Some Power-save changes in 802.11e Draft May 2004 Some Power-save changes in 802.11e Draft Mathilde Benveniste - Avaya Labs Mark Bilstad - Cisco Systems Steve Emeott, Floyd Simpson, Stephen Wang - Motorola Jarkko Kneckt, Jari Jokela - Nokia Keith Amann, SpectraLink Andrei Kojukhov, TI Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

The power-save method was simplified and enhanced as follows: May 2004 SCOPE The power-save method was simplified and enhanced as follows: Stations may continue to use Unscheduled APSD for all-traffic (periodic and non-periodic) At the same time, stations have information and control over the amount of buffered traffic received per service period Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

Unscheduled APSD - generalization of legacy power save May 2004 Unscheduled APSD - generalization of legacy power save The station lets the AP know when it is awake to receive frames The arrival of an uplink frame (trigger) is used to inform the AP that a PS station is awake This initiates the delivery of buffered frames (a service period) More than one buffered frame may be delivered; the AP decides which and how many Both periodic and non-periodic traffic may be retrieved APSD signaling used to terminate a service period A PS poll is used as in legacy PS; it causes the release of a single frame Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

What we had before in the 802.11e draft May 2004 What we had before in the 802.11e draft The TIM and More Data bit indicate whether traffic is buffered at the AP The AP is required to send at least one frame (if one is buffered), but may send more U-APSD was enabled on a per AC basis TSPECs were used by a station to enable use of U-APSD for each AC/TS Legacy and APSD can be used by the same station Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

May 2004 What is different now Unscheduled APSD is not restricted to specific ACs No TSPECs needed for unscheduled APSD More features added The AP may optionally indicate information on the state of buffered traffic The station can restrict the number of buffered frames delivered Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

Use of APSD Scheduled and Unscheduled APSD may co-exist for a station Both APSD methods cannot be used for the same AC/TS The use of Scheduled APSD for an AC/TS will be indicated by sending a TSPEC The use of Unscheduled APSD will be indicated by sending trigger frames A trigger frame is a data/Null frame with a non-zero Max SP Length [new field] value Scheduled SPs shall not overlap by schedule design Unscheduled APSD SPs will never overlap A trigger frame arriving at the AP during an unscheduled SP shall not be considered a new trigger An unscheduled SP may overlap with a scheduled SP A scheduled SP will end upon receipt of a frame with the EOSP bit set and TID corresponding to the TSPEC; all other TIDs on a frame with the EOSP bit set will end an unscheduled SP Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

What happens with buffered frames at the AP May 2004 What happens with buffered frames at the AP Frames associated with an admitted TSPEC with S-APSD bit set must be delivered during a scheduled SP For APSD capable QAP, data frames not associated with an admitted TSPEC (with S-APSD bit set) will be delivered by the following options: in an unscheduled SP in response to a PS poll if the station transitioning to Active mode The non-AP QSTA does not request frames of a specific AC The maximum number of frames sent during a SP is limited by the non-AP QSTA (see slide 11) The QAP is allowed to release frames of multiple AC’s during a single SP, provided the frame with EOSP set is the final DL frame transmitted in the SP Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

Termination of an Unscheduled SP May 2004 Termination of an Unscheduled SP Problem: If the frame with the EOSP bit set is transmitted by the AP before other frames released in the same service period, the station will go to sleep before it receives all transmitted frames Requirement: The EOSP bit must be set in the final downlink frame transmitted in a service period A way to meet this requirement (informative): Frames go through the same access/transmit buffer in a service period; e.g. In a service period, frames are released from a single triggered buffer, and all have the same AC The AP will chose the buffer for frame release it will release frames from the highest-priority non-empty buffer Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

May 2004 Example: Possible organization of triggered buffers & frame release (Informative) If there are as many triggered buffers as ACs, there is one triggered buffer per AC If the AP employs fewer triggered buffers than ACs, ACs are (dynamically) mapped into buffers monotonically. E.g. All higher priority triggered buffers, except for the lowest, receive frames corresponding to a single AC The lowest-priority triggered buffer receives frames corresponding to the remaining ACs Frames released in a service period are transmitted from the same access/transmit buffer; this ensures that the EOSP frame arrives last. E.g. In a service period, frames are released from a single triggered buffer and have the same AC Example: 3 active ACs 2 triggered buffers AC=3 AC=1 AC=0 Arriving frames by AC 2 triggered buffers per trigger-enabled station Triggered Buffer 2 Triggered Buffer 1 Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

Optional signaling on buffered load and priority May 2004 Optional signaling on buffered load and priority A single TIM (and a single More Data bit) for all traffic gives rise to ambiguity concerning the priority of the buffered frames; this may cause a problem on the retrieval decision for devices needing to perform other urgent tasks To help with this decision, we propose the addition of optional signaling in a field that is currently transmitted, but reserved Bits 9-15 in the QoS control field of the DL frame (which correspond to Queue Size in an uplink frame) are used to convey information about data remaining buffered when the DL frame is released This information consists of flag indicating whether the AP will indicate the state of buffered traffic, found in bit 9 AC of the highest-priority frame buffered, found in bits 10-11 the AP buffer load – I.e. total buffered traffic (in units of 4096 octets), found in bits 12-15. When this value of this field is 14, the queue is greater than 57344 octets. Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

May 2004 Limit on the SP length In order to provide more control to the station on the amount to buffered traffic sent per SP, the station shall indicate the maximum number of frames in an SP in a trigger frame. The AP shall attempt comply with this requirement as quickly as possible When bit 4=0 and bit 7=1, the value in Bits 8-10 in the QoS control field of the trigger frame is the Max SP Length A PS-Poll may be used as a trigger frame with maximum SP length of 1 frame Max SP Length (frames) Interpretation Do not start service period 1-6 Maximum number of downlink frames in the SP 7 No limit imposed on the maximum number of frames in the SP Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

Summary of proposed changes May 2004 Summary of proposed changes Unscheduled APSD is not restricted to specific ACs No TSPECs needed for unscheduled APSD A station indicates its intent to use unscheduled APSD by sending a trigger The AP may optionally indicate information on the state of buffered traffic The station can restrict the number of buffered frames delivered Unscheduled SPs of a station cannot overlap A station tracks overlapping scheduled and unscheduled SPs by the TID of the frame The final frame transmitted in the service period must have the EOSP set to 1 Avaya, Cisco, Motorola, Nokia, SpectraLink, TI

May 2004 Motion Move to adopt normative text changes in IEEE 04/620r2 into TGe draft D8.0. Avaya, Cisco, Motorola, Nokia, SpectraLink, TI