. (CSMA/CA carrier sense multiple access with collision avoidance). , , , .
802.11 . DCF (distributed coordination function) , , . ( CW ‒ contention window), . 4.17[3]. . .
. 4.17.
DCF . 4.18. , ; , .. . DIFS. , , . ACK SIFS (. 4.19)..
. 4.18. DCF
. 4.19. DCF
DIFS, SIFS . 4.4.
4.4
IFS | 802.11b | 802.11g | 802.11a | 802.11n 2,4 | 802.11n 5 |
SIFS, | |||||
, | 20 () 9 () | 20 () 9 () | |||
DIFS, | 50 () 28 () | 50 () 28 () |
Wi-Fi , (). , ( ) . DCF, PCF (point coordination function). (. 4.20). PCF , IP-, .
. 4.20.
Wi-Fi 4 , :
Voice ,
Video ,
Best Effort -,
Background .
|
|
(hybrid coordination function, HCF). HCF :
, (contention-based channel l access);
(controlled channel access).
, , (enhanced distributed channel access, EDCA), , HCF (HCF controlled channel access, HCCA). 2 : (CP) (CFP). EDCA CP, HCCA . HCF DCF CF, . HCF , . DIFS AIFS (Arbitration Interframe Space), (. 4.21).
. 4.21. AIFS
[1] , .
[2] UNII - Unlicensed National Information Infrastructure; ISM - industrial, scientific and medical radio band
[3] Cmin=15 IEEE802.11n IEEE802.11ac