Business Data Communications and Networking - Chapter 3: Physical Layer

Business Data Communications and Networking 8th Edition Jerry Fitzgerald and Alan DennisJohn Wiley & Sons, Inc Prof. M. UlemaManhattan CollegeComputer Information Systems1Copyright 2005 John Wiley & Sons, IncChapter 3Physical Layer2Copyright 2005 John Wiley & Sons, IncOutlineCircuitsConfiguration, Data Flow, Communication MediaDigital Transmission of Digital DataCoding, Transmission Modes, Analog Transmission of Digital DataModulation, Voice Circuit Capacity, Digital Transmission of Analog DataPulse Amplitude Modulation, Voice Data Transmission, Instant Messenger Transmitting Voice DataAnalog/Digital ModemsMultiplexingFDM, TDM, STDM, WDM, Inverse Multiplexing, DSL3Copyright 2005 John Wiley & Sons, IncPhysical Layer - OverviewIncludes network hardware and circuitsNetwork circuits: physical media (e.g., cables) and special purposes devices (e.g., routers and hubs).Types of Circuits Physical circuits connect devices & include actual wires such as twisted pair wiresLogical circuits refer to the transmission characteristics of the circuit, such as a T-1 connection refers to 1.5 MbpsCan be the same or different. For example, in multiplexing, one wire carries several logical circuitsPhysical LayerNetwork LayerData Link Layer4Copyright 2005 John Wiley & Sons, IncTypes of Data TransmittedAnalog dataProduced by telephonesSound waves, which vary continuously over time Can take on any value in a wide range of possibilitiesDigital dataProduced by computers, in binary form, represented as a series of ones and zeros Can take on only 0 ad 15Copyright 2005 John Wiley & Sons, IncTypes of TransmissionAnalog transmissions Analog data transmitted in analog form (vary continuously) Examples of analog data being sent using analog transmissions are broadcast TV and radioDigital transmissionsMade of square waves with a clear beginning and endingComputer networks send digital data using digital transmissions.Data converted between analog and digital formats Modem (modulator/demodulator): used when digital data is sent as an analog transmissionCodec (coder/decoder): used when analog data is sent as a digital transmission6Copyright 2005 John Wiley & Sons, IncData Type vs. Transmission TypeAnalogTransmissionDigital TransmissionAnalogDataRadio, Broadcast TVPCM & Video standards using codecsDigital DataModem-basedcommunicationsLAN cable standards7Copyright 2005 John Wiley & Sons, IncDigital Transmission: AdvantagesProduces fewer errorsEasier to detect and correct errors, since transmitted data is binary (1s and 0s, only two distinct values))Permits higher maximum transmission ratese.g., Optical fiber designed for digital transmissionMore efficientPossible to send more digital data through a given circuitMore secureEasier to encryptSimpler to integrate voice, video and data Easier to combine them on the same circuit, since signals made up of digital data 8Copyright 2005 John Wiley & Sons, IncCircuit ConfigurationBasic physical layout of the circuitConfiguration types:Point-to-Point ConfigurationGoes from one point to anotherSometimes called “dedicated circuits”Multipoint ConfigurationMany computers connected on the same circuitSometimes called “shared circuit”9Copyright 2005 John Wiley & Sons, IncPoint-to-Point ConfigurationUsed when computers generate enough data to fill the capacity of the circuitEach computer has its own circuit to any other computer in the network (expensive)10Copyright 2005 John Wiley & Sons, IncMultipoint Configuration+ Cheaper (no need for many wires) and simpler to wire - Only one computer can use the circuit at a timeUsed when each computer does not need to continuously use the entire capacity of the circuit11Copyright 2005 John Wiley & Sons, IncData Flow (Transmission)data flows move in one direction only, (radio or cable television broadcasts)data flows both ways, but only one direction at a time (e.g., CB radio) (requires control info)data flows in both directions at the same time12Copyright 2005 John Wiley & Sons, IncSelection of Data Flow MethodMain factor: ApplicationIf data required to flow in one direction onlySimplex Methode.g., From a remote sensor to a host computer If data required to flow in both directionsTerminal-to-host communication (send and wait type communications)Half-Duplex MethodClient-server; host-to-host communication (peer-to-peer communications)Full Duplex MethodHalf-duplex or Full DuplexCapacity may be a factor tooFull-duplex uses half of the capacity for each direction13Copyright 2005 John Wiley & Sons, IncCommunications MediaPhysical matter that carries transmissionGuided media:Transmission flows along a physical guide (Media guides the signal))Twisted pair wiring, coaxial cable and optical fiber cableWireless media (aka, radiated media) No wave guide, the transmission just flows through the air (or space) Radio (microwave, satellite) and infrared communications14Copyright 2005 John Wiley & Sons, IncTwisted Pair (TP) WiresCommonly used for telephones and LANsReduced electromagnetic interferenceVia twisting two wires together (Usually several twists per inch)TP cables have a number of pairs of wiresTelephone lines: two pairs (4 wires, usually only one pair is used by the telephone)LAN cables: 4 pairs (8 wires)Also used in telephone trunk lines (up to several thousand pairs)Shielded twisted pair also exists, but is more expensive15Copyright 2005 John Wiley & Sons, IncCoaxial CableWire mesh ground(protective jacket )More expensive than TP (quickly disappearing)used mostly for CATVLess prone to interference than TP (due to (shield) 16Copyright 2005 John Wiley & Sons, IncFiber Optic CableLight created by an LED (light-emitting diode) or laser is sent down a thin glass or plastic fiberHas extremely high capacity, ideal for broadbandWorks better under harsh environmentsNot fragile, nor brittle; Nit heavy nor bulkyMore resistant to corrosion, fire, etc., Fiber optic cable structure (from center):Core (v. small, 5-50 microns, ~ the size of a single hair)Cladding, which reflects the signalProtective outer jacket17Copyright 2005 John Wiley & Sons, IncTypes of Optical FiberMultimode (about 50 micron core)Earliest fiber-optic systemsSignal spreads out over short distances (up to ~500m)InexpensiveGraded index multimodeReduces the spreading problem by changing the refractive properties of the fiber to refocus the signal Can be used over distances of up to about 1000 metersSingle mode (about 5 micron core)Transmits a single direct beam through the cableSignal can be sent over many miles without spreadingExpensive (requires lasers; difficult to manufacture)18Copyright 2005 John Wiley & Sons, IncOptical Fiber(different parts of signal arrive at different times)Excessive signal weakening and dispersionCenter light likely to arrive at the same time as the other parts19Copyright 2005 John Wiley & Sons, IncRadioWireless transmission of electrical waves over airEach device has a radio transceiver with a specific frequencyLow power transmitters (few miles range)Often attached to portables (Laptops, PDAs, cell phones)Includes AM and FM radios, Cellular phonesWireless LANs (IEEE 802.11) and BluetoothMicrowaves and SatellitesInfrared“invisible” light waves (frequency is below red light)Requires line of sight; generally subject to interference from heavy rain, smog, and fogUsed in remote control units (e.g., TV)Wireless Media20Copyright 2005 John Wiley & Sons, IncMicrowave RadioHigh frequency form of radio communicationsExtremely short (micro) wavelength (1 cm to 1 m)Requires line-of-sightPerform same functions as cablesOften used for long distance, terrestrial transmissions (over 50 miles without repeaters)No wiring and digging requiredRequires large antennas (about 10 ft) and high towersPossesses properties similar to lightReflection, Refraction, and focusingCan be focused into narrow powerful beams for long distance21Copyright 2005 John Wiley & Sons, IncSatellite CommunicationsA special form of microwave communicationsin a geosynchronous orbitSignals sent from the ground to a satellite; Then relayed to its destination ground station Long propagation delay Due to great distance between ground station and satellite (Even with signals traveling at light speed)22Copyright 2005 John Wiley & Sons, IncFactors Used in Media SelectionType of networkLAN, WAN, or Backbone CostAlways changing; depends on the distanceTransmission distanceShort: up to 300 m; medium: up to 500 mSecurityWireless media is less secureError ratesWireless media has the highest error rate (interference)Transmission speedsConstantly improving; Fiber has the highest 23Copyright 2005 John Wiley & Sons, IncMedia SummaryFigure 3.9 goes here24Copyright 2005 John Wiley & Sons, IncDigital Transmission of Digital DataComputers produce binary dataStandards needed to ensure both sender and receiver understands this dataCoding: language that computers use to represent letters, numbers, and symbols in a messageSignaling (aka, encoding): language that computers use to represent bits (0 or 1) in electrical voltageBits in a message can be send in A single wire one after another (Serial transmission) Multiple wires simultaneously (Parallel transmission)25Copyright 2005 John Wiley & Sons, IncCodingMain character codes in use in North AmericaASCII: American Standard Code for Information Interchange Originally used a 7-bit code (128 combinations), but an 8-bit version (256 combinations) is now in useEBCDIC: Extended Binary Coded Decimal Interchange CodeAn 8-bit code developed by IBMA character  a group of bits Letters (A, B, ..), numbers (1, 2,..),special symbols (#, $, ..)100000126Copyright 2005 John Wiley & Sons, IncTransmission ModesParallel modeUses several wires, each wire sending one bit at the same time as the othersA parallel printer cable sends 8 bits together Computer’s processor and motherboard also use parallel busses (8 bits, 16 bits, 32 bits) to move data aroundSerial ModeSends bit by bit over a single wireSerial mode is slower than parallel mode27Copyright 2005 John Wiley & Sons, IncParallel Transmission ExampleUsed for short distances (up to 6 meters) (since bits sent in parallel mode tend to spread out over long distances)(8 separate copper wires)28Copyright 2005 John Wiley & Sons, IncSerial Transmission ExampleCan be used over longer distances (since bits stay in the order they were sent)29Copyright 2005 John Wiley & Sons, IncSignaling of BitsDigital Transmission Signals sent as a series of “square waves” of either positive or negative voltage Voltages vary between +3/-3 and +24/-24 depending on the circuitSignaling (encoding) Defines what voltage levels correspond to a bit value of 0 or 1Examples:Unipolar, BipolarRTZ, NRZ, ManchesterData rate: how often the sender can transmit data64 Kbps  once every 1/64000 of a second30Copyright 2005 John Wiley & Sons, IncSignaling (Encoding) TechniquesUnipolar signalingUse voltages either vary between 0 and a positive value or between 0 and some negative valueBipolar signalingUse both positive and negative voltagesExperiences fewer errors than unipolar signalingSignals are more distinct (more difficult (for interference) to change polarity of a current)Return to zero (RZ) Signal returns to 0 voltage level after sending a bitNon return to zero (NRZ)Signals maintains its voltage at the end of a bitManchester encoding (used by Ethernet)31Copyright 2005 John Wiley & Sons, IncManchester EncodingUsed by Ethernet, most popular LAN technologyDefines a bit value by a mid-bit transitionA high to low voltage transition is a 0 and a low to high mid-bit transition defines a 1Data rates: 10 Mb/s, 100 Mb/s, 1 Gb/s, ..10- Mb/s  one signal for every 1/10,000,000 of a second (10 million signals (bits) every second)Less susceptible to having errors go undetectedNo transition  an error took place32Copyright 2005 John Wiley & Sons, IncDigital Transmission TypesUnipolarBipolarNRZBipolarRZManchester33Copyright 2005 John Wiley & Sons, IncAnalog Transmission of Digital DataA well known exampleUsing phone lines to connect PCs to InternetPCs generates digital dataPhone lines use analog transmission technologyModems translate digital data into analog signals Phone lineCentral Office(Telco)Analog transmissionPCMTelephone NetworkInternetDigital dataM34Copyright 2005 John Wiley & Sons, IncTelephone NetworkOriginally designed for human speech (analog communications) onlyPOTS (Plain Old Telephone Service)Enables voice communications between two telephonesHuman voice (sound waves) converted to electrical signals by the sending telephoneSignals travel through POTS and converted back to sound wavesSending digital data over POTSUse modems to convert digital data to an analog formatOne modem used by sender to produce analog dataAnother modem used by receiver to regenerate digital data35Copyright 2005 John Wiley & Sons, IncSound Waves and CharacteristicsAmplitudeHeight (loudness) of the waveMeasured in decibels (dB)Frequency: Number of waves that pass in a second Measured in Hertz (cycles/second) Wavelength, the length of the wave from crest to crest, is related to frequency and velocityPhase: Refers to the point in each wave cycle at which the wave begins (measured in degrees)(For example, changing a wave’s cycle from crest to trough corresponds to a 180 degree phase shift).0o90o360o180o270o36Copyright 2005 John Wiley & Sons, IncWavelength vs. Frequencyλv = f λv = 3 x108 m/s = 300,000 km/s = 186,000 miles/sExample: if f = 900 MHzλ = 3 x108 / 900 x 10 3 = 3/9 = 0.3 metersspeed = frequency * wavelength 37Copyright 2005 John Wiley & Sons, IncModulationΜodification of a carrier wave’s fundamental characteristics in order to encode informationCarrier wave: Basic sound wave transmitted through the circuit (provides a base which we can deviate)Βasic ways to modulate a carrier wave:Amplitude Modulation (AM)Also known as Amplitude Shift Keying (ASK)Frequency Modulation (FM)Also known as Frequency Shift Keying (FSK)Phase Modulation (PM)Also known as Phase Shift Keying (PSK)38Copyright 2005 John Wiley & Sons, IncAmplitude Modulation (AM) Changing the height of the wave to encode dataOne bit is encoded for each carrier wave changeA high amplitude means a bit value of 1Low amplitude means a bit value of 0 More susceptible noise than the other modulation methods39Copyright 2005 John Wiley & Sons, IncFrequency Modulation (FM) Changing the frequency of carrier wave to encode dataOne bit is encoded for each carrier wave changeChanging carrier wave to a higher frequency encodes a bit value of 1No change in carrier wave frequency means a bit value of 040Copyright 2005 John Wiley & Sons, IncPhase Modulation (PM) Changing the phase of the carrier wave to encode data One bit is encoded for each carrier wave changeChanging carrier wave’s phase by 180o corresponds to a bit value of 1No change in carrier wave’s phase means a bit value of 041Copyright 2005 John Wiley & Sons, IncConcept of SymbolSymbol: Each modification of the carrier wave to encode informationSending one bit (of information) at a timeOne bit encoded for each symbol (carrier wave change)  1 bit per symbolSending multiple bits simultaneously Multiple bits encoded for each symbol (carrier wave change)  n bits per symbol, n > 1Need more complicated information coding schemes42Copyright 2005 John Wiley & Sons, IncSending Multiple Bits per SymbolPossible number of symbols must be increased1 bit of information  2 symbols 2 bits of information  4 symbols3 bits of information 8  symbols4 bits of information  16 symbols .n bits of information  2n symbolsMultiple bits per symbol might be encoded using amplitude, frequency, and phase modulatione.g., PM: phase shifts of 0o, 90o, 180o, and 270oSubject to limitations: As the number of symbols increases, it becomes harder to detect43Copyright 2005 John Wiley & Sons, IncExample: Two-bit AM4 symbols44Copyright 2005 John Wiley & Sons, IncCombined Modulation TechniquesCombining AM, FM, and PM on the same circuitExamplesQAM - Quadrature Amplitude ModulationA widely used family of encoding schemesCombine Amplitude and Phase ModulationA common form: 16-QAM Uses 8 different phase shifts and 2 different amplitude levels16 possible symbols  4 bits/symbolTCM – Trellis-Coded ModulationAn enhancement of QAM Can transmit different number of bits on each symbol (6,7,8 or 10 bits per symbol)45Copyright 2005 John Wiley & Sons, IncBit Rate vs. Baud Ratebit: a unit of informationbaud: a unit of signaling speedBit rate (or data rate): bNumber of bits transmitted per secondBaud rate (or symbol rate): s number of symbols transmitted per secondGeneral formula: b = s x n where b = Data Rate (bits/second) s = Symbol Rate (symbols/sec.) n = Number of bits per symbolExample: AM n = 1  b = sExample: 16-QAM n = 4  b = 4 x s46Copyright 2005 John Wiley & Sons, IncBandwidth of a Voice CircuitDifference between the highest and lowest frequencies in a band or set if frequenciesHuman hearing frequency range: 20 Hz to 14 kHzBandwidth = 14,000 – 20 = 13,980 HzVoice circuit frequency range: 0 Hz to 4 kHzDesigned for most commonly used range of human voicePhone lines transmission capacity is much bigger1 MHz for lines up to 2 miles from a telephone exchange300 kHz for lines 2-3 miles away47Copyright 2005 John Wiley & Sons, IncData Capacity of a Voice CircuitFastest rate at which you can send your data over the circuit (in bits per second)Calculated as the bit rate: b = s x nDepends on modulation (symbol rate)Max. Symbol rate = bandwidth (if no noise)Maximum voice circuit capacity:Using QAM with 4 bits per symbol (n = 4)Max. voice channel carrier wave frequency: 4000 Hz = max. symbol rate (under perfect conditions) Data rate = 4 * 4000  16,000 bps48Copyright 2005 John Wiley & Sons, IncModem - Modulator/demodulatorDevice that encodes and decodes data by manipulating the carrier waveV-series of modem standards (by ITU-T)V.22An early standard, now obsoleteUsed FM, with 2400 symbols/sec  2400 bps bit rateV.34One of the robust V standardsUsed TCM (8.4 bits/symbol), with 3,428 symbols/sec  multiple data rates(up to 28.8 kbps)Includes a handshaking sequence that tests the circuit and determines the optimum data rate49Copyright 2005 John Wiley & Sons, IncData Compression in ModemsUsed to increase the throughput rate of data by encoding redundant data stringsExample: Lempel-Ziv encodingUsed in V.44Creates (while transmitting) a dictionary of two-, three-, and four-character combinations in a messageAnytime one of these patterns is detected, its index in dictionary is sent (instead of actual data)Average reduction: 6:1 (depends on the text)Provides 6 times more data sent per second50Copyright 2005 John Wiley & Sons, IncDigital Transmission of Analog DataAnalog voice data sent over digital network using digital transmissionRequires a pair of special devices called Codecs - Coder/decoders A device that converts an analog voice signal into digital formAlso converts it back to analog data at the receiving endUsed by the phone system 51Copyright 2005 John Wiley & Sons, IncTranslating from Analog to DigitalMust be translated into a series of bits before transmission of a digital circuitDone by a technique called Pulse Amplitude Modulation (PAM) involving 3 steps:Measuring the signalEncoding the signal as a binary data sampleTaking samples of the signalCreates a rough (digitized) approximation of original signalQuantizing error: difference between the original signal and approximated signal52Copyright 2005 John Wiley & Sons, IncPAM – Measuring Signal Uses only 8 pulse amplitudes for simplicity Can be depicted by using only a 3-bit codeOriginal wave8 pulse amplitudes Signal (original wave) quantized into 128 pulse amplitudesRequires 8-bit (7 bit plus parity bit) code to encode each pulse amplitude Example: 53Copyright 2005 John Wiley & Sons, IncPAM – Encoding and SamplingPulse Amplitudes8 pulse amplitudes000 – PAM Level 1001 – PAM Level 2010 – PAM Level 3011 – PAM Level 4100 – PAM Level 5101 – PAM Level 6110 – PAM Level 7111 – PAM Level 8Digitized signal8,000 samples per second For digitizing a voice signal,8,000 samples x 3 bits per sample  24,000 bps transmission rate needed 8,000 samples then transmitted as a serial stream of 0s and 1s54Copyright 2005 John Wiley & Sons, IncMinimize Quantizing ErrorsIncrease number of amplitude levelsDifference between levels minimized  smoother signalRequires more bits to represent levels  more data to transmitAdequate human voice: 7 bits  128 levelsMusic: at least 16 bits  65,536 levelsSample more frequentlyWill reduce the length of each step  smoother signalAdequate Voice signal: twice the highest possible frequency (4Khz x 2 = 8000 samples / second)RealNetworks: 48,000 samples / second55Copyright 2005 John Wiley & Sons, IncPCM - Pulse Code Modulationlocal loopphone switch(DIGITAL)Central Office(Telco)Analog transmissionTo other switchestrunkDigital transmissionconvert analog signals to digital data using PCM (similar to PAM)8000 samples per second and 8 bits per sample (7 bits for sample+ 1 bit for control)  64 Kb/s (DS-0 rate) DS-0: Basic digital communications unit used by phone networkCorresponds to 1 digital voice signal56Copyright 2005 John Wiley & Sons, IncADPCMAdaptive Differential Pulse Code ModulationEncodes the differences between samplesThe change between 8-bit value of the last time interval and the current oneRequires only 4 bits since the change is small  Only 4 bits/sample (instead of 8 bits/sample), Requires 4 x 8000 = 32 Kbps (half of PCM)Makes it possible to for IM to send voice signals as digital signals using modems (which has <56 Kbps)Can also use lower sampling rates, at 8, 16 kbpsLower quality voice signals.57Copyright 2005 John Wiley & Sons, IncV.90 and V.92 ModemsCombines analog and digital transmissionUses a technique based on PCM conceptRecognizes PCM’s 8-bit digital symbols (one of 256 possible symbols) 8,000 per secondResults in a max of 56 Kbps data rate (1 bit used for control)V.90 StandardBased on V.34+ for Upstream transmissions (PC to Switch)Max. upstream rate is 33.4 KbpsV.92 Standard (most recent)Uses PCM symbol recognition technique for both waysMax. upstream rate is 48 kbpsVery sensitive to noise  lower rates 58Copyright 2005 John Wiley & Sons, IncMultiplexingBreaking up a higher speed circuit into several slower (logical) circuitsSeveral devices can use it at the same timeRequires two multiplexer: one to combine; one to separateMain advantage: costFewer network circuits neededCategories of multiplexing:Frequency division multiplexing (FDM)Time division multiplexing (TDM)Statistical time division multiplexing (STDM) Wavelength division multiplexing (WDM)59Copyright 2005 John Wiley & Sons, IncFrequency Division MultiplexingDividing the circuit “horizontallyMakes a number of smaller channels from a larger frequency bandGuardbands needed to separate channelsTo prevent interference between channelsUnused frequency bands ,wasted capacityUsed mostly by CATV 3000 Hz available bandwidthcircuitFDMFDMFour terminalsHost computer60Copyright 2005 John Wiley & Sons, IncTime Division MultiplexingDividing the circuit “vertically”Allows multiple channels to be used by allowing the channels to send data by taking turns4 terminals sharing a circuit, with each terminal sending one character at a time61Copyright 2005 John Wiley & Sons, IncComparison of TDMTime on the circuit shared equallyEach channel getting a specified time slot, (whether it has any data to send or not )More efficient than FDMSince TDM doesn’t use guardbands, (entire capacity can be divided up between channels)62Copyright 2005 John Wiley & Sons, IncStatistical TDM (STDM) Designed to make use of the idle time slots(In TDM, when terminals are not using the multiplexed circuit, timeslots for those terminals are idle.)Uses non-dedicated time slotsTime slots used as needed by the different terminals Complexities of STDMAdditional addressing information neededSince source of a data sample is not identified by the time slot it occupiesPotential response time delays (when all terminals try to use the multiplexed circuit intensively)Requires memory to store data (in case more data come in than its outgoing circuit capacity can handle)63Copyright 2005 John Wiley & Sons, IncWavelength Division MultiplexingTransmitting data at many different frequenciesLasers or LEDs used to transmit on optical fibersPreviously single frequency on single fiber (typical transmission rate being around 622 Mbps)Now multi frequencies on single fiber  n x 622+ MbpsDense WDM (DWDM)Over a hundred channels per fiberEach transmitting at a rate of 10 GbpsAggregate data rates in the low terabit range (Tbps) Future versions of DWDM Both per channel data rates and total number of channels continue to risePossibility of petabit (Pbps) aggregate rates64Copyright 2005 John Wiley & Sons, IncInverse Multiplexing (IMUX)Shares the load by sending data over two or more lines (instead of using a single line)e.g., two T-1 lines used (creating a combined multiplexed capacity of 2 x 1.544 = 3.088 Mbps)Bandwidth ON Demand Network Interoperability Group (BONDING) standardCommonly used for videoconferencing applicationsSix 64 kbps lines can be combined to create an aggregate line of 384 kbps for transmitting video65Copyright 2005 John Wiley & Sons, IncDigital Subscriber Line (DSL)Became popular as a way to increase data rates in the local loop.Uses full physical capacity of twisted pair (copper) phone lines (up to 1 MHz)Instead of using the 0-4000 KHz voice channel1 MHz capacity split into (FDM): a 4 KHz voice channelan upstream channel a downstream channelRequires a pair of DSL modemsOne at the customer’s site; one at the CO siteMay be divided further (via TDM) to have one or more logical channels66Copyright 2005 John Wiley & Sons, IncxDSLSeveral versions of DSLDepends on how the bandwidth allocated between the upstream and downstream channelsa: A for Asynchronous, H for High speed, etcG.Lite - a form of ADSL Provides a 4 Khz voice channel 384 kbps upstream1.5 Mbps downstream (provided line conditions are optimal).67Copyright 2005 John Wiley & Sons, IncImplications for ManagementDigital is betterEasier, more manageable , and less costly to integrate voice, data, and videoOrganizational impactConvergence of physical layer causing convergence of phone and data departmentsImpact on telecom industryDisappearance of the separation between manufacturers of telephone equipment and manufacturers of data equipment68Copyright 2005 John Wiley & Sons, IncCopyright 2005 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein. 69Copyright 2005 John Wiley & Sons, Inc