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

2. May 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. May 2008
The scheduled peer PSM is complementary to the unscheduled peer PSM defined in 11z D1.0
When one peer STA supports PSM client mode and the other STA supports PSM AP mode, they can utilize asymmetric peer PSM
Because different STAs may support either AP mode or client mode, some of the following cases are not addressed in D1.0
Both peer STAs support PSM AP mode:
Both always stay awake and never go into power save mode over the direct link (No PSM is needed)
They negotiate as to which one can go into power save mode and which one has to stay active (Asymmetric peer PSM combined with a negotiation procedure)
Both want to go into power save mode (Symmetric peer PSM is needed)
Both peer STAs support PSM client mode:
Neither one wants to go into power save mode over the direct link (No PSM is needed)
At least one wants to go into power save mode (Symmetric peer PSM is needed)
The goal is to have a joint Unscheduled Power Save Mode (UPSM) and Scheduled Power Save Mode (SPSM) proposal that can cover a broad range of usage scenarios
Michelle Gong (Intel Corp) et al.

4. Month Year
doc.: IEEE yy/xxxxr0
May 2008
To support the combined PSM mode, two peer STAs exchange Request/Response frames AP
QSTA2 changes to Power Save Mode
QSTA1 changes to Power Save Mode 3 3
QSTA2
QSTA1
QSTA1 wakes up at scheduled time 4 5
Buffered DATA frame (EOSP is set to 1)
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

5. Month Year
doc.: IEEE yy/xxxxr0
May 2008
Peer STAs exchange TDLS PSM Request and Response frames over the direct link
Frame format of the TDLS PSM Request frame
Order
Information
Notes 1
Link Identifier
The link identifier is specified in section z1 of
802.11z D1.0 2
Dialog Token
The Dialog Token is set to a non-zero value that is
unique among TDLS PSM Request frames for which a
corresponding TDLS Switch Response frame has not
been received. 4
Wakeup
Schedule IE
The Wakeup Schedule IE describes the schedule for the
wakeup period.
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

6. Frame format of the TDLS PSM Response frame
Month Year
doc.: IEEE yy/xxxxr0
May 2008
Frame format of the TDLS PSM Response frame
Order
Information
Notes 1
Link Identifier
The link identifier is specified in section z1
of z D1.0 2
Dialog Token
The Dialog Token is set to the non-zero value
contained in the TDLS PSM Request frames to
identify the request/response transaction. 3
Result
The Result identifies the result of the response 4
Wakeup
Schedule IE
The Wakeup Schedule IE describes the counter-
proposal schedule for the wakeup period.
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

7. Accept with my own schedule
May 2008
Format of the Result IE
Result
Information
Accept 1
Accept with my own schedule 2
Reject
3-255
Reserved
Note: Upon receiving “Accept with my own schedule”, the initiator may send out a second request frame that contains the wakeup schedule defined in the first TDLS PSM Response frame
Michelle Gong (Intel Corp) et al.

8. An example Wakeup Schedule IE has the following fields
Month Year
doc.: IEEE yy/xxxxr0
May 2008
An example Wakeup Schedule IE has the following fields
Element ID
Length
Sleep
State
TSF
Start
Time
Offset
Periodicity
Fraction
Min
Duration
Max
Octets 1 4
Sleep State: 0: Always awake 1:No scheduled wakeup period 2: Wakeup schedule as specified in this IE
Offset, Periodicity, Beacon Interval (BI) and Fraction has the following relationship
An example formula:
TSF mod floor(BI * Periodicity/Fraction) = offset
Offset field indicates the timing offset from the TSF Start Time
The value of the offset can be randomly selected to avoid overlapping wakeup schedules for different direct links
Overlapping with beacons and MCBC is not recommended
Periodicity is introduced to facilitate a longer sleep interval than a beacon interval or a DTIM interval
Fraction is introduced for flexibility and shorter sleep intervals
Example: BI=100 TUs, Periodicity = 60, Fraction=16, offset=15 TUs
Awake at 15, 390, 765, 1140, …
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

9. May 2008
Minimum Duration and Maximum Duration of the wakeup period are also important parameters
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
The peer STAs may go back to doze state when data exchanges complete successfully before the Minimum Duration time
Both STAs remain awake until all data exchanges complete successfully or for Maximum Duration after the beginning of the wakeup period
The Maximum Duration is useful for off-channel operation where one or both peer STAs need to go back to the main channel at a certain time, for instance to receive DTIM beacons or buffered traffic
Michelle Gong (Intel Corp) et al.

10. Month Year
doc.: IEEE yy/xxxxr0
May 2008
Each peer STA may initiate one or more service periods within one wakeup period
The shortest data exchange in a wakeup period: A data (EOSP=1)/ SIFS / ACK/A data (EOSP=1)/ SIFS / ACK
11n reverse direction grant can be utilized to exchange data in both directions in a single channel access
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

11. Data exchanges between two STAs in PS occur during the wakeup period
Month Year
doc.: IEEE yy/xxxxr0
May 2008
Data exchanges between two STAs in PS occur during the wakeup period
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 has no more frames buffered for STA B. STA A sets the EOSP bit in the last data frame to 1 to indicate that it has no buffered traffic for STA B
If STA A has frames buffered for STA B but max duration has elapsed since the beginning of the wakeup period, STA A sets the EOSP bit to 1 in the first data frame sent after the time expires. STA A should not send additional data frames to STA B until the next wakeup period
STA B can transmit its frames to STA A while it’s receiving STA A’s packets, which means two service periods that are started by STA A and STA B respectively can overlap. Note that multiple buffered packets may be delivered during this period.
Both STA A and STA B shall remain awake until all buffered frames have been delivered to them or the max duration timer expires
After both STAs indicate the completion of data transmission by setting the EOSP bit to 1 in data frames, both STAs go back to doze state
Michelle Gong (Intel Corp) et al.
John Doe, Some Company

12. May 2008
In summary, the combined peer PSM is more flexible and addresses a broader range of use cases
UPSM and SPSM allow one or both STAs to go into power save mode while still maintaining the peer link
The procedure is as follows:
Two STAs negotiate the peer power save mode that they would be in and a wakeup schedule
STAs wakeup at or before the start of the wakeup period and start data packet exchange
Either STA can initiate a peer service period
The owner of the peer service period terminates the period
We will update the normative text in r0
Michelle Gong (Intel Corp) et al.