BSS Transition Improvements

1. BSS Transition Improvements Authors: Date: 2009-12-xx Allan Thomson, Cisco Systems

2. Abstract This proposal highlights improvements to BSS Transition that enable the AP to provide a “better” set of transition candidates to the non-AP STA The goal is to provide an improved roaming behavior for both the non-AP STA and the AP managing the BSS Allan Thomson, Cisco Systems

3. Problem The AP determines the BSS Transition Candidate list based on its own knowledge of the environment This results in potentially a BSS Transition Candidate List that does match the non-AP STA’s list or preferences Non-AP STAs have no way of providing to the AP the list of preferred BSS Transition candidates from their perspective Allan Thomson, Cisco Systems

4. Solution Overview Extend BSS Transition Query and Request/Response frames to enable improved BSS Transition candidate lists Define additional behavior on the protocol Allan Thomson, Cisco Systems

5. Use Case 1 (The implication in here and the following use cases is that the AP would have used the client’s list and preferences to make best recommendation in the request.) Allan Thomson, Cisco Systems

6. Use Case 2 Allan Thomson, Cisco Systems

7. Use Case 3a Allan Thomson, Cisco Systems

8. Use Case 3b Allan Thomson, Cisco Systems

9. Use Case 4 Allan Thomson, Cisco Systems

10. Add BSS Transition Candidate List Entries field • Allows the non-AP STA to provide a list of target transition BSSs and relative preferences • Add BSS Transition Query Reason code • (ANA) Providing STA BSS Transition Candidate List • Enhance AP Behavior • Will consider them in addition with the AP’s own candidates when determining the best BSS transition candidates for the non-AP STA Query Frame Changes Allan Thomson, Cisco Systems

11. Add BSS Transition Candidate List Entries field • Allows non-AP STA to provide the AP with a list of target transition BSSs and the relative preferences for transitioning there • Add a Status code • (5) Reject – STA BSS Transition Candidate List provided • Enhance AP Behavior • AP will consider them in addition with the AP’s own candidate list when determining the best BSS transition candidates for this non-AP STA Response Frame Changes Allan Thomson, Cisco Systems

12. The AP sends a BSS Transition Management Request frame with • Disassociation Imminent field set to 0 • Preferred Candidate List Included field set to 0 • The non-AP STA shall reply with a BSS Transition Management Response frame, wherein the Status Code is set to 5 (Reject - STA BSS Transition Candidate List provided) • If the non-AP STA has information on BSS transition candidates or wishes to share such information, then the non-AP can include them in the BSS Transition Candidate List of the response frame; otherwise the list is empty. Behavior Changes (1a): The AP wishes to obtain the non-AP STA’s preferred list of BSS candidates Allan Thomson, Cisco Systems

13. The non-AP STA has provided a non-empty BSS Transition Candidate List Entries in a Query or Response frame • Then in any BSS Transition Management Request frames that the AP sends to this non-AP STA, the frame shall include at least one BSS from the non-AP’s list entries • This entry shall not have preference value of 0 • (0 = refrain from associating to this listed BSS) Behavior Changes (1b): The AP must include at least one BSS that the non-AP STA has provided Allan Thomson, Cisco Systems

14. The AP sends a BSS Transition Management Request frame with: • Disassociation Imminent field set to 1 • Preferred Candidate List Included field set to 1 • An non-empty list of ranked BSS transition candidates • If the non-AP STA is satisfied with the AP’s list: • The non-AP shall reply with a BSS Transition Management Response frame with Status code set to 0 (Accept) • The non-AP shall disassociate with the current AP • The non-AP STA shall attempt to re-associate with the BSSs in listed in the Request frame’s BSS Transition Candidate List Behavior Changes (2): The non-AP STA is satisfied with the AP’s preferred list of BSS transition candidates Allan Thomson, Cisco Systems

15. After the first BSS Transition Management Request frame sent to a non-AP STA with Disassociation Imminent field set to 1: • The Disassociation Timer field is a number of TBTTs that is at least 30 seconds or “0” (disassociate time not decided yet) • AP keeps a countdown timer starting with the Disassociation Timer value (if it is not “0”) or a number of TBTT at least 30 seconds (if Timer is “0”) • Countdown timer is decremented by 1 with each beacon transmitted • In any subsequent BSS Transition Management Request frame sent to this non-AP STA, the Disassociation Timer shall be set to the value in the countdown timer Behavior Changes (3): Time before disassociation is at least 30 seconds Allan Thomson, Cisco Systems

16. After the first BSS Transition Management Request frame sent to a non-AP STA with Disassociation Imminent field set to 1 • AP begins a countdown timer for this non-AP STA (see previous slide) • The AP shall not send a Disassociate frame to this non-AP STA before the countdown timer for this non-AP STA has attained value 0 • If the AP changes its mind on disassociating this non-AP STA, then the AP simply sends a new Request frame with Disassociation Imminent set to 0 Behavior Changes (4): The AP cannot disassociate a STA before time in countdown timer is up for this STA Allan Thomson, Cisco Systems

17. Questions ? Allan Thomson, Cisco Systems