View source for DCF Interframe Space

The [[IEEE 802.11]] family of standards describe the [[Distributed Coordination Function|DCF]] protocol, which controls access to the physical medium. A station must sense the status of the wireless medium  before transmitting. If it finds that the medium is continuously idle for '''DCF Interframe Space''' (DIFS) duration, it is then permitted 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) <ref>{{cite book|url=https://ieeexplore.ieee.org/document/7786995|title=IEEE 802.11 Standard|doi=10.1109/IEEESTD.2016.7786995 |isbn=978-1-5044-3645-8 }}, 2016, Equation (10-6), page 1332.</ref>

{| class="wikitable"
|-
! Standard
! Slot time (μs)
! DIFS (μs)
|-
| [[IEEE 802.11-1997]] (FHSS)
| 50
| 128
|-
| [[IEEE 802.11-1997]] (DSSS)
| 20
| 50
|-
| [[IEEE 802.11b]]
| 20
| 50
|-
| [[IEEE 802.11a]]
| 9
| 34
|-
| [[IEEE 802.11g]]
| 9 or 20
| 28 or 50
|-
| [[IEEE 802.11n]] (2.4 GHz)
| 9 or 20
| 28 or 50
|-
| [[IEEE 802.11n]] (5 GHz)
| 9
| 34
|-
| [[IEEE 802.11ac]] (5 GHz)
| 9
| 34
|}

[[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 ==
* [[Short Interframe Space | SIFS]]
* [[PCF Interframe Space | PIFS]]
* [[Arbitration inter-frame spacing | AIFS]]
* [[Reduced Interframe Space | RIFS]]
* [[Extended_Interframe_Space | EIFS]]
* [[Distributed_Coordination_Function | DCF]]

== References ==
{{reflist}}

[[Category:IEEE 802.11|D]]
[[Category:Media access control]]


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