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An understanding of the following key
points should have been achieved:
- Waves are energy traveling from one
place to another, and are created by disturbances. All waves have
similar attributes such as amplitude, period, and frequency.
- Sine waves are periodic,
continuously varying functions. Analog signals look like sine waves.
- Square waves are periodic functions
whose values remain constant for a period of time and then change
abruptly. Digital signals look like square waves.
- Exponents are used to represent very
large or very small numbers. The base of a number raised to a
positive exponent
is equal to the base multiplied by itself exponent times. For
example, 103 = 10x10x10 = 1000.
- Logarithms are similar to exponents.
A logarithm to the base of 10 of a number equals the exponent to
which 10 would have to be raised in order to equal the number. For
example, log10 1000 = 3 because 103 = 1000.
- Decibels are measurements of a gain
or loss in the power of a signal. Negative values represent losses
and positive values represent gains.
- Time-domain analysis is the graphing
of voltage or current with respect to time using an oscilloscope.
Frequency-domain analysis is the graphing of voltage or power with
respect to frequency using a spectrum analyzer.
- Undesirable signals in
a communications system are called noise. Noise originates from other cables, RFI, and EMI.
White noise affects all frequencies, while narrowband interference
affects only a certain subset of frequencies.
- Analog bandwidth is the frequency
range that is associated with certain analog transmission, such as
television or FM radio.
- Digital bandwidth measures how much
information can flow from one place to another in a given amount of
time. Its units are in various multiples of bits per second.
- Most LAN problems occur at the
physical layer. The only way to prevent or troubleshoot many of
these problems is through the use of cable testers.
- Proper cable installation according
to standards increases LAN reliability and performance.
- Copper media is available in
shielded and unshielded forms. Unshielded cable is more susceptible
to noise.
- Signal degradation is due to various
factors such as noise, attenuation, impedance mismatch, and several
types of crosstalk. These factors cause decreased network
performance.
- 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.
- Optical fiber must also be tested
according to networking standards.
- Category 6 cable must meet more
rigorous frequency testing standards than Category 5 cable.
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