High Voltage

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High Voltage!!
By Allan Johnson
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Parts of An Atom

• Proton
• Neutron
• Electron

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Flowing Electrons

• Electrons are negatively charged
• Protons are positively charged
• Opposite charges attract
• Velocity of electrons keep them in orbit around
  nucleus
• Electrons pulled free from the atom is what we
  call electricity!

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Dynamic Electricity

• Electricity can be viewed as a dynamic process.
• Dynamic means changing.
• Electrons are changingmoving from one atom to
  another.
• This flowing of electrons is called an
  electrical current.

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Static Electricity

• Static means stationary or unchanging.
• Electrons have been loosened from the atom and
  stay in one place.
• The electrons have voltage but lack a
  current.
• A conductor supplies the currentor pathfor
  static electricity to discharge.

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ESD

• Electrostatic Discharge (ESD) is the process of
  static electrons jumping to a conductor.
• Simple experiment
• Rub your shoes on a carpet (this will cause a
  voltage to build up around your body)
• Touch a metal door knob (the metal is a conductor
  providing a path for the flow of electronshigh
  voltage electricity!!)

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Conductors

• Conductors have a large number of loosely
  attached electrons.
• These electrons can easily be freed from the
  nucleus of the atom when voltage is applied.
• See this web page for a demonstration
• Free the Electron!

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Examples of Conductors

• Metals
• Gold
• Silver
• Copper (Cat 5 Cable)
• Water
• Humans!!

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Insulators

• Material with a high resistance to electrical
  current.
• Electron orbits are very close to the nucleus.
• Examples
• Plastic
• Glass
• Wood
• Air and other gases

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Semiconductors

• With semiconductor materials, the flow of
  electrons can be precisely controlled.
• Examples
• Carbon
• Germanium
• And Silicon!!
• Because silicon is widely available (sand), it is
  the material we use for computer chips.

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Networking Uses All Three!!

• We use conductors to provide a path for the
  electrical current.
• For example, copper wire in our cables.
• We use insulators to keep the flow of electrons
  going in one direction.
• For example, the plastic sheathing on cables.
• We use semiconductors to precisely control the
  flow of electrons.
• For example, computer chips use silicon.

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Measuring Electricity

• Voltageforce or pressure caused by the
  separation of electrons and protons.
• Unit of measurement Volts (V)
• Currentthe path provided for the free flow of
  electrons in an electrical circuit.
• Unit of measurement Ampere (amp)
• Resistanceimpedance or opposition to the flow of
  electrons conductorlow resistance
  insulatorshigh resistance.
• Unit of measurement ohms (O)

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Two Types of Current

• Alternating Current (AC)electrical current flows
  in both directions positive and negative
  terminals continuously trade places (polarity)
• Example Electricity provided by CPL
• Direct Current (DC)electrical current flows in
  one direction negative to positive
• Example Electricity provided by batteries

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Three Required Partsof an Electrical Circuit
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Safety Ground Wire

• Safety Ground Wire prevents electrons from
  energizing metal parts of the computer.
• Without grounding, severe shock and fires can
  occur.
• Safety grounds are connected to the exposed metal
  parts of the computers chassis.

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Multimeter Basics

• A Multimeter is used to measure
• Voltage
• Resistance
• Continuity (level of resistance)
• When using a Multimeter, you must properly set it
  to either AC or DC, depending on the voltage
  youre trying to measure.

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Analog vs. Digital Signals

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

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Analog vs. Digital Signals

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

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Networks Use Digital Signaling

• Bits are represented by either no voltage (0) or
  3 to 6 Volts (1).
• A Signal Reference Ground attached close to a
  computers digital circuits establishes the
  baseline for no voltage.
• Bits must arrive at the destination undistorted
  in order to be properly interpreted.
• What six things can distort a bit?

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Bits Are Distorted By...
Propagation
Propagation
Attenuation
Attenuation
Reflection
Reflection
Noise
Noise
Timing Problems
Timing Problems
Collisions
Collisions
Lets look at each in more detail
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Bits Are Distorted By...

• Propagation
• Attenuation
• Reflection
• Noise
• Timing Problems
• Collisions

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Propagation

• Propagation means travel
• A bit takes at least a small amount of time to
  travel (propagate) down the wire.
• If the receiving device cannot handle the speed
  of the arriving bits, data will be lost.
• To avoid data loss, the computer 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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Bits Are Distorted By...

• Propagation
• Attenuation
• Reflection
• Noise
• Timing Problems
• Collisions

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Attenuation

• Attenuation is the loss of signal strength.
• The signal degrades or losses amplitude as it
  travels (propagates) along the medium
• 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 mediums distance requirement
  (100 meters for Cat 5 cable)
• By using repeaters that amplify the signal

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Bits Are Distorted By...

• Propagation
• Attenuation
• Reflection
• Noise
• Timing Problems
• Collisions

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Reflection

• Reflection refers to reflected energy resulting
  from an impedance mismatch between the NIC and
  network media.
• Impedance is the resistance to the flow of
  current in a circuit provided by the insulating
  material.
• When impedance is mismatched, the digital signal
  can bounce back (reflect) causing it to be
  distorted as bits run into each other.

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Bits Are Distorted By...

• Propagation
• Attenuation
• Reflection
• Noise
• Timing Problems
• Collisions

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Noise

• Noise is unwanted additions to the signal
• Noise is unavoidable
• Too much noise can corrupt a bit turning a binary
  1 into a binary 0, or a 0 into a 1, thus
  destroying the message.
• There are five kinds of noise
• NEXT A Thermal Noise Impulse/Reference Ground
  Noise EMI/RFI NEXT B

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Noise

• Our signaling is usually strong enough to
  override the effects of thermal noise.
• Reference Ground Noise can usually only be solved
  by an electrical contractor.
• Noise threats we can control directly include
• NEXT (Near End Cross Talk) whether at the source
  (A) or the destination (B)
• EMI/RFI

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NEXT Noise

• Near End Cross Talk (NEXT) originates from other
  wires in the same cable.
• Crosstalk 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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EMI/RFI Noise

• EMI (Electromagnetic Interference) and RFI (Radio
  Frequency Interference) attack the quality of
  electrical signals on the cable.
• Sources of EMI/RFI include
• Fluorescent lighting (EMI)
• Electrical motors (EMI)
• Radio systems (RFI)

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EMI/RFI Noise Example

• Source computer sends out a digital signal.

• Along the path, the signal encounters EMI noise.

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

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EMI/RFI Noise

• Two ways to prevent EMI/RFI Noise
• Through shielding the wires in the cable with a
  metal braid or foil. (Increases cost and diameter
  of the cable)
• Through cancellation the wires are twisted
  together in pairs to provide self-shielding
  within the network media.

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Canceling EMI/RFI Noise

• UTP Cat 5 has eight wires twisted into four
  pairs.
• In each pair, one wire is sending data and the
  other is receiving.
• As the electrons flow down the wire, they create
  a small, circular magnetic field around the wire.

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Canceling EMI/RFI Noise

• Since the two wires are close together, their
  opposing magnetic fields cancel each other.
• They also cancel out outside magnetic fields
  (EMI/RFI).
• Twisting of the wires enhances cancellation

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Bits Are Distorted By...

• Propagation
• Attenuation
• Reflection
• Noise
• Timing Problems
• Collisions

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Timing Problems

• Dispersionsimilar to attenuation is the
  broadening of a signal as it travels down the
  media.
• Jittercaused by unsynchronized clocking signals
  between source and destination. This means bits
  will arrive later or earlier than expected.
• Latencyis the delay of a network signal caused
  by
• Time it takes a bit to travel to its destination
• Devices the bit travels through

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Bits Are Distorted By...

• Propagation
• Attenuation
• Reflection
• Noise
• Timing Problems
• Collisions

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Collisions

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

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Final Topic Encoding

• Encoding is the process of converting binary data
  into a form that can travel on a physical
  communications link.
• For our purposes, you only need to know the two
  types of encoding schemes most commonly used
• Manchester
• NRZ (non-return to zero)

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Good Luck on the Test!!