1. Cleaning Up 802.11 MAC/PHY Interface Timing
November 2001
Cleaning Up MAC/PHY Interface Timing
Michael Fischer
Intersil Corporation Medical Drive San Antonio, TX voice: fax:
Michael Fischer, Intersil

2. November 2001
Summary of the Problem
There is an error in the MAC-PHY interface timing specified in :
The equations within Figures 58 & 58.1 require SlotTime longer than SIFS:
The SIFS is shown as being a sequence of the intervals D1, M1 and Rx/Tx while SlotTime is a sequence of the intervals Rx/Tx, D2, CCAdel and M2
where: D1 = aRxRFDelay + aRxPLCPDelay D2 = D1 + AirPropagationDelay M1 = M2 = aMACPrcDelay (which should be aMACProcessingDelay)
so: SIFS = Rx/Tx + M1 + D1 SlotTime = Rx/Tx + M1 + D1 + AirPropagationDelay + CCADel
hence: SlotTime = SIFSTime + AirPropagationDelay + CCAdel
therefore SlotTime < SIFSTime
This time relationship happened to be true for the 3 PHYs known at the time Figure 58 was generated, but was not a requirement for all PHYs.
The equations are incorrect for the a PHY.
The equations in the general text beneath Figure 58 (in ) are correct, but do not match the interval names in the figure, so the relationship of the equations to the timing of events at the MAC/PHY interface is unclear.
Michael Fischer, Intersil

3. Corrected Labeling for Figure 58
November 2001
Corrected Labeling for Figure 58
aSIFSTime
aSlotTime
PHY-RXEND.indication
aSlotTime
aSlotTime
aSlotTime
D1 = aRxRFDelay + aRxPLCPDelay (starts at the end of the last symbol of a frame on the medium)
D2 = aAirPropagationTime
Rx/Tx = aRxTxTurnaroundTime (starts when the MAC issues a PHY-TXSTART.request)
M1 = M2 = aMACProcessingDelay
CCAdel = aCCATime
Michael Fischer, Intersil

4. Clarifications Appropriate in 10.4.3.2
November 2001
Clarifications Appropriate in
Change the description of aCCATime in the table in as shown:
The minimum time (in µs) the CCA mechanism uses (has available) to assess the medium within every time slot to determine whether the medium is busy or idle.
Change the description of aRxPLCPDelay in the table in as shown:
The nominal time (in µs) that the PLCP uses to deliver (a) the last bit of the last symbol from the PMD receive path to the MAC.
Michael Fischer, Intersil

5. November 2001
Motion
Move to empower the TGe editor to incorporate the changes to figures 58 and 58.1 and the table in as given on slides 3 and 4 of 01/127r0 into the TGe draft.
Michael Fischer, Intersil