Transmission Basics
February 21 (Day); February 16 (Night)
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Transmission refers to either the process of transmitting of signals or the process of signals
after they have been transmitted.
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Analog and Digital Signaling
o
On a network, information can be transmitted via one of two signaling methods:
analog or digital.
o
In analog signals, voltage varies continuously and appears as a wavy line over
time.
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An example of an analog wave would be a sound wave.
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Properties of the analog wave:

A wave’s amplitude is a measure of its strength at any given
point in time.
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Frequency is the number of times that a wave’s amplitude cycles
from its starting point, through its highest amplitude and its
lowest amplitude, and back to its starting point over a fixed point
in time.

The distance between corresponding points on a wave’s cycle is
called its wavelength.
1. Wavelength varies inversely frequency.
o
Digital signals are composed of pulses of precise, positive voltages and zero
voltages.
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A pulse of positive voltage represents a 1.
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A pulse of zero voltage represents a 0.
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Noise is any type of interference that may degrade a signal. Analog waves are more
susceptible to noise than digital signals.
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Overhead is a term used to describe the nondata information that must accompany data for a
signal to be properly routed and interpreted by the network.
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Transmission Direction:
o
In cases where data travels in only one direction, the transmission is considered
simplex.
o
In half-duplex transmission, signals may travel in both directions over a medium
but in only one direction at a time.
o
When signals are free to travel in both directions over a medium simultaneously,
the transmission is considered full-duplex.
o
A channel is a distinct communications path between nodes. There are physical
channels and logical channels.
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o
A physical channel is basically the cable.
A form of transmission that allows multiple signals to travel simultaneously over
one medium is known as multiplexing.

For example, the data from three computers could be multiplexed into
three different signals on the same cable. Therefore, one physical
channel would contain three logical channels.
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When data is sent through multiplexing, it would be de-multiplexed on
the other end.
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Relationships Between Nodes:
o
Point-to-point transmission involves only one transmitter and one receiver.
o
Broadcast transmission involves one transmitter and multiple receivers.
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Baseband and Broadband:
o
Baseband is a transmission form in which digital signals are sent through direct
current (DC) pulses applied to the wire.
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A baseband signal requires exclusive use of the wire.
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Every device on a baseband network shares the same channel. When one
node is transmitting data on a baseband system, all other devices must
wait. They are half-duplex.
o
Broadband is a transmission form that uses multiple frequency ranges.
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Broadband has a very high transmission rate.
Transmission Flaws:
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Noise is any undesirable influence that may degrade or distort a signal.

Common sources of noise are waves from electrical devices (motors,
power line, TVs) or radio waves (TV towers, radio towers).
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Crosstalk occurs when a signal traveling on one wire interferes with a
signal traveling on an adjacent wire.
o
Attenuation is the loss of a signal’s strength as it travels away from its source.
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Both analog and digital signals are strengthened en route so that they can
travel farther.
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Amplifiers increase the voltage of analog signals.
An analog wave being distorted and then amplified. After being amplified, the wave is stronger, but not
as good as normal.
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Digital signals may be retransmitted in their original form through the
use of a repeater.
A digital signal being distorted and then repeated. After being repeated, the signal is as good as normal.
o
Latency is the delay between by the transmission of a signal and its receipt.
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Latency is most affected by the length of cable involved (how far does it
have to go) and the existence of any intervening connectivity devices
(how many stops does it have to make).