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Clarification on Some HCF Frame Exchange Rules

This document provides clarification on several HCF frame exchange rules including response depending on frame subtypes, error handling, ACK or not, SIFS or PIFS, and RTS/CTS during CFP and CFB.

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Clarification on Some HCF Frame Exchange Rules

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  1. Clarification on Some HCF Frame Exchange Rules Sunghyun Choi and Javier del Prado Philips Research USA sunghyun.choi@philips.com Srinivas Kandala and Ken Nakashima Sharp Labs srini@sharplabs.com S. Choi, Philips & S. Kandala, Sharp

  2. Outline • Response depending on frame subtypes • ACK or not • ACK vs. QoS CF-ACK • Error handling • SIFS or PIFS • RTS/CTS during CFP and CFB S. Choi, Philips & S. Kandala, Sharp

  3. Changes from 546r0 • 546r0 was based on 802.11e/D1.2 • 546r1 is based on 802.11e/D1.3 and D1.4 S. Choi, Philips & S. Kandala, Sharp

  4. ACK or Not? • Whether different subtypes of Data frames require an acknowledgement is not explicitly specified. • It was more true with 802.11-1999, but we have “No Ack” bit in QoS control field with 802.11e. • Resolution: Clarify that • A data type frame of any subtype with “No Ack” bit set to zero will require an acknowledgement. • A detailed usage of QoS control field should be reflected in Table 3.5. S. Choi, Philips & S. Kandala, Sharp

  5. QoS CF-ACK or ACK? • Which of QoS CF-ACK or ACK should be used to acknowledge a QoS data reception is not clear. • QoS CF-ACK is a data type with 30 bytes typically, and ACK is a control type with 14 bytes. • As described in 9.10.3.1 of D 1.3, QoS CF-ACK can request a longer TXOP and update the queue status for a TC with HC. • Per 802.11-1999, ACK is used under DCF and CF-ACK is supposed to be used for CF-pollable STAs under PCF. S. Choi, Philips & S. Kandala, Sharp

  6. QoS CF-ACK or ACK? (Cont.) • In terms of the function, ACK is equivalent to QoS CF-ACK w/ NF=1 & No Ack = 1. • Resolution: • Clarify that ACK and QoS CF-ACK w/ NF=1 & No Ack = 1 are equivalent, and either of them can be used for relevant situations. • Clarify that ACK cannot be used instead of QoS CF-ACK w/ either or both of NF & No Ack bits set to zero. S. Choi, Philips & S. Kandala, Sharp

  7. PIFS or SIFS after Error? • When an ESTA (including HC) in charge of channel recovery does not start receiving an expected frame within PIFS, it will recover by transmitting a frame after PIFS. • What happens when an erroneous frame is received by such an ESTA is not clear. • Resolution: add the following in 9.10.1.2. • If an erroneous frame is received at the ESTA, which expects a response to its transmission, the ESTA may initiate the recovery by transmitting a frame after SIFS from the end of the last reception. S. Choi, Philips & S. Kandala, Sharp

  8. RTS/CTS during CFP/CFB • RTS/CTS exchange is allowed during both CP and CFP. • However, what happens if the RTS/CTS exchange is not successful under HCFshould be clearly stated. • Apparently, we don’t want the HC or the TXOP holder to go to the back-off when it does not receive a CTS successfully. S. Choi, Philips & S. Kandala, Sharp

  9. RTS/CTS during CFP/CFB (Cont.) • Resolution: add the following in 9.10.3.2. • The HC and TXOP holder after transmitting RTS may recover from the failure of the successful CTS reception by transmitting a frame (1) within PIFS from the end of the RTS transmission if the PHY-CCA-indicate(busy) does not occur, and (2) within SIFS from the end of the last frame reception if the frame after the RTS transmission is received in error. S. Choi, Philips & S. Kandala, Sharp

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