Hey everyone, thanks for coming back to Wi Fi fundamentals with location and analytics. This course will help you to master the air. In the first part of csma ca we saw how DC f actually coordinates the time between transmissions of every station in your BSS. DCF is based on this rules. Before every transmission the station has to wait a period of time. DFS is used almost always the rule is if you are not sure it is your turn to transmit but you want to transmit Wait a DI Fs if you are sure that it is your turn to transmit, use si Fs which is a shorter period.

So let's see it in action. station at the top sensor data frame. Every other station around including our access point turns their physical carrier sense. Remember that in our stations data frame header, there is a duration value, which our second station can hear and set up its own nav timer. Throughout the Neff time, our access point waits a safe. It is a short period when you are sure that you need to transmit and then sends the acknowledgement frame to our station.

Your data frame arrived. As the Nef timer ends, our station waits at this an interspace frame that is used mostly between stations who are not sure if it is their turn. As the diff ends the contention will To start and our station generates a back off timer, this time of three time periods slots. Each slot is in microsecond a very short time. And now it can transmit. Now let's assume that another station wants to transmit instead of our access point.

So the other station would wait the same as our previous station at nighttime at diffs and will generate for time periods slots. So who's to win our station, it sends again the data frame and when it sends the data frame, the other station waits in their turn and turn on their physical carrier sets. Return the duration value and wait at this next up frequencies. See you soon