1. doc.: IEEE 802.11-09/1299r0 Submission Dec 2009 Allan Thomson, Cisco SystemsSlide 1 BSS Transition Improvements Date: 2009-12-xx Authors:

2. doc.: IEEE 802.11-09/1299r0 Submission Dec 2009 Allan Thomson, Cisco SystemsSlide 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

3. doc.: IEEE 802.11-09/1299r0 Submission Dec 2009 Allan Thomson, Cisco SystemsSlide 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

4. doc.: IEEE 802.11-09/1299r0 Submission Dec 2009 Allan Thomson, Cisco SystemsSlide 4 Solution Overview Extend BSS Transition Query and Request/Response frames to enable improved BSS Transition candidate lists Define additional behavior on the protocol

5. doc.: IEEE 802.11-09/1299r0 Submission Use Case 1 Dec 2009 Allan Thomson, Cisco SystemsSlide 5 Use casePossible reasonsEnsuing actions with a cooperating client Ensuing actions with a non-cooperating client A transition event is triggered on the client or the client feels that the preferred AP list that it last supplied to the AP is now stale -Client feels performance over the link with current AP is not satisfactory -Client feels that it has roamed to a different location -Client sends BSS Transition Query to current AP with client’s list of preferred APs. -Current AP sends BSS Transition Req to client with current AP’s list of preferred APs. (The Disassociation Imminent bit here is assumed to be set to 0, since this reply from the AP was initiated by the client’s query.) -If client decides to transition, then it should attempt to associate with the APs on the AP’s list. -Client moves to an AP that it likes without consulting with current AP, or ignores the recommendations sent by the current AP. (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.)

6. doc.: IEEE 802.11-09/1299r0 Submission Use Case 2 Dec 2009 Allan Thomson, Cisco SystemsSlide 6 Use casePossible reasonsEnsuing actions with a cooperating client Ensuing actions with a non-cooperating client Current AP wishes to move a client to another AP -Current AP performs load balancing -Current AP feels there’s another AP that can give client better performance, etc. -Current AP sends a BSS Transition Req with the Disassociation Imminent field set to 0 and without a list of preferred APs. -Client shall replies with a BSS Trans Response with a list of his preferred APs. -Then AP sends a BSS Transition Req with the Disassociation Imminent field set to 1 and with a list of preferred AP. -Since the client just supplied his list to the AP, the client has no doubts with the staleness of it and the client does not feel need to delay or reject the transition request, so the client replies with a BSS Trans Response with Status Code of Accept. -Since it’s an Accept, then the client shall attempt to associate with the APs on the AP’s list. -Client responds with a bogus or empty list. -Client ignores the recommendations sent by the current AP and moves to an AP that he likes. -If Client does nothing, AP eventually disassociates this client

7. doc.: IEEE 802.11-09/1299r0 Submission Use Case 3a Dec 2009 Allan Thomson, Cisco SystemsSlide 7 Use casePossible reasons Ensuing actions with a cooperating client Ensuing actions with a non-cooperating client Current AP wishes to move a client to another AP. AP has never asked the client for the client’s preferred list or it’s been a while since the AP asked. The cooperating client feels it should supply its preferences to the AP. Same as Case 2-Then AP sends a BSS Transition Request with the Disassociation Imminent field set to 1 and with a list of preferred AP. -Client sends a BSS Transition Query to the AP with his latest preferred list (probably after the client has performed some scanning) -Client will have at least 30 seconds to do this before being disassociated -Upon receiving of the Query frame, the AP replies with a BSS Transition Request to client with a (possibly new) list of preferred APs (and the Disassociation Imminent field set) -The client is more satisfied with the present candidate list and there’s no need to delay or reject the transition request, so the client replies with a BSS Transition Response with Status Code of Accept. -Since it’s an Accept, then the client shall attempt to associate with the APs on the AP’s list. -Client ignores the recommendations sent by the current AP and moves to an AP that he likes. -If Client does nothing, AP eventually disassociates this client

8. doc.: IEEE 802.11-09/1299r0 Submission Use Case 3b Dec 2009 Allan Thomson, Cisco SystemsSlide 8 Use casePossible reasons Ensuing actions with a cooperating client Ensuing actions with a non-cooperating client Current AP wishes to move a client to another AP. AP has never asked the client for the client’s preferred list or it’s been a while since the AP asked. But the cooperating client is happy with the AP’s list of target BSS. Same as Case 2-Then AP sends a BSS Transition Req with the Disassociation Imminent field set to 1 and with a list of preferred AP. -The client is satisfied with the current candidate list and there’s no need to delay or reject the transition request, so the client replies with a BSS Transition Response with Status Code of Accept. -Since it’s an Accept, then the client shall attempt to associate with the APs on the AP’s list. -Client ignores the recommendations sent by the current AP and moves to an AP that he likes. -If Client does nothing, AP eventually disassociates this client

9. doc.: IEEE 802.11-09/1299r0 Submission Use Case 4 Dec 2009 Allan Thomson, Cisco SystemsSlide 9 Use casePossible reasons Ensuing actions with a cooperating client Ensuing actions with a non-cooperating client Current AP wishes to obtain a fresh preferred target AP list from the client AP is just planning ahead -Current AP sends a BSS Transition Request with the Disassociation Imminent field set to 0 and without a list of preferred AP. -Client shall reply with a BSS Trans Response with a list of its preferred APs, list may be empty. -Client responds with a bogus or empty list.

10. doc.: IEEE 802.11-09/1299r0 Submission 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 Dec 2009 Allan Thomson, Cisco SystemsSlide 10

11. doc.: IEEE 802.11-09/1299r0 Submission 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 Dec 2009 Allan Thomson, Cisco SystemsSlide 11

12. doc.: IEEE 802.11-09/1299r0 Submission Behavior Changes (1a): The AP wishes to obtain the non-AP STA’s preferred list of BSS candidates 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. Dec 2009 Allan Thomson, Cisco SystemsSlide 12

13. doc.: IEEE 802.11-09/1299r0 Submission Behavior Changes (1b): The AP must include at least one BSS that the non-AP STA has provided 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) Dec 2009 Allan Thomson, Cisco SystemsSlide 13

14. doc.: IEEE 802.11-09/1299r0 Submission Behavior Changes (2): The non-AP STA is satisfied with the AP’s preferred list of BSS transition candidates 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 Dec 2009 Allan Thomson, Cisco SystemsSlide 14

15. doc.: IEEE 802.11-09/1299r0 Submission Behavior Changes (3): Time before disassociation is at least 30 seconds 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 Dec 2009 Allan Thomson, Cisco SystemsSlide 15

16. doc.: IEEE 802.11-09/1299r0 Submission Behavior Changes (4): The AP cannot disassociate a STA before time in countdown timer is up for this STA 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 Dec 2009 Allan Thomson, Cisco SystemsSlide 16

17. doc.: IEEE 802.11-09/1299r0 Submission Dec 2009 Allan Thomson, Cisco SystemsSlide 17 Questions ?