The IEEE 802.15.4 standard defines a specific time that is alotted for the MAC sublayer to process received data. The interframe spacing (IFS) is used to prevent two frames from being transmitted too close together. If the transmission is requesting an acknowledgement, the space before the second frame shall be at least one IFS period.
IFS is determined to be one of the following:
- IFS equals macMinSIFSPeriod (12 symbols) if the MPDU is less than or equal to aMaxSIFSFrameSize (18 octets) octets
- IFS equals macMinLIFSPeriod (40 symbols) if the MPDU is larger than aMaxSIFSFrameSize
Using the efficient assisted modes in RADIO, the TIFS will be programmed with the correct value based on the frame being transmitted. If the assisted modes are not in use, the TIFS register must be updated manually. The following figure provides details on what IFS period is valid in both acknowledged and unacknowledged transmissions.