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Cleaning Up 802.11 MAC/PHY Interface Timing

Cleaning Up 802.11 MAC/PHY Interface Timing. Michael Fischer Intersil Corporation 4242-3 Medical Drive San Antonio, TX 78229 voice: +1-210-614-4096 fax: +1-210-614-8192 mfischer@choicemicro.com. Summary of the Problem. There is an error in the MAC-PHY interface timing specified in 9.2.10:

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Cleaning Up 802.11 MAC/PHY Interface Timing

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  1. Cleaning Up 802.11 MAC/PHYInterface Timing Michael Fischer Intersil Corporation4242-3 Medical DriveSan Antonio, TX 78229voice: +1-210-614-4096fax: +1-210-614-8192mfischer@choicemicro.com Michael Fischer, Intersil

  2. Summary of the Problem • There is an error in the MAC-PHY interface timing specified in 9.2.10: • 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/Txwhile SlotTime is a sequence of the intervals Rx/Tx, D2, CCAdel and M2 • where: D1 = aRxRFDelay + aRxPLCPDelayD2 = D1 + AirPropagationDelayM1 = M2 = aMACPrcDelay(which should be aMACProcessingDelay) • so: SIFS = Rx/Tx + M1 + D1SlotTime = 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 802.11 PHYs. • The equations are incorrect for the 802.11a PHY. • The equations in the general text beneath Figure 58 (in 802.11-1999) 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 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 • Change the description of aCCATime in the table in 10.4.3.2 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 10.4.3.2 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. Motion • Move to empower the TGe editor to incorporate the changes to figures 58 and 58.1 and the table in 10.4.3.2 as given on slides 3 and 4 of 01/127r0 into the TGe draft. Michael Fischer, Intersil

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