Understanding the network.pdf - Back to Home

• Cycle—The shift in the electromagnetic wave from its peak positive
amplitude to its peak negative amplitude. The completion of a single
cycle is known as a period.
This alternating current flow is called oscillation. Common household current is 110
volts 60hz, which means the current alternates from a positive flow to a negative
flow 60 times a second. Data is sent across a computer network using a similar
method. Computers use binary ones (on) and zeros (off) to represent data. An
electrical signal that has a smooth oscillation from positive to negative is known as
a sine wave. To represent ones and zeros, a data signal or encoding scheme
combines different sine waves and specific voltages to create square waves that are
used to represent ones and zeros.
In order for the transmission signals to be understood correctly, they need to be
sent across a transmission medium that will maintain its integrity. Loss of signal is
attributed to attenuation and noise. Attenuation is the loss of structure in the signal
as it travels across the medium. Attenuation is the result of the medium's resistance
and impedance. If a signal suffers enough attenuation, it will become
unrecognizable. Noise is the result of outside electrical interference. Copper cable is
similar to a radio antenna in that it picks up outside electrical signals and
electromagnetic radiation.
These elements can alter the shape of the transmission signals and make them
unrecognizable. To ensure data integrity, network distribution schemes have
maximum and minimum distance requirements for the length of a media segment
and the distances between connected devices.
For each medium, there are ranges of frequencies that can be sent across the wire
without significant loss within a certain range. The range specifies the amount of
data that can be transmitted through the medium and is known as bandwidth. The
amount of bandwidth available is dependent on the impedance and the
signal-encoding scheme used.
Voltage Encoding Techniques
Baseband and broadband are voltage-encoding schemes used to send trans mission
signals across transmission media. You learned from the previous section that
transmission signals send data digitally (using binary coding) across the medium
using variable DC voltage. How the signal voltage is applied to the medium
determines which encoding technique will be used.