel ratechannel rate

– 4 of STS-3 tributaries are multiplexed to STS-12 622.08 Mb/S 4 of STS-3 tributaries are multiplexed to STS-12 622.08 Mb/S channel ratechannel rate

– 4 of STS-12 tributaries are multiplexed to STS-48 2.4883 Gb/S 4 of STS-12 tributaries are multiplexed to STS-48 2.4883 Gb/S channel ratechannel rate

22ndnd stage: scrambling ( stage: scrambling (disarranging the components of the disarranging the components of the transmission in order to make unintelligible to interception and transmission in order to make unintelligible to interception and avoid long sequences of “0” or “1” states to run out of the avoid long sequences of “0” or “1” states to run out of the synchronizing clock; back arranging based on header informationsynchronizing clock; back arranging based on header information))

33rdrd stage: Electric-to-optic conversion to optical stage: Electric-to-optic conversion to optical carrier signal denoted OC-carrier signal denoted OC-nn. (when carries STS-. (when carries STS-nn channel) E.g. OC-3 (starting), OC-9, -12, -36, -48.channel) E.g. OC-3 (starting), OC-9, -12, -36, -48.

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SONET and SDH multiplex data rates

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SONET Physical LayerSONET Physical Layer 4 sublayers architecture:4 sublayers architecture:

– Photonic sublayer specifies the physical Photonic sublayer specifies the physical properties of the light rays and fiber guides.properties of the light rays and fiber guides.

– Section sublayer transmits standard frames Section sublayer transmits standard frames between each two consecutive repeaters by between each two consecutive repeaters by amplifying and regeneration of the single amplifying and regeneration of the single bits.bits.

– Line sublayer multiplexes several tributaries Line sublayer multiplexes several tributaries in a channel and demultiplexes it in the next in a channel and demultiplexes it in the next consecutive multiplexer. Repeaters are consecutive multiplexer. Repeaters are transparent to this sublayer.transparent to this sublayer.

– Path sublayer organize end-to-end Path sublayer organize end-to-end connection between source and destination connection between source and destination multiplexers.multiplexers.

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Switching Methods - Circuit Switching Methods - Circuit SwitchingSwitching

Circuit switchingCircuit switching - establishment of temporary - establishment of temporary dedicated physical connection from-end-to-end dedicated physical connection from-end-to-end before and during the whole transfer. The before and during the whole transfer. The connection exists:connection exists:– from the moment of realization of the transmission initiativefrom the moment of realization of the transmission initiative– till the moment of request for end of the transfer by either till the moment of request for end of the transfer by either

of the parties (or for some technical reason/problem).of the parties (or for some technical reason/problem). Structure of circuit switching: user device Structure of circuit switching: user device

(phone/computer…); end switching office; hierarchy (phone/computer…); end switching office; hierarchy of intermediate switching offices.of intermediate switching offices.

Time diagram of the processes by circuit switching:Time diagram of the processes by circuit switching:– propagation time for each signal (in copper 5mSmpropagation time for each signal (in copper 5mSm-6-6))– request/acknowledge signals before setting up the request/acknowledge signals before setting up the

connection (by phones ack={signal, vabusy}); request connection (by phones ack={signal, vabusy}); request delayed by: delayed by:

• time for propagationtime for propagation• time for finding outgoing trunks in the switching officestime for finding outgoing trunks in the switching offices

Dedicated channel: no possibility of interruptions Dedicated channel: no possibility of interruptions and clipped signal until the end of the connectionand clipped signal until the end of the connection

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Switching Methods – Switching Methods – Connectionless SwitchingConnectionless Switching

Message switchingMessage switching: transmission of arbitrary long : transmission of arbitrary long buffered blocks - “messages” - to the next switching buffered blocks - “messages” - to the next switching office which is actually a router. office which is actually a router.

Time diagram of the processes by message Time diagram of the processes by message switching:switching:– propagation time for each message propagation time for each message – queuing delay in the consecutive routers (interactive queuing delay in the consecutive routers (interactive

communications (e.g. phone calls) have priority over non-communications (e.g. phone calls) have priority over non-interactive ones interactive ones undefined delays for intercomputer undefined delays for intercomputer communications; possibility for perceivable delays by communications; possibility for perceivable delays by interactive communications.interactive communications.

Packet switchingPacket switching: transmission of small fixed size : transmission of small fixed size buffered blocks - “packets”. Demonopolization of buffered blocks - “packets”. Demonopolization of the channels capacity the channels capacity

Time diagram of the processes by packet switching:Time diagram of the processes by packet switching:– propagation time for each packet (shorter than by the message propagation time for each packet (shorter than by the message

sw.) sw.) – channel congestion, reduced delay; possible perceivable brakes in channel congestion, reduced delay; possible perceivable brakes in

the interactive communicationsthe interactive communications

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Connection-oriented vs. Con-Connection-oriented vs. Con-nectionless [Packet] nectionless [Packet]

SwitchingSwitching

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Switching Systems - Switching Systems - Hierarchy Hierarchy

Basically tree structure of hierarchy Basically tree structure of hierarchy levels (AT&T levels (AT&T 5 levels) but: 5 levels) but:– the nearer the root - the denser the nearer the root - the denser

connections in that level (up to full connections in that level (up to full graph of connections)graph of connections)

– interlevel shortcuts (“direct trunks) for interlevel shortcuts (“direct trunks) for overloaded routesoverloaded routes

Service Access Points are at the Service Access Points are at the lowest hierarchy level (at tree lowest hierarchy level (at tree leaves)leaves)

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Switching Systems - CrossbarsSwitching Systems - Crossbars nnxxnn (in parallel computers: (in parallel computers: nnxxmm) crossbar ) crossbar

(“crosspoint”) connects (“crosspoint”) connects nn inputs full duplex inputs full duplex to to nn outputs - one stage switch. outputs - one stage switch.

The matrix of elementary switches has The matrix of elementary switches has nn2 2

components. components. The elementary switches are automatically The elementary switches are automatically

controlled in manner : icontrolled in manner : inn:o:omm requires i requires imm:o:onn;; no impossible combinations (full graph of no impossible combinations (full graph of connectivity)connectivity)

DelaysDelays– by switching - hardly depends on hardware; by switching - hardly depends on hardware;

down to down to SS– by signal propagation - no delay (commutation by signal propagation - no delay (commutation

independence)independence)

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Switching Systems - Switching Systems - InterLAN CrossbarsInterLAN Crossbars

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Switching Systems - Switching Systems - Multistage Switches Multistage Switches

Multistage switchesMultistage switches consist of consist of ss stages stages Each stage Each stage ii consists of of consists of of nnii

independent independent nn::kk (e.g. 2:2, 4:4) (e.g. 2:2, 4:4) crossbar elements (CE)crossbar elements (CE)

Static interstage connection scheme Static interstage connection scheme (usually so called Banyan switching)(usually so called Banyan switching)

NO intrastage and interstage loopsNO intrastage and interstage loops Less hardware than crossbars: 8:8 Less hardware than crossbars: 8:8

crossbar needs 64 elementary crossbar needs 64 elementary switches; 8:8 Banyan multistage switches; 8:8 Banyan multistage needs 12 CE by 4 elementary switches needs 12 CE by 4 elementary switches = 48, BUT = 48, BUT

Possible rejected connections Possible rejected connections Delays:Delays:

– by switching = delay for one by switching = delay for one switching elementswitching element

– by signal propagation = delay for by signal propagation = delay for one switching element x one switching element x ss

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Switching Systems - Switching Systems - Time Division SwitchingTime Division Switching

Components: Components: nn-input multiplexer; -input multiplexer; nn-slots -slots interchange buffer with associated interchange buffer with associated nn-pointers -pointers mapping table and n-output demultiplexermapping table and n-output demultiplexer

Switching method:Switching method: Round robin scanning (multiplexing) of Round robin scanning (multiplexing) of nn input lines and input lines and

storing the content in the indexed bufferstoring the content in the indexed buffer Reordering the contents of the buffer according to the Reordering the contents of the buffer according to the

scheme in the mapping table in scheme in the mapping table in nn steps [for double space steps [for double space buffers: in one step buffers: in one step input and output process overlap - input and output process overlap - “conveyer”]“conveyer”]

Output the contents of the reordered buffer to n serial Output the contents of the reordered buffer to n serial output lines (demultiplexing)output lines (demultiplexing)

Delays:Delays:– by reordering: for non-conveyered switching the by reordering: for non-conveyered switching the

delay depends on delay depends on nn; for conveyered switching the ; for conveyered switching the delay depends on the R/W RAM cycle of the bufferdelay depends on the R/W RAM cycle of the buffer

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Electromagnetic spectrum

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Radio TransmissionRadio Transmission

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