Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2005 TGn Sync MAC Response to Reasons and Cures Relating to Reverse Direction Date: 2005-05-16 Authors: Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair <stuart.kerry@philips.com> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <patcom@ieee.org>. Robert Stacey, Intel John Doe, Some Company

Authors (continued): May 2005 Month Year doc.: IEEE 802.11-yy/xxxxr0 Robert Stacey, Intel John Doe, Some Company

Reasons and Cures Feedback for Reverse Direction Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2005 Reasons and Cures Feedback for Reverse Direction General support for piggybacking data with ack Concern regarding complexity (#49, #64, #85.1, #92) No benefit to RD under HCCA (#77) Concern that RD is introducing HCCA-like scheduling to EDCA (#77) Cures suggested in comments: Remove RD altogether (#49) Simplify protocol, e.g. allow single data frame response (#41.2) Follow TXOP with short response TXOP (#64) Piggyback data with CTS in subsequent TXOP (#64) Robert Stacey, Intel John Doe, Some Company

Discussion of Benefit We like contention based access Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2005 Discussion of Benefit We like contention based access It provides a robust, efficient, simple mechanism for sharing network bandwidth TGe TXOP and Block Ack provided significant efficiency gain while retaining the benefits of contention based access Aggregation improves efficiency within TXOP (broad agreement) RD provides significant additional gain under EDCA by Piggybacking BA with data Improving TXOP utilization Reducing contention Robert Stacey, Intel John Doe, Some Company

Discussion of Benefit Network traffic is asymmetric Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2005 Discussion of Benefit Network traffic is asymmetric Over short periods the majority of the traffic is in one direction with small amounts in the reverse direction The majority of traffic is to or from a single node – the AP  TXOPs are often underutilized in one direction Consider two scenarios: Traffic from one STA to another Traffic from AP to multiple STAs Robert Stacey, Intel John Doe, Some Company

Immediate BA May 2005 Month Year doc.: IEEE 802.11-yy/xxxxr0 STA1 (AP) TXOP TXOP TXOP TXOP TXOP STA1 (AP) RA2 RA2 RA2 STA2 RA1 RA1 TXOPs are often underutilized (especially uplink) Radio turnaround per data block for BA TXOP TXOP TXOP TXOP TXOP TXOP STA1 (AP) RA2 RA3 RA4 STA2 RA1 STA3 RA1 STA4 RA1 Contention [+ collision detect] Data BA Robert Stacey, Intel John Doe, Some Company

No Ack BA May 2005 No Ack BA Allows BA to be aggregated with data Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2005 No Ack BA TXOP TXOP TXOP TXOP TXOP STA1 (AP) RA2 RA2 RA2 STA2 RA1 RA1 Radio turnaround for BA eliminated and BA piggybacked with data improving TXOP efficiency, but… TXOP TXOP TXOP TXOP TXOP TXOP TXOP STA1 (AP) RA2 RA3 RA2 RA3 RA4 STA2 RA1 RA1 STA3 RA1 RA1 STA4 RA1 …the uplink TXOP is still frequently underutilized No Ack BA Allows BA to be aggregated with data But TXOPs are frequently underutilized Contention [+ collision detect] Data BA Robert Stacey, Intel John Doe, Some Company

Reverse Direction May 2005 Reverse Direction Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2005 Reverse Direction All TXOPs are efficiently utilized… TXOP TXOP TXOP TXOP STA1 (AP) RA2 RA2 RA2 RA2 STA2 RA1 RA1 …either with pure downlink traffic… … or with mixed uplink and downlink traffic TXOP TXOP TXOP TXOP STA1 (AP) RA2 RA3 RA4 RA2 STA2 RA1 RA1 STA3 RA1 STA4 RA1 Reverse Direction Allows BA to be aggregated with data And improves TXOP utilization Contention [+ collision detect] Data BA Robert Stacey, Intel John Doe, Some Company

Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2005 Power Efficiency downlink Medium Busy Medium Busy Medium Busy uplink U-APSD STA Awake A PS STA wants to complete exchange in as short a time as possible No guarantees, but reverse direction data has potential for completion in single TXOP with 3 PPDUs Robert Stacey, Intel John Doe, Some Company

Additional Simulation Results Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2005 Additional Simulation Results An attempt was made to reuse 11e CF-Poll semantics to achieve equivalent to reverse direction data Remainder of TXOP is transferred (TT) to peer using CF-Poll TT Ack = CF-Poll is ACKed TT Simple = CF-Poll ACK is piggybacked on data Compared with existing reverse direction data protocol Example sequences shown Robert Stacey, Intel John Doe, Some Company

Additional Simulation Results Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2005 Additional Simulation Results All simulations use same simple heuristic If the initiator can’t use the full TXOP limit, offer the remainder to the responder The responder opportunistically uses the offered period if it has data to transmit Protection using LongNAV Robert Stacey, Intel John Doe, Some Company

Additional Simulation Results Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2005 Additional Simulation Results Gain is significantly reduced with CF-Poll like semantics Robert Stacey, Intel John Doe, Some Company

Addressing Concerns Complexity No benefit from RD under HCCA Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2005 Addressing Concerns Complexity Optional in proposal, but still relatively simple to implement Simulations use a simple heuristic that advertises and then grants any remaining TXOP to peer Peer opportunistically uses advertised duration if it has data to send No benefit from RD under HCCA Largely True – benefit derives primarily from improved TXOP utilization mitigating contention overhead RD introduces HCCA-like scheduling to EDCA Disagree – simple heuristics provide significant gain There are simplifications that have been discussed and will be put before the members in a straw poll Robert Stacey, Intel John Doe, Some Company

May 2005 References 11-05-0391-00-000n-tgnsync-mac-response-to-reasons-and-cures.xls Robert Stacey, Intel