The methods described so far are intended to improve the maximum physically possible data throughput. The methods described below are used in 802.11n networks to optimize net data throughput, i.e. the throughput of actual payload data.
- Frame aggregation
In addition to the actual payload data, each data packet includes management information, which is important for the smooth exchange of data. Frame aggregation is used to combine several data packets (frames) into one large packet. As a consequence, management information only needs to be specified once for the complete data packet, and the proportion of payload data to the total data volume increases.
- Block acknowledgement
Each data packet is acknowledged on receipt. In this way, the transmitter is informed that the packet was received correctly and does not need to be repeated. This principle also applies to aggregated frames in 802.11n.
However, some packets in an aggregated frame may be delivered successfully while others are not. In order to avoid having to retransmit an entire aggregated frame from which perhaps just one data packet was not delivered, a separate acknowledgement is generated for every single WLAN packet in the aggregated frame. These acknowledgements are again combined to form a block and relayed back to the sender as a group (block acknowledgement). The sender receives information about the receipt status of every single WLAN packet and can, if necessary, resend only those specific packets that were not successful.