This is because wireless terminals are far away from APs. As a result, radio signals are weak. In this case, the association rate that is negotiated by the wireless terminals is low. Specifically, the signal transmission rate of 802.11g APs includes 54 Mbit/s, 48 Mbit/s, 36 Mbit/s, 24 Mbit/s, 18 Mbit/s, and 12 Mbit/s.
The 802.11n is backward compatible with the 802.11b/g, so the 802.11n APs can be encrypted in the mode of WEP or TKIP. The association rate displayed on the STAs may be only 54 Mbit/s because the 802.11n standard does not define the WEP or TKIP encryption mode. If the 802.11n APs use the WEP or TKIP encryption mode, the STAs are associated only at 802.11g rates.
Some NICs of the STAs support only the 802.11b/g APs. When the STAs are associated with the 802.11n APs, the maximum association rate is only 54 Mbit/s. The 802.11n APs can also be configured with the 802.11b/g radio frequency type, because the 802.11n is backward compatible with the 802.11b/g.
You can associate it with 802.11n AP if the AP does not set the 802.11n-only mode. However, the signal transmission rate of the APs in 802.11b mode is low. In contrast, the time that the 802.11n APs take to transmit radio signals at 300 Mbit/s accounts for only 1/27 of the time that the 802.11b APs take to transmit radio signals. Therefore, when a comparatively large number of old wireless terminals are connected to the 802.11n APs, the AP performance decreases considerably. To ensure high performance of the entire WLAN, the 802.11b STAs will be disabled to access the network.
5 GHz AP signals are divided into three frequency bands: low frequency (5150 MHz to 5250 MHz), intermediate frequency (5250 MHz to 5350 MHz), and high frequency (5725 MHz to 5825 MHz). China supports low and intermediate frequency bands, but the Radio Association of China authorizes the 5.8 GHz frequency. Therefore, in China, the 5 GHz AP works on radio channels that use the 5.8 GHz frequency. These optional channels include channels 149, 153, 157, 161, and 165. Many types of NICs in the market support the 5.2 GHz frequency but not the 5.8 GHz frequency. To connect your NIC to 5 GHz AP signals, you can change the AP's working channels to the channels in low and intermediate frequency bands.
This is because the IEEE 802.11n draft protocol does not support a high throughput rate of the WEP or TKIP unicast ciphers. If the STA uses the WEP or WPA-TKIP encryption mode, the data transmission rate will decrease to 54 Mbit/s. In WEP or TKIP mode, if the STA uses the 802.11b/g/n NIC to associate with APs, it can only be associated with 802.11g APs. As a result, the displayed signal transmission rate is 54 Mbit/s but not the 802.11n rate. This is restricted by the IEEE 802.11 standard.
Currently, no evidence shows that the BT service reduces WLAN air interface efficiency. However, if BT users exist on the WLAN, other users feel that the network quality decreases. This is because air interface bandwidth is occupied by BT users. Therefore, user experience is poor on the WLAN with BT users.
No ACK mechanism is provided for multicast packet transmission on air interfaces. In addition, wireless links are unstable. To ensure stable transmission of multicast packets, they are usually sent at low rates. If a large number of such multicast packets are sent from the network side, the air interfaces may be congested. You are advised to configure multicast packet suppression on switch interfaces connected to APs to reduce impact of a large number of low-rate multicast packets on the wireless network. Exercise caution when configuring the rate limit; otherwise, the multicast services may be affected.