The Reverse Direction Grant feature was introduced in 802.11n. The Reverse direction grant was a feature which would allow for better usage of a Transmit opportunity (TXOP) as defined in WMM/EDCA. The need for Reverse Direction Grant (RDG) was felt as described in the next paragraph.
The WMM/EDCA mechanism allowed for an 802.11 station to contend for the medium. On winning access to the transmission medium – the 802.11 station could select an appropriate Access Category as per EDCA rules. Each Access category (Voice/Video/Best Effort/Background) was provided a time duration for which it could access the medium. The time durations for the different Access Categories are shown below
| Access Category | AIFSN | CWmin | CWmax | TXOP time |
| Voice | 1 | 3 | 7 | 1.5ms |
| Video | 1 | 7 | 15 | 3.0ms |
| Best Effort | 3 | 15 | 63 | 0 |
| Back Ground | 7 | 15 | 1023 | 0 |
A TXOP like Voice would have 1.5ms of transmission time and video 3.0ms of time.
The two below reasons can best describe the desire for Reverse Direction Grant
- Not all the time for the TXOP is occupied for transmission.
- Also, if the 802.11 station were to relinquish the TXOP – the receiver 802.11 station would still need to contend for the medium before transmitting response ACKS/frames.
Since a single station occupies the transmit medium for a long duration – certain higher layer protocols such as TCP would suffer. This is because most TCP congestion algorithms depend on the number of successful packets transmitted. If the transmit acknowledgements for the packet transmissions from the 802.11 station takes time – the TCP congestion algorithm does not scale the data rate fast enough causing a decrease in throughput.
In such scenarios – the Reverse Direction Grant would allow the Receiver station to transmit the ACKs/Frames in the same Transmit Opportunity of the Transmitter 802.11 station. This could allow the TCP congestion algorithm to scale the data rate faster, thus leading to a higher throughput.