The transmission rate of the station can depend on the type of WLAN protocol that the station follows (e.g., 802.11b, 802.11n, 802.11ac, etc.) and which of the multiple rates specified within each protocol that the station chooses. The transmission rate can also depend on the conditions of the wireless channel between the source and the destination. The conditions of the wireless channel can vary over time, thus leading to changes of the transmission rate of the station.

For downstream transmissions, typically the AP 110 decides the order of transmission among the multiple stations. In some instances, the multiple stations that share the wireless channel can have different transmission rates. When one station's transmission rate is significantly slower than the others and the AP 110 transmits each station a same amount of data (e.g., 1 unit of data) each time the station is allocated airtime, stations having a higher transmission rate will spend most of the time waiting for the transmissions to the slower station to be completed. For example, say station 1 has a very low bit rate compared to station 2, and therefore a packet for station 1 takes much longer to transmit than a comparable packet for station 2. In this example, station 2 spends most of its time waiting for transmissions to station 1 to complete. As a result, the packet rate of station 2 is equal to the packet rate of station 1, even though the transmission rate of station 2 is much higher than station 1. Thus, the low transmission rate of station 1 limits the overall throughput of the network.