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Proposed AP Collaboration Comment Resolution

Proposed AP Collaboration Comment Resolution. Authors:. Date: 2008-11-09. Abstract.

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Proposed AP Collaboration Comment Resolution

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  1. Proposed AP CollaborationComment Resolution Authors: Date: 2008-11-09 Lusheng Ji, AT&T et. al.

  2. Abstract AP Collaboration was identified as an important component of TGv’s work from the beginning (as long ago as May 2005 in Cairns). It was one of the reasons TGv was begun. Support for provisions to allow improved interference control via AP collaboration has been documented in the objectives and reinforced by group approval. This contribution addresses LB133 comments 1274, 1404, 1411, and 400 for AP collaboration within an infrastructure BSS complex and recommends a MIB-based foundation for time-sharing of the radio resource by multiple APs over the DS. Emulation results disclose significant loss of throughput with overlapping BSSs, reinforcing previous simulations by other contributors. No impact on air interface overhead will result from adoption, the feature uses an existing Spectrum Management mechanism, and the MIB variables would be exercised only by those who wish to leverage the technique. Lusheng Ji, AT&T et. al.

  3. AP Collaboration – A TGv Retrospective • AP Load Balancing 05/0370r2, Qi, Epstein, Cairns 2005 • AP Collaboration introduced by Epstein, Cairns 2005 • AP Collaboration/Load Balancing moved into TGv Objectives, July 2005 • Spectrum Etiquette05/0906r0, Roger Durand incl. AP Time Sharing • Numerous contributions on Load Balancing • San Diego, Pat Calhoun “Filters” Objectives by Vote (AP Coordination Endorsed by Group) • Ashley Contribution on AP Collaboration (08-0086r0) • Ashley/AT&T Contribution adds DS Collaboration (07-2115r0) • TGv endorses keeping AP Collaboration Active Prior to First Ballot • Graham Smith Contribution Interference/QoS analysis (07-2684r1) • AP Collaboration via DS MIB Variable “Hooks”, Ji, May 08, (08-0419r1) • 08/1059r0 presented Sept 2008, comment declined with reworded resolution and approved by group. Lusheng Ji, AT&T et. al.

  4. AP Collaboration – This Updated Contribution • Replies to comment CID #1274 and similar comments • Responds to feedback from group and comment resolution • Provides improvements/clarifications • MIB update executed only when no associations / sessions are underway (responsive only to interference caused by cell coverage areaoverlap) • AP issues CTS-to-self if any clients non-DFS compliant • Clarification on AP quiet-period overlap (allowed) • Requests entry of revised normative text into TGv draft Lusheng Ji, AT&T et. al.

  5. A Typical Enterprise Application Lusheng Ji, AT&T et. al.

  6. AP Collaboration – Why Is It Important Now? • Failure to provide the “hooks” to address the problem will place 802.11 at a disadvantage in managed network environments. • Increasingly dense AP configurations with finite radio resource • Heavy adoption of 802.11g due to 2.4 GHz indoor propagation benefits (very limited set of clear channels) • Current Problem: Sharing in unplanned or loosely-planned AP layouts must depend on CSMA and “trial & error” frequency planning to manage the radio resource. • Longer Term Problem: In automatically-optimized environments, co-channel interference may be irreducible due to limited reuse complement and unavoidable propagation-coupling between cells. • Multimedia traffic requires stronger wireless network management (streaming tolerates less error and latency, elevates throughput demand) • Outdoor/indoor OBSS situations becoming more common. • 802.11n requires more channel bandwidth and higher S/N to sustain throughput / link quality, reducing channel reuse complement further. • AP Collaboration extensions could improve 802.11n 20/40 MHz sharing. Lusheng Ji, AT&T et. al.

  7. Motivation for AP Collaboration Capability • OBSS has been discussed as a problem for a very long time (pre-QoS). Simulations have well-documented the difficulties. • Managed infrastructure systems provide sufficiently constrained sub-case to make the OBSS problem tractable. • Previous proposal (08-0419r1) generated concerns regarding quantification of interference deterioration due to OBSSs. • Action: Investigate conjecture that random access protocols like CSMA have scalability problems in dense wireless environments by measuring two related phenomena: • Data rate degradation (radio resource utility) • Latency and time jitter increase (quality) • Create radio emulation to quantify degree of impairment. The following experiments and results are excerpted from: “An experimental study of inter-cell interference effects on system performance in unplanned wireless LAN deployments”. M. A. Ergin, K. Ramachandran, and M. Gruteser. Computer Networks (Elsevier), Volume 52, Issue 14, October 2008, pp. 2728-2744. Lusheng Ji, AT&T et. al.

  8. ORBIT Testbed • ORBIT Wireless Testbed at WINLAB, Rutgers University http://www/orbit-lab.org , consists of 400 802.11 nodes arranged in a rectangular grid. Mini ITX PC Antennas Lusheng Ji, AT&T et. al.

  9. Test Setup Lusheng Ji, AT&T et. al.

  10. Legend 1 Access Point Client < 20 m 2 Coverage 3 < 2 m 4 < 20 m Experiment Setup: 1-4 APs, 75 clients, all within carrier sense range of each other Lusheng Ji, AT&T et. al.

  11. Conclusion: CSMA does not scale with #APs 1 AP, 75 STA 2 APs, 75 STA 4 APs, 75 STA 3 APs, 75 STA Steady-state throughput drops by 50% as number of APs are increased from 1 to 4. Lusheng Ji, AT&T et. al.

  12. Jitter Increases with #APs Simulated VoIP MOS results for varying intensities of multimedia traffic carried over one and four AP networks using IEEE 802.11e (WMM) Lusheng Ji, AT&T et. al.

  13. Establishing Quiet Periods Lusheng Ji, AT&T et. al.

  14. ns-2 AP Collaboration Simulation Simulation Details: ns-2 yans, 802.11e, 5 GHz, all VoIP traffic, G.711 codec, 20 ms packet interval, 200 bytes, 5% packet loss maximum to determine call limit, random distribution of clients over OBSSs. Lusheng Ji, AT&T et. al.

  15. AP Collaboration - Comment Resolution Responsesand Contribution Revisions The TG considered adopting the text in 08-0419-02; The motion to adopt the text failed, 7-6-7. Concerns include: Synchronous voice and video will be suppressed, without the ability for codecs to compensate. Codecs improve performance to adapt to the links. Response: Normative text added to indicate radio resource partitioning will not be conducted with assocations/streams underway. This also eliminates the need for multiple MIB quiet element table growth to avoid “freezing out” active synchronous traffic. Lusheng Ji, AT&T et. al.

  16. AP Collaboration - Comment Resolution Responsesand Contribution Revisions (cont.) Legacy 2.4 GHz STAs (including dual-mode cell phones) will not honor the Quiet element, and many do not have a dot11SpectrumManagementEnabled MIB variable. Response: It is believed that widespread adoption of 802.11k will result from the need of carrier-operated systems to sample the radio environment. The quiet element will thus gain wider use in 2.4 GHz. Moreover, cellphone product cycles are such that any non-compliant 802.11-equipped units will be “flushed” from use as time progresses. If any non-capabile clients associate, the AP will create a CTS-to-self. Other task groups (e.g. TGn) have used AP CTS-to-self to create an equivalent quiet period. Lusheng Ji, AT&T et. al.

  17. AP Collaboration - Comment Resolution Responses and Contribution Revisions (cont.) No provision for asynchronous MIB changes among the APs is provided - with bad radio links, how do the incremental MIB changes affect BSS operation during the MIB changes - how does QoS work while the dot11APCEntry suppression tables are being changed, and when  dot11xxxAPCollaborationEnabled changes value, how to calculate and communicate the new TCLAS? Response: The normative text has been updated to indicate the MIB changes will only take effect when there are no sessions in progress. The MIB is updated over the DS, not over the air. As updates are not allowed while accociations/sessions are underway, it is not necessary to modify TCLAS, TSPECs, and schedule elements “on the fly” (this also eliminates MIB table depth concerns). Lusheng Ji, AT&T et. al.

  18. AP Collaboration – Comment Resolution Responsesand Contribution Revisions (cont.) No exceptions to suppression in order to meet regulatory requirements like E-9-1-1 Response: If an E-9-1-1 or other session is active, the MIB change will not be executed. No exceptions to suppression when operating in shared bands - to report radar, change channel, DSE, etc. Response: The inhibition on MIB changes with sessions in progress includes sessions which may be subject to power saving sleep/wake or other processes. Lusheng Ji, AT&T et. al.

  19. Conclusions/Recommendations • Need for AP collaboration justified via measurements. • Simulation data presented to demonstrate improvement using capability • No impact on air overhead, or those who do not wish to use • Limitation on when collaboration may be initiated imposed, treating September 2008 comment feedback . • Normative text updated to reflect improvements (08/0419r3). • Recommend incorporating normative text into TGv draft • Motion offered. Lusheng Ji, AT&T et. al.

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