CompTIA exam study guide presentations by instructor Brian Ferrill, PACE-IT (Progressive, Accelerated Certifications for Employment in Information Technology) "Funded by the Department of Labor, Employment and Training Administration, Grant #TC-23745-12-60-A-53" Learn more about the PACE-IT Online program: www.edcc.edu/pace-it

1. Basic network
concepts I.

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Instructor, PACE-IT Program – Edmonds Community College
Areas of Expertise Industry Certification
 PC Hardware
 Network Administration
 IT Project Management
 Network Design
 User Training
 IT Troubleshooting
Qualifications Summary
Education
 M.B.A., IT Management, Western Governor’s University
 B.S., IT Security, Western Governor’s University
Entrepreneur, executive leader, and proven manger
with 10+ years of experience turning complex issues
into efficient and effective solutions.
Strengths include developing and mentoring diverse
workforces, improving processes, analyzing
business needs and creating the solutions
required— with a focus on technology.

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– Encapsulation.
– Modulation.
PACE-IT.

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Basic network concepts I.

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TheOSI(OpenSystems
Interconnection)reference
modelusesalayeredapproach
toenabledisparatedevicestobe
abletocommunicateeffectively.
During communication between two devices or nodes, each layer
is only responsible for being understood by the corresponding
layer on the other device.
As data flows down from the application layer through to the
physical layer, it is encapsulated—layer information is wrapped
around the data—at each layer with information to help the
corresponding layer at the other end of the communication line
understand what is happening.
As the data is received at the other end, it is de-encapsulated—
unwrapped—as it moves up the OSI stack.
Basic network concepts I.

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– Encapsulation at work.
» The application layer begins the process by sending data that is
encapsulated, or wrapped, with application layer control
information to the presentation layer.
• The encapsulated data is called a PDU (protocol data unit).
» The application layer PDUs are segmented by the presentation
layer, with each segment being encapsulated by presentation
layer control information. They are now presentation layer
PDUs.
• The process of segmenting and encapsulating continues
down through the OSI stack until it is transmitted as bits by
the physical layer.
» The receiving physical layer passes the bits to the receiving
data link layer, which reads the data link layer PDU information
and then de-encapsulates and de-segments it, sending the new
packets to the network layer as network layer PDUs.
• The process of de-encapsulating and de-segmenting
continues up the OSI stack until it is received by the
application layer, where it is finally fully de-encapsulated and
fully reassembled.
Basic network concepts I.

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Basic network concepts I.

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The physical layer of the OSI
stack is responsible for
transmitting bits (literal zeros
and ones) of data across some
form of media (e.g., a cable).
The question arises, how does the physical layer
transmit the data across the media?
The bits of data are modulated (or encoded) by the
physical layer and placed on the carrier signal
(which can also be called a carrier channel) of the
media, which carries the modulated data on to its
next destination.
Once the bits are received, they are de-modulated
(un-encoded) by the receiving physical layer.
Basic network concepts I.

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– Carrier signal defined.
» A carrier signal is a standard waveform, usually in the form of a
sine wave, that is used as the base carrier of another input
signal.
• A sine wave is a mathematical curve that is represented by a
smooth repeating oscillation.
– Modulation defined.
» Modulation is the process of varying one or more properties of
a carrier signal with an input signal—usually for the purpose of
conveying information.
• Modulation can be used to encode digital network traffic onto
media that uses a digital carrier signal (e.g., using an ISDN
connection between two networks).
• Modulation can be used to encode a digital signal onto a
media that uses an analog carrier signal—digital network
traffic traveling over the public switched telephone network
(PSTN).
• Multiplexing can be used to increase the number of
modulated signals that can be placed onto a carrier signal.
Basic network concepts I.

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– Multiplexing explained.
» The type of carrier signal will determine if multiplexing can
occur.
• A baseband carrier signal cannot have multiplexing occur, as
the modulated signal will consume all of the available
frequency (or channel width).
• Multiplexing can be utilized on a broadband carrier channel,
as each modulated input is assigned a portion of the channel
width of the carrier signal.
» Multiplexing can use one of two methods to weave streams of
modulated signal into the carrier signal.
• Frequency division multiplexing is the process of
mathematically dividing the carrier channel frequency into
multiple segments and assigning the results to modulated
input signals.
• Time division multiplexing is the process of mathematically
dividing the carrier channel width into multiple time segments
and assigning the time slots to different modulated signal
input streams.
Basic network concepts I.

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– Baseband.
» A stream of data that is sent over a carrier channel as a digital
modulated signal.
• The digital signal will take all of the carrier signal’s available
frequency (or time).
• While the modulated input does take all of the carrier
channel’s available frequency, the communication is
bidirectional (it can flow back and forth).
– Broadband.
» A stream of data that is sent over a carrier channel as an
analog modulated signal.
• The analog signal will be assigned a portion of either the
carrier channel’s available frequency or time.
• While the modulated input doesn’t take all of the carrier
channel’s available frequency, the communication is not
bidirectional. For two way communication to take place,
multiplexed channels must be created (a channel for each
direction).
Basic network concepts I.

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Basic network concepts I.
The OSI network model relies upon a layered approach to ensure
communication can occur between disparate systems. The OSI model uses
encapsulation to help the layers understand the communication. When
sending, each layer segments and encapsulates the data that it receives
from the layer above it. When receiving the data, each layer unwraps its
layer’s control information and hands it up to the next layer.
Topic
Encapsulation.
Summary
The physical layer is responsible for modulating the data stream and
placing it on the network’s carrier signal. A carrier signal is a waveform that
can be represented as a sine wave. Modulation is the process of changing
one or more properties of the carrier channel, as a means of encoding data
into the signal. In some situations, multiplexing—either through frequency
or time division—can be used to place multiple data streams onto a carrier
signal at the same time. Baseband is when a digital modulated signal
occupies all of the carrier channel. Broadband is when an analog modulated
signal occupies only a portion of a carrier channel, allowing multiplexing to
take place.
Modulation.

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