In a WLAN, packets can be a stream of video, voice, or data, which each have different priorities to be served by an access point.
It is represented as a four-bit number (0-3), identifying QoS traffic within MAC data services.
[1] There are 16 (24) possible values for TID; out of them, only 8 are practically usable to identify differentiated services.
A QoS-enabled 802.11 header uses the TID to classify and prioritize processing of incoming or outgoing frames.
A TID value from 0-7 are defined for user traffic priority and mapped to Access Categories (AC) while TID range 8-15 is reserved for management and control frames.