IEEE 802.11
, IEEE 802.11 802, MAC (Media Access Control) LLC (Logical Link Control). 802, 802.11 , MAC, LLC LAN ( 1.8).
LLC | LLC | |||||
MAC | PCF | |||||
DCF | ||||||
802.11 | 802.11a | 802.11b | 802.11g | 802.11n | ||
2,4 FHSS 1 / 2 / | 2,4 DSSS 1 / 2 / | 5 OFDM 54 /c | 2,4 DSSS CCK 11 /c | 2,4 OFDM 54 /c | 2,4 5 OFDM 600 /c | |
1.8. IEEE 802.11
, , . MAC, MAC .
802.11
802.11 MAC ( 1.8):
DCF (Distributed Coordination Function);
PCF (Point Coordination Function).
1) DCF
, DCF. (Carrier Sense Multiple Access with Collision Avoidance, CSMA/CA). CSMA/CD, . , . - , - , .
DCF . 802.11 ( 1.9). - , .
1.9. DCF
, , . IEEE802.11 ( ): . . , , RTS/CTS , ( ) . , , .. , . , , (Inter Frame Space, IFS). IFS , . - , . , CSMA/CD. , [0, CW], CW Contention Window - ).
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1.9. 3. ( ) 3 . , 1, , .
, , . .
- , , . , . , . , , .
; , FHSS 28 , DSSS 1 . , , . , , . , , .
, .
, . , . [0, CW], , . , , 8 ( CW= 7), 16 (CW= 15), 32 . . CW 802.11 , .
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CSMA/CD, , 802.11 . N , , . , .
, ( ) , ( 1.10) . , , .
1.10.
DCF . , , RTS (Request To Send, ). CTS (Clear To Send, ), - . CTS , -, -, -.
802.11 2346 , RTS- 20 , CTS- 14 . RTS- CTS- , , RTS- CTS- , . RTS- CTS- . , , , RTS- CTS-.
, , , . ‑ MAC , - . ( 1.11). , . ; , - , , . .
1.11.
. . , , . , , DCF.
, - 802.11. , 802.11 MAC, . - . .
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2) PCF
, , , PCF, . , .
PCF 802.11 DCF. ( 1.12).
1.12. PCF DCF
, :
- (Short IFS, SIFS);
- PCF (PIFS);
- DCF (DIFS).
DCF , , , DIFS. IFS DCF DIFS , .
SIFS , CTS- , .
PIFS , SIFS, , DIFS. PIFS DIFS . , , . , , DCF , , . , , . , DIFS DCF.
PCF. , , . , , , ( , ).
- , . .
PCF, .
MAC-
1.13 802.11. , .
FC
D/I /
SC
1.13. MAC IEEE 802.11
:
- . ( ).
- /. , ( ), MAC. , .
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- . . : , , , .
- . 4- , , 12- , , .
- . LLC MAC.
- . 32- .
, 1.14, :
- . 802.11, ‑ 0.
- . : , .
- . . 1.1.
PS-opoc | |||
(F)- | |||
CF- + CF- | |||
+ CF- | |||
+ CF-opoc | |||
+ CF- + CF-opoc. | |||
( ) | |||
+ CF- | |||
+ CF-opoc | |||
+ CF- + CF-opoc |
1.1.
- DS. MAC 1, .
- DS. MAC 0, .
- . 1, .
- . 1, .
- . 1, .
- . , . .
- WEP. 1, (Wired Equivalent Privacy, WEP). WEP .
- . 1, , , .
DS MD
MF W
RT 0
1.14.
MAC.
. :
- (PS-). , . , , , .
- (RTS). , . , , , , .
- (CTS). . - - .
- (). , PS-opoc.
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- (F)-. ; .
- CF- + CF-. CF-. , .
, . , -. :
- . . , .
- + CF-. . .
- + CF-opoc. , .
- + CF- + CF-opoc. .
. , , . , , . (CF-, CF-opoc, CF- + CF-opoc) , ( + CF-, + CF-opoc, + CF- + CF-opoc), .
. :
- . (Basic Service Set, BSS). , , , .
- . , .
- . BSS, BSS. , , .
- . , .
- . . BSS IEEE 802.11.
- . .
- . , BSS.
- . ( ), , .
- . .
- . .
- . .