1. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 1 Access Point Collaboration for enhancing QoS and Spectrum Efficiency 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, 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@ok-brit.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.http:// ieee802.org/guides/bylaws/sb-bylaws.pdf stuart@ok-brit.compatcom@ieee.org Date: 2007-04-14 Authors:

2. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 2 Abstract This presentation describes a mechanism to allow multiple APs on the same channel to cooperatively share time on the wireless medium This enables enhanced QoS by allowing collaborating APs to avoid allocating overlapping CFPs and reduced probability of EDCA collisions Proposal fulfils item 2a “Access Point Coordination – Intra ESS” in the TGV accepted work list

3. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 3 Introduction We want to use 802.11 for “carrier grade” wireless voice & video distribution system Current QoS solutions not well suited to multiple BSS on the same channel –In some bands there are insufficient channels for every home to have its own channel –Enterprise environment may have even higher AP densities Fulfils item 2a on TGv work list –“Time coordination between APs for resource management. Could be useful for 802.11e to perform time slicing. Site Survey mode to perform tuning of the APs. Could be an initial install or on-going process.”

4. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 4 Scope Improved throughput & QoS for multiple BSS on same channel within RF range –In both domestic and enterprise environments Domestic –Over-the-air communication –No central management entity Enterprise –Wireless or DS used for communication –Possibly a central management entity

5. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 5 Example Domestic Application Multiple dwelling unit Many homes within radio range of each other Homes share channels either due to insufficient channels or imperfect channel selection

6. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 6 A Typical Enterprise Application

7. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 7 Requirements Provides benefits in all QoS modes and even non-QoS BSS –DCF, EDCA, PCF, HCCA Simple to implement –Simple to implement in AP –No changes to non-AP STAs

8. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 8 Requirements Compatible with legacy equipment Does not reduce robustness to rogue STAs –Based on “politeness” rather than ordering neighbours to be silent Allows for dynamic changes in each BSS –E.g. Number of active streams in a BSS changes Channel conditions change

9. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 9 Assumptions Only consider time-based collaboration –Assume existing amendments / management entity for optimal channel selection Relatively few BSS on same channel within radio range –Typically 2 to 3 overlapping BSS Does not try to provide perfect solution in all cases –Worst case behaviour is no worse than existing standard –Optimal solution in general case probably NP-complete

10. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 10 Time-sharing on a channel Allow two or more APs to share time on a channel –Without coordination, collisions & back-offs can cause total throughput to fall below required level Can be used to improve PCF & HCCA selection of CFP –Contention free period assumes no uncoordinated traffic Also helps CSMA/CA traffic –Reduces chances of collision with traffic from other BSS –Improves EDCA by silencing AC from other QBSS

11. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 11 AP Collaboration Proposal AP advertises that it supports collaboration –A new capability bit (from Extended Capabilities IE) in beacons and probe responses BitInformationNotes 2Time CollaborationA STA shall set the Time Collaboration capability bit to true if dot11WirelessManagementImplemented is true and the AP supports sharing of time on the wireless medium and implements the CFP Offer and CFP Offer Response action frames. Otherwise this capability bit shall be set to false. 3-nReserved

12. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 12 AP Collaboration Proposal (2) An AP can choose to offer silent time to another AP –If accepted, the AP silences its associated STAs for the specified time However, an AP can choose to “defect” –An AP does not have to repay the sacrifice of another AP –An AP offering silence can choose not to honour its offer This is an example of the “Prisoner's Dilemma” –The incredibly simple “tit-for-tat” approach has been shown to be an optimal solution –“tit-for-tat with forgiveness” better suited to a wireless network as messages can be lost

13. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 13 Tit-for-tat Collaboration Round nRound n+1 AP1AP2AP1AP2 Collaborate Defect Collaborate DefectCollaborate Defect AP1AP2Outcome Collaborate Both APs get some time on the network while the other one is silent CollaborateDefectAP2 gains extra network time at the expense of AP1 DefectCollaborateAP1 gains extra network time at the expense of AP2 Defect Both APs exhibit standard 802.11 behaviour

14. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 14 Over-the-air Collaboration Uses 2 new action frames –CFP Offer, CFP Offer Response Contents of these action frames use existing IEs –No new IEs required OrderInformation 1Category 2Action 3Dialog Token 4Quiet Element OrderInformation 1Category 2Action 3Dialog Token 4Status Code 5Quiet Element (optional) Table v53—CFP Offer frame bodyTable v54—CFP Offer Response frame body

15. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 15 Via-DS Collaboration Aimed at larger-scale enterprise applications Favors more centralized coordination architectures Key to organized radio resource reuse layouts Uses Ethernet and possibly dedicated server to coordinate APs. Contribution covers capability enablement rather than method Assumes synchronization of APs (e.g., clocking, network time) Sharing Period = Only 1 for efficiency/simplicity Requires MIB variables and related Beacon/Silent Period adjustment capability. –Capability bit (ability to comply with feature) –Beacon Offset (from absolute time reference) –Silent Period Offset (from beacon time reference) –Silent Period Duration –Grant Period Offset (from beacon time reference) –Grant Period Duration

16. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 16 Via-DS Sharing Diagram Beacon AP #1 Beacon AP #2 Beacon Offset Silent Period Offset Exclusive Use - AP #2 CFP AP #2 Silent Period Duration Grant Period Offset Grant Period Duration

17. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 17 Collaboration State Machine

18. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 18 Simulation Results Based on “medium” house model –House size based on typical UK housing –Based on typical UK construction materials Two video streams –At rates between 1Mbit/sec and 10Mbit 2.4GHz band –11g, no throughput extensions –No DLS, 2 hops per packet –EDCA and HCCA modes Each combination repeated 20 times with different random number seed –800 simulation runs, ≈6 simulated hours

19. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 19 Simulation Results For EDCA, average gain was 9% (peak gain 34%) For HCCA, average gain was 6% (peak gain 22%)

20. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 20 When is collaboration beneficial? 1.On a lightly loaded network, no need for collaboration 2.As network load increases, chances of inter-BSS collisions increase. Collaboration reduces these collisions to allow greater throughout 3.As network load exceeds achievable throughput, benefits from collaboration reduce 4.At close distances, maximum probability of collisions. 5.Eventually a sufficient distance is reached so that BSS no longer overlap 1 2 4 3 5

21. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 21 Summary The proposal described in this presentation: Improves efficiency and QoS –Reduces chances of collisions for CSMA/CA traffic –Reduces chances of CFP collisions when using PCF or HCCA Simple to implement –Largely based on existing 802.11 features –A simple Tit-for-tat algorithm provides fairness –Method to silence the BSS does not need to be specified Robust to rogue STAs –Does not provide a new vector for rogue STAs to perform denial-of- service attacks Alternative Via-DS approach for Enterprise-like use –MIB-based –Assumes synchronization means

22. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 22 Motion Motion: “Instruct the editor to include the changes in document 11-07-0084-02-000v-access-point- collaboration-enhancing-qos-and-spectrum- efficiency.doc into the TGv draft” Mover/Seconder: Result –Yes –No –Abstain

23. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 23 Straw Poll Would the group be supportive of the state diagrams from the “reference implementation” as an informative addition? Result –Yes –No

24. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 24 References

25. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 25 (Backup Material)

26. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 26 Simulation Parameters House –Size 27’ x 27’ (729 sq feet) –Brick outer wall construction with plaster on inside face –2 layers drywall inner wall construction –Plaster & wood floor construction –2 floors –8 rooms Network –2.4GHz (11bg) in European regulatory domain (ETSI EN 300 328) –100ms beacon interval –1 AP per home –6 STAs per home –2 RTP UDP video streams, each from non-AP STA to non-AP STA –7 MPEG-2 TS packets (of 188 bytes) per RTP packet Collaboration –owMin=1 –owMax=16 –offerDuration = 20ms

27. doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 27 Prisoner's Dilemma Prisoner B Stays SilentPrisoner B Betrays Prisoner A Stays SilentBoth serve six monthsPrisoner A serves ten years Prisoner B goes free Prisoner A BetraysPrisoner A goes free Prisoner B serves ten years Both serve two years Two suspects, A and B, are arrested by the police. The police have insufficient evidence for a conviction, and, having separated both prisoners, visit each of them to offer the same deal: if one testifies for the prosecution against the other and the other remains silent, the betrayer goes free. Both prisoners only care about minimizing their own jail terms. In the iterated prisoner’s dilemma, repeated rounds are made where each prisoner has memory of their previous encounters.