Hey everyone, thanks for coming back to Wi Fi fundamentals with location and analytics. This course will help you to master the air. we're advancing and in this part we will look at frame control, probably the most important field in your Wi Fi frame. As you remember, your WiFi frame consists of a header, a payload and the frame check sequence. In your header There are nine major fields we will look closely at the first one at frame control. The frame control field holds 11 sub fields inside.
The first one mentions that it runs under the Wi Fi protocol. The second subfield type includes a bit value, the bit value is equal to the type of the frame. If it is zero it is a management frame. If it equals one, it is a control frame. If it equals two it is a data frame. But type is not enough though.
So we have the sub type sub field, which tells us exactly which type of frame is it. It has a four bit value and each frame has its own unique value. The following subfields can be treated and should be treated as one two DS and from DS this two bit subfield indicate from where and to whom the frame is headed. Is it a frame that comes from a station had the to an access point or a frame that comes from an access point added to the station the following tables should make it more clear. If the bit value in the first subtype to DS is zero and the second value is zero, then it is an ad hoc network. If the first value in 2d S is zero and the second bit value in from the earth is one, it is data that is exiting the access point towards the station.
And if the bit value is one in 2d s and zero in from the earth, then it is a data that enters the access point from our station. The more fragments subfield indicates that the frame has more fragments that are waiting to come. The retry sub field indicates if the frame has been reached. transmitted, and that happens a lot in Wi Fi due to interferences, bet signals and more. Each station will shut down its radio components from time to time to save power. If the power management bits value is set to one, that is the station's way to let the access point know that it goes into a power save mode.
The protected frame sub field indicates if the frame body is encrypted, if so, expect this flag bit to be one. And the more data subfield indicates to a station that there is more data buffered by the AP by the access point for him. Remember that our station goes from time to time to sleep. That's the way that the access point can tell us station Hey wake up there is more data for you. And the order subfield indicates to the receiving station that the frames data must be processed in order. Next up frames, Part Three