1. Peer Power Save Mode for TDLS
Month Year
doc.: IEEE yy/xxxxr0
July 2008
Peer Power Save Mode for TDLS
Date:
Authors:
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

2. July 2008
In some usage scenarios, both peer STAs may want to go into PS mode over a direct link
For instance, when a laptop is communicating with a handheld device over a direct link, both want to save power while still maintaining the direct link
The existing asymmetric peer PSM mechanism as defined in 11z D1.0 does not address this usage scenario
Michelle Gong (Intel Corp) et al.

3. Month Year
doc.: IEEE yy/xxxxr0
July 2008
To support the peer PSM mode, two peer STAs exchange Request and Response frames AP
QSTA1 changes to Power Save Mode
QSTA2 changes to Power Save Mode 5
Buffered DATA frame (EOSP is set to 1) 3 3
QSTA2
QSTA1
QSTA1 wakes up at scheduled time 4
QSTA2 wakes up at scheduled time 4 2
Encapsulated DATA frame (TDLS PSM Switch Response)
Encapsulated DATA frame (TDLS PSM Switch Request) 1
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

4. Format of the TDLS PSM Request frame
Month Year
doc.: IEEE yy/xxxxr0
July 2008
Format of the TDLS PSM Request frame
Order
Information
Notes 1
Dialog Token
The Dialog Token is set to a non-zero value that is unique among TDLS Peer PSM Request frames for which a corresponding TDLS Switch Response frame has not been received. 2
Link Identifier
The link identifier is specified in section z1 3
Wakeup Schedule IE
The Wakeup Schedule IE describes a schedule for the wakeup time 4
Vendor Specific
One or more vendor-specific information elements may be in this frame.
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

5. Format of the TDLS PSM Response frame
Month Year
doc.: IEEE yy/xxxxr0
July 2008
Format of the TDLS PSM Response frame
Order
Information
Notes 1
Dialog Token
The Dialog Token is set to the non-zero value contained in the TDLS Peer PSM Request frames to identify the request/response transaction 2
Status Code
The Status code identifies the result of the response as defined in Table 7-23. 3
Link Identifier
The link identifier is specified in section z1 4
Wakeup Schedule IE
The Wakeup Schedule IE describes a schedule for the wakeup time 5
Vendor Specific
One or more vendor-specific information elements may be in this frame.
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

6. A STA may reject a wakeup schedule for various reasons
July 2008
A STA may reject a wakeup schedule for various reasons
Status code
Meaning
<ANA>
Wakeup schedule rejected but alternative schedule provided
Wakeup schedule rejected because not going into power save
Wakeup schedule rejected for unspecified reason
Michelle Gong (Intel Corp) et al.

7. The Wakeup Schedule IE has the following fields
Month Year
doc.: IEEE yy/xxxxr0
July 2008
The Wakeup Schedule IE has the following fields
Element ID
Length
Start
Time
Interval
Min
Duration
Idle Count
Octets 1 8 4 2
The Start Time field is 8 octets and indicates the anticipated time, expressed in microseconds, when both STAs need to wakeup
It represents the TSF timer value at the start of the first wakeup period (WP)
StartTime can be set to a beacon TBTT plus an offset
The Interval field indicates the time, expressed in microseconds, between two successive wakeup periods
The Idle Count field indicates how many consecutively empty wakeup periods a peer STA would allow before it suspends the direct link
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

8. July 2008
Minimum Duration is introduced so that two STAs have time to access the channel
Both peer STAs wake up at or before the scheduled wakeup period and stay awake for Minimum Duration after the beginning of the wakeup period
A bi-directional peer service period begins after an acknowledged frame exchange
A STA shall remain awake until it receives an MPDU with EOSP bit set to 1
The peer service period is terminated when both peer STAs transmitted an MPDU with the EOSP bit set
The peer STAs may go back to doze state when data exchanges complete successfully before the Minimum Duration time
Minimum duration
Interval
Michelle Gong (Intel Corp) et al.

9. Peer STAs wake up at or before the start of a wakeup period
Month Year
doc.: IEEE yy/xxxxr0
July 2008
Peer STAs wake up at or before the start of a wakeup period
STA B
STA A
TDLS PSM Switch Request
TDLS PSM Switch Response
Minimum wakeup period
Buffered DATA (EOSP=0)
Buffered DATA (EOSP=1)
Buffered DATA (EOSP=0)
Buffered DATA (EOSP=1)
A peer service period begins after an acknowledged frame exchange between the peer STAs
The scenario when the “More data” bit in ACK is supported is in the backup slides
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

10. Month Year
doc.: IEEE yy/xxxxr0
July 2008
A service period between two STAs in PS mode may be initiated within the minimum wakeup duration
If STA A has buffered traffic for STA B, STA A can directly send buffered data frames to STA B within the minimum duration
STA A sets the EOSP bit of all its data frames to 0, until it does not intend to transmit more frames to STA B. STA A sets the EOSP bit in the last data frame to 1
STA B can transmit its frames to STA A while it’s receiving STA A’s packets
After a service period is initiated, both STA A and STA B shall remain awake until one of the following conditions are met
If “More Data” bit in ACK is supported: Peer STAs may go back to doze state after one acknowledged frame exchange with the EOSP bit in an MPDU set to 1 and the More Data bit in the ACK frame set to 0
If “More Data” bit in ACK is not supported: Peer STAs may go back to doze state after one acknowledged frame exchange in each direction with the EOSP bit in the MPDU set to 1
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

11. July 2008
In summary, this peer PSM scheme is flexible and addresses a broader range of use cases
The peer PSM allows one or both STAs to go into power save mode while still maintaining the peer link
The procedure is as follows:
Two STAs negotiate a wakeup schedule
STAs wakeup at or before the start of a wakeup period and start data packet exchange
A peer service period is initiated by an acknowledged frame exchange between the peer STAs
The peer service period is terminated 1) when both peer STAs transmitted an MPDU with the EOSP bit set to 1 or 2) through one acknowledged frame exchange with the EOSP bit in the MPDU set to 1 and “More data” bit in the ACK set to 0
Peer STAs may stay in doze state after “Idle Count” number of consecutive empty wakeup periods
Detailed information can be found in 11-08/0668r8
Michelle Gong (Intel Corp) et al.

12. July 2008
Backup
Michelle Gong (Intel Corp) et al.

13. Utilize the More Data bit in the ACK frame
Month Year
doc.: IEEE yy/xxxxr0
July 2008
Utilize the More Data bit in the ACK frame
QSTA1
QSTA2
Buffered DATA (EOSP=0)
Minimum Duration
ACK (More data=1)
Buffered DATA (EOSP=1)
ACK (More data=1)
Remain awake
Buffered DATA (EOSP=0)
ACK (More data=0)
Buffered DATA (EOSP=1)
ACK (More data=0)
Go back to sleep
Go back to sleep
The shortest frame exchange during one wakeup period (Data(EOSP=1) / SIFS / ACK (MoreData=0)
Michelle Gong (Intel Corp) et al.
John Doe, Some Company