802.11 protocol inter-frame interval-sifs,difs,pifs,eifs

SIFS

Short interframe Space (SIFS): SIFS is a fixed value in the 802.11 series WLAN, SIFS is the smallest inter-frame interval, so nodes with SIFS have the highest priority to access the wireless link. It is equal to the time it takes for the node to switch from the sending State to the receiving State and to decode it correctly, or the time it takes to transition from the receive State to the sending State, the packets that may be sent after the sifs expires include ACK, CTS frames, and the sifs values specified in different standards are different.

Standard	SIFS (μs)
IEEE 802.11b	10
IEEE 802.11a	16
IEEE 802.11g	10

DIFS

DCF Interframe Space (DIFS): In the DCF protocol, nodes need to monitor whether the channel is idle before starting to send data. If the channel is idle, the node still waits difs for a period of time before the data is sent, and if the channel is monitored as busy at any time within the difs time period, the node has to postpone its data transmission. The computational relationship between Difs and SIFs is as follows:

DIFS = SIFS + (2 * Slot time)

Standard	Slot Time (Μs)	DIFS (Μs)
IEEE 802.11b	20	50
IEEE 802.11a	9	34
IEEE 802.11g	9 or 20	or 50

PIFs

PCF interframe Space (pifs):P CF allows the AP to wait for PIFs instead of difs time to access the channel due to difs > PIFs > SIFS, so the AP always has a higher access channel priority than the normal node.

PIFs = SIFS + Slot time

Standard	Slot Time (Μs)	PIFs (Μs)
IEEE 802.11b	20	30
IEEE 802.11a	9	25
IEEE 802.11g	9 or 20	30 or

EIFS

Extended interframe Space (EIFS): In the case of an error in the previous frame, the sending node has to delay EIFS instead of the difs time period before sending the next frame.

EIFS = transmission time of Ack frame at lowest basic rate + SIFS + DIFS