1. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 1 AP Load Balancing Requirements 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 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.pdfstuart.kerry@philips.compatcom@ieee.org Date:2005-05-18 Authors:

2. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 2 Abstract This document suggests AP load balancing requirements for Wireless Network Management, specifically providing motive for the concept, reviewing some current practices, and suggesting requirements based on use case.

3. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 3 Agenda Rationale for AP Load Balancing Current Practices AP-STA Cooperative Load Balancing Suggested Load Balancing Messages

4. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 4 Unbalanced Wireless Network Throughput No. of users AP and Clients need to collaborate for optimal network use

5. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 5 AP Load Balancing Throughput No. of users AP and Clients balance load to optimize network use

6. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 6 Rationale for AP Load Balancing Increase WLAN aggregate throughput by increasing individual STA throughput Improve user experience by more optimally distributing the load over serving APs Balancing load to improve QoS effectiveness for VoIP and Video stream Suggested Requirement: TGv shall support AP load balancing to improve wireless network throughput and QoS effectiveness.

7. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 7 Current Practices: Client This is only a summary, glossing over many details. There are many ways of improving, often significantly, the following mechanism; these are not suggestions Client-based Load Balancing –Often assumes AP will offer service to the client if the client asks Typical approach –Client maintains scan list, of channels and BSSs available on each channel –When client scans, it builds information about the quality of the channel How busy is the channel? Characterization of signal and noise Number of serving APs –Some methods further are able to derive AP-reported load information from the beacon 802.11e QBSS load field provides this mechanism; there are private mechanisms as well

8. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 8 Current Practices: Client (2) Advantages: –Client may have better information about its intended load (if client drives load) –Client specifically knows the amount of signal and the degree of interference that it receives –Client knows exactly which APs the client can hear, and can find out which APs can hear it –Once implemented, works with many different flavors of APs that do not track load, often showing immediate improvements; makes no preconditions on the network Disadvantages: –Network has better view of BSS loads: client selection can lead to both global and local non- optimization –AP can not directly measure channel conditions at client –Not enough visibility to administrator as to why a client made a decision, or what its second choices, etc., are –Not fair to other clients in a strongly heterogeneous client environment; sometimes also does not provide local gains in that case –Can have difficulties converging when AP also tries to balance load

9. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 9 Current Practices: Network This is only a summary, glossing over many details. There are many ways of improving, often significantly, the following mechanism; these are not suggestions Network-based Load Balancing –Often assumes client will make selection decisions based on reception of particular frames (Probe Responses, etc.), or that client selection algorithm is stable Typical approach –Network maintains list of APs that can serve a particular client –Network maintains measurements of both channel and BSS load and AP- sensed channel characteristics –Network selects which AP ought to serve the client –Client entry: when client sends Probe Requests to the APs, the intended serving AP responds and the others don’t –Steady state: AP Deauthenticates client, moves to “Client entry” state

10. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 10 Current Practices: Network (2) Advantages: –Network can have global view of channel and BSS load: can avoid global and local non- optimalities –Network may have more accurate measurements of channel than scanning clients –As the number of APs << number of clients, and as APs are always connected, managing and diagnosing the load balancing “parameters” or inputs can be far easier –Can enforce fairness or fight self-serving behavior –Can lead to determinacy Disadvantages: –High overhead –Often requires assumptions on client’s scanning/selecting behavior –Client has better view of which APs it can see than the network –Client has better view of intended load and application (perhaps obviated with admission control in a QoS context) –Client has better view of channel conditions at client, given equal observation times –Makes a major precondition on the network –Might not work well when more than one network offers service in the same area: fringe issues –Can have difficulties converging when client also tries to balance load

11. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 11 Recommendation Split by use case Require a flexible schema/format definition for exchanging AP- provided lists of preferred APs Require that policies can determine whether such information exchange as behavioral requirements on client Require that the intended behavior is apparent in every frame that effects load balancing Suggested Requirements: TGv shall require the use of one and only one format for representing the list of BSSIDs and channels to the station, to indicate roaming options TGv shall require that the one format be embeddable in the necessary management frames that provides the indication for load balancing TGv shall require that the required behavior of the client be evident from each and every frame that provides the indication for load balancing

12. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 12 AP-STA Cooperative Load Balancing AP sends STA Load Balancing management message, which includes: –A list of one or more nearby lightly loaded APs (candidate APs) that it recommends, which may include fields from Neighbor Report Element (TGk) and Fast BSS Transition IEs (TGr) –Timeliness indication for expiration time –Strong/Mild indication for gravity (e.g. Strong = STA really should consider this or face potential service degradation or disruption; Mild = service would probably be better if STA moved; etc) Once STA receives this message, STA can decide which AP to roam from the recommended AP list, and initiate attempts to gain service from the selected AP in order of gravity. The STA must exhaust the given list before attempting to gain service on APs not on that list Suggested Requirement: TGv shall support AP and STA Cooperative Load Balancing

13. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 13 Possible Load Balancing Messages Load Balancing Message –TGv Action Frame Disassociation (or D. Imminent) Message if AP requires motion –For unambiguity, if we expect no more need for connectivity with current AP Admission Control Response Message if the status is rejected –802.11e Action Frame (Re-)association Response Message if the status is rejected –802.11 Management Frame –There may be authentication problems with this approach that we might have to resolve somehow

14. doc.: IEEE 802.11-05/0370r2 Submission May 2005 Emily Qi et alSlide 14 Feedback?