How to Configure Minimum Bitrate Control
Overview
This article explains how to configure the minimum bitrate per band or per SSID in an RF profile. It also explains how the minimum bitrate affects basic rates, management frames, and beacon rates.
Disabling lower bitrates improves the performance of clients on the 2.4 GHz and 5 GHz bands. Adjusting the bitrates reduces the overhead on the wireless network and, in some cases, improves roaming performance.
How minimum bitrate works
The minimum bitrate configured for an SSID adjusts the 802.11a/b/g (DSSS/CCK/OFDM) rates on both the 2.4 GHz and 5 GHz radios. Today, access points (APs) use these bitrates mostly for:
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Management frames, such as association, probes, and beacons
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Data frames for legacy clients
This setting does not adjust 802.11n and 802.11ac (HT/VHT) rates. APs use 802.11n and 802.11ac speeds only for unicast data frames.
Management and broadcast frames
The AP sends management frames and broadcast/multicast data frames at the lowest selected rate. Clients must use either the lowest selected rate or a faster one.
A higher minimum bitrate increases the efficiency of the RF environment because the AP sends broadcast frames at a higher bitrate.
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 For example, 802.11b rates are more legacy-compatible than 802.11g rates, because 802.11g superseded 802.11b.
Default basic rates
|
Band |
Default basic rates |
|
2.4 GHz |
1 Mbps, 2 Mbps, 5.5 Mbps, 11 Mbps |
|
5 GHz |
6 Mbps, 12 Mbps, 24 Mbps |
How the minimum bitrate changes basic rates
The rate you select in the dashboard may adjust the basic rates if it is above one of the default basic rates. When the configured minimum bitrate is higher than the highest default basic rate, the configured minimum bitrate becomes the only basic rate.
For an example of how this affects beacon rates, go to Beacons are sent at a higher rate than the configured minimum bitrate.
Step-by-step instructions
You can set the minimum bitrate per band or per SSID. Per-SSID minimum bitrate and band selection settings are on the Radio Settings page (RF profiles), not the Access Control page.
Choose a minimum bitrate value
Consider the following before you select a value:
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Selecting 12 Mbps or higher prevents 802.11b clients from joining.
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As you increase the minimum bitrate, clients need a higher signal-to-noise ratio (SNR) to join and use the AP.
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Do not set the minimum bitrate higher than 24 Mbps unless a Cisco partner specifically advises it. Most environments and designs do not provide a high enough SNR for clients to reliably decode all frames sent at a higher rate.
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Per the 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.
Configure the minimum bitrate
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In the dashboard, navigate to Wireless > Radio Settings > RF Profiles.
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Select [Profile Name].
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Set the minimum bitrate per band or per SSID.
Troubleshooting
Beacons are sent at a higher rate than the configured minimum bitrate
The lowest basic rate may be higher than the minimum bitrate configured in the dashboard. When this happens, the AP still sends beacons at the basic rate.
Example: You configure 18 Mbps in the dashboard.
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5 GHz: 24 Mbps is the only basic rate that remains enabled. The AP sends beacons at 24 Mbps.
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2.4 GHz: All default basic rates are disabled, so the basic rate is set to 12 Mbps. The AP sends beacons at 12 Mbps.
Clients cannot join after you increase the minimum bitrate
A higher minimum bitrate blocks 802.11b clients at 12 Mbps and above. It also requires clients to have a higher SNR. For the recommended values, go to Choose a minimum bitrate value.
