1. Use of EDCA Access During HCF Polling
doc.: IEEE /457
November 2003
Use of EDCA Access During HCF Polling
Mathilde Benveniste
Avaya Labs – Research
Avaya Labs

2. November 2003
INTRODUCTION
According to TGe D5.0 and D5.1, a station with an active TS (an admitted HCCA TSPEC request) could not send EDCF frames generated by that TS if the Access Policy bit did not allow it
This is overly restrictive
In order to simplify poll scheduling and error recovery, and to improve performance, TGe D5.0 and D5.1 also allowed use of EDCA by such stations under certain conditions
EDCA access would not be used indiscriminately by polled traffic streams
Avaya Labs

3. Unrestricted Hybrid Access (UHA)
November 2003
Unrestricted Hybrid Access (UHA)
Following comment resolution on 11/13/03, the restrictions on the use of Hybrid Access were removed
A station with an active TS may send EDCA frames generated by that TS without any restriction, provided that the Access Policy bit allows it
Individual stations have the incentive to pursue unrestricted hybrid access
EDCA stations would set up a TS for polled access to use in case the EDCA access causes delay
HCCA stations would benefit from EDCA access on a noisy channel by providing faster retries and recovery from missed/delayed polls
Avaya Labs

4. Performance under Unrestricted Hybrid Access
November 2003
Performance under Unrestricted Hybrid Access
In lightly loaded systems, UHA may accelerate access for EDCA stations pursuing hybrid access, as they now have the polls as a backup
In lightly loaded systems, UHA may accelerate access (with increased jitter) for HCCA stations pursuing hybrid access, as they can send frames in advance of their polls
In heavily loaded systems, UHA increases access delay for all stations because of the increased number of polls - which have priority over the EDCA frames.
UHA would waste bandwidth in heavily loaded systems, as more polled TSs would be set up, and many of their polls would be returned unanswered
Avaya Labs

5. November 2003
Conclusion
While there may be advantages to unrestricted HA in lightly loaded systems, there are clear performance disadvantages when the system is heavily loaded
Since the stations have an incentive to pursue unrestricted HA, there should be a way for the AP to restrict hybrid access when appropriate.
Avaya Labs

6. _____________________
November 2003
Restricted Hybrid Access*
To eliminate the incentive for stations to pursue hybrid access when inappropriate, there should be a way to constrain HA as follows:
A station may send a frame from an admitted TS using EDCF only under the following conditions:
Error recovery: if the ack to a previously transmitted frame is not received
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*Note: Restricted Hybrid Access was available in TGe D5.0 and D5.1, until it was removed during comment resolution on 11/13/03
Avaya Labs

7. November 2003
Motion
Instruct the editor to modify the text in subclause of the TGe draft to permit use of EDCA to transmit MSDUs belonging to traffic streams for which there is a strict HCCA policy under the following conditions:
1.     The MSDU has been sent previously but an acknowledgement has not been received
When frames associated with a TSPEC are transmitted over contention-based channel access, they shall use the EDCA parameters associated with the UP specified in the TSPEC.
Modify Table 20.4 accordingly.
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