1. Enhancing BSS Transition Management
March 2009
doc.: IEEE /1294r1
March 2009
Enhancing BSS Transition Management
Date:
Authors:
Kenan Xu, Nortel Networks
Kenan Xu, Nortel Networks

2. March 2009
doc.: IEEE /1294r1
March 2009
Abstract
Amendment proposals (on IEEE802.11v) are made to enable a streamlined network-initiated BSS transition process when the current AP cannot honor more resource (TSPEC) requests, while neighboring APs have abundant unused radio resource.
The resulting network-initiated load shifting process is more effective, efficient and deterministic than an STA-initiated BSS transition process.
Kenan Xu, Nortel Networks
Kenan Xu, Nortel Networks

3. Overview BSS transition management in IEEE 802.11v
March 2009
Overview
BSS transition management in IEEE v
Issues with current BSS transition management process
Proposed solution to enhance the BSS transition process
Standard amendment proposal
Straw polls
Kenan Xu, Nortel Networks

4. 802.11v BSS Transition Management Procedures
March 2009
802.11v BSS Transition Management Procedures
Current AP
STA
1.TSPEC rejection
2. Load balancing
3. Excessive frame loss
4. Excessive delay, etc.
BSS Transition Query (Reason Code )
BSS Transition Request (Neighbor Report element)
BSS Transition Response (status code, target BSSID)
Kenan Xu, Nortel Networks

5. STA-initiated Load Shifting due to TSPEC Rejection
March 2009
doc.: IEEE /1294r1
March 2009
STA-initiated Load Shifting due to TSPEC Rejection
STA
Associated AP
ADDTS Request (TSPEC)
1. SUCCESS
2. INVALID_PARAMETERS
3. REJECTED_SUGGESTED_CHANGES (TSPEC)
4. REJECTED_FOR_DELAY_PERIOD
5. Tclas is not supported
6. Have no sufficient Tclas resource
There is no existing status code to indicate the opportunity of BSS transition. Hence, individual vendors must chose which status code to send and how to interpret the code.
ADDTS Response
(?status code)
BSS Transition Query (TSPEC rejection)
When the TS request is rejected, the handset doesn't know its full range of possible next steps. Currently it can retry with new Tspec settings, retry another AP based on its own logic, request a BSS transition, reject the session or wait. The best option is missing - this where the AP proactively requests a BSS transition.
BSS Transition Request (Neighbor Report element)
AP is better aware of the available network resources than the STA. AP could inform the STA of the opportunity to transition and initiate the process.
BSS Transition Response
Kenan Xu, Nortel Networks
Kenan Xu, Nortel Networks

6. Consequences of STA-initiated Load Shifting
March 2009
Consequences of STA-initiated Load Shifting
If the ADDTS Request is rejected, the mobile STA doesn't know its full range of possible next steps.
Currently, the mobile STA can:
retry with new TSPEC settings,
transition to another AP based on its own logic,
issue a BSS transition query to the current AP,
reject the session, or
wait.
Each of those alternatives involves a multistep sequence which could fail, require successive attempts or result in delays in obtaining the desired traffic service.
The best alternative is missing – this where the AP proactively orchestrates a BSS transition by the mobile STA to another nearby AP that can accommodate the ADDTS Request.
Kenan Xu, Nortel Networks

7. Benefits of Network Initiated Load Shifting Alternative
March 2009
Benefits of Network Initiated Load Shifting Alternative
Driving the BSS transition from the AP at the precise time it is needed would create an efficient network initiated load shifting mechanism
Improves the efficiency of the transition process
This is especially important for voice handsets at call initiation, when response time is critical.
Coupling the initiation of the BSS transition to the ADDTS Response reduces the multiple alternative courses of action into a definitive directive to the mobile STA.
a single atomic operation, which makes the transition process much more deterministic.
Kenan Xu, Nortel Networks

8. Network-Initiated Load Shifting Solution
March 2009
Network-Initiated Load Shifting Solution
A status code indicates the BSS Transition opportunity.
Neighbor report element piggybacked on the ADDTS Response frame leads to a streamlined BSS transition process.
STA
Associated AP
ADDTS Request (TSPEC)
ADDTS Response (status, BSS Transition Candidate List)
Kenan Xu, Nortel Networks

9. ADDTS Response Frame March 2009
n+3 BSS Transition Candidate List Entries
Kenan Xu, Nortel Networks

10. Including All the Transition Information
March 2009
Including All the Transition Information
For an effective network initiated BSS Transition, more information than just the BSS Transition Candidate List is needed as part of the ADDTS Response frame.
That information is already defined as the BSS Transition Request frame, see v D4.01 clause
Hence, all the needed BSS transition information can be included by appending the entire contents of the BSS Transition Request frame to the ADDTS Response frame under the cited conditions, i.e. when the new status code is used.
Kenan Xu, Nortel Networks

11. ADDTS Response Frame March 2009 n+3 BSS Transition Request frame
Kenan Xu, Nortel Networks

12. Standard Amendment Proposal
March 2009
Standard Amendment Proposal
Add the new status code REJECTED_WITH_SUGGESTED_BSS_TRANSITION, to be optionally used by an AP within an ADDTS Response frame.
If an AP rejects a TSPEC request and is aware of alternative candidate APs that can meet the request and the non-AP STA supports the BSS Transition capability, the AP can set the status code to REJECTED_WITH_SUGGESTED_BSS_TRANSITION and append the BSS Transition Request frame to the ADDTS Response frame.
Within the appended BSS Transition Request frame the following must be provided:
Preferred Candidate List Included = 1
Abridged = 0
BSS Transition Candidate List Entries
A non-AP STA receiving such a message immediately starts the BSS transition process.
Affected clauses:
Status Code field
ADDTS Response frame format
MLME-ADDTS.confirm
MLME-ADDTS.response
TS Setup
BSS Transition Management for Network Load Balancing
Kenan Xu, Nortel Networks

13. March 2009
Summary
Proposal to streamline network-initiated BSS transition (load shifting) by coupling the TS setup process to the BSS transition process using a designated status code.
A STA becomes aware of all opportunities when a TSPEC request is denied. The BSS transition process is expedited by adopting one of the entries in the BSS Transition Candidate List in the ADDTS Response frame.
The solutions are simple (limited amendments) and effective (compared to STA-initiated process).
Kenan Xu, Nortel Networks

14. References IEEE Std. 802.11-2007 IEEE 802.11v D4.01, January 2009
March 2009
doc.: IEEE /1294r1
March 2009
References
IEEE Std
IEEE v D4.01, January 2009
v-Enhancing-BSS-Transition-Management.doc, this is the corresponding .doc submission to accompany this presentation.
Kenan Xu, Nortel Networks
Kenan Xu, Nortel Networks

15. March 2009
doc.: IEEE /1294r1
March 2009
Straw Poll Questions
Do you agree that there is a need to streamline the BSS transition process as described in this presentation? Yes: No: Abstain:
Do you agree that the solution presented in this presentation should be included in the new revision of the v draft? Yes: No: Abstain:
Kenan Xu, Nortel Networks
Kenan Xu, Nortel Networks