UniFi supports QoS based on WMM (aka WME).
The UniFi AP maps DSCP value to WMM priorities and process these packets accordingly. UAP considers either DSCP or COS. It compares COS with DSCP (the first 3 bits) and takes whichever has higher value to map to WMM AC according to the table below:
DSCP to 802.1d mapping per WMM specifications, as supported by UniFi APs.
DSCP values (Decimal) => WMM AC
- 0 to 7 => Best Effort
- 8 to 23 => Background
- 24 to 31 => Background
- 32 to 47 => Video (except 46)
- 48 and above (and 46 since UniFi v.2.3,6) => Voice
Starting from v2.3.6, DSCP 46 is considered as a special case that will be mapped to VO.
On the AP receiving end, 802.11 is on top of ethernet frame. AP thus sends packets onto the wire the way it receives over-the-air (without 802.11 header of course). For example, a VoIP phone sends VO packets in DSCP 46 and that will be the DSCP value of the ether frames that AP sends out on wire.