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802.11-08/0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 1 Peer Traffic Indication enhancements Date: 2008-07-15 Authors:

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1 /0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 1 Peer Traffic Indication enhancements Date: Authors:

2 /0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 2 Abstract The presentation describes mechanisms to enhance the power save principles by using Peer Traffic Indication frame. The enhancements introduce capability to detect ‘out- dated’ PTI frame and define a simple activation mechanism for the Direct Link.

3 /0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 3 Outdated PTI frame problem 1.STA1 transmits a PTI frame through AP to peer STA2 2.STA2 triggers a service period with the STA1 before it gets the PTI indication from the AP. Service period between STA1 and STA2 is performed and terminated 3.The STA2 gets indication of buffered traffic in AP through the Beacon and fetches the buffered PTI frame 4.Because of the received “out-dated" PTI frame, the STA2 triggers a unnecessarily a service period with STA1, while the traffic is already transmitted in previous service period This is likely scenario, because Beacon transmission periodicity is usually ~100ms and not all Beacons are necessarily received by the STA in power save mode AP STA1 Active mode STA2 Power save mode 2. Service period Service period

4 /0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 4 Solution, detection of the out-dated PTIs A PTI frame needs an information element which enables the receiver of the PTI frame to detect if the PTI frame is out-dated –Detection may be done by including a Sequence Number of the last transmitted frame in the Direct Link of the highest AC which backlogged field was set to non-zero value to PTI frame If target STA detects that PTI frame is out-dated, it may ignore the frame –This eliminates unnecessary service periods and results in better power save

5 /0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 5 Two STAs supporting Peer U-ASPD According to current draft even though two stations indicate support for Peer U-APSD only one peer STA at a time may operate in power save mode –The selection of the operation in power save mode is based on the competition: Slower STA to signals operation in power save mode is forced to operate in active mode This creates a race condition: battery powered STA wants only to operate in power save mode – If it temporarily changes itself to active mode, it may be forced to operate in active mode, i.e. its peer STA is able to signal the operation in power save mode AP STA1 Active mode STA2 Power save mode Direct Link Association

6 /0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 6 Peer U-ASPD, Peer STAs operating in power save mode Both Peer STAs need to be allowed to operate in power save mode –To avoid unbalanced power consumption between STAs –To avoid race condition and optimal power management mode selection based on offered traffic PTI frame may be used to setup a service period when both peer STAs operate in power save mode

7 /0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 7 Two different wakeup schedule negotiation procedures in Peer PSM In Peer PSM wakeup schedule negotiation between peer STAs is done in two ways: –Over the direct link (when starting Peer PSM operation) Before negotiation both STAs in awake state on direct link, i.e. the direct link is used for frames transmission –Over the AP path (when activating the schedule) Before negotiation both STAs in doze state on direct link, i.e. the direct link cannot be used for frames transmission

8 /0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 8 Unified wakeup schedule negotiation procedure This mechanism assumes that both STAs are in awake state before starting schedule negotiation procedure. – When wakeup schedule is deactivated PTI frame transmission over the AP path can be used to assure that both STAs are in awake state. –After both STAs are in awake state wakeup schedule negotiation over the direct link can take place

9 /0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 9 Additional advantage of PTI frame If STA cannot buffered packets until the next wakeup period (e.g. due to missed wakeup periods) then it has to discard buffered packets Solution PTI frame is used to indicate that a STA has buffered frames for peer STA on direct link The same usage as in Peer U-APSD could be advantages for STAs in Peer PSM Allowing STA to trigger intermediate PSP with PTI frame could help to improve that situation

10 /0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 10 Strawpolls Does the group support the proposed framework to address outdated PTI frames? –Yes –No –Not sure Does the group see the need to address Peer U-APSD use case where both the STAs are in PS mode to ensure completeness of the Peer U-APSD mechanism ? –Yes –No –Not sure

11 /0853r1 Submission July 2008 Jakub Majkowski (Nokia)Slide 11 Strawpolls Does the group see the need for a single wake up schedule negotiation procedure ? –Yes –No –Not sure Does the group support using PTI frame to have a fall back mechanism to address data overflow ? –Yes –No –Not sure


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