Categories : PowerSave , WLAN

Before we go for comparison between WMMPS and PowerSave Poll we should know the details about WMMPS and Legacy PS-POLL.


1.STA and AP must support WMM to use WMMPS.STA and AP supports or do not support WMM , can use PS-POLL.
2.AP should indicate WMMPS support in Beacon.AP has to support PS-POLL by default. There is no field to indicate that AP supports or does not support PS-POLL.
3.Association has to be WMM Association.Association does not have to be WMM association.
4.After association is successful. STA sends null frame to AP with PM=1 to go to powersave.Same here.
5.If all ACs are WMMPS enabled by STA in Association Request, then AP uses TIM bit to indicate WMMPS buffered data for STA.AP always use TIM bit to indicate legacy buffered data for STA.
6.Suppose 2 ACs are not WMMPS by STA in Association Request. Then AP does not use TIM to indicate to WMMPS buffered data.TIM is used for non-wmmps buffered data.AP always uses TIM for legacy buffered data.
7.STA has to send trigger frame to get WMMPS buffered data.STA has to send PS-POLL to get buffer data.
8.Upon receiving trigger frame AP can send more than 1 buffered frame depending on Max SP Length declared by STA in Association Request.Upon receiving PS-POLL AP can send only one buffered data. If STA wants more buffered data from AP then STA has to send one more PS-POLL frame to AP.
9.When AP sends buffered WMMPS data, the gap between two data are SIFS duration. In another way we can say, AP does not have to content for medium for each buffered data. This is called TXOP burst. This speed up clearing buffered data.For sending each buffered data AP has to perform back off algorithm. This slows down clearing buffered data.
10.It’s not mandatory for STA to wait for Beacon to indicate buffered data for STA. STA can send trigger frame anytime to AP. If AP does not have any buffered data it replies with QoS Null frame where More Data=0 and EOSP=1.In legacy power save STA has to wait for Beacon to indicate about buffered data for STA AID.
11.Trigger frame can be Null data frame or any data packet (Ex: DUP). Trigger frame PM bit will be set to 1.STA has to send PS-POLL frame to get buffered data. PS-POLL frame PM bit will be set to 1.
12.In general, AC of trigger frame is Voice. AC can be changed depending on scenario.PS-POLL is control frame so no AC specified.

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4 comments on “WMMPS vs Legacy PS-POLL


    • October 25, 2020 at 2:12 pm

    Nice article, loved it !!


      • October 25, 2020 at 4:15 pm

      Thank you Supriya.


    • October 25, 2020 at 10:41 am

    Nice article.


      • October 25, 2020 at 10:42 am

      Thank you Sukumar.

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