Remedy to the Lost Ack Problem while Power Saving Mathilde Benveniste benveniste@ieee.org Avaya Labs - Research Submission addresses D5.0 ballot comments: 441, 210, (209, 330, 331, 324, 325, 460, 466, 467, 526)

Problem of the Lost Ack to a Downlink frame If the Ack to the last downlink frame is the last frame sent by a station before going back to sleep, the AP will keep retransmitting the same frame APSD is not vulnerable to this problem because the station keeps awake to send uplink frames after receiving downlink frames In reverse polling downlink frames are transmitted last; if no special measures are adopted, retransmission of the frame whose Ack was lost will keep repeating

The QAP If the QAP does not receive an acknowledgement to a frame sent to an APSD station with the ‘last downlink transmission’ indication, the QAP shall retransmit that frame once and, if an Ack is not received, it shall wait until the next service period to retransmit

The station The APSD station that acknowledged a frame from the QAP with the ‘last downlink transmission’ indication shall not go to sleep until it receives another frame. If the frame is not directed to the station, the station may go to sleep. If the frame is directed to the station, the station shall acknowledge the frame and then go to sleep.

Motion Adopt Normative Text changes in doc 03/796r0