Module 4

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Module 4

• Cable Testing

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Waves

• Pulse If a disturbance is deliberately caused,
  and involves a fixed, predictable duration.
• Pulses are important in electrical signals
  because they determine the value of the data
  being transmitted.

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Sine Waves

• Sine waves are periodic, which means that they
  repeat the same pattern at regular intervals.
• Sine waves are graphical representations of many
  natural occurrences that change regularly over
  time.
• Sine waves are continuously varying, which means
  that no two adjacent points on the graph have the
  same value.

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Sine Waves
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Square Waves

• Square waves, like sine waves, are periodic which
  means that they repeat the same pattern at
  regular intervals.
• Square wave graphs do not continuously vary with
  time.
• Their value is held for some time, and then
  quickly changes back to the original value.

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Square Waves
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Exponents and logarithms

• In networking, there are three important number
  systems
• Base 2 binary
• Base 10 decimal
• Base 16 hexadecimal

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Calculating Gain or LossUnits of Measure

• Watts
• Decibels
• Volts

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Calculating Gain or LossUnits of Measure

• dB 10 log10 (Pfinal / Pref)
• dB 20 log10 (Vfinal / Vreference)
• The first formula describes decibels in terms of
  power (P), and the second in terms of voltage
  (V).
• Typically, light waves on optical fiber and radio
  waves in the air are measured using the power
  formula.
• Electromagnetic waves on copper cables are
  measured using the voltage formula.

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Viewing signals in time and frequency

• Analyzing signals using an oscilloscope is called
  time-domain analysis, because the x-axis or
  domain of the mathematical function represents
  time.
• There are usually two y-axis inputs, so two waves
  can be observed and measured at the same time.

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Noise in Time and Frequency

• Noise can originate from natural and
  technological sources, and is added to the data
  signals in communications systems.
• Sources
• Nearby cables which carry data signals
  crosstalk.
• Radio frequency interference (RFI), which is
  noise from other signals being transmitted nearby
  
• Electromagnetic interference (EMI), which is
  noise from nearby sources such as motors and
  lights
• Laser noise at the transmitter or receiver of an
  optical signal

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Bandwidth

• Two ways of considering communication system
  capacity are analog bandwidth and digital
  bandwidth.
• Analog bandwidth typically refers to the
  frequency range of an analog electronic system.
• Digital bandwidth measures how much information
  can flow from one place to another in a given
  amount of time. Speed of Transmission

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Signaling over Copper and Fiber Optic Cabling

• There are two basic types of copper cable
  shielded and unshielded.
• In shielded cable, shielding material protects
  the data signal from external sources of noise
  and from noise generated by electrical signals
  within the cable.
• The shielding also helps eliminate signal loss by
  keeping the transmitted signal confined to the
  cable.
• Uses inner foil shields to protect each wire pair
  from noise generated by the other pairs.

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Signaling over Copper and Fiber Optic Cabling

• Coaxial cable is a type of shielded cable.
• It uses
• braided conductive shielding.
• inner foil shields sometimes referred to as
  Screen
• Fiber optic cable is used to transmit data
  signals by increasing and decreasing the
  intensity of light to represent binary ones and
  zeros.
• Light/No light.
• Optical signals are not affected by electrical
  noise, and optical fiber does not need to be
  grounded. It is also easier to install and
  terminate. Therefore, optical fiber is often
  used between buildings and between floors within
  the building.

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Signaling over Copper and Fiber Optic Cabling

• Fiber Optic cabling prevents crosstalk
• Absence of electrical signals
• No electromagnetic wave generation

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Attenuation and Insertion loss on Copper Media

• There are several factors that contribute to
  attenuation.
• Long cable lengths.
• Low signal frequencies.
• Defective connectors

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Attenuation and Insertion loss on Copper Media

• Impedance is a measurement of the resistance of
  the cable to alternating current (AC) and is
  measured in ohms.
• If a connector is improperly installed on Cat5,
  it will have a different impedance value than the
  cable. This is called an impedance discontinuity
  or an impedance mismatch.

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Attenuation and Insertion loss on Copper Media

• Impedance discontinuities cause attenuation
  because a portion of a transmitted signal will be
  reflected back to the transmitting device rather
  than continuing to the receiver, much like an
  echo.
• This is called jitter or reflection and results
  in data errors.

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Sources of Noise on Copper Media

• Crosstalk involves the transmission of signals
  from one wire to a nearby wire.

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Cable Testing Standards

• The TIA/EIA-568-B standard specifies ten tests
  that a copper cable must pass if it will be used
  for modern, high-speed Ethernet LANs.
• Wire map
• Insertion loss
• Near-end crosstalk (NEXT)
• Power sum near-end crosstalk (PSNEXT)
• Equal-level far-end crosstalk (ELFEXT)
• Power sum equal-level far-end crosstalk
  (PSELFEXT)
• Return loss
• Propagation delay
• Cable length
• Delay skew

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Cable Testing Standards
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