SIFS/DIFS/PIFS (802.11 Mac Layer)

1.What is Short Inter-frame Space (SIFS)?

Ans : the small time interval between the data frame and its acknowledgment. Used for the highest priority transmissions enabling stations with this type of information to access the radio link first.

2.What is the content of SIFS ?

Ans :This value is fixed per PHY and is calculated in such a way that transmitting station will be able to switch back to receive mode and be capable of decoding the incoming packets. A SIFS duration is a constant value and it depends on the amendments.

3.What is DCF inter-frame space(DIFS) ?

Ans : The DIFS is used by stations operating under the DCF method to transmit data frames and management.(Read more : DCF Method)

4.How to use DIFS?

Ans : A station using the DCF is allowed to transmit if it determines that the medium is idle for the duration of the DIFS, or if it determines that the medium is idle for the duration of the DIFS + the remaining back-off time following the reception of a correctly received frame. (Read more :Random Back-Off)

5.What is PIFS?

Ans : Because AP always has more priority to access the medium, we don't want wait that long like DIFS time, thus create a PIFS(PCF inter-frame space) time.

The timing diagram of SIFS/DIFS/PIFS : (SIFS<PIFS<DIFS)