Do Aerohive AP121's support Power Save Polling (PSP)?

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Do Aerohive AP121's support Power Save Polling (PSP)?
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CJ

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Posted 2 years ago

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Mike Kouri, Official Rep

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CJ,
The AP121 was first released in July 2012, so it's probably a safe assumption that we have always supported this capability which came from the specs in 2005 (802.11e). There have been further evolutions in dealing with clients that go into a power-saving mode, APSD and U-APSD are two that immediately come to mind. 

think (but you should get your reseller or Aerohive support to confirm/deny) that AP121 supports APSD but not U-APSD.
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Roberto Casula, Champ

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Power Save Polling (legacy power save) is the oldest mechanism (pre-dating 802.11e and WMM). As far as I know, pretty much every Enterprise-grade AP supports it (though a few low-end consumer-grade APs do not). It is massively inefficient and never really provided much benefit (and as data rates and traffic volumes increased, it became a liability rather than a benefit due to the control frame overhead).

802.11e introduced APSD (Automatic Power Save Delivery) in two modes, Scheduled (S-APSD) and Unscheduled (U-APSD).

I've never seen support for S-APSD in an Aerohive spec-sheet.

The AP121 definitely does support U-APSD, but it is disabled by default. It can be enabled on a per-SSID basis. U-APSD requires WMM to be enabled.

Few clients these days use legacy power save and either operate as "always awake" (never setting the power-save bit in transmissions) or operate with full U-APSD enabled. There are some clients that will fall back to legacy mode if U-APSD support is not available on the AP.

In some cases though, applications on a client device will request the driver to use U-APSD only for certain WMM access classes (typically voice and video) while other applications may fall back to using legacy power save polling (if buffered traffic remains after using a U-APSD trigger for the voice/video classes). If you want to see this in action, grab a packet capture of a Spectralink phone, for example, and weep!

802.11n introduced Power Save Multi-Poll (PSMP) which, as far as I know, isn't supported on any Aerohive APs (I don't have any AP121s to hand, but I just checked what our AP230s advertise, and they don't advertise support for APSD or PSMP, but do advertise support for U-APSD on the SSID where I have it enabled).
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Mike Kouri, Official Rep

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Silly me, I should have known you would jump in with much more detail and color! Thanks, as always, for helping out here!!