(c) all rights reserved by professor wen-tsuen chen1 chapter 2 physical layer © all rights...

(C) All rights reserved by Professor (C) All rights reserved by Professor Wen-Tsuen ChenWen-Tsuen Chen

11

Chapter 2Physical LayerChapter 2Physical Layer

© All rights reserved. No part of these slides may be reproduced, in any© All rights reserved. No part of these slides may be reproduced, in any form or by any means, without permission in writing from form or by any means, without permission in writing from Professor Wen-Tsuen Chen (email: [email protected]).Professor Wen-Tsuen Chen (email: [email protected]).

Data Rate of a ChannelData Rate of a Channel Transmission MediaTransmission Media Data Transmission / EncodingData Transmission / Encoding Multiplexing and SwitchingMultiplexing and Switching Data Communication InterfaceData Communication Interface


22

Maximum Data Rate of a ChannelMaximum Data Rate of a Channel

Nyquist’s theoremNyquist’s theorem

levels. discrete : and bandwidth, : Where

channel) (noiseless

bits/sec log2ratedata .max 2

VH

VH

Shannon’s theoremShannon’s theorem

.ratio rate noise-to-signal : and , bandwidth: Where

channel)(noisy

bits/sec )1(logratedata .max 2

NSH

N

SH


33

Transmission MediaTransmission Media

BandwidthBandwidth Data RateData Rate RepeaterRepeater SpacingSpacing Error RateError Rate


44

Twisted Pair Twisted Pair

BandwidthBandwidth Data rate ~ 5MbpsData rate ~ 5Mbps Repeater spacing 2 to 10 kmRepeater spacing 2 to 10 km Error rate ~ 10Error rate ~ 10-6-6

Unshielded Twisted Pair(UTP), telephone wire, suUnshielded Twisted Pair(UTP), telephone wire, subject to external electromagnetic interference ,bject to external electromagnetic interference , Category 3 UTP, up to 16 Mbps, Category 5 UTP, up to Category 3 UTP, up to 16 Mbps, Category 5 UTP, up to

100 Mbps with limited distances.100 Mbps with limited distances.

Shielded Twisted pair(STP), reduced interference, Shielded Twisted pair(STP), reduced interference,

more expensivemore expensive..


55

Coaxial CableCoaxial Cable

Bandwidth ~ 350 MHzBandwidth ~ 350 MHz Data Rate ~ 500 MbpsData Rate ~ 500 Mbps Repeater spacing 1~10 kmRepeater spacing 1~10 km Error rate ~ 10Error rate ~ 10-7-7

Baseband Coaxial Cable, 50-ohm, used in EthernetBaseband Coaxial Cable, 50-ohm, used in Ethernet Broadband Coaxial Cable, 75-ohm, used in Cable TVBroadband Coaxial Cable, 75-ohm, used in Cable TV


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Optical FiberOptical Fiber

Greater capacity : > 50,000 Gbps (theoretically), 1Greater capacity : > 50,000 Gbps (theoretically), 100 Gbps currently in Lab, a few Gbps in use.00 Gbps currently in Lab, a few Gbps in use.

Smaller size and lighter weight.Smaller size and lighter weight. lower attenuation : constant over a wide range.lower attenuation : constant over a wide range. Electromagnetic isolation ; lower error rate .Electromagnetic isolation ; lower error rate . Greater repeater spacing : AT&T demonstrated a Greater repeater spacing : AT&T demonstrated a

data rate of 3.5 Gbps over a distance of 318 km widata rate of 3.5 Gbps over a distance of 318 km without repeaters.thout repeaters.


77

Multi-mode fiber vs. single-mode fiber.Multi-mode fiber vs. single-mode fiber. Optical transmission system : light source , the traOptical transmission system : light source , the tra

nsmission medium, and the photo detector.nsmission medium, and the photo detector.

Optical Fiber (cont.)Optical Fiber (cont.)


88

Wireless TransmissionWireless Transmission

Radio : omnidirectional, AM, FM Radio, TV, ALOHA datRadio : omnidirectional, AM, FM Radio, TV, ALOHA data network. 30MHz to 1Gbps.a network. 30MHz to 1Gbps.

Microwave : directionalMicrowave : directional Terrestrial Microwave, long-haul common carrier, goveTerrestrial Microwave, long-haul common carrier, gove

rnment communications.rnment communications. Satellite MicrowaveSatellite Microwave

A communication satellite is a microwave relay statA communication satellite is a microwave relay station.ion.

Infrared : does not penetrate walls, for indoor wireless LAInfrared : does not penetrate walls, for indoor wireless LANs.Ns.


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Cellular RadioCellular Radio

Paging System (one way) vs. Mobile Telephones (two way)Paging System (one way) vs. Mobile Telephones (two way) Cordless TelephonesCordless Telephones

CT2 : make calls, not receive them.CT2 : make calls, not receive them. CT3,DECT and PHS : roaming over base stations .CT3,DECT and PHS : roaming over base stations .

Analog Cellular TelephonesAnalog Cellular Telephones AMPS (Advanced Mobile Telephone System)AMPS (Advanced Mobile Telephone System)

first installed in US 1982.first installed in US 1982. uses 832 full-duplex channels.uses 832 full-duplex channels. security issue.security issue.


1111

Cellular Radio(cont.)Cellular Radio(cont.)

Digital Cellular TelephonesDigital Cellular Telephones IS-54 and IS-135 : backward compatible with AIS-54 and IS-135 : backward compatible with A

MPS.MPS. IS-95 : direct sequence spread spectrum.IS-95 : direct sequence spread spectrum. GSM(Global Systems for Mobile CommunicatiGSM(Global Systems for Mobile Communicati

on)on) 1.8GHz ; 50 ~ 200KHz bands : FDM 1.8GHz ; 50 ~ 200KHz bands : FDM multiple users in each band : TDMmultiple users in each band : TDM


1212

PCS-Personal Communications Services or PCNPCS-Personal Communications Services or PCN

use cellular Technology , but with microcells , 50 use cellular Technology , but with microcells , 50 ~100 meter wide.~100 meter wide.


1313

Communication SatellitesCommunication Satellites

Geosynchronous Satellites.Geosynchronous Satellites. VSATs(Very Small Aperture Terminals).VSATs(Very Small Aperture Terminals). Low Orbit Satellites.Low Orbit Satellites.


1414


1515


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Data TransmissionData Transmission

Data are entities that convey meaning.Data are entities that convey meaning. Signals are electric or electromagnetic encoding of Signals are electric or electromagnetic encoding of

data.data. Data Transmission is the communication of data bData Transmission is the communication of data b

y the propagation and processing of signals.y the propagation and processing of signals. Analog (continuous) vs. digital (discrete) transmisAnalog (continuous) vs. digital (discrete) transmis

sion.sion.


1717

Data TransmissionData Transmission

datadata


1818


1919

Data Encoding and ModulationData Encoding and Modulation


2020

Digital Data to Digital SignalDigital Data to Digital Signal


2121


2222

Digital Data to Analog SignalDigital Data to Analog Signal


2323


2424

Analog Data to Digital SignalAnalog Data to Digital Signal

Pulse Code Modulation (PCM).Pulse Code Modulation (PCM). Based on the sampling theorem : Based on the sampling theorem :

If a signal f(t) is sampled at regular intervals of time If a signal f(t) is sampled at regular intervals of time and at a rate higher than twice the highest significant signal and at a rate higher than twice the highest significant signal frequency then the samples contain all the information of the frequency then the samples contain all the information of the original signal. The function f(t) may be reconstructed from original signal. The function f(t) may be reconstructed from these samples by the use of a low-pass filter.these samples by the use of a low-pass filter.

For 4-kHz telephone channel , 8000 samples/sec (125 For 4-kHz telephone channel , 8000 samples/sec (125 sec sec /sample), each sample represented by a 7- or 8-bit number./sample), each sample represented by a 7- or 8-bit number.


2525

Analog Data to Digital SignalAnalog Data to Digital Signal


2626

Analog to Digital ConversionAnalog to Digital Conversion


2727


2828

Analog Data to Analog SignalAnalog Data to Analog Signal


2929

MultiplexingMultiplexing

Frequency Division MultiplexingFrequency Division Multiplexing Time Division MultiplexingTime Division Multiplexing Wavelength Division MultiplexingWavelength Division Multiplexing Code Division MultiplexingCode Division Multiplexing


3030

Frequency Division MultiplexingFrequency Division Multiplexing


3131

Wavelength MultiplexingWavelength Multiplexing

Has been used in high-capacity, long-distance Has been used in high-capacity, long-distance transmission.transmission.


3232

Time Division MultiplexingTime Division Multiplexing Multiple digital signals can be carried on a single Multiple digital signals can be carried on a single

transmission path by interleaving portions of each transmission path by interleaving portions of each signal in time.signal in time.


3333

T1 Digital Carrier SystemT1 Digital Carrier System


3434

TDM Digital HierarchyTDM Digital Hierarchy


3535

SONET(Synchronous Optical Network)SONET(Synchronous Optical Network)

An optical transmission interface proposed by BellAn optical transmission interface proposed by Bellcore and standardized by ANSI .core and standardized by ANSI .

A compatible version, Synchronous Digital HierarA compatible version, Synchronous Digital Hierarchy(SDH), published by ITU in 1989.chy(SDH), published by ITU in 1989.

The SONET specification defines a hierarchy of stThe SONET specification defines a hierarchy of standardized digital data rates. The basic rate, referrandardized digital data rates. The basic rate, referred to as STS-1(Synchronous Transport signal leveed to as STS-1(Synchronous Transport signal level 1) or OC-1(Optical Carrier level 1) is 51.84 mbpl 1) or OC-1(Optical Carrier level 1) is 51.84 mbps.s.


3636


3737


3838


3939


4040


4141


4242

Code Division Multiplexing (Spread Spectrum)

Code Division Multiplexing (Spread Spectrum)

Initially developed for military and intelligenInitially developed for military and intelligence purposece purpose

To spread the information signal over a wider To spread the information signal over a wider bandwidth in order to make jamming and intebandwidth in order to make jamming and interception more difficult rception more difficult

Each pair of two communication stations sharEach pair of two communication stations share a code sequence , a pseudorandom sequence a code sequence , a pseudorandom sequence. All code sequences are pairwise orthogonal.e. All code sequences are pairwise orthogonal.


4343

General model of spread spectrum digital communication system

General model of spread spectrum digital communication system

Two types of spread spectrum: Frequency-Two types of spread spectrum: Frequency-hopping and direct-sequence spectrum.hopping and direct-sequence spectrum.


4444

Frequency-hopping spread spectrumFrequency-hopping spread spectrum


4545

Direct sequence spread spectrumDirect sequence spread spectrum


4646


4747

SwitchingSwitching Circuit Switching vs. Packet SwitchingCircuit Switching vs. Packet Switching


4848


4949


5050

Crossbar SwitchCrossbar Switch

The Problem of a crossbar switch : The Problem of a crossbar switch : # of Crossbar # of Crossbar NN22,, where where N N is the # is the #

of lines of lines


5151

Space Division SwitchesSpace Division Switches

Clos NetworksClos Networks# of cross points = 2k# of cross points = 2kNN + k( + k(NN/n)/n)22

For large k, more expensive, lower blocking Prob. Clos showed that For large k, more expensive, lower blocking Prob. Clos showed that when k=2n-1 => nonblocking. when k=2n-1 => nonblocking.


5252

Self routingSelf routing # of cross points = # of cross points = loglog22NN

A blocking networkA blocking network

N2

Multistage Interconnection NetworksMultistage Interconnection Networks


5353


5454

Time Division SwitchTime Division Switch

Equivalent to space division switchesEquivalent to space division switches Main switch architecture in LAN switches and ATM Main switch architecture in LAN switches and ATM

switches.switches.


5555

Statistical TDMStatistical TDM In some applications, even if all data sources are active, In some applications, even if all data sources are active,

most of the time there in no data transfer at any particular most of the time there in no data transfer at any particular source.source.


5656

Data Communication InterfaceData Communication Interface


5757

Data Communication Interface(Cont.)Data Communication Interface(Cont.)

EIA-232, first issued by the Electronic Industries EIA-232, first issued by the Electronic Industries Association in 1962, as RS-232. Current version Association in 1962, as RS-232. Current version EIA-232-E issued in 1991.EIA-232-E issued in 1991.

Corresponding specification in ITU-T, V.24 (only Corresponding specification in ITU-T, V.24 (only specify functional and procedural aspects of the specify functional and procedural aspects of the interface; mechanical: ISO 2110; electrical V.28)interface; mechanical: ISO 2110; electrical V.28)


5858

An Interface between DTE and DCE has four characteristics: An Interface between DTE and DCE has four characteristics: Mechanical, electrical, functional, and Procedural.Mechanical, electrical, functional, and Procedural.

The mechanical characteristics: Actual physical connection of the The mechanical characteristics: Actual physical connection of the DTE to the DCE.DTE to the DCE.


5959


6060

Electrical characteristics: voltage levels and timinElectrical characteristics: voltage levels and timing of voltage changes g of voltage changes In EIA-232, voltage levels are the same as that in NRZ-In EIA-232, voltage levels are the same as that in NRZ-

L code; data rate < 20 kbps; distance < 15 m.L code; data rate < 20 kbps; distance < 15 m.

Functional characteristics: meanings of each of the Functional characteristics: meanings of each of the interchange circuits.interchange circuits.

Procedural characteristics: the physical layer protoProcedural characteristics: the physical layer protocol that specifies the sequence of events for transmcol that specifies the sequence of events for transmitting data.itting data.


6161


6262


6363


6464

ISDN (Integrated Services Digital Network)ISDN (Integrated Services Digital Network)

The ISDN standards, called the I-series of The ISDN standards, called the I-series of recommendations, were first issued by ITU-T in 1984.recommendations, were first issued by ITU-T in 1984.

Intended to be a worldwide public telecommunication Intended to be a worldwide public telecommunication network to replace existing public telecommunication network to replace existing public telecommunication networks and deliver a wide variety of services.networks and deliver a wide variety of services.

The second generation of ISDN is referred to as broadband The second generation of ISDN is referred to as broadband ISDN (B-ISDN) using the ATM (Asynchronous transfer ISDN (B-ISDN) using the ATM (Asynchronous transfer mode) technology, its standard issued in 1988.mode) technology, its standard issued in 1988.


6565

ISDN SystemISDN System


6666


6767

ISDN Mechanical InterfaceISDN Mechanical Interface


6868

ISDN Mechanical Interface(cont.)ISDN Mechanical Interface(cont.)

Fewer circuits (8 pins) but more logic at the DTE Fewer circuits (8 pins) but more logic at the DTE and DCE interface.and DCE interface.

ISO 8877 specifies interface between TE and NE.ISO 8877 specifies interface between TE and NE.


6969

Electrical specification: pseudoternary coding voltage levels Electrical specification: pseudoternary coding voltage levels 750mv 10% for basic rate; For primary rate, Bipotar-AMI 750mv 10% for basic rate; For primary rate, Bipotar-AMI with B8ZS (1.544 Mbps) or HDB3 (2.049 Mbps) code.with B8ZS (1.544 Mbps) or HDB3 (2.049 Mbps) code.

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