High Voltage!!High Voltage!!By: Allan Johnson

Parts of An AtomParts of An Atom

ProtonProton

NeutronNeutron

ElectronElectron

electron

neutron

proton

Flowing ElectronsFlowing Electrons

Electrons are negatively chargedElectrons are negatively charged Protons are positively chargedProtons are positively charged Opposite charges attractOpposite charges attract Velocity of electrons keep them in orbit Velocity of electrons keep them in orbit

around nucleusaround nucleus Electrons pulled free from the atom is what Electrons pulled free from the atom is what

we call electricity!we call electricity!

““Dynamic” ElectricityDynamic” Electricity

Electricity can be viewed as a dynamic Electricity can be viewed as a dynamic process.process.

Dynamic means “changing.”Dynamic means “changing.” Electrons are changing—moving from one Electrons are changing—moving from one

atom to another.atom to another. This flowing of electrons is called an This flowing of electrons is called an

“electrical current.”“electrical current.”

Static ElectricityStatic Electricity

““Static” means stationary or unchanging.Static” means stationary or unchanging. Electrons have been “loosened” from the Electrons have been “loosened” from the

atom and stay in one place.atom and stay in one place. The electrons have “voltage” but lack a The electrons have “voltage” but lack a

“current.”“current.” A conductor supplies the current—or path—A conductor supplies the current—or path—

for static electricity to discharge.for static electricity to discharge.

ESDESD

Electrostatic Discharge (ESD) is the process Electrostatic Discharge (ESD) is the process of static electrons jumping to a conductor.of static electrons jumping to a conductor.

Simple experiment:Simple experiment:– Rub your shoes on a carpet (this will cause a Rub your shoes on a carpet (this will cause a

voltage to build up around your body)voltage to build up around your body)– Touch a metal door knob (the metal is a Touch a metal door knob (the metal is a

conductor providing a path for the “flow of conductor providing a path for the “flow of electrons”—high voltage electricity!!)electrons”—high voltage electricity!!)

ConductorsConductors

Conductors have a large number of loosely Conductors have a large number of loosely attached electrons.attached electrons.

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

See this web page for a demonstration: See this web page for a demonstration: – Free the Electron!Free the Electron!

Examples of ConductorsExamples of Conductors

MetalsMetals– GoldGold

– SilverSilver

– Copper (Cat 5 Cable)Copper (Cat 5 Cable)

WaterWater

Humans!!Humans!!

InsulatorsInsulators

Material with a high resistance to electrical Material with a high resistance to electrical current.current.

Electron orbits are very close to the nucleus.Electron orbits are very close to the nucleus. Examples:Examples:

– PlasticPlastic– GlassGlass– WoodWood– Air and other gasesAir and other gases

SemiconductorsSemiconductors

With semiconductor materials, the flow of With semiconductor materials, the flow of electrons can be precisely controlled.electrons can be precisely controlled.

Examples:Examples:– CarbonCarbon– GermaniumGermanium– And Silicon!!And Silicon!!

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

Networking Uses All Three!!Networking Uses All Three!!

We use We use conductorsconductors to provide a path for the to provide a path for the electrical current.electrical current.– For example, copper wire in our cables.For example, copper wire in our cables.

We use We use insulatorsinsulators to keep the flow of to keep the flow of electrons going in one direction.electrons going in one direction.– For example, the plastic sheathing on cables.For example, the plastic sheathing on cables.

We use We use semiconductorssemiconductors to precisely control to precisely control the flow of electrons.the flow of electrons.– For example, computer chips use silicon.For example, computer chips use silicon.

Measuring ElectricityMeasuring Electricity VoltageVoltage—force or pressure caused by the —force or pressure caused by the

separation of electrons and protons.separation of electrons and protons.– Unit of measurement: Volts (V)Unit of measurement: Volts (V)

CurrentCurrent—the path provided for the free —the path provided for the free flow of electrons in an electrical circuit.flow of electrons in an electrical circuit.– Unit of measurement: Ampere (amp)Unit of measurement: Ampere (amp)

ResistanceResistance—impedance or opposition to the —impedance or opposition to the flow of electrons: flow of electrons: conductor=low resistance; conductor=low resistance;

insulators=high insulators=high resistance.resistance.– Unit of measurement: ohms Unit of measurement: ohms (Ω)(Ω)

Two Types of CurrentTwo Types of Current

Alternating Current (AC)Alternating Current (AC)—electrical —electrical current flows in both directions; positive current flows in both directions; positive and negative terminals continuously trade and negative terminals continuously trade places (polarity)places (polarity)– Example: Electricity provided by CPLExample: Electricity provided by CPL

Direct Current (DC)Direct Current (DC)—electrical current —electrical current flows in one direction; negative to positiveflows in one direction; negative to positive– Example: Electricity provided by batteriesExample: Electricity provided by batteries

Three Required PartsThree Required Partsof an Electrical Circuitof an Electrical Circuit

Source or Battery Complete PathResistance

Safety Ground WireSafety Ground Wire

Safety Ground Wire Safety Ground Wire prevents electrons prevents electrons from energizing metal from energizing metal parts of the computer.parts of the computer.

Without grounding, Without grounding, severe shock and fires severe shock and fires can occur.can occur.

Safety grounds are Safety grounds are connected to the connected to the exposed metal partsexposed metal parts of of the computer’s the computer’s chassis.chassis.

Multimeter BasicsMultimeter Basics

A Multimeter is used to measure:A Multimeter is used to measure:– VoltageVoltage

– ResistanceResistance

– Continuity (level of resistance)Continuity (level of resistance)

When using a Multimeter, you When using a Multimeter, you must properly set it to either AC must properly set it to either AC or DC, depending on the voltage or DC, depending on the voltage you’re trying to measure.you’re trying to measure.

Analog vs. Digital SignalsAnalog vs. Digital Signals

Analog signals have a continuously Analog signals have a continuously varying voltage-versus-time graphvarying voltage-versus-time graph

Analog vs. Digital SignalsAnalog vs. Digital Signals

Digital signals have a square wave Digital signals have a square wave with instant transitions from low to with instant transitions from low to high voltage states (0 to 1).high voltage states (0 to 1).

Networks Use Digital SignalingNetworks Use Digital Signaling

Bits are represented by either no voltage (0) or Bits are represented by either no voltage (0) or +3 to +6 Volts (1).+3 to +6 Volts (1).

A Signal Reference Ground attached close to A Signal Reference Ground attached close to a computer’s digital circuits establishes the a computer’s digital circuits establishes the baseline for no voltage.baseline for no voltage.

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

What six things can distort a bit?What six things can distort a bit?

CollisionsCollisions

Bits Are Distorted By...Bits Are Distorted By...

Let’s look at each in more detail

PropagationPropagation

CollisionsCollisions

PropagationPropagation

AttenuationAttenuation

ReflectionReflection

NoiseNoise

Timing ProblemsTiming Problems

AttenuationAttenuation

ReflectionReflection

NoiseNoise

Timing ProblemsTiming Problems

Bits Are Distorted By...Bits Are Distorted By...

PropagationPropagation AttenuationAttenuation ReflectionReflection NoiseNoise Timing ProblemsTiming Problems CollisionsCollisions

PropagationPropagation Propagation means Propagation means traveltravel A bit takes at least a small amount of time A bit takes at least a small amount of time

to travel (propagate) down the wire.to travel (propagate) down the wire. If the receiving device cannot handle the If the receiving device cannot handle the

speed of the arriving bits, data will be lost.speed of the arriving bits, data will be lost. To avoid data loss, the computer either...To avoid data loss, the computer either...

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

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

Bits Are Distorted By...Bits Are Distorted By...

PropagationPropagation AttenuationAttenuation ReflectionReflection NoiseNoise Timing ProblemsTiming Problems CollisionsCollisions

AttenuationAttenuation Attenuation is the loss of signal strength.Attenuation is the loss of signal strength. The signal degrades or losses amplitude as The signal degrades or losses amplitude as

it travels (propagates) along the mediumit travels (propagates) along the medium Loss of amplitude means that the receiving Loss of amplitude means that the receiving

device can no longer distinguish a 1 bit device can no longer distinguish a 1 bit from a 0 bit.from a 0 bit.

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

requirement (100 meters for Cat 5 cable)requirement (100 meters for Cat 5 cable)– By using repeaters that “amplify” the signalBy using repeaters that “amplify” the signal

Bits Are Distorted By...Bits Are Distorted By...

PropagationPropagation AttenuationAttenuation ReflectionReflection NoiseNoise Timing ProblemsTiming Problems CollisionsCollisions

ReflectionReflection Reflection refers to Reflection refers to reflected energy reflected energy

resulting from an impedance mismatchresulting from an impedance mismatch between the NIC and network media.between the NIC and network media.

Impedance is the resistance to the flow of Impedance is the resistance to the flow of current in a circuit provided by the current in a circuit provided by the insulating material.insulating material.

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

Bits Are Distorted By...Bits Are Distorted By...

PropagationPropagation AttenuationAttenuation ReflectionReflection NoiseNoise Timing ProblemsTiming Problems CollisionsCollisions

NoiseNoise

Noise is unwanted additions to the signalNoise is unwanted additions to the signal Noise is unavoidableNoise is unavoidable Too much noise can corrupt a bit turning a Too much noise can corrupt a bit turning a

binary 1 into a binary 0, or a 0 into a 1, thus binary 1 into a binary 0, or a 0 into a 1, thus destroying the message.destroying the message.

There are five kinds of noise:There are five kinds of noise:– NEXT A; Thermal Noise; Impulse/Reference NEXT A; Thermal Noise; Impulse/Reference

Ground Noise; EMI/RFI; & NEXT BGround Noise; EMI/RFI; & NEXT B

NoiseNoise

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

Reference Ground NoiseReference Ground Noise can usually only can usually only be solved by an electrical contractor.be solved by an electrical contractor.

Noise threats we can control directly Noise threats we can control directly include:include:– NEXT (Near End Cross Talk) whether at the NEXT (Near End Cross Talk) whether at the

source (A) or the destination (B)source (A) or the destination (B)– EMI/RFIEMI/RFI

NEXT NoiseNEXT Noise

Near End Cross Talk (NEXT) originates Near End Cross Talk (NEXT) originates from other wires in the same cable.from other wires in the same cable.

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

procedures (Chapter 5);procedures (Chapter 5);– Using high quality twisted pair cablingUsing high quality twisted pair cabling

EMI/RFI NoiseEMI/RFI Noise

EMI (Electromagnetic Interference) and EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) attack RFI (Radio Frequency Interference) attack the quality of electrical signals on the cable.the quality of electrical signals on the cable.

Sources of EMI/RFI include:Sources of EMI/RFI include:– Fluorescent lighting (EMI)Fluorescent lighting (EMI)– Electrical motors (EMI)Electrical motors (EMI)– Radio systems (RFI)Radio systems (RFI)

EMI/RFI Noise ExampleEMI/RFI Noise Example

Source computer sends out Source computer sends out a digital signal.a digital signal.

Along the path, the signal Along the path, the signal encounters EMI noise.encounters EMI noise.

The digital signal and EMI The digital signal and EMI combine to distort the signal.combine to distort the signal.

Digital Signal

EMI

Distorted Signal

EMI/RFI NoiseEMI/RFI Noise

Two ways to prevent EMI/RFI Noise:Two ways to prevent EMI/RFI Noise:– Through Through shieldingshielding the wires in the cable with a the wires in the cable with a

metal braid or foil. (Increases cost and diameter metal braid or foil. (Increases cost and diameter of the cable)of the cable)

– Through Through cancellationcancellation the wires are the wires are twistedtwisted together in pairs to provide self-shielding together in pairs to provide self-shielding within the network media.within the network media.

Canceling EMI/RFI NoiseCanceling EMI/RFI Noise

UTP Cat 5 has eight UTP Cat 5 has eight wires twisted into four wires twisted into four pairs.pairs.

In each pair, one wire is In each pair, one wire is sending data and the sending data and the other is receiving.other is receiving.

As the electrons flow As the electrons flow down the wire, they down the wire, they create a small, circular create a small, circular magnetic field around the magnetic field around the wire.wire.

Since the two wires are Since the two wires are close together, their close together, their opposing magnetic fields opposing magnetic fields cancel each other.cancel each other.

They also cancel out They also cancel out outside magnetic fields outside magnetic fields (EMI/RFI).(EMI/RFI).

Twisting of the wires Twisting of the wires enhances cancellationenhances cancellation

Canceling EMI/RFI NoiseCanceling EMI/RFI Noise

Bits Are Distorted By...Bits Are Distorted By...

PropagationPropagation AttenuationAttenuation ReflectionReflection NoiseNoise Timing ProblemsTiming Problems CollisionsCollisions

Timing ProblemsTiming Problems DispersionDispersion—similar to attenuation; is the —similar to attenuation; is the

broadening of a signal as it travels down the broadening of a signal as it travels down the media.media.

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

LatencyLatency—is the —is the delaydelay of a network signal of a network signal caused by:caused by:– Time it takes a bit to travel to its destinationTime it takes a bit to travel to its destination– Devices the bit travels throughDevices the bit travels through

Bits Are Distorted By...Bits Are Distorted By...

PropagationPropagation AttenuationAttenuation ReflectionReflection NoiseNoise Timing ProblemsTiming Problems CollisionsCollisions

CollisionsCollisions Collisions occur in broadcast topologies Collisions occur in broadcast topologies

where devices share access to the network where devices share access to the network media.media.

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

Collisions destroy data requiring the source Collisions destroy data requiring the source to retransmit.to retransmit.

The prevention of collisions will be The prevention of collisions will be discussed in more detail later in the semester.discussed in more detail later in the semester.

Final Topic: EncodingFinal Topic: Encoding

Encoding is the process of converting Encoding is the process of converting binary data into a form that can travel on a binary data into a form that can travel on a physical communications link.physical communications link.

For our purposes, you only need to know For our purposes, you only need to know the two types of encoding schemes most the two types of encoding schemes most commonly used:commonly used:– ManchesterManchester– NRZ (non-return to zero)NRZ (non-return to zero)

Good Luckon the

Test!!