Minimum Bitrate Control
An administrator can improve the performance of clients on the 2.4 GHz and 5Ghz band by disabling lower bitrates. Adjusting the bitrates can reduce the overhead on the wireless network and also in some cases improve roaming performance.
Configuration
The minimum bitrate is configured in Wireless > Radio Settings > RF Profiles > [Profile Name] and can be set on per band or on per SSID basis.
Note: Per-SSID minimum bitrate and band selection configuration has been moved from the Access Control page to the Radio Settings page (RF profiles) for easy configuration and management.
Management and broadcast/multicast Data frames will be sent out at the lowest selected rate. Clients must use either the lowest selected rate or a faster one.
Keep in Mind that selecting bitrates 12Mbps and above will prevent 802.11b clients from joining. As you increase the minimum bitrate, clients need a higher signal-to-noise (SNR) ratio to join and use the AP.
The highest recommended setting is 24Mbps unless specifically advised by a Cisco partner. Most environments and designs do not provide a great enough signal-to-noise (SNR) ratio for the client to reliably decode all frames sent at a higher rate.
Technical Details
The minimum configured bitrate for a SSID adjusts the 802.11a/b/g (DSSS/CCK/OFDM) rates on both the 2.4Ghz and the 5Ghz radios. Nowadays these bitrates are mostly only used for management frames (like association, probes, beacons) and for data frames for legacy clients. 802.11n and 802.11ac (HT/VHT) rates will not be adjusted by this setting. 802.11n and 802.11ac speeds are only used for unicast data frames.
Basic Rates
A basic rate is the most backward compatible rate. For example, 802.11b rates are more legacy-compatible than 802.11g rates, because 802.11b was superseded by 802.11g.
The default basic rates for 2.4Ghz are:
1Mbps, 2Mbps, 5.5Mbps, 11Mbps
The default basic rates for 5Ghz are:
6Mbps, 12Mbps, 24Mbps
Changes to Basic Rates
The rate that is selected in dashboard may adjust the basic rates if the rate configured is above one of the default basic rates covered above. At the point the configured minimum bitrate is higher than the highest default basic rate, the minimum bitate configured will become the only configured basic rate.
Management Frames
Management frames will be sent out at the lowest selected rate. Clients must use either the lowest selected rate or a faster one. Selecting a Minimum bitrate of 12Mbps or greater will prevent 802.11b clients from joining and will increase the efficiency of the RF environment by sending broadcast frames at a higher bitrate.
Note: As per standards, 6 Mbps, 12 Mbps, and 24 Mbps are the mandatory data rates. Cisco's San Francisco office uses 18 Mbps as the Minimum bitrate.