Chapter Four Transmission Basics and Networking Media.

Chapter FourChapter FourTransmission Basics and Transmission Basics and

Networking MediaNetworking Media

ObjectivesObjectives

Explain data transmission concepts including full-Explain data transmission concepts including full-duplexing, attenuation, and noiseduplexing, attenuation, and noiseDescribe the physical characteristics of coaxial Describe the physical characteristics of coaxial cable, STP, UTP, and fiber-optic mediacable, STP, UTP, and fiber-optic mediaExplain the benefits and limitations of different Explain the benefits and limitations of different networking medianetworking mediaIdentify the best practices for cabling buildings and Identify the best practices for cabling buildings and work areaswork areasDescribe the methods of transmitting data through Describe the methods of transmitting data through the atmospherethe atmosphere

Transmission BasicsTransmission Basics

Transmission has two meanings:Transmission has two meanings: Refers to process of issuing data signals on a Refers to process of issuing data signals on a

mediummedium Refers to progress of data signals over a Refers to progress of data signals over a

mediummedium

On a data network, information can be On a data network, information can be transmitted via one of two methods:transmitted via one of two methods: AnalogAnalog DigitalDigital


Both analog and digital signals are generated Both analog and digital signals are generated by electrical current, pressure of which is by electrical current, pressure of which is measured in measured in voltsvolts

In analog signals, voltage varies continuouslyIn analog signals, voltage varies continuously

In digital signals, voltage turns off and on In digital signals, voltage turns off and on repeatedlyrepeatedly


Figure 4-1: Example of an analog signal


AmplitudeAmplitude Measure of a signal’s strengthMeasure of a signal’s strength

FrequencyFrequency Number of times a signal’s amplitude changes Number of times a signal’s amplitude changes

over a period of timeover a period of time Expressed in Expressed in hhertz (Hz)ertz (Hz)

WavelengthWavelength Distances between corresponding points on a Distances between corresponding points on a

wave’s cyclewave’s cycle


PhasePhase Refers to progress of a wave over time in relationship to a fixed pointRefers to progress of a wave over time in relationship to a fixed point

Figure 4-2: Phase differences


Figure 4-3: A complex analog signal representing human speech


BinaryBinary system encodes using 1s and 0s system encodes using 1s and 0s

BitsBits can only have a value of either 1 or 0 can only have a value of either 1 or 0

Eight bits together form a Eight bits together form a bytebyte

NoiseNoise or any interference that may degrade or any interference that may degrade signals affects digital signals less than analog signals affects digital signals less than analog signalssignals


Figure 4-4: Example of a digital signal

Data ModulationData Modulation

ModemModem Name reflects function as modulator/demodulatorName reflects function as modulator/demodulator

ModulationModulation Technique for formatting signalsTechnique for formatting signals

Frequency modulation (FM)Frequency modulation (FM) Method of data modulation in which frequency of Method of data modulation in which frequency of

carrier signal is modified by application of a data signalcarrier signal is modified by application of a data signal

Amplitude modulation (AM)Amplitude modulation (AM) Modulation technique in which amplitude of carrier Modulation technique in which amplitude of carrier

signal is modified by application of a data signalsignal is modified by application of a data signal

Data ModulationData Modulation

Figure 4-5: A carrier wave modified by frequency modulation

Transmission DirectionTransmission Direction

SimplexSimplex Signals travel in only one directionSignals travel in only one direction

Half-duplexHalf-duplex Signals may travel in both directions over a Signals may travel in both directions over a

medium but in only one direction at a timemedium but in only one direction at a time

Full-duplexFull-duplex Signals are free to travel in both directions Signals are free to travel in both directions

over a medium simultaneouslyover a medium simultaneously Also referred to just as Also referred to just as duplexduplex


ChannelChannel Distinct communication path between two or more nodesDistinct communication path between two or more nodes

Figure 4-6: Simplex, half-duplex, and full-duplex transmission


MultiplexingMultiplexing Allows multiple signals to travel simultaneously Allows multiple signals to travel simultaneously

over one mediumover one medium To accommodate multiple signals, single medium To accommodate multiple signals, single medium

is logically separated into is logically separated into subchannelssubchannels For each type of multiplexing:For each type of multiplexing:

Multiplexer (mux)Multiplexer (mux) is required at sending end of is required at sending end of channelchannel

Demultiplexer (demux)Demultiplexer (demux) separates the combined separates the combined signals and regenerates them in original formsignals and regenerates them in original form


Time division multiplexing (TDM)Time division multiplexing (TDM) Divides channel into multiple intervals of timeDivides channel into multiple intervals of time

Figure 4-7: Time division multiplexing


Wavelength division multiplexing (WDM)Wavelength division multiplexing (WDM) Used only with fiber-optic cableUsed only with fiber-optic cable Data is transmitted as pulses of lightData is transmitted as pulses of light Fiber-optic modem (FOM)Fiber-optic modem (FOM) is a demultiplexer used on fiber is a demultiplexer used on fiber

networks that employ WDMnetworks that employ WDM

Figure 4-9: Wavelength division multiplexing

Relationships Between NodesRelationships Between Nodes

Point-to-pointPoint-to-point Transmission involving one transmitter and Transmission involving one transmitter and

one receiverone receiver

BroadcastBroadcast Transmission involving one transmitter and Transmission involving one transmitter and

multiple receiversmultiple receivers

WebcastingWebcasting Broadcast transmission used over the WebBroadcast transmission used over the Web

Relationships Between NodesRelationships Between Nodes

Figure 4-10: Point-to-point versus broadcast transmission

Throughput and BandwidthThroughput and Bandwidth

ThroughputThroughput is amount of data the medium is amount of data the medium can transmit during a given period of timecan transmit during a given period of time Also called Also called capacitycapacity

BandwidthBandwidth measures difference between measures difference between highest and lowest frequencies a media can highest and lowest frequencies a media can transmittransmit Range of frequencies is directly related to Range of frequencies is directly related to

throughputthroughput

Transmission FlawsTransmission Flaws

Electromagnetic interference (EMI)Electromagnetic interference (EMI) Interference that may be caused by motors, Interference that may be caused by motors,

power lines, television, copiers, fluorescent lights, power lines, television, copiers, fluorescent lights, or other sources of electrical activityor other sources of electrical activity

Radiofrequency interference (RFI)Radiofrequency interference (RFI) Interference that may be generated by motors, Interference that may be generated by motors,

power lines, televisions, copiers, fluorescent power lines, televisions, copiers, fluorescent lights, or broadcast signals from radio or TV lights, or broadcast signals from radio or TV towerstowers


Figure 4-11: An analog signal distorted by noise


Figure 4-12: A digital signal distorted by noise


AttenuationAttenuation Loss of signal strength as transmission travels away from sourceLoss of signal strength as transmission travels away from source Analog signals pass through an Analog signals pass through an amplifieramplifier, which increases not , which increases not

only voltage of a signal but also noise accumulatedonly voltage of a signal but also noise accumulated

Figure 4-13: An analog signal distorted by noise, and then amplified


RegenerationRegeneration Process of retransmitting a digital signalProcess of retransmitting a digital signal

RepeaterRepeater Device used to regenerate a signalDevice used to regenerate a signal

Figure 4-14: A digital signal distorted by noise, and then repeated

Coaxial CableCoaxial Cable

Consists of Consists of central central copper core copper core surrounded surrounded by an by an insulator, insulator, braidingbraiding, , and outer and outer cover called cover called a a sheathsheath

Figure 4-15: Coaxial cable

Coaxial CableCoaxial Cable

Table 4-2: Some types of coaxial cable

Thicknet (10Base5)Thicknet (10Base5)

Also called Also called thickwire Ethernetthickwire EthernetRigid coaxial cable used on original Ethernet Rigid coaxial cable used on original Ethernet networksnetworks

IEEE designates Thicknet as IEEE designates Thicknet as 10Base510Base5 EthernetEthernetAlmost never used on new networks but you Almost never used on new networks but you may find it on older networksmay find it on older networks Used to connect one data closet to another as Used to connect one data closet to another as

part of network part of network backbonebackbone

Thicknet CharacteristicsThicknet Characteristics

ThroughputThroughput According to IEEE 802.3, Thicknet transmits According to IEEE 802.3, Thicknet transmits

data at maximum rate of 10 Mbpsdata at maximum rate of 10 Mbps

CostCost Less expensive than fiber-optic but more Less expensive than fiber-optic but more

expensive than some other types of coaxial expensive than some other types of coaxial cablecable

ConnectorConnector Can include a few different types of Can include a few different types of

connectors, which are very different from connectors, which are very different from those used on modern networksthose used on modern networks


N-series connector (or n connector)N-series connector (or n connector) Screw-and-barrel arrangement securely connects coaxial Screw-and-barrel arrangement securely connects coaxial

cable segments and devicescable segments and devices

Figure 4-18: N-Series connector


Noise immunityNoise immunity Because of its wide diameter and excellent Because of its wide diameter and excellent

shielding, has the highest resistance to noise shielding, has the highest resistance to noise of any commonly used types of network wiringof any commonly used types of network wiring

Size and scalabilitySize and scalability Because of its high noise resistance, it allows Because of its high noise resistance, it allows

data to travel longer than other types of data to travel longer than other types of cablingcabling

Thinnet (10Base2)Thinnet (10Base2)

Also known as Also known as thin Ethernetthin Ethernet

Characteristics:Characteristics: ThroughputThroughput

Can transmit at maximum rate of 10 MbpsCan transmit at maximum rate of 10 Mbps CostCost

Less expensive than Thicknet and fiber-optic cableLess expensive than Thicknet and fiber-optic cable

More expensive than twisted-pair wiringMore expensive than twisted-pair wiring ConnectorsConnectors

Connects wire to network devices with Connects wire to network devices with BNC T-connectorsBNC T-connectors

A seen in Figure 4-19, A seen in Figure 4-19, BNC barrel connectorsBNC barrel connectors are used are used to join two Thinnet cable segments togetherto join two Thinnet cable segments together


Characteristics Characteristics (cont.):(cont.): Size and scalabilitySize and scalability

Allows a maximum Allows a maximum of 185 m per of 185 m per network segment network segment (see Figure 4-20)(see Figure 4-20)

Noise immunityNoise immunityMore resistant than More resistant than twisted-pair wiringtwisted-pair wiring

Less resistant than Less resistant than twisted-pair wiringtwisted-pair wiring Figure 4-19: Thinnet BNC connectors


Signal bounceSignal bounce Caused by Caused by

improper improper termination on termination on a bus networka bus network

Travels Travels endlessly endlessly between two between two ends of ends of networknetwork

Prevents new Prevents new signals from signals from getting throughgetting through

Figure 4-20: A 10Base2 Ethernet network

Twisted-Pair (TP) CableTwisted-Pair (TP) CableColor-coded pairs of Color-coded pairs of insulated copper wires insulated copper wires twisted around each twisted around each other and encased in other and encased in plastic coatingplastic coating

Twists in wire help Twists in wire help reduce effects ofreduce effects of crosstalkcrosstalk

Number of twists per Number of twists per meter or foot known as meter or foot known as twist ratiotwist ratio

Alien CrosstalkAlien Crosstalk When signals from When signals from

adjacent cables interfere adjacent cables interfere with another cable’s with another cable’s transmissiontransmission

Figure 21: Twisted-pair cable

Shielded Twisted-Pair (STP)Shielded Twisted-Pair (STP)

STP cable consists of twisted wire pairs that are STP cable consists of twisted wire pairs that are individually insulated and surrounded by shielding individually insulated and surrounded by shielding made of metallic substancemade of metallic substance

Figure 4-22: STP cable

Unshielded Twisted-PairUnshielded Twisted-Pair

Consists of one or more insulated wire pairs Consists of one or more insulated wire pairs encased in a plastic sheathencased in a plastic sheathDoes not contain additional shieldingDoes not contain additional shielding

Figure 4-23: UTP cable

Unshielded Twisted-PairUnshielded Twisted-Pair

To manage To manage network cabling, it network cabling, it is necessary to be is necessary to be familiar with familiar with standards used on standards used on modern networks, modern networks, particularly particularly Category 3 (CAT3) Category 3 (CAT3) and Category 5 and Category 5 (CAT5)(CAT5)

Figure 4-24: A CAT5 UTP cable

Comparing STP and UTPComparing STP and UTP

ThroughputThroughput Both can transmit up to 100 MbpsBoth can transmit up to 100 Mbps

CostCost Typically, STP is more expensiveTypically, STP is more expensive

ConnectorConnector Both use Both use RJ-45RJ-45 connectors (see Figure 4-27) and data connectors (see Figure 4-27) and data

jacksjacks

Noise immunityNoise immunity STP is more noise-resistantSTP is more noise-resistant

Size and scalabilitySize and scalability Maximum segment length for both is 100 metersMaximum segment length for both is 100 meters

RJ-45 ConnectorRJ-45 Connector

Figure 4-27: An RJ-45 connector

Fiber-Optic CableFiber-Optic Cable

Contains one or Contains one or several glass several glass fibers at its fibers at its corecore Surrounding Surrounding

the fibers is a the fibers is a layer of glass layer of glass called called claddingcladding

Figure 4-28: A fiber-optic cable


Single-mode Single-mode fiberfiber Carries light Carries light

pulses along pulses along single pathsingle path

Multimode fiberMultimode fiber Many pulses of Many pulses of

light generated light generated by LED travel at by LED travel at different anglesdifferent angles Figure 4-29: Single-mode and

multimode fiber-optic cables


ThroughputThroughput Reliable in transmitting up to 1 gigabit per Reliable in transmitting up to 1 gigabit per

secondsecond

CostCost Most expensive type of cableMost expensive type of cable


Noise immunityNoise immunity Unaffected by either EMI or RFIUnaffected by either EMI or RFI

Size and scalabilitySize and scalability Network segments made from fiber can span Network segments made from fiber can span

100 meters100 meters Signals transmitted over fiber can experience Signals transmitted over fiber can experience

optical lossoptical loss


Two popular connectors used with fiber-optic cable:Two popular connectors used with fiber-optic cable: ST connectorsST connectors SC connectorsSC connectors

Figure 4-30: ST and SC fiber connectors

Atmospheric Transmission MediaAtmospheric Transmission Media

Infrared transmissionInfrared transmission InfraredInfrared networks use infrared light networks use infrared light

signals to transmit data through spacesignals to transmit data through space Direct infrared transmissionDirect infrared transmission depends depends

on transmitter and receiver remaining on transmitter and receiver remaining within line of sightwithin line of sight

In In indirect infrared transmissionindirect infrared transmission, , signals can bounce off of walls, ceilings, signals can bounce off of walls, ceilings, and any other objects in their pathand any other objects in their path

Atmospheric Transmission MediaAtmospheric Transmission Media

RF transmissionRF transmission Radio frequency (RF)Radio frequency (RF) transmission relies transmission relies

on signals broadcast over specific frequencieson signals broadcast over specific frequencies Two most common RF technologies:Two most common RF technologies:

NarrowbandNarrowband

Spread spectrumSpread spectrum

Choosing the Right Transmission Choosing the Right Transmission MediaMedia

Areas of high EMI or RFIAreas of high EMI or RFI

Corners and small spacesCorners and small spaces

DistanceDistance

SecuritySecurity

Existing infrastructureExisting infrastructure

GrowthGrowth

Chapter SummaryChapter Summary

Information can be transmitted via analog or digital Information can be transmitted via analog or digital methodologymethodology

Throughput is the amount of data a medium can Throughput is the amount of data a medium can transmit during a given period of timetransmit during a given period of time

Noise is interference that distorts an analog or Noise is interference that distorts an analog or digital signaldigital signal

Costs depend on many factorsCosts depend on many factors

There are three specifications that dictate size and There are three specifications that dictate size and scalability of networking mediascalability of networking media

Connectors connect wire to the network deviceConnectors connect wire to the network device


Coaxial cable consists of central copper core Coaxial cable consists of central copper core surrounded by an insulator and a sheathsurrounded by an insulator and a sheathThicknet cabling is a rigid coaxial cable used Thicknet cabling is a rigid coaxial cable used for original Ethernet networksfor original Ethernet networksBoth Thicknet and Thinnet coaxial cable rely Both Thicknet and Thinnet coaxial cable rely on bus topology and must be terminated at on bus topology and must be terminated at both ends with a resistorboth ends with a resistorTwisted-pair cable consists of color-coded Twisted-pair cable consists of color-coded pairs of insulated copper wires, twisted around pairs of insulated copper wires, twisted around each other and encased in plastic coatingeach other and encased in plastic coating


STP cable consists of twisted pair wires STP cable consists of twisted pair wires individually insulated and surrounded by a individually insulated and surrounded by a shielding made of metallic substanceshielding made of metallic substance

UTP cabling consists of one or more insulated UTP cabling consists of one or more insulated wire pairs encased in a plastic sheathwire pairs encased in a plastic sheath

Fiber-optic cable contains one or several Fiber-optic cable contains one or several glass fibers in its coreglass fibers in its core

On today’s networks, fiber is used primarily as On today’s networks, fiber is used primarily as backbone cablebackbone cable

Chapter Four Transmission Basics and Networking Media.

Documents

time signals

multiple signals

analog signals slide

digital signals

progress of data signals

data signal slide

duplex transmission

direction signals travel