A method, an apparatus, and a computer-readable medium for wireless communication are provided. In an aspect, the apparatus is configured to receive at least one frame from at least one wireless device and to generate a BA frame that may include a block ACK bitmap based on the received at least one frame. The BA frame may include a fragment number field and a bitmap length indicator within the fragment number field that indicates a length of the block ACK bitmap within the BA frame. The apparatus may be configured to transmit the generated BA frame to the at least one wireless device.