1. HCF medium access rules
<month year>
doc.: IEEE /429r0
July 2001
HCF medium access rules
Wim Diepstraten
Agere Systems
Wim Diepstraten, Agere Systems
<author>, <company>

2. July 2001
Backgound
HCF can operate in the Contention Free Period (CFP) and the Contention Period (CP).
All ESTA are pollable, but piggy-back Ack is not supported.
Within the Contention Free Bursts (CFB) contention free access rules are applied.
The HCF medium access rules should allow for EDCF contention during the CP.
However the current rules specify that the HC can access the medium after a PIFS.
A max duration of the CFB is defined, but with the PIFS rule the HC can immediately start a next CFB.
This allows for infinitely extended CFBs.
Clearly there is a conflict in these rules.
Wim Diepstraten, Agere Systems

3. July 2001
HC access objectives
The HC shall allow for EDCF contention when operating in the CP.
The CFB duration should be limited to limit the access delay for EDCF access.
Given its role, and the traffic distribution the HC should be given extra access priority opportunities, to improve efficiency, and reduce contention overhead.
Wim Diepstraten, Agere Systems

4. Proposed CFB access rules
July 2001
Proposed CFB access rules
CFB access rules should allow EDCF contention opportunities when used during the CP.
CFB duration is limited to allow EDCF contention opportunities.
Between bursts the HC should use EDCF access procedures.
Thereby contending with ESTA using EDCF.
CFB can be allowed to piggyback its access on (E)DCF access from any station within the same BSS.
Only if that station belongs to the same BSS, to prevent overlap issues.
And the total duration of the burst is limited to the CFB max duration.
This gives the HC the opportunity to gain access without contention for every (E)DCF access of any station within that BSS.
Note that this also applies to legacy station.
Wim Diepstraten, Agere Systems

5. CFB start details in CP Each CFB start shall allow EDCF contention.
July 2001
CFB start details in CP
Each CFB start shall allow EDCF contention.
The HC can start a CFB after any Data/Mgmt frame exchange from the same BSS with NF=0.
Note that this does in most cases traffic to the AP, which the AP needs to Ack.
The total burst duration should always be limited to CFB duration limit.
Wim Diepstraten, Agere Systems

6. July 2001
HC access rules
At a start of a CFB the HC shall use the normal EDCF access rules.
Which allows immediate access when medium was free longer then the applicable AIFS.
Effectively the HC should enter a Postbackoff procedure at the end of a CFB.
If no traffic is Q’ed then a low priority AIFS and CWmin should be used.
If traffic is still Q’ed for transmission the appropriate AIFS and CWmin for that TC should be used for the postbackoff.
If a station wins the contention, then the HC can piggyback its access at the end of the frame exchange by the station.
So the HC will only experience a delay of one station access up to its TxOp limit.
Wim Diepstraten, Agere Systems

7. July 2001
General issues:
What is the priority of a sequence-initiating Control frame?
E.g. RTS, CF-Poll, PS-Poll
RTS priority is the same as the data associated with it.
PS-Poll ??
QoS no-data+CF-Poll ?? And what should the TCID field be?
should have the same priority then the data that it is associated with.
Note: CTS and Ack are response frames only.
What is the relation between:
TxOp limit.
Max CFB duration.
Probably want a separate limit for both.
Wim Diepstraten, Agere Systems

8. Normative text changes
July 2001
Normative text changes
Clause 9.10,
line 32: Delete “using higher medium access priority than ESTA’s”.
Add: The HCF shall perform the EDCF access procedure to start a CFB, or it can start a CFB at SIFS after a completed EDCF frame exchange (NF=0) of a (E)STA within the same BSS, provided that the total duration of the frame exchange + CFB is not longer then CFB limit.
Wim Diepstraten, Agere Systems

9. Simplified CFB limit rules
July 2001
Simplified CFB limit rules
Independent TxOp and CFB limit.
HC does not need to dynamically decide what to put in its CFB, based on the previous (E)STA exchange.
Wim Diepstraten, Agere Systems

10. Motion to adopt following change:
July 2001
Motion to adopt following change:
Clause 9.10,
line 32: Delete “using higher medium access priority than ESTA’s”.
Add: The HCF shall perform the EDCF access procedure to start a CFB, or it can start a CFB at SIFS after a completed EDCF frame exchange (NF=0) of a (E)STA within the same BSS.
Note that the question what CWmin to use for HC EDCF access is a separate discussion.
Wim Diepstraten, Agere Systems