1. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 1 CFB Ending Rule under HCF Srinivas Kandala, Ken Nakashima, Yashihiro Ohtani and Satoshi Terada Sharp srini@sharplabs.com Sunghyun Choi and Javier del Prado Philips Research-USA Briarcliff Manor, New York sunghyun.choi@philips.com

2. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 2 Current Rules for Ending CFB Per 802.11e/D1.3, there are five ways : 1.HC received a QoS Data frame with NF=0 and relevant ACK frame. 2.HC received a QoS Null frame with NF=0. 3.HC received a management frame. 4.HC received a legacy data frame. 5.Granted TXOP expired.

3. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 3 Problematic Situation (1) If QoS Data ( NF=0, NoACK=0 ) & its relevant ACK or the QoS Null are not received by the HC correctly, but are received by the other ESTA correctly... –TXOP holder thinks that CFB was finished. –HC does not reclaim the channel until the TXOP limit is expired. –The ESTA that had received this frame, will reset its NAV, and resume the EDCF contention. HC happens to lose the control over the channel.

4. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 4 Solution to Problem (1) Delete the following rules in 9.10.2.1 of IEEE 802.11e/D1.3: –"During the CP, when a QoS data type frame is received with an SA value which matches the saved TXOP holder address, has Non-final bit in the QoS control field set to 0, and has No Ack bit in the QoS control field set to 1, the NAV may be reset at the PHY-RXEND.indication corresponding to the QoS data type frame." –"During the CP, when a QoS data type frame is received with an SA value which matches the saved TXOP holder address, has Non-final bit in the QoS control field set to 0, and has No Ack bit in the QoS control field set to 0, the NAV may be reset after (aSIFSTime + QoS CF-Ack_Time) starting at the PHY-RXEND.indication." The above deletion ensures that the ESTAs do not reset their NAVs. ESTAs NAV shall be reset only when they receive a CF-POLL to HC with duration/ID set to 0.

5. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 5 Motion To instruct the editor to incorporate the solution in slide 4 of document 01/605r2.

6. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 6 Problematic Situation (2) The previous change helps, but still: If QoS Data ( NF=0, NoACK=0 ) & its relevant ACK or the QoS Null are not received by the HC correctly... –TXOP holder infers that the control has been transferred back to the HC. –HC does not reclaim the channel until the originally granted TXOP limit expires, and as it is the responsibility of the TXOP holder to attempt any recovery. Results in an under-utilization of channel with channel remaining idle until the granted TXOP expires.

7. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 7 Solution to the Problem (2) The TXOP holder shall send a designated "final frame" addressed to the HC for which an acknowledgement is expected, when it has no further data to send, and if there is enough residual TXOP duration to send a final frame and receive an ACK frame. –Details of the sequences are described after the next slide.

8. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 8 Frame Exchange Sequence (normal sequence) HC Sender Receiver CF-Poll QoS Data S QoS Data CF-Poll ・・・ Other STA NAV from CF-Poll final frame TXOP limit from CF-Poll P NAV from CF-Poll S QoS Data S QoS Data S S ACK QoS Data S SIFS P PIFS S ? Addressed ESTA could not receive this frame correctly but, could hear the CCA of this frame Addressed ESTA could receive this frame correctly. CF-Poll QoS CF-Poll (no data) frame ACK Normal ACK frame QoS Data QoS Data frame

9. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 9 Frame Exchange Sequence (error recovery sequence) HC Sender Receiver CF-Poll QoS Data S QoS Data CF-Poll ・・・ S ACK Other STA NAV from CF-Poll final frame TXOP limit from CF-Poll P NAV from CF-Poll S QoS Data S QoS Data S? final frame S ? P final frame S ACK QoS Data S SIFS P PIFS S ? Addressed ESTA could not receive this frame correctly but, could hear the CCA of this frame Addressed ESTA could receive this frame correctly. CF-Poll QoS CF-Poll (no data) frame ACK Normal ACK frame QoS Data QoS Data frame

10. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 10 Candidates for the final frame When there is residual time left in the TXOP: The frames that may be used (addressed to HC) –A unicast QoS Data frame with NF=0, NoACK=0 –A QoS Null frame with NF=0, NoACK = 0 –A unicast management frame –A legacy data frame The frames that can not be used –A unicast QoS Data frame with NoACK = 1 –A QoS Null frame with NoACK = 1 –A frame that is addressed to non-HC ESTA –A multicast frame

11. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 11 Behavior of the TXOP Holder 1.The TXOP holder sends a final frame to the HC if there is enough time remaining in the TXOP for the final frame and the ACK. 2.If the final frame is sent, the TXOP holder senses the channel for PIFS interval. –If the CCA is idle, it should transmit one of the designated final frame at that time if enough time still remains. –If the CCA is busy it means that the channel control has been successfully transferred and no further action is necessary.

12. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 12 Behavior of the HC 1.The HC sends an ACK when it receives the final frame from the TXOP holder. 2.The HC senses the channel for PIFS interval from the acknowledgement of the transmission –If the CCA is idle, it may send a frame for the next sequence at that time (e.g. QoS CF-Poll).

13. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 13 Motion To incorporate the normative text in the document 01/605r1. Raju’s amendment : Amend 605r1 to r2 and add If the CCA is busy at the ESTA which is expecting the ACK responseduring the first slot following SIFS after the end of the transmission of the final frame, it means that the channel control has been successfully transferred and no further action is necessary, even though the ACK from HC is not correctly received.

14. doc.: IEEE 802.11-01/605r3 Submission November 2001 S. Kandala, et. al. Slide 14 And Add an explicit frame that can end a TXOP: –A QoS Null frame with NF=0, NoACK = 0 And add to –all occurrences of QoS Null frame with NoAck=0 with the phrase “TXOP duration requested field set to 0”.