SIFS

SIFS, or Short Interframe Space, is a timing parameter in IEEE 802.11 wireless local area networks. It defines the minimum amount of time that must elapse between the end of one frame transmission and the start of the next, for high-priority control frames. SIFS is the shortest of the interframe spaces defined in 802.11, shorter than DIFS (Distributed Interframe Space) and EIFS (Extended Interframe Space), which gives immediate responses priority over regular data transmissions.

In operation, after a data frame is received, the receiver waits SIFS and then transmits an acknowledgment (ACK); after RTS/CTS exchanges, the corresponding responses are also sent after a SIFS interval. Because SIFS is short, it reduces the likelihood of another station transmitting in the window and improves link efficiency, particularly during short control exchanges and contention-free periods.

The exact duration of SIFS is specified for each 802.11 PHY edition and can vary with different amendments, bands, and data rates. It is designed to facilitate timely control signaling and acknowledgments rather than data payload transfers.

Other uses of the acronym SIFS exist in different fields, but this article focuses on the wireless networking term Short Interframe Space. For other meanings, see SIFS (disambiguation).