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tom_uea,

Here are some excerpts from "ANSI/IEEE Std 802.11, 1999 Edition" that may be helpful.

9.2.3 Interframe space (IFS)

The different IFSs shall be independent of the STA bit rate. The IFS timings shall be defined as time gaps on the medium, and shall be fixed for each PHY (even in multirate-capable PHYs). The IFS values are determined from attributes specified by the PHY.

9.2.10 DCF timing relations

aSIFSTime and aSlotTime are fixed per PHY.

aSIFSTime is: aRxRFDelay + aRxPLCPDelay + aMACProcessingDelay + aRxTxTurnaroundTime.

aSlotTime is: aCCATime + aRxTxTurnaroundTime + aAirPropagationTime
+ aMACProcessingDelay.


10.4.3.2 Semantics of the service primitive

aRxRFDelay

The nominal time (in ???¦Ìs) between the end of a symbol at the air interface to the issuance of a PMD-DATA.indicate to the PLCP. The end of a symbol is defined to be 1/2 symbol period after the center of the symbol for FH, or 1/2 chip period after the center of the last chip of the symbol for DS, or 1/2 slot time after the center of the corresponding slot for IR.

aRxPLCPDelay

The nominal time (in ???¦Ìs) that the PLCP uses to deliver a bit from the PMD receive path to the MAC.

aMACProcessingDelay

The nominal time (in ???¦Ìs) that the MAC uses to process a frame and prepare a response to the frame.

aRxTxTurnaroundTime

The maximum time (in ???¦Ìs) that the PHY requires to change from receiving to transmitting the start of the first symbol. The following equation is used to derive the RxTxTurnaroundTime: aTxPLCPDelay + aRxTxSwitchTime + aTxRampOnTime + aTxRFDelay.

aCCATime

The minimum time (in ???¦Ìs) the CCA mechanism has available to assess the medium within every time slot to determine whether the medium is busy or idle.

aAirPropagationTime

The anticipated time (in ???¦Ìs) it takes a transmitted signal to go from the transmitting station to the receiving station.


The attributes for some of the PHYs can be found in these documents (This is where you may be able to relate SIFS to time):

See "ANSI/IEEE Std 802.11, 1999 Edition- 15.3.3 DS PHY characteristics"
See "ANSI/IEEE Std 802.11b-1999- A.4.9 High Rate, direct sequence PHY functions"
See "IEEE P802.11a/D7.0 - 17.4.4 OFDM PHY characteristics
See "IEEE Std 802.11g-2003 - 19.8.4 ERP-OFDM PLCP PSDU definition"

In case you don't have the Standards they can be found here:

http://www.ieee802.org/11/

Enjoy!

moe