1. Hybrid Coordination Function (HCF) Frame Exchange and NAV Details
February 2001
Hybrid Coordination Function (HCF) Frame Exchange and NAV Details
First version: Revision 1:
Michael Fischer
Intersil Corporation Medical Drive San Antonio, TX voice: fax:
Michael Fischer, Intersil

2. 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

3. Legacy Frame Exchange Sequences
February 2001
Legacy Frame Exchange Sequences
To the right are the frame exchanges defined in Table 21 of 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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