Assignment on Wireless Network Communication
Wireless networks use Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) to
control media access and avoid (rather than detect) collisions.
Collision avoidance uses the following steps (processes):
[A] The sending device listens to make sure that no other device is transmitting. If another
device is transmitting, the device waits a random period of time (called a back off period)
before attempting to send again.
[B] If no other device is transmitting, the sending device broadcasts a Request to send (RTS)
message to the receiver or AP. The RTS includes the source and destination, as well as
information on the duration of the requested communication.
[C] The receiving device responds with a Clear to send (CTS) message. The CTS also includes
the communication duration period. Other devices use the information in the RTS and
CTS to delay send attempts until the communication duration period (and subsequent
acknowledgement) has passed.
[D] The sending device transmits the data. The receiving device responds with an
acknowledgement (ACK). If an acknowledgement is not received, the sending device
assumes a collision occurred and retransmits the affected packet.
[E] After the time interval specified in the RTS and CTS has passed, other devices can start the
process again to attempt to transmit.
Question (write 1-2 pages of Paper)
 Summarize the above collision detection processes (stages) explaining the following key
[A] Describe why the use of RTS and CTS (steps 2 and 3) is optional and depends on the
capabilities of the wireless devices.
[B] Describe why without RTS/CTS, collisions are more likely to occur.
[C] Devices can both send and receive, but not at the same time.
[D] Explain why devices must take turns using the transmission channel.
[E] Explain why once a party begins receiving a signal, it must wait for the transmitter to
stop transmitting before it can reply.
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