interframe space (802.11) (IFS)

The interframe space (IFS) is used for priority control in the CSMA/ CA procedure in WLANs according to 802.11. The interframe space is the time span for which a station willing to transmit listens to the radio channel in the CSMA/CA procedure. This is a fixed minimum time. This is followed by the backoff and only then can the station willing to transmit send the next frame.

For prioritizing the transmission, in addition to the fixed interframe space, there are also those with different waiting times for priority control, which are provided by the radio channel management. These include the Short Interframe Space( SIFS) with the shortest waiting times for asynchronous data services, the Distributed Interframe Space ( DIFS) with the longest waiting times, and the Point Interframe Space( PIFS) for time-critical services with medium waiting times. There is also the Arbitrated Interframe Space( AIFS), which represents the minimum waiting time after which the transmission medium can be accessed, and the Reduced Interframe Space( RIFS), which was introduced in 802.11n and increases efficiency.

Prioritization in WLANs using Interframe Spaces (IFS)

To prevent stations with the same prioritization from affecting each other, the stations are divided into categories and given backoff times of different lengths, which are added to the IFS interval times.