CSMACD shortcut for Carrier Sense Multiple
Access/Collision Detect, it is the protocol for carrier transmission access in
Ethernet networks. Moreover, how network devices
respond is defined by CSMACD, basically when
two devices attempt to use a data channel at the same time and come across a
data collision. After that, each device will wait for random time and will try again
until it is transmission sent successfully.

Furthermore, the CSMA/CD method is specified in IEEE 802.3 and ISO 8802.3 standard. The next figure shows the
process of CSMACD method.

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The best example for CSMA/CD is to assume that there are many
people in a meeting having a conversation. Each one has a chance to speak while
the others listen to the one whose speaking and waiting for their opportunity
to speak. This resembles the Carrier Sense Multiple Access(CSMA) which is a
protocol of a network that senses or listens to the network signal over a
medium before any data is transmitted. Once the speaker is over, a moment of
silence takes place. After that, other or others will try to speak and if more
than one person speak at the same time, collision will occur. As a result, one
is allowed to speak while others are silenced, this is known as collision
detection (CD).


However, CSMACD is not suitable for Wi-Fi
because Wi-Fi networks have hidden node problem which is basically as shown in figure
2, assuming B is the Access Point, station A is able to transmit information to
station B(AP), and B (AP) can transmit information to A as well. However,
stations A and C are hidden from each other so they cannot transmit any information
between them. As a result, Carrier Sense Multiple Access/Collision Detect CSMACD
will not be able to work in this case and collisions will happen. Therefore, the
best solution is to use Carrier Sense Access/Collision Avoidance CSMA/CA.


While the best
example to understand how Carrier Sense Access/Collision Avoidance
CSMA/CA works is to assume that there is a lecture. Once the lecturer is over,
the lecturer will ask the student if there are any questions regarding the
lecture. Where all the student getting prepared to ask some question and this
known as Multiple Access (MA). Then one of the student will look right and left
to see if anyone is going to ask question and this is knowns as Carrier Sense. When
there is one student wants to ask question, the rest are waiting for question
to be asked, this is known as Collision Avoidance (CA).  


CSMACA shortcut for Carrier Sense Multiple Access/Collision
Avoidance, it is the protocol for carrier transmission access in Wi-Fi
networks. It checks or listen to the medium before a node transmits data. the
node send it’s signal when the medium is not busy. After that, it will back off
and wait for a random amount of time and try again if it detects the medium is
used. Furthermore, CSMA/CA tries to prevent collisions before they happen
unlike CSMA/CD which deals with transmissions after a collision has occurred.