doc.: ieee 802.11-08-1059 r1 submission november, 2008 lusheng ji, at&t et. al.slide 1 proposed...
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November, 2008
Lusheng Ji, AT&T et. al.
Slide 1
doc.: IEEE 802.11-08-1059 r1
Submission
Proposed AP CollaborationComment Resolution
Date: 2008-11-09
Name Affiliations Address Phone email R. R. Miller Leonid Razoumov
AT&T 180 Park Avenue Florham Park, NJ, 07932
+1 973-236-6920 +1 973-360-8745
[email protected], [email protected]
Kishore Ramachandran
WINLAB, Rutgers University
WINLAB, 671 Rt. 1 New Brunswick, NJ
+1 518-221 8072
Bill Marshall AT&T 180 Park Avenue Florham Park, NJ, 07932
+1 973-360-8718
David Hunter Panasonic 550 S. Winchester San Jose, CA 95128
+1 805-259-8564
Authors:
November, 2008
Lusheng Ji, AT&T et. al.
Slide 2
doc.: IEEE 802.11-08-1059 r1
Submission
AbstractAP 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.
November, 2008
Lusheng Ji, AT&T et. al.
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doc.: IEEE 802.11-08-1059 r1
Submission
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 Etiquette 05/0906r0, 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.
November, 2008
Lusheng Ji, AT&T et. al.
Slide 4
doc.: IEEE 802.11-08-1059 r1
Submission
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 area overlap)– 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
November, 2008
Lusheng Ji, AT&T et. al.
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doc.: IEEE 802.11-08-1059 r1
Submission
A Typical Enterprise Application
November, 2008
Lusheng Ji, AT&T et. al.
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doc.: IEEE 802.11-08-1059 r1
Submission
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.
November, 2008
Lusheng Ji, AT&T et. al.
Slide 7
doc.: IEEE 802.11-08-1059 r1
Submission
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:1. Data rate degradation (radio resource utility)2. 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.
November, 2008
Lusheng Ji, AT&T et. al.
Slide 8
doc.: IEEE 802.11-08-1059 r1
Submission
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.
Antennas
Mini ITX PC
November, 2008
Lusheng Ji, AT&T et. al.
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doc.: IEEE 802.11-08-1059 r1
Submission
Test Setup
Attribute Value
Wireless Modems Atheros AR5212 mini-PCI 802.11a/g, 18dBm Tx max.
PHY/Freq./Rate 802.11a, UNII 5.2GHz, up to 54Mbits/sec
Software Linux 2.6.18 with MadWifi svn.21XX
Radio Nodes 1GHz VIA C3 Processor, 512MB RAM, 20GB HDD
Node Topology 20 x 20 Rectangular grid of 400 nodes. Up to 12 nodes are APs, up to 399 randomly-chosen nodes are STAs
Traffic Types TCP, UDP, VoIP
November, 2008
Lusheng Ji, AT&T et. al.
Slide 10
doc.: IEEE 802.11-08-1059 r1
Submission
Experiment Setup: 1-4 APs, 75 clients, all within carrier sense range of each other
3
4
1
2
Access Point
Client
Legend
Coverage
< 20 m
< 2 m
< 20 m
November, 2008
Lusheng Ji, AT&T et. al.
Slide 11
doc.: IEEE 802.11-08-1059 r1
Submission
Conclusion: CSMA does not scale with #APs
1 AP, 75 STA 2 APs, 75 STA
3 APs, 75 STA 4 APs, 75 STA
Steady-state throughput drops by 50% as number of APs are increased from 1 to 4.
November, 2008
Lusheng Ji, AT&T et. al.
Slide 12
doc.: IEEE 802.11-08-1059 r1
Submission
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)
November, 2008
Lusheng Ji, AT&T et. al.
Slide 13
doc.: IEEE 802.11-08-1059 r1
Submission
Establishing Quiet Periods
AP#1
AP#2
Beacon AP#1
Beacon AP#2
Channel access suppressed
Channel access suppressed
Precedence in channel access
Precedence in channel access
Beacon Offset
Grant Period Duration
Suppressed Period Offset
Suppressed Period Duration
Grant Period Offset
Grant Period Duration
Suppressed Period Offset
Suppressed Period Duration
Grant Period Offset
November, 2008
Lusheng Ji, AT&T et. al.
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doc.: IEEE 802.11-08-1059 r1
Submission
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.
November, 2008
Lusheng Ji, AT&T et. al.
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doc.: IEEE 802.11-08-1059 r1
Submission
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.
November, 2008
Lusheng Ji, AT&T et. al.
Slide 16
doc.: IEEE 802.11-08-1059 r1
Submission
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.
AP Collaboration - Comment Resolution Responsesand Contribution Revisions (cont.)
November, 2008
Lusheng Ji, AT&T et. al.
Slide 17
doc.: IEEE 802.11-08-1059 r1
Submission
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).
November, 2008
Lusheng Ji, AT&T et. al.
Slide 18
doc.: IEEE 802.11-08-1059 r1
Submission
AP Collaboration – Comment Resolution Responsesand Contribution Revisions (cont.)
No exceptions to suppression in order to meet regulatory requirements like E-9-1-1Response: 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.
November, 2008
Lusheng Ji, AT&T et. al.
Slide 19
doc.: IEEE 802.11-08-1059 r1
Submission
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.