Layer 1 Electronics and Signals

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Layer 1 Electronics and Signals

• Shawn Shuoh-Ren Tsai
• Cisco Academy Training Center
• David Ta-Wei Shih
• CGUIC

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atom

• The names of the parts of the atom are
• nucleus - the center part of the atom, formed by
  protons and neutrons
• protons - particles have a positive charge , and
  along with neutrons, form the nucleus
• neutrons - particles have no charge (neutral),
  and along with protons, form the nucleus
• electrons - particles have a negative charge, and
  orbit the nucleus

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ESD

• static electricity.
• Loosened electrons that stay in one place,
  without moving and with a negative charge
• electrostatic discharge (ESD).
• If these static electrons have an opportunity to
  jump to a conductor, this can lead to
  electrostatic discharge (ESD).

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Types of electrical materials

• Electrical insulators
• Electrical conductors
• Electrical semiconductors

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Electrical Semiconductors

• Semiconductors are materials where the amount of
  electricity they conduct can be precisely
  controlled
• These materials are listed together in one column
  of the periodic chart.
• Examples include carbon (C), germanium (Ge), and
  the alloy, gallium arsenide (GaAs). The most
  important semiconductor, the one that makes the
  best microscopic-sized electronic circuits, is
  silicon (Si).

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Measuring electricity

• Voltage
• V / volt
• Current
• I / Amp
• Impedance
• Z / ohm (O)
• Resistance
• R / ohm (O)

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Multimeter

• The multimeter can perform voltage, resistance,
  and continuity
• Continuity refers to the level of resistance of a
  path
• If a path is intentionally made into a
  low-resistance path, for use by two connected
  electrical devices, then the path has what is
  called continuity. If a path is unintentionally
  made into a low-resistance path, then it is
  called a short circuit.

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Multimeter (Cont.)

• DC VoltageThe meter must be set to DC when
  measuring DC voltages.
• AC VoltageThe meter must be set to AC when
  measuring AC voltages

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Analog and Digital Signals

• An analog signal has the following
  characteristics
• is wavy
• has a continuously varying voltage-versus-time
  graph
• is typical of things in nature
• has been widely used in telecommunications for
  over 100 years
• amplitude (A) - its height and depth - and its
  period (T) - length of time to complete 1 cycle.

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Analog and Digital Signals (Cont.)

• A digital signal has the following
  characteristics
• has discrete, or jumpy, voltage-versus-time
  graphs
• square wave
• can be built by using the right combination of
  sine waves.

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Propagation

• Propagation
• Travel from one place to another
• The time it takes the bit to travel from one end
  of the medium and back again is referred to as
  the round trip time, (RTT).

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Attenuation

• Attenuation
• the loss of signal strength
• Carefully choose media
• Use repeater

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Reflection

• Reflection
• When voltage pulses, or bits, hit a discontinuity
  some energy can be reflected. 
• If not carefully controlled, this reflected
  energy can interfere with later bits.

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Noise

• Noise is unwanted additions to voltage, optical,
  or electromagnetic signals
• keep the signal-to-noise (S/N) ratio as high as
  possible

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EMI/RFI

• electromagnetic interference (EMI), and radio
  frequency interference (RFI)
• lighting, electrical motors, and radio systems
• Two techniques that cable designers have used
  successfully in dealing with EMI and RFI are
• shielding and cancellation
• Twisting the wires can enhance this cancellation
  effect
• In cable that employs shielding, a metal braid or
  foil surrounds each wire pair or group of wire
  pairs.

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Dispersion, jitter, and latency

• Dispersion is when the signal broadens in time
• If the clock on the source host is not
  synchronized with the destination, which is quite
  likely, you will get timing jitter.
• Latency
• delay

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Collision

• A collision occurs when two bits from two
  different communicating computers are on a
  shared-medium at the same time.

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