1. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 1 HC Recovery and Backoff Rules Sunghyun Choi and Javier del Prado Philips Research USA Briarcliff Manor, New York sunghyun.choi@philips.com

2. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 2 Introduction Status as of 802.11e/D2.0a

3. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 3 Problem Statement 802.11e/D2.0a has both recovery and backoff rule of HC, which look inconsistent HC backoff is not needed if the HC has the full control over the medium However, backoff is desirable if Overlapping BSS (OBSS) exists HC Backoff may result in collision with its own ESTAs in the QBSS

4. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 4 802.11e/D2.0a Says … Clause 9.10 of D2.0a reads: “A HC may perform a backoff following an interruption of a frame exchange sequence due to lack of an expected response from an (E)STA, or due to detection of CCA busy within a CFP or CFB. This backoff shall occur under the rules of the EDCF, using dot11CWmin[7] and dot11AIFS[7].”

5. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 5 802.11e/D2.0a Says … And Clause 9.10.1.2 of D2.0a reads: “ESTAs, including the HC, are required to respond within any frame exchange sequence after a SIFS period. If the beginning of reception of an expected response, as detected by the occurrence of PHY-CCA.indication(busy) at the ESTA which is expecting the response, does not occur during the first slot time following SIFS, that ESTA may initiate recovery by transmitting after PIFS from the end of the last transmission. This recovery after PIFS is only permitted by the ESTA expecting the response. This ESTA is the HC in case of a QoS (+)CF-Poll frame, and is the TXOP holder in case of a QoS data type frame transmitted during a CFB”

6. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 6 Proposed Solution

7. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 7 Proposed Solution (1) If PHY-CCA.indication (busy) is not detected within PIFS after the HC sending any frame which requires response, e.g., QoS (+)CF- Poll, the HC may recover transmission or perform backoff both after PIFS –Which one to do is up to the HC algorithm, and out of the scope of 802.11e spec. –For example, the HC may want to backoff if it knows the OBSS existence.

8. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 8 Example HC recovery HC may backoff (if OBSS detected)

9. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 9 Proposed Solution (2) If PHY-CCA.indication (busy) is detected within PIFS after the HC sending a QoS (+)CF-Poll frame: –The HC assumes that the TXOP was granted successfully. –The HC checks if PHY-RXSTART.indication occurs before PHY-CCA.indication (idle). –Continued next page …

10. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 10 –If PHY-RXSTART.indication does not occur and the HC does not receive any frame from the TXOP holder during the granted TXOP, it could mean a collision of the QoS (+)CF-Poll with another frame, e.g., from neighboring HC, so HC may perform backoff after the expiration of the granted TXOP.

11. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 11 Example Successful TXOP grant Potential collision with OBSS; may backoff

12. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 12 Proposed Solution (3) If PHY-CCA.indication(busy) is detected within PIFS after the HC sending an RTS or non-CF- Poll QoS Data(+) frame: –If there were PHY-RXSTART.indication, PHY- CCA.indication(idle), and PHY-RXEND.indication, and the response is not received correctly, e.g., FCS error, the HC may retransmit the frame or transmit another frame after SIFS from PHY- CCA.indication(idle) –If there was not PHY-RXSTART.indication before PHY-CCA.indication (idle), it may perform backoff as it may mean a collision

13. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 13 Example Successful frame transmission w/ unsuccessful response reception Potential collision with OBSS; may backoff

14. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 14 HC Backoff Rules For the random backoff procedure HC shall use: –MIB value: dot11AIFS HC = 1 (i.e., AIFS HC = PIFS) –MIB values: CW HC using dot11CW min and dot11CW max –CW HC could be fixed at dot11CW min = dot11CW max =3 (ref. 01/128r1) –The random backoff will reduce collisions with other HCs The HC may set AIFS [i] for every i to > PIFS+ dot11CW max –Increasing the AIFS [i] will avoid collisions with EDCF channel access

15. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 15 Why HC “may” backoff, not “shall”? The fact that the receiver of an HC frame does not respond does not always mean a collision with another HC. We believe that having multiple HCs within their transmission/reception ranges will not be very common. Note that backoff may result in the loss of HC control over medium unless AIFS [i] is adjusted as proposed.

16. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 16 Why HC Should Not Recover after PIFS Idle Time? It is not desired for HC to recover after PIFS idle time during a polled TXOP. We believe that allowing TXOP holder to do whatever it wants during a polled TXOP is a good idea. See.11h TPC-related issue IEEE 802.11- 01/412r0 “Aligning 802.11e HCF and 802.11h TPC operations ” Also see an example in the next slide …

17. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 17 Wireless Distribution System QAP 1 polls QAP 2, then QAP 2 polls QSTA 2,1. Transmissions by QSTA 2,1 may not be visible by QAP1 at all.

18. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 18 Summary HC recovery or backoff depending on PHY- RXSTART.indication(.) as well as PHY- CCA.indication(.) Random backoff with fixed contention window size for HCs to avoid collisions with other HCs Increasing AIFS[i] for EDCF access to avoid collision with HC A best-effort & simple approach to handle OBSS problem

19. doc.: IEEE 802.11-01/630r4a Submission S. Choi, Philips Research January 2002 Slide 19 Motion Empower the editor to incorporate the normative text found in the word document 01/630r4, and to change wording to make the revised draft to be consistent with the above changes.