Clarifications for Peer Service Period

1. Clarifications for Peer Service Period Authors: Date: 2009-03-05 Jarkko Kneckt, Nokia

2. Abstract • The presentation defines simplifications to Peer Service Period initiation • The document describes the use of EOSP bit and handling logic for the service periods as response to 11-09/121r0 Jarkko Kneckt, Nokia

3. Recap of Peer Service Period • The Peer Service Periods consists of three phases: • Initiation • Simplified conditions for Peer Service Period triggering when Mesh STAs operate in power save mode • Data transfer, one or multiple TXOPs • No changes to logic • Termination, last transmitted frame contains EOSP bit set to 1 • No changes to logic Jarkko Kneckt, Nokia

4. Peer Service Period triggering according to 802.11s D2.07 • The Peer Service Periods may be triggered during the Awake Window or after indication of the buffered traffic • During Awake Window one peering may trigger multiple peer service periods • After indication of buffered frames to Mesh STA in light sleep mode, a trigger frame from the light sleep mode Mesh STA is expected Jarkko Kneckt, Nokia

5. Motivation to Change the Triggering Logic • The duration of the Awake Window may be difficult to estimate, in fact 802.11s D2.07 allows the Awake Window to continue depending on the frames in transmission • The longer the Awake Window is, the better opportunity to trigger a peer service period • The Awake Window should offer an opportunity to trigger a Peer Service Period • If multiple peer service periods are triggered, the duration of the service period needs to be known precisely to determine is the peer service period triggered or not Jarkko Kneckt, Nokia

6. Simplification for Peer Service Period Triggering • Only one Peer Service Period may be triggered per one Awake Window or per indication of available traffic to peer STA in light sleep mode • Acknowledgement to Peer Trigger frame confirms also the initiation of the peer service period Jarkko Kneckt, Nokia

7. Examples of the Current Triggering Mechanisms Jarkko Kneckt, Nokia

8. Current Awake Window Handling (1/3) During the Awake Window, the Peer Service Periods between Mesh STAs may be closed by the owner of the Awake Window. A data or null frame from peer STA will always triggers a peer service period. Beacon Data|Null frame, EOSP=0 Ack Data|Null frame, EOSP=1 Ack Data|Null frame, EOSP=1 Ack Data|Null frame, EOSP=1 Ack = Awake Window Mesh STA B Mesh STA A = Mesh STA is transmitter in Peer Service Period = Mesh STA is receiver in Peer Service Period Jarkko Kneckt, Nokia

9. Current Awake Window Handling (2/3) After the Awake Window has expired, the received frame will not trigger a peer service period. Here the problem is that both STAs should have the same understanding of the Awake Window duration. Beacon Data|Null frame, EOSP=0 Ack Data|Null frame, EOSP=1 Ack Data|Null frame, EOSP=1 Ack = Awake Window = Mesh STA is transmitter in Peer Service Period = Mesh STA is receiver in Peer Service Period Mesh STA B Mesh STA A Jarkko Kneckt, Nokia

10. Current Handling of Overlapping Awake Windows (3/3) If peer STAs have overlapping Awake Windows, the STAs may return to doze state only after both Awake Windows have expired. Similar problem that the both Mesh STAs should know the exact durations of the both Awake Windows. Beacon Beacon Data|Null frame, EOSP=0 Ack Data|Null frame, EOSP=1 Ack Data|Null frame, EOSP=1 Ack Data|Null frame, EOSP=1 Ack = Awake Window Data|Null frame, EOSP=1 Ack = Mesh STA is transmitter in Peer Service Period = Mesh STA is receiver in Peer Service Period Mesh STA B Mesh STA A Jarkko Kneckt, Nokia

11. Simplification, One Peer Trigger Frame per Beacon Interval of a Mesh STA Jarkko Kneckt, Nokia

12. Simplified Awake Window Handling, One Peer Trigger per Awake Window Beacon During the Awake Window one trigger frame to owner of the Awake Window may be transmitted. After the trigger frame transmission, the following frames are not considered as trigger frames The peer service periods continue until they are terminated by the set EOSP bit in the last transmitted frame. Data|Null frame, EOSP=0 Ack Data|Null frame, EOSP=1 Ack Data|Null frame, EOSP=1 Ack Mesh STA B Mesh STA A = Awake Window = Mesh STA is transmitter in Peer Service Period = Mesh STA is receiver in Peer Service Period Jarkko Kneckt, Nokia

13. Simplified Handling of Overlapping Awake Windows (1/2) If both Mesh STAs have transmitted their Mesh Beacons the same trigger frame during the overlapping Awake Windows serves the both STAs. Beacon Beacon Data|Null frame, EOSP=0 Ack • Triggering for both Awake Windows • Even if the both Mesh STAs set own trigger frames into transmission, the frames may be transmitted without problems: • EOSP bit in the transmitted frame coordinates is the transmitter continuing data transmissions in peer service period, i.e. the transmitter has full control to the service period Data|Null frame, EOSP=1 Ack Data|Null frame, EOSP=1 Ack = Awake Window = Mesh STA is transmitter in Peer Service Period = Mesh STA is receiver in Peer Service Period Mesh STA B Mesh STA A Jarkko Kneckt, Nokia

14. Simplified Handling of Overlapping Awake Windows (2/2) A Mesh STA has transmitted Beacon and the Service period is still ongoing when the other STA transmits its Beacon. The frame after Mesh STA B Beacon transmission is considered as trigger frame. Beacon Data|Null frame, EOSP=0 Ack Data|Null frame, EOSP=1 Ack Triggering for Awake Window owned by Mesh STA B Beacon Data|Null frame, EOSP=0 Triggering for Awake Window owned by Mesh STA A If a peer service period is already ongoing, it cannot be reinitialized, i.e. it continues normally Ack Data|Null frame, EOSP=1 Ack Data|Null frame, EOSP=1 Ack = Awake Window = Mesh STA is transmitter in Peer Service Period = Mesh STA is receiver in Peer Service Period Mesh STA B Mesh STA A Jarkko Kneckt, Nokia

15. Light Sleep Mode Beacon, buffered frames for Mesh STA B • Mesh STA A and Mesh STA B are expecting a trigger frames from each other. • One trigger frame triggers peer service periods in both sides and transmission of two trigger frames are not needed. • Even if the both Mesh STAs set own trigger frames into transmission, the frames may be transmitted without problems: • EOSP bit in the transmitted frame coordinates is the transmitter continuing data transmissions in peer service period Beacon, buffered frames for Mesh STA A Data|Null frame, EOSP=0 Ack Data|Null frame, EOSP=1 Ack Data|Null frame, EOSP=1 Ack Mesh STA B Mesh STA A = Awake Window = Mesh STA is transmitter in Peer Service Period = Mesh STA is receiver in Peer Service Period Jarkko Kneckt, Nokia

16. Peer Service Period Triggering when Peer Operates in Active Mode Jarkko Kneckt, Nokia

17. Triggering when one STA in Active Mode and other in Power Save Mode Beacon The Mesh STA in power save mode does not use peer service periods when it transmits frames to active mode Mesh STA. The active mode Mesh STA may operate only as transmitter in peer service periods. The amount of trigger frame transmissions from power save mode to active mode STA is not limited, i.e. Mesh STA in power save mode may trigger multiple peer service periods within beacon interval. The Active mode Mesh STA may transmit only one trigger frame within Awake Window of the Mesh STA in power save mode. Beacon Data|Null frame, EOSP=0 Ack Data|Null frame Ack Data|Null frame, EOSP=1 Ack Data|Null frame Ack Data|Null frame, EOSP=1 Ack = Awake Window = Mesh STA is transmitter in Peer Service Period = Mesh STA is receiver in Peer Service Period Mesh STA B in Active Mode Mesh STA A in Power Save Mode Jarkko Kneckt, Nokia

18. EOSP Bit Handling Jarkko Kneckt, Nokia

19. EOSP bit Operation • Mesh STA signals through the EOSP bit its desire to continue data transmission within a peer service period • When the EOSP bit is set to 0, the mesh STA continues data transmissions in peer service period • When the EOSP bit is set to 1, the mesh STA terminates the peer service period and will not continue data transmission • The power saving mesh STAs in the peering maintain the value of the transmitted EOSP bits • after the mesh STA has transmitted a frame with EOSP bit set to 1, the next peer service period may be triggered during the next Awake Window, or if the mesh operates in light sleep mode, after the beacon indicating buffered traffic from the peer mesh STA • Note: if mesh STA has a trigger or other frames in transmission for the peer Mesh STA, it uses EOSP bit set to 0 in transmissions for the peer Mesh STA Jarkko Kneckt, Nokia

20. Peer service period initiation and termination • Lets assume a peer service period initiation/termination which is the same situation as shown in slide 14: Try to retrieve the buffered traffic from mesh STA-B and initiate (reverse) peer service period. … Trigger frame RX Data frames RX ACK time mesh STA-A EOSP=0 RX Trigger frame RX ACK time mesh STA-B EOSP=1 This reception is interpreted as peer service period continuation. This is not a transmission of the last frame within service period, so EOSP bit is set to 0 Try to retrieve the buffered traffic from mesh STA-A and initiate (reverse) peer service period. Jarkko Kneckt, Nokia

21. Summary • Only one triggering should be performed per Awake Window or indicated traffic to mesh STA in light sleep mode • The EOSP bit is set to: • 0, if mesh STA wants to continue or to trigger peer service period in which the mesh STA operates as transmitter • 1, if mesh STA wants to terminate or not to trigger peer service period in which the mesh STA operates as transmitter Jarkko Kneckt, Nokia

22. References Jarkko Kneckt, Nokia