PowerPoint PresentationLayer 1: Electronics and Signals
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Understand the basics of digital multimeters
Understand the basics of signals and noise in communications systems
Understand the basics of encoding networking signals
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Protons – particles that have positive charge
Neutrons – particles that have no charge (neutral)
Electrons – particles that have negative charge and orbit the nucleus
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Creating Stable Atoms
Electrons in certain atoms can be pulled free from the atom and made to flow – this is electricity (a free flow of electrons).
Static Electricity
Loosened electrons that stay in one place, without moving and with a negative charge.
Can create electrostatic discharge, which can create serious problems for computers.
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Conductors
Semiconductors
Carbon, germontum, gallium arsenide, silicon
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Graphing AC and DC Voltage
Constructing a Simple Series Electrical Current
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Surge suppressors, uninterruptible power supplies, and wall outlets all connect to a transformer and to the earth ground.
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Network Signal Propagation
Propagation delay (half the round-trip time) for a bit traveling from Host A to Host B
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Network Reflection Noise
Caused by discontinuities in the medium (that is, kinks in a cable or poorly terminated cables)
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Noise
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Noise
Next
When two wires are near each other and untwisted, energy from one wire can wind up in an adjacent wire.
NEXT-A Near End Crosstalk at computer A.
NEXT-B Near End Crosstalk at computer B.
Thermal Noise
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Noise
EMI and RFI
Electromagnetic interference
Flow of Current
Electrical current in a wire induces a magnetic field around the wire.
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Collision
Occurs when 2 bits from 2 different communicating computers are on a shared medium at the same time.
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Messages in Terms of Bits
Bits string together to form bytes, and bytes link together to form frames.
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