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 II.

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Instructor, PACE-IT Program – Edmonds Community College
Areas of expertise Industry Certifications
 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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PACE-IT.
– Network transmission concepts.
– CSMA/CD and CSMA/CA.

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Basic network concepts II.

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Basic network concepts II.
– Wavelength.
» A measurement of the distance between peaks in the wave
patterns emitted by electromagnetic radiation (e.g., light, radio,
and microwave).
• Each type of electromagnetic radiation falls into a specific
range of wavelengths. By modifying a wavelength, data can
be encoded into the wavelength and transmitted to a receiving
device, which then decodes the transmission.
– Baud rate and bit rate.
» The baud rate was originally used to measure the speed of a
telegraph transmission. It is a measure of the number of state
changes in a given period of time.
• The usual state change that was measured was electricity
(e.g., the number of times the state changed from .5 volts to
1.5 volts).
» The bit rate is a measure of the number of zeros and ones that
can be transmitted across a medium in a given period of time
(usually measured in bits per second, or bps).
• The bit rate is a more accurate measure of transmission
throughput than the baud rate.

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Basic network concepts II.
– Sampling size.
» When converting from an analog audio signal to a digital signal,
a computer (or other device) captures the analog audio
waveform and mathematically converts the captured sample
into different wavelengths (which is how we get the discrete
sounds). This occurs over a specific period of time, which is
called the size of the sample.
– Carrier detect and carrier sense.
» Carrier detect is when a device can only tell when a carrier
signal or channel is present by the reception of a control signal.
• The presence of the control signal signifies that transmissions
can occur.
• The control signal controls the order of transmissions, so data
collisions are not possible.
• The control signal can also be used to establish the maximum
speed of the transmission that can be used.
» Carrier sense is when a device uses feedback from a receiver
to determine if a carrier channel is present.
• If a carrier signal is detected, the device can send
transmissions.
• Data transmission collisions are possible with carrier sense.

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Basic network concepts II.

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The carrier detect method of
network transmission works
well when there are just a
few nodes that need to be
connected together.
However, as the number of nodes that need to
transmit increases, the efficiency of carrier detect
begins to decrease to the point where it can become
unmanageable.
Although the carrier sense method of network
transmission is not as efficient when the scale of the
network is small, as the number of nodes increases,
it becomes more efficient than the carrier detect
method.
Basic network concepts II.

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Basic network concepts II.
– CSMA/CD (Carrier Sense Multiple Access
with Collision Detection).
» Uses the carrier sense method of network transmission.
• Every device on the network uses feedback from a receiver to
determine if a carrier channel is present.
» Every device connected to the network has an equal
opportunity to place a transmission on the carrier channel (the
multiple access part of the name).
» Before placing a transmission on the carrier channel, a device
will listen to the channel to determine if another node is
transmitting.
• If it detects a signal on the carrier signal, the node will wait
before attempting to transmit.
• If no signal is detected, the node is free to send.
» If two devices send a transmission at the same time, a collision
between the transmissions is possible.
• Sending devices listen for transmission collisions. If a collision
is detected, a jamming signal is sent informing all nodes that a
collision has taken place.
• All devices that receive the jamming signal, will wait for a
random amount of time before attempting to transmit.

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Basic network concepts II.
– CSMA/CA (Carrier Sense Multiple Access
with Collision Avoidance).
» Operates in the same manner as CSMA/CD with one exception, it
uses a collision avoidance scheme through the use of a controlling
device.
• Before attempting to send data, a device will place a specific
signal on the network called a request to send (RTS) packet.
• If no other device is utilizing the network, the controlling device
will respond with another specific signal called a clear to send
(CTS) packet.
• Once the sending device receives the CTS, it knows it can send
a transmission without a collision occurring.
– CSMA/CD vs. CSMA/CA.
» CSMA/CD is better suited for high speed, high throughput
networks and is the specified network transmission standard for
the 802.3 Ethernet networking standard, as it has a low amount of
network overhead.
» CSMA/CA is better suited for lower speed, lower throughput types
of networks where the possibility of data collisions is higher. It is
the specified standard for 802.3 wireless (Wi-Fi) networks.

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Basic network concepts II.
Wavelength is a measure of distance between the peaks of a waveform;
transmissions can be encoded into a wavelength. Baud rate is a measure of
the number of state changes over time. Bit rate is a measure of the number
of bits transmitted over time. Sampling size is used in the process of turning
analog sound into a digital signal. With carrier detect, a control signal is
used to denote the presence of a carrier signal. With carrier sense, a device
uses feedback from a receiver to detect the presence of a carrier signal.
Topic
Network transmission
concepts.
Summary
The carrier detect method is efficient as long as the number of nodes is
small. Carrier sense becomes the more effective method as more devices
need to send network traffic. With CSMA/CD, all devices have an equal
opportunity to place transmissions on the network. If a collision occurs, it is
detected and, after a random length back off period, devices will resend the
data. With CSMA/CA, all devices have an equal opportunity to place
transmissions on the network, but they must first get permission from a
controlling device. CSMA/CD is used in Ethernet networks, while CSMA/CA
is used in wireless networks.
CSMA/CD and CSMA/CA.

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THANK YOU!

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