SUNY Ulster Cisco Semester 1

1
SUNY UlsterCisco Semester 1

• Unit 4 Cable Testing
• K. Wick CCAI

2
Background

• Signals and Noise
• Note to instructor Have curriculum open

3
Sine Waves

• Shape
• Amplitude
• Frequency
• Wavelength
• Period 1/f
• Objective 4.1.1 has a nice demo of sinusoidal
  waves.

4
Square Waves

• Objective 4.1.2 does NOT show a pure square wave.
  
• It shows a square wave with a DC component. (Wave
  is offset from zero)
• Square wave vs Periodic Pulse vs Pulse

5
Logarithms

• Logarithms are a way to express differences
  between numbers that are orders of magnitude
  apart.
• If we ask To what power do we raise ten to be
  equal to a number in question, that is the
  logarithm of the number.
• Log 1 0 because 100 1
• Log 8 0.9031 because 100..9031 8

6
Logarithms

• Run interactive activities in 4.1.3
• The logarithm of ten raised to any power is the
  power itself.
• Log 1000 log 103 3
• Log 1,000,000 log 106 6

7
Decibels

• Cisco says, There are two formulas for
  calculating decibels
• dB 10 log10 (Pfinal / Pref)
• dB 20 log10 (Vfinal / Vreference)
• They are partially correct.
• These formulas depend on equal input and output
  impedance.

8
Decibels

• Answers to examples in 4.1.4
• -30 decibels. A loss
• 1.7 microwatts
• -113.9 decibels. A major loss.

9
Measuring Devices

• A multimeter or digital multimeter (DMM) measures
  voltage, current, resistance, continuity and
  sometimes other parameters.
• An oscilloscope gives a visual display of voltage
  versus time.
• A Cable meter will test a cable for correct wiring

10
Fourier Analysis ????

• Cisco is insane!
• OK here is a basic
• Every complex waveform can be made by adding a
  series of sinusoids of proper frequency and
  amplitude.
• A square wave is the sum of the series
• A sin(x) A/3 sin(3x) A/5 sin(5x)

11
Building a Square Wave
12
Measuring Devices

• Spectrum Analyzer.
• Gives a bar graph representing all frequencies
  and amplitudes present in a waveform.

13
Measuring Devices

• Time Delay Reflectometer
• Because the wires inside the cable are twisted,
  signals actually travel farther than the physical
  length of the cable.
• A TDR measurement sends a pulse signal down a
  wire pair and measures the amount of time
  required for the pulse to return on the same wire
  pair.

14
Measuring Devices

• Time Delay Reflectometer
• Also used to identify the distance to wiring
  faults such as shorts and opens.
• This presumes that we know the propagation speed
  of the specific wire type.

15
Ten tests for Category 5 cable

• 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

16
Types of Signal Degradation
17
Propagation and Delay

• Propagation means travel of a signal
• Propagation Delay is the time it takes a signal
  to travel from point to point.
• It is measured in hundreths of nanoseconds.
• Skew The difference in delay between pairs.
• Read CISCO questions carefully, watch the exact
  wording!

18
Attenuation

• Attenuation means loss of signal amplitude
• If a signal gets too small, it can not be decoded
  at the receiving end

19
Reflection

• Sometimes on a physical medium a signal travels
  to the end of the medium and part of the signal
  reflects back toward the source.
• This reflection can interfere with the original
  signal.
• Reflections are especially bad with impedance
  mismatches in the physical layer.
• (Caused by wrong media or bad connections)
• Nominal Z for Cat 5 cable is 100 ohms

20

• Attenuation (signal deterioration) and noise
  (signal interference) cause problems in networks
  because the data is not recognizable when it is
  received.
• Proper attachment of cable connectors and proper
  cable installation are important. If standards
  are followed in these areas, attenuation and
  noise levels are minimized.

21
Noise Where are the 1s and 0s?
5 volts
22
Analog vs Digital Bandwidth

• Analog bandwidth typically refers to the
  frequency range of an analog electronic system.
• The units of measurement for analog bandwidth is
  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.

23
Analog vs Digital Bandwidth

• Digital bandwidth measures how much information
  can flow from one place to another in a given
  amount of time.
• The fundamental unit of measurement for digital
  bandwidth is bits per second (bps).
• Since LANs are capable of speeds of millions of
  bits per second, measurement is expressed in
  kilobits per second (Kbps) or megabits per second
  (Mbps).

24
Analog vs Digital Bandwidth

• During cable testing, analog bandwidth is used to
  determine the digital bandwidth of a copper
  cable.
• Analog frequencies are transmitted from one end
  and received on the opposite end.
• The two signals are then compared, and the amount
  of attenuation of the signal at each frequency is
  calculated.
• In general, media that will support higher analog
  bandwidths without high degrees of attenuation
  will also support higher digital bandwidths.

25
Noise Pickup

• External
• Impulse
• Radio - EMI RFI
• Line to ground
• Motor
• Crosstalk - NEXT
• Twisted Pairs minimize noise pickup

26
Crosstalk and other evils
27
Crosstalk

• Near End at near end of link.
• Far End
• Power Sum cumulative effect of crosstalk on all
  pairs in the cable.
• For all Larger negative numbers mean LESS
  crosstalk. (-30dB vs -20dB).
• Some testers leave out the minus sign.

28
Wiring Errors (Fluke Tester)
Or Crossover Cable
29
Fiber Optic Cable Testing

• Remember that a fiber link consists of two
  separate glass fibers functioning as independent
  data pathways.
• Fiber optic cable does not suffer from crosstalk
  or noise pickup.
• Attenuation does occur on fiber links, but to a
  lesser extent than on copper cabling.
• Fiber links are subject to the optical equivalent
  of UTP impedance discontinuities.

30
Fiber Optic Cable Testing

• Just as with UTP cable, improperly installed
  connectors are the main cause of light reflection
  and signal strength loss in optical fiber.
• If attenuation weakens the light signal at the
  receiver, then data errors will result. Testing
  fiber optic cable primarily involves shining a
  light down the fiber and measuring whether a
  sufficient amount of light reaches the receiver.
• If the fiber fails the test, the cable test
  instrument should indicate where the optical
  discontinuities occur along the length of the
  cable link.

31
Category 6 UTP and STP

• Cables certified as Cat 6 cable must pass the
  same ten tests as Cat 5 cable.
• Cat 6 cable must pass these tests with higher
  scores to be certified.
• It must be capable of carrying frequencies up to
  250 MHz (vs 100 MHz) and must have lower levels
  of crosstalk and return loss.

32
End of Chapter 4