Channel Sensing(Carrier Sensing) in Action

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(A) : Before a device try to transmit any data, it start Carrier Sensing.

(B) : If the device detect any carrier signal (i.e, some other device is using the channel), it just go back to 'Waiting' mode and would not try further carrier sensing for a BackOff Period.

(C) : Even if the carrier is not busy (i.e, even if nobody is using the channel), the device keep sensing the carrier for a certain duration (DIFS). If it detect any carrier signal during this period, it go back to 'Waiting' mode and would not try further carrier sensing for a BackOff Period.

(D) : If no carrier signal is detected for a certain period (DIFS), the device assume that the channel is clear (nobody is using the channel) and it transmit its own data.