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Semester 1Semester 1

CHAPTER 4CHAPTER 4

Le Chi TrungLe Chi Trung

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ContentContent

• Electricity

• The digital multimeter - LAB

• Signals and noise

• The encoding of networking signals

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ScheduleSchedule

No Name Est time No Name10-May Chapter 3 Online Exam

4.1 Electricity 0:20:004.3 Signals and noise in communications systems 0:30:00 Discussion

4.4 The encodeing of networking signals 0:10:00

12-May 4.2 The digital multimeter 0:30:004.2.1 Safe Handling and use of a multimeter4.2.2 Resistance measurement4.2.3 Voltage measurement4.2.4 Series circuits4.2.5 Communication circuits

Summary Chapter 4 0:30:0015-May Chapter 4 Online Exam

DayLesson Lab

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ELECTRICITYELECTRICITY

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Periodic tablePeriodic table

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ConductorsConductors

• Materials that allow electrons to flow through them with great ease.

• These electrons can easily be freed from the atom when voltage is applied.

• Examples :

– Metals : Gold, Silver, Copper...

– Water.

– Humans!!

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InsulatorsInsulators

• Materials that allow electrons to flow through them with great difficulty, or not at all.

• Electron orbits are very close to the nucleus.

• Examples :

– Plastic, glass, wood …

– Air and other gases.

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Semi-conductorsSemi-conductors

• Materials where the amount of electricity they conduct can be controlled.

• Because silicon is widely available (sand), it is the material we use for computer chips.

• Examples :

– Carbon.

– Germanium.

– Silicon.

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Parts of an atomParts of an atom

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Forces within an atomForces within an atom

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Stable atomStable atom

• Why don't the electrons fly in towards the protons?

– Velocity of electrons keep them in orbit around nucleus.

• Why don't the protons fly away from each other?

– Nuclear force keep the protons don't fly away from each other.

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Static electricityStatic electricity

• Electrons have been loosened from the atom and stay in one place, without moving.

• Electrostatic discharge (ESD).

– ESD, though usually harmless to people, can create serious problems for sensitive electronic equipment.

– How to handle the printed circuit boards ?

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Measuring electricity:Measuring electricity: Voltage Voltage

• Force or pressure caused by the separation of electrons and protons.

• Symbol: U.

• Volt (V).

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Measuring electricity:Measuring electricity: Current Current

• The flow of charges that is created when electrons move.

• Symbol: I.

• Ampere (A).

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Measuring electricity:Measuring electricity: Resistance Resistance

• Property of a material that opposes, and can control the electrical flow.

• Symbol: R.

• Ohm (Ω).

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Simple circuitSimple circuit

I = U / R

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Electrical definitions:Electrical definitions: AC and DC AC and DC

• Alternating Current (AC):

– Electrical current flows in both directions; positive and negative terminals continuously trade places (polarity).

• Direct Current (DC):

– Electrical current flows in one direction; negative to positive.

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OscilloscopeOscilloscope

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Electrical definitions:Electrical definitions: Impedance Impedance

• Total opposition to the flow of electrons. Equivalent to resistance but for AC and pulsed circuits.

• Symbol: Z.

• Ohm (Ω).

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Electrical definitions:Electrical definitions: Ground Ground

• Ground can refer to the place on the earth.

• Ground can also mean the reference point, or the 0 volts level, when making electrical measurements.

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Safety ground wire (SGW)Safety ground wire (SGW)

• SGW prevents electrons from energizing metal parts of the equipments.

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ReviewReview

• Conductor, insulator, semi-conductors.

• Measuring electricity.

• Definitions.

• Grounding.

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THE DIGITAL MULTIMETERTHE DIGITAL MULTIMETER

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MultimeterMultimeter

• Voltage measurement.

• Current measurement.

• Resistance measurement.

• Continuity measurement.

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Preparation for LABPreparation for LAB

• 4.2.1: Use of multimeter.

• 4.2.2: Resistance measurement.

• 4.2.3: Voltage measurements.

• Lab companion:

– 4.2.1.

– 4.2.2.

– 4.2.3.

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ReviewReview

• Using digital multimeter.

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SIGNALS AND NOISESIGNALS AND NOISE

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SignalsSignals

• Signal refers to a form to carry information.

• Example:

– A desired electrical voltage.

– A light pattern.

– A modulated electromagnetic wave.

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Analog signalsAnalog signals

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Digital signalsDigital signals

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Fourier synthesisFourier synthesis

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One bit on physical mediaOne bit on physical media

• Voltage level

• Light intensity

• Burst of waves

• Bits must arrive at the destination undistorted in order to be properly interpreted.

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Bits on travelBits on travel

• Propagation

• Attenuation

• Reflection

• Timing Problems

• Collisions

• Noise

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PropagationPropagation

• A bit takes at least a small amount of time to travel (propagate) down the wire.

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Propagation (cont.)Propagation (cont.)

• If the receiving device cannot handle the speed of the arriving bits, data will be lost.

• To avoid data loss, the device either...

– Buffers the arriving bits into memory for later processing, or.

– Sends a message to the source to slow down the speed of propagation.

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AttenuationAttenuation

• The signal degrades or losses amplitude as it travels along the medium.

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Attenuation (cont.)Attenuation (cont.)

• Loss of amplitude means that the receiving device can no longer distinguish a 1 bit from a 0 bit.

• Attenuation is prevented by:– Not exceeding a medium’s distance

requirement (100 meters for Cat 5 cable).

– By using repeaters that regenerate the signal.

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ReflectionReflection

• Reflection refers to reflected energy.

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Reflection (cont.)Reflection (cont.)

• When impedance is mismatched, the digital signal can “bounce back” (reflect) causing it to be distorted as bits run into each other.

• If enough energy is reflected, the binary, two-state system can become confused by all the extra energy bouncing around.

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Timing problemsTiming problems

• Dispersion, Jitter, Latency

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Timing problems (cont.)Timing problems (cont.)

• Dispersion: similar to attenuation, is the broadening of a signal as it travels down the media.

• Jitter: caused by unsynchronized clocking signals between source and destination. This means bits will arrive later or earlier than expected.

• Latency: is the delay of a network signal.

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CollisionsCollisions

• A collision happens when two bit are on a point of media at the same time.

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Collisions (cont.)Collisions (cont.)

• Collisions occur in broadcast topologies where devices share access to the network media.

• A collision happens when two devices attempt to communicate on the shared-medium at the same time.

• Collisions destroy data requiring the source to retransmit.

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NoiseNoise

• Noise is unwanted additions to the signal.

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Noise (cont.)Noise (cont.)

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Noise (cont.)Noise (cont.)

• Too much noise can corrupt a bit, thus destroying the message.

• Noise is unavoidable.

• Kinds of noise:– Thermal Noise.

– Near end cross talk.

– AC Power/Reference Ground Noise.

– Electromagnetic Interference (EMI).

– Radio Frequency Interference (RFI).

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Noise:Noise: Thermal Thermal

• Due to the random motion of electrons, thermal noise is unavoidable.

• Our signaling is usually strong enough to override the effects of thermal noise.

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Noise:Noise: NEXT NEXT

• Near end cross talk (NEXT) : when two wires are near each other, energy from one wire can wind up in an adjacent wire and vice versa.

• Cross talk is avoided by a network technician using proper installation procedures including:– Strict adherence to RJ-45 termination

procedures (chapter 5).

– Using high quality twisted pair cabling.

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Noise:Noise: AC Power/Reference groundAC Power/Reference ground

• The signal reference ground is not completely isolated from the electrical ground.

• AC power line act as an antenna for electrical noise interferes with the digital signals.

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Noise:Noise: EMI/RFI EMI/RFI

• Sources of EMI/RFI include:– Fluorescent lighting (EMI).

– Electrical motors (EMI).

– Radio systems (RFI).

• Two ways to prevent EMI/RFI Noise:– Through shielding the wires in the cable

with a metal braid or foil.

– Through cancellation the wires are twisted together in pairs to provide self-shielding.

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CancellationCancellation

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ReviewReview

• Digital signal.

• By what bits are distorted.

• Kind of noise.

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BASIC OF ENCODINGBASIC OF ENCODING

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EncodingEncoding

• Encoding is the process of converting information into a form that can travel on a physical link.

• Example:

– Smoke signals.

– Morse mode.

– Telephone.

– TV/Radio.

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Signal modulationSignal modulation

• AM (amplitude modulation): the amplitude, or height, of a carrier sine wave is varied to carry the message.

• FM (frequency modulation): the frequency, or wiggly-ness, of the carrier wave is varied to carry the message.

• PM (phase modulation): the phase, or beginning and ending points of a given cycle, of the wave is varied to carry the message.

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Binary encodingBinary encoding

• TTL: Transistor-Transistor logic

• NRZ-L: Non-Return to Zero-Level

• NRZI: Non-Return to Zero-Inverted

• NRZ-M: Non-Return to Zero-Mark

• Manchester Tx (Transmit)

• MLT3: Multi-Level Threshold-3

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Binary encoding:Binary encoding: TTL TTL

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Binary encoding:Binary encoding: NRZ-L, I NRZ-L, I

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Binary encoding:Binary encoding: Manchester Manchester

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Binary encoding:Binary encoding: MLT3 MLT3

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Binary encoding:Binary encoding: Used Used

• Ethernet:

– Manchester Tx+, Tx-

• Token-ring:

– Differential Manchester

• Fast Ethernet:

– MLT-3

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ReviewReview

• Encoding and Modulation.

• Binary encoding schemes.