Similar to delayed block Ack, an HT-Delayed Block Ack session provides the WLAN station to receive/transmit a Block Ack frame at a later time from the time when an A-MPDU was transmitted.
HT-Delayed Block Ack is an optional feature. The HT-Delayed Block Ack support is advertised in the HT capabilities information field.
Fig Courtesy – 802.11-2012 Standard
The BlockAck response to an HT-delayed BlockAckReq is transmitted after an unspecified delay and when the recipient of the BlockAckReq next has the opportunity to transmit.
The Block Ack frame that is sent in a subsequent TXOP have the ack policy field set to NoAck.
The below frame exchange shows the Delayed Block Ack mechanism
