CCNA SEMESTER 1 V 3.0. CHAPTER 4 – Cable testing. Students completing this chapter should be able to:. Differentiate between sine waves and square waves. Define and calculate exponents and logarithms. Define and calculate decibels .
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CHAPTER 4 – Cable testing
Decibels are measurements of a gain or loss in the power of a signal.
Formulas for calculating decibels
The x-axis on the display represents time, and the y-axis represents voltage or current.
Analyzing signals using an oscilloscope is called time-domain analysis, because the x-axis or domain of the mathematical function represents time.
In frequency-domain analysis, the x-axis represents frequency.
Affects all transmission frequencies equally
Only affects small ranges of frequencies
Refers to the frequency range of an analogelectronic system.
The units of measurement is Hertz
Digital bandwidth measures how much information can flow from one place to another in a given amount of time.
The unit of measurement is bits per second (bps).
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.
Coaxial cable is a type of shielded cable
Fiber optic cable is used to transmit data signals by increasing and decreasing the intensity of light to represent binary ones and zeros.
Long cable lengths and high signal frequencies contribute to greater signal attenuation
Crosstalkis another from of noice.
Involves the transmission of signals from one wire to a nearby wire
Poorly terminated network cabling is a cause of crosstalk
Types of crosstalk are
Due to attenuation, crosstalk occurring further away from the transmitter creates less noise on a cable than NEXT. This is called far-end crosstalk, or FEXT.
Power Sum NEXT (PSNEXT) measures the cumulative effect of NEXT from all wire pairs in the cable.
Untwisting of wire pairs must be kept to an absolute minimum to reduce crosstalk of data or noise signals from an adjacent wire pair and to ensure reliable LAN communications.
The Ethernet standard specifies that each of the pins on an RJ-45 connector have a particular purpose. A NIC transmits signals on pins 1 and 2, and it receives signals on pins 3 and 6. The wires in UTP cable must be connected to the proper pins at each end of a cable.
Short circuit.Two wires are connected to each other
Open circuit. The wire does not attach properly at the connector
Category 6 cable must meet more rigorous frequency testing standards than Category 5 cable.
A fiber test instrument checks whether the optical link loss budget has been exceeded. If the fiber fails the test, the cable test instrument should indicate where the optical discontinuities occur along the length of the cable link. Usually, the problem is one or more improperly attached connectors
Calibrated Light Source and Power Meter
A quality cable tester similar to the Fluke DSP-4000 series or Fluke OMNIScanner2 can perform all the test measurements required for Cat 5, Cat 5e, and Cat 6 cable certifications of both permanent links and channel links.
Fluke DSP-LIA013 Channel/Traffic Adapter for Cat 5e