Hybrid Coordination Function (HCF) Frame Exchange and NAV Details February 2001 Hybrid Coordination Function (HCF) Frame Exchange and NAV Details First version: 2000-02-07 Revision 1: 2000-02-26 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 Michael Fischer, Intersil

Symbols for Frame Exchange Diagrams February 2001 Symbols for Frame Exchange Diagrams Frames are shown using 4- and 6-sided symbols, with enclosing round-cornered rectangle to show the scope of optional or repeatable subsets: (E)DCF contention and IFS periods are shown using 3- and 5-sided symbols: Michael Fischer, Intersil

Legacy Frame Exchange Sequences February 2001 Legacy Frame Exchange Sequences To the right are the frame exchanges defined in Table 21 of 802.11-1999 illustrated using this symbology. Note: The last CF-Sequence of each CFP includes 1 instance of CF-End followed by DIFS. All other CF-Sequences include 0 instances of CF-End. Michael Fischer, Intersil

HCF Frame Exchanges for CF-Bursts February 2001 HCF Frame Exchanges for CF-Bursts To the right are the frame exchanges required for HCF QoS Data transfers. Each CF-Burst comprises one or more TxOp. Note: Management frames can only be sent as the sole or final frame of a TxOp, since with no TCID field they default to NF=0. Michael Fischer, Intersil

February 2001 Start of TXOP Details There is one null and one non-null case for the start of a polled TXOP. There are three possible optimizations/deoptimizations of the non-null case. Michael Fischer, Intersil

February 2001 End of TXOP Details There are two cases for the end of a TXOP, based on whether the HC has additional traffic to transmit and/or additional ESTAs to poll. Michael Fischer, Intersil

February 2001 TXOP Requests QoS Null with TS=1 can be used to activate or deactivate periodic polling under an admitted Tspec. QoS Null with TS=0 can be used to request an immediate TXOP longer than the current EDCF TXOP limit. CC defines a controlled contention interval (CCI) when WSTAs that need more bandwidth may send RR frames. Michael Fischer, Intersil

Recovery from Non-Responses February 2001 Recovery from Non-Responses If the addressed ESTA does not respond to RTS or QoS Data at SIFS, the TXOP holder may resume transmission at PIFS unless PHY reports CCA(busy). If the TXOP holder does not resume transmission at PIFS, the TXOP terminates and the HC may resume transmission at DIFS or may allow the to CFB end. Michael Fischer, Intersil

February 2001 NAV Usage During TXOP This diagram shows the periods covered by the NAV, based on Duration field values in the various frames of a TXOP during which the polled ESTA initiates several QoS Data frame exchanges. Michael Fischer, Intersil

Multicast Delivery by HC February 2001 Multicast Delivery by HC Both HCF and PCF transmit queued broadcast and multicast frames directly following DTIM Beacons. The HC uses PIFS immediately after each broadcast/multicast frame, and terminates the CFP early if CCA(busy) is detected during any such PIFS. The HC typically sends CF-End immediately after the last queued broadcast/multicast frame, and provides reserved bandwidth and priority access for QoS traffic using controlled TXOPs during the CP. However, the HC may provide some TXOPs as CF-Sequences during the CFP. Michael Fischer, Intersil