What to Expect with TWT
Features > Target Wake Time (TWT)
The intention behind the 802.11ah TWT feature is to provide a mechanism for low-power, low-throughput devices to sleep for long periods of time and then wake up briefly to report some uplink data. The following points outline some points to note when using this functionality.
- iPerf and other high-throughput traffic will not work well, nor will TCP traffic in general.
- TWT-sleeping STAs cannot transmit or receive traffic outside of the configured service period.
- The AP cannot reliably deliver broadcast traffic to a TWT sleeping STA
- Service period is signalled by the STA sending a QOS NULL at the start and end of the service period to indicate wake & sleep respectively.
Also to ensure that TWT functions as expected, please note the following:
- IPv6 can cause unexpected periodic traffic from the STA (due to router solicitation), which will prevent the STA from entering TWT sleep. It is recommended to disable IPv6.
- When the PTKSA expires (by default after 12 hours), the STA will need to disconnect and reconnect. Since the STA may be asleep for long periods it may miss this re-key and get disassociated. The STA should re-negotiate a TWT agreement with the AP upon reassociation. If desired, it is possible to disable re-keying, though this is not recommended for production setups. To do this set the following values in hostapd.conf:
wpa_ptk_rekey=0
wpa_group_rekey=0 - HostAPD has a BSS max idle period after which a non-responding STA will be deassociated and deauthenticated. To reduce the amount of wake ups the STA needs to send keepalive frames, this interval should be set to the maximum value.