block acknowledgement (802.11) (BA)

Block Acknowledgement (BA) is an optional technique to improve the media access method( MAC) of WLANs. It was developed for 802.11e and later adopted in 802. 11n and 802.11ac and is the high-throughput technique in 802.11n devices.

As can be seen from the name Block Acknowledgement, this method does not work with individual positive acknowledgements( ACK) for each protocol data unit, but with a block acknowledgement for several protocol data units. The block acknowledgement contains a total of 64 x 16 bits and shows the error-free or error status of the data unit.

There are several block ACK variants: the Basic Block ACK, the Block ACK Request, the Compressed Block ACK and the Immediate Block ACK.

According to the 802.11e specifications, a receiver can use the Basic Block ACK to acknowledge an individual 802.11 fragment from a group of frames. With the enhancement in 802.11n, the protocol is increased in efficiency with 802.11n networks.

The FrameBlock ARC Request (BAR) is sent before the transmitter acknowledges a group of frames. Without this BAR frame, the receiver cannot send block ACKs.

The Compressed Block ACK is an extension of the 802.11n specifications. The "Compressed" refers only to the acknowledgement of non-fragmented frames. As for the Immediate Block ACK, the "Immediate" refers to the transmission that takes place immediately after the confirmed frame.