Module 4: Cable Testing

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Module 4 Cable Testing

• CCNA 1
• Version 3.0

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Waves

• A wave is energy traveling from one place to
  another waves disturbance
• A bucket of water that is completely still has no
  waves because there is no disturbances
• Ocean waves can be described in terms of their
  height, or amplitude, which is measured in
  meters.
• The higher the wave, the higher amplitude it has
• They can also be described in terms of how
  frequent
• The frequency is the number of waves that reach
  the shore each second, measured in Hertz.
• The period is the amount of time to complete one
  cycle (one wave)
• Hertz 1 wave per second, or one cycle per
  second.

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High amplitude high frequency
High amplitude low frequency
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Low amplitude and high frequency
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More on Waves

• Networking focuses on voltage waves on copper
  media, light waves in optical fiber, and
  alternating electric and magnetic fields called
  electromagnetic waves.
• The amplitude of a electrical signal still
  represents height, but it is measured in volts
  instead of meters
• If a disturbance is deliberately caused, and
  involves a fixed, predictable duration, it is
  called a pulse.
• Pulses determine the value of the data being
  transmitted.

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Sine Waves analog

• Sine waves are periodic, which means that they
  repeat the same pattern at regular intervals
• Occur naturally and change regularly over time
• Distance from earth to the sun
• Distance from the ground while riding a Ferris
  wheel
• Time of day that the sun rises
• No two adjacent points on a graph have same value
  
• Since sine waves are continuously varying, they
  are examples of analog waves

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Analog Signals

• A Amplitude (height or depth of wave)
• T Period (time to complete 1 wave cycle)
• F Frequency (how often are they reaching shore)
• Continuous voltage
• Voltage varies as time progresses
• Humans speak in analog
• Voices rise and falls as words are emphasized
• Analog and digital bandwidth are common ways in
  which the capacities of communication systems are
  measured

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Square Waves digital

• Square waves, like sine waves, are periodic -
  however, square wave graphs do not continuously
  vary with time
• Wave holds one value for some time, and then
  suddenly changes to a different value
• 1s to 0s (on and off)
• PCs speak in digital
• Repeat same pattern at regular intervals
• Repeat the flat pattern on both top and bottom of
  wave

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Digital Signals

• A Amplitude (height of pulses)
• Discrete pulses (not continuous)
• Determine the value of the data being transmitted
• Deliberate, fixed disturbances of predictable
  duration
• Can only have one to two states (1/0, on/off)
• Voltage jumps between levels
• Digital bandwidth measures speed of the
  transmission

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Numbering Systems

• Base 2 binary
• Base 10 decimal
• Base 16 hexadecimal

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Decibels

• Decibel (dB) a unit of measurement important in
  describing networking signals
• dB measures the loss or gain of the power of a
  wave
• A way of measuring signals on copper, optical,
  and wireless media.
• The decibel is related to the exponents and
  logarithms
• There are two formulas for calculating decibels
  
• dB 10 log10 (Pfinal / Preferrence) (power
  formula)
• dB 20 log10 (Vfinal / Vreference) (voltage
  formula)

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The Variables Represent the Following Values

• dB measures the loss or gain of the power of a
  wave
• log10 implies that the number in parenthesis will
  be transformed using the base 10 logarithm rule
• Pfinal is the delivered power measured in Watts
• Preference is the original power measured in
  Watts
• Vfinal is the delivered voltage measured in Volts
  
• Vreference is the original voltage measured in
  Volts

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• Power formula measures light waves on optical
  fiber and radio waves in the air
• Voltage formula measures electromagnetic waves
  on copper cables

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• One of the most important facts of the
  information age is that data symbolizing
  characters, words, pictures, video, or music can
  be represented electrically by voltage patterns
  on wires and in electronic devices.
• The data represented by these voltage patterns
  can be converted to light waves or radio waves,
  and then back to voltage waves.

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Oscilloscope

• Electronic device used to view electrical
  signals, such as voltage waves and pulses.
• The x-axis on the display represents time, and
  the y-axis represents voltages or current.
• Usually 2 y-axis inputs, so 2 waves can be
  observed and measured simultaneously
• Analyzing signals using an oscilloscope is called
  time-domain analysis, because the x-axis or
  domain of the mathematical function represents
  time.

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Noise in Time and Frequency

• While noise usually refers to undesirable sounds,
  noise related to communications refers to
  undesirable signals.
• Noise can originate from natural and
  technological sources, and is added to the data
  signals

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Noise in Time and Frequency

• Noise related to communications refers to
  undesirable signals.
• There are many possible sources of noise
• Nearby cables which carry data signals
  crosstalk
• Radio frequency interference (RFI), which is
  noise from other signals being transmitted nearby
  radio transmitters
• Electromagnetic interference (EMI) - noise from
  nearby sources such as electrical motors and
  lights
• Laser noise at the transmitter or receiver of an
  optical signal
• Noise is added to the data signal this is NOT
  good!

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Bandwidth

• Two types in networking analog bandwidth and
  digital bandwidth.
• Analog bandwidth typically refers to the
  frequency range of an analog electronic system
  (radio station)
• Measured in Hertz, the same as the unit of
  frequency.
• Examples of analog bandwidth values are 3 kHz for
  telephony, 20 kHz for audible signals, 5 kHz for
  AM radio stations, and 200 MHz for FM radio
  stations.

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Bandwidth

• Digital bandwidth measures how much information
  can flow from one place to another in a given
  amount of time (bps)
• Physical media, current technologies, and the
  laws of physics limit bandwidth.

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Signaling Over Copper and Fiber Optic Cabling

• On copper cable, data signals are represented by
  voltage levels that represent binary ones and
  zeros.
• The voltage levels are measured with respect to a
  reference level of zero volts at both the
  transmitter and the receiver.
• This reference level is called the signal ground.
  
• It is important that both transmitting and
  receiving devices refer to the same zero volt
  reference point. When they do, they are said to
  be properly grounded.

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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 .

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Signaling Over Copper and Fiber Optic Cabling

• Coaxial cable is a type of shielded cable.
• Has a braided conductive shielding.
• The braided shielding is electrically grounded to
  protect the inner conductor from external
  electrical noise.
• The shielding also helps eliminate signal loss by
  keeping the transmitted signal confined to the
  cable.
• This helps make coaxial cable less noisy than
  other types of copper cabling, but also makes it
  more expensive.
• The need to ground the shielding and the bulky
  size of coaxial cable make it more difficult to
  install than other copper cabling.

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Signaling Over Copper and Fiber Optic Cabling

• STP cable contains an outer conductive shield
  that is electrically grounded to insulate the
  signals from external electrical noise.
• STP also uses inner foil shields to protect each
  wire pair from noise generated by the other
  pairs.
• STP cable is more expensive, more difficult to
  install, and less frequently used than UTP.
• UTP contains no shielding and is more susceptible
  to external noise but is the most frequently used
  because it is inexpensive and easier to install.

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Signaling Over Copper and Fiber Optic Cabling

• Fiber optic cable is used to transmit data
  signals by increasing and decreasing the
  intensity of light to represent binary ones and
  zeros.
• Optical signals are not affected by electrical
  noise, and optical fiber does not need to be
  grounded.
• 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

• Copper Media
• Coaxial, STP UTP (most common)
• Binary ones and zeros represent
• 5 volts
• 0 volts
• Fiber Optic
• Binary ones and zeros represent
• light/no light
• Increasing/decreasing light intensity

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Attenuation and Insertion Loss on Copper Media

• Attenuation - the decrease in signal amplitude
  over the length of a link (signal deterioration)

• Attenuation is expressed in decibels (dB) using
  negative numbers smaller is better!
• Causes
• Long cable runs, defective connectors, energy
  leaks through insulations

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Impedance

• Impedance - a measurement of the resistance of
  the cable to alternating current (AC) and is
  measured in ohms
• The normal, or characteristic, impedance of a
  Cat5 cable is 100 ohms
• Impedance mismatch - If a connector is improperly
  installed on Cat5, it will have a different
  impedance value than the cable.

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Impedance

• Attenuation happens 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.
• When this returning reflection strikes the first
  discontinuity, some of the signal rebounds in the
  direction of the original signal, creating
  multiple echo effects.
• The echoes strike the receiver at different
  intervals making it difficult for the receiver to
  accurately detect data values on the signal.
• This is called jitter and results in data errors.

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Impedance

• Thus problems associated with impedance
  mismatches in copper cabling are
• Jitter
• Reflection

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Sources of Noise on Copper Media

• Noise is any electrical energy on the
  transmission cable that makes it difficult for a
  receiver to interpret the data sent from the
  transmitter
• Possible sources radio transmitters, electrical
  motors, crosstalk
• Crosstalk involves the transmission of signals
  from one wire to a nearby wire
• Common units of measure used in formulas for
  calculating the amount of gain or loss include
• Watts Volts - Decibels

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Types of Crosstalk

• Near-end Crosstalk (NEXT)
• computed as the ratio of voltage amplitude
  between the test signal and the crosstalk signal
  when measured from the same end of the link
• Far-end Crosstalk (FEXT)
• not as significant a problem as NEXT
• Power Sum Near-end Crosstalk (PSNEXT)
• measures the cumulative effect of NEXT from all
  wire pairs in the cable
• computed for each wire pair based on the NEXT
  effects of the other three pairs

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Shielding in Copper-Based Media

• Protects one pair of wires within the cable from
  noise generated by electrical signals on another
  pair
• Protects the data signals from external sources
  of noise
• Eliminate signal loss by keeping the transmitted
  signal confined to the cable

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Cable Testing Standards

• Wire map 568B standard
• Insertion loss 568B standard
• 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 568B standard
• Cable length
• Delay skew

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Cable Testing Standards Wire Mapping
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Time-based Parameters

• Propagation delay - simple measurement of how
  long it takes for a signal to travel along the
  cable being tested
• Delays are measured in hundredths of nanoseconds.
  One nanosecond is one-billionth of a second, or
  0.000000001 second
• TIA/EIA-568-B standard sets a limit for
  propagation delay for the various categories of
  UTP
• The delay difference between pairs is called
  delay skew

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Testing Optical Fiber

• A fiber link consists of two separate glass
  fibers functioning as independent data pathways.
• No crosstalk problems on fiber optic cable
• Because absence of electrical signals
• No generation of electromagnetic waves
• No electrical interference
• Attenuation properties better than copper
• Testing fiber optic cable primarily involves
  shining a light down the fiber and measuring
  whether a sufficient amount of light reaches the
  receiver.
• Optical link loss budget acceptable signal loss

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A New Standard

• On June 20, 2002, the Category 6 (or Cat 6)
  addition to the TIA-568 standard was published.
• The official title of the standard is
  ANSI/TIA/EIA-568-B.2-1
• Cables certified as Cat 6 cable must pass all ten
  tests.

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Module 4 Cable Testing

• CCNA 1
• Version 3.0

THE END