The QoS Control field is a 16-bit field that identifies the quality of service (QoS) parameters of a data frame. In other words, the QoS control field is only used in the MAC header of QoS data frames.
As shown in Table 3.4, the QoS Control field is comprised of five subfields called traffic identifier (TID) subfield, end of service period (ESOP) subfield, ACK policy subfield, and a reserved subfield.
For example, a TID subfield could indicate a UP of 6, meaning that access category would be for voice traffic.
The ESOP subfield is 1 bit in length and is used by the access point to indicate the end of the current service period (SP). The last frame sent during the service period will have the bit set to a value of 1 to tell the WMM-PS client station that either the service period is over or that the AP’s buffer is empty. The WMM-PS client station can then go back asleep.
As shown in Table 3.4, the QoS Control field is comprised of five subfields called traffic identifier (TID) subfield, end of service period (ESOP) subfield, ACK policy subfield, and a reserved subfield.
The first sub field of the QoS control field is the 4 bit TID. The traffic indicator (TID) subfield is used to identify the user priority (UP) and traffic access category of the QoS data frame.
User Priority (UP) level points wired 802.3 Ethernet network and Access Category points Wi-Fi Multimedia Access Categories.
Above pictures from CWAP
For example, a TID subfield could indicate a UP of 6, meaning that access category would be for voice traffic.
The fourth subfield of the QoS Control field is 1 bit and is currently reserved for future use.
The fifth subfield of the QoS Control field is 8 bits in length and can be used for a variety of purposes. The fifth subfield can be used as a TXOP Limit, an AP PS Buffer State, a TXOP Duration Requested, or a Queue Size.
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