1. doc.: IEEE 802.11-08/0846r0 Submission July 2008 Mathilde BenvenisteSlide 1 Power save for wireless mesh Mathilde Benveniste benveniste@ieee.org

2. doc.: IEEE 802.11-08/0846r0 Submission July 2008 Mathilde BenvenisteSlide 2 Introduction A wireless mesh may consist of a mix of power-saving and non-power-saving MPs It is assumed that all mesh points support power saving for peer MPs The goal of a PS protocol is to 1.minimize time a PS MP must be awake 2.reduce the power overhead associated with power save (e.g. TIM transmission, and PS Poll and trigger frame transmissions) Power save protocol that requires no beacon TIMs, PS Polls or trigger frames

3. doc.: IEEE 802.11-08/0846r0 Submission July 2008 Mathilde BenvenisteSlide 3 Description of proposed PS protocol Every power-saving (PS) MP must be awake to receive buffered frames from its peers at a known time The time interval an MP must be awake, called a “receive window” (RW), is defined in terms of –an offset Rwoffset –a duration RWLength, and –a period RWP Each MP advertises its RW(s) in its beacon An MP with buffered unicast and multicast frames for a PS MP may transmit them during an RW of the PS MP A PS MP (one that has the PM bit set in its frames) wakes up at the start of the RW and may go to sleep if no frames are received during the RW; otherwise, it must stay awake until t receives a frame with EOSP=1 The frames that can be sent by a buffering MP to a PS MP in a RW cannot take longer than MaxSPLength

4. doc.: IEEE 802.11-08/0846r0 Submission July 2008 Mathilde BenvenisteSlide 4 Initialization and adaptation of RWs When a PS MP joins a mesh, it selects an RW, which is advertised in its beacon* –The RW choice reflects the expected traffic streams for the PS MP –A RW can be adapted over time at the request of the buffering MP in order to avoid overlap with the RWs of other PS MPs, alleviate queue buildup at the buffering MP, or increase the efficiency of power save –A PS MP may modify its RW by announcing the new RW on its beacon A PS MP may increase the RW period interval and reduce RW duration when it shifts from an active call to stand by –Adaptation of the RWs may be directed from the outside (e.g. by a central controller) Each periodic RW has an associated ID –The ID is used for modification and/or deletion of the RW A PS MP may have multiple RWs – A PS MP may receive traffic from multiple buffering MPs, each possibly using different RWs –Different traffic streams may lead to different RWs at a PS MPs, with possibly different durations and period intervals * Selection of the initial RW and way to adapt to traffic is not specified; however the RW selection rules determine the effectiveness of power save

5. doc.: IEEE 802.11-08/0846r0 Submission July 2008 Mathilde BenvenisteSlide 5 RWs of a PS MP All MPs in this example are PS MPs with bi-directional traffic The Receive Windows (RWs) repeat at equal intervals, the RW Period Interval A DTIM interval contains several RW Period Intervals The RW specification may change over time depending on the activity of the MPs MP1 MP2 MP3 RW Period Length Beacon RW offset Receive Transmit MP1MP2 MP3

6. doc.: IEEE 802.11-08/0846r0 Submission July 2008 Mathilde BenvenisteSlide 6 Receive Window Setup The RW Setup information element is used to publicize the time when a PS MP is awake to receive frames and by a buffering MP to request a PS peer MP to set up a periodic sequence of RWs –This information element is transmitted in the beacon of the PS MP –It is also found in individually addressed PS action frames sent by a buffering MP to the PS MP to modify the parameters of an existing RW or to request a new RW The RW period interval is a fraction of the DTIM interval, which is obtained from the DTIM interval by division by an integer Each RW is identified by a RW ID Modification of an RW is signaled by using the RW ID with the new parameters A 0 value in the RW Duration field signals deletion of an established RW Octets: 1111121 Element IDLengthRW IDRW Duration RW Period Length RW Offset Max RW Length

7. doc.: IEEE 802.11-08/0846r0 Submission July 2008 Mathilde BenvenisteSlide 7 Receive Window Response The RW Setup Response element is used to reply to an RW Setup Request. The alternate RW is the description of suggested receive period parameters to be used in a new RW Setup Request The reply code explains whether the request is accepted and if an alternate is supplied Octets: 11116 Element IDLengthRW IDReply Code Alternate RW

8. doc.: IEEE 802.11-08/0846r0 Submission July 2008 Mathilde BenvenisteSlide 8 Reason Code The RW Setup Response element is used to reply to an RW Setup Request. The alternate RW is the description of suggested service period parameters to be used in a RW Request The reply code explains whether the request is accepted and why Reply CodeMeaning 0Accept 1Reject 2Reject: suggested window supplied OtherReserved

9. doc.: IEEE 802.11-08/0846r0 Submission July 2008 Mathilde BenvenisteSlide 9 Examples of RWs for a linear mesh All three MPs are power saving 1.Initial RWs are set upon association with mesh 2.MPs adapt their RWs based on when traffic is received and buffered –MP1 and MP3 set the RWs of MP2 by requesting an RW to occur when traffic is buffered –MP2 sets the RW of MP1 and MP3 –The buffering MPs awaken to transmit during the RWs of their peer PS MPs –Each MP must awaken twice 3.MPs may adapt their RWs for contiguous awake intervals –MP1 may request MP2 to delay its RW –MP2 requests MP3 to delay its RW before it agrees to MP1’s request –Transmission MP1-MP3 is delayed and followed immediately by transmission from MP3-MP1 –All MPs awaken once per period MP1MP2 MP3 MP1 MP2 MP3 MP1 MP2 MP3 MP1 MP2 MP3 1 2 3 Receive Window Transmit Window Receive Window Transmit Window

10. doc.: IEEE 802.11-08/0846r0 Submission July 2008 Mathilde BenvenisteSlide 10 Examples of RWs for a linear mesh MP 1 is not power saving 1.Initial RWs are set upon association with mesh 2.MPs adapt their RWs based on when traffic is received and buffered –MP2 sets the RW of MP3 –MP3 sets the RW of MP2 by requesting an RW to occur when traffic is buffered –The buffering MPs is awake to transmit during the RWs of their peer PS MPs –Each PS MP must awaken twice 3.MPs may adapt their RWs for contiguous awake intervals –MP2 requests MP3 to delay its RW –MP2 adapts the RW used to receive from MP1 by publicizing in its beacon –Transmission MP1-MP3 is delayed and followed immediately by transmission from MP3-MP1 –All PS MPs awaken once per period MP1MP2 MP3 MP1 MP2 MP3 MP1 MP2 MP3 MP1 MP2 MP3 v 1 2 3 Receive Window Transmit Window v v

11. doc.: IEEE 802.11-08/0846r0 Submission July 2008 Mathilde BenvenisteSlide 11 Advantages of proposed PS protocol Buffering MPs need not broadcast TIMs on their beacons PS MPs need not awaken to listen to the beacons for the TIMs –RWs need not start or include a beacon PS MPs need not send PS Polls or trigger frames to retrieve buffered frames