DCF Interframe Space

In the DCF protocol, a station has to sense the status of the wireless medium before transmitting. If the medium is continuously idle for DCF Interframe Space (DIFS) duration, only then it is supposed to transmit a frame. If the channel is found busy during the DIFS interval, the station should defer its transmission.

DIFS duration can be calculated by the following method.

DIFS = SIFS + (2 * Slot time) ^[1]

Standard	Slot time (µs)	DIFS (µs)
IEEE 802.11b	20	50
IEEE 802.11a	9	34
IEEE 802.11g	9 or 20	28 or 50

IEEE 802.11g is backward compatible with IEEE 802.11b. When these devices are associated with same AP all the timing parameters are changed to 802.11b.

See also

• SIFS
• PIFS
• AIFS
• RIFS
• EIFS
• DCF

References

1. ^ "IEEE 802.11 Standard". http://standards.ieee.org/getieee802/download/802.11-2007.pdf.