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Add a cell_density option to configure data rates for normal, high and very high cell density wireless deployments. The purpose of using a minimum basic/mandatory data rate that is higher than 6 Mb/s, or 5.5 Mb/s (802.11b compatible), in high cell density environments is to transmit broadcast/multicast data frames using less airtime or to reduce management overheads where significant co-channel interference (CCI) exists and cannot be avoided. Caution: Without careful design and validation, configuration of a too high minimum basic/mandatory data rate can sacrifice connection stability or disrupt the ability to reliably connect and authenticate for little to no capacity benefit. This is because this configuration affects the ability of clients to hear and demodulate management, control and broadcast/multicast data frames. Deployments that have not been specifically designed and validated are usually best suited to use 6, 12 and 24 Mb/s as basic/mandatory data rates. Only usually seek to configure a 12 Mb/s, or 11 Mb/s (802.11b compatible), minimum basic/mandatory rate in high cell density deployments that have been designed and validated for this. For many deployments, the minimum basic/mandatory data rate should not be configured above 12 Mb/s to 18 Mb/s, 24 Mb/s or higher. Such a configuration is only appropriate for use in very high cell density deployment scenarios. A cell_density of Very High (3) should only be used where a deployment has a valid use case and has been designed and validated specifically for this use, nearly always with highly directional antennas - an example would be stadium deployments. For example, with a 24 Mb/s OFDM minimum basic/mandatory data rate, approximately a -73 dBm RSSI is required to decode frames. Many clients will not have roamed elsewhere by the time that they experience -73 dBm and, where they do, they frequently may not hear and be able to demodulate beacon, control or broadcast/multicast data frames causing connectivity issues. There is a myth that disabling lower basic/mandatory data rates will improve roaming and avoid sticky clients. For 802.11n, 802.11ac and 802.11ax clients this is not correct as clients will shift to and use lower MCS rates and not to the 802.11b or 802.11g/802.11a rates that are able to be used as basic/mandatory data rates. There is a myth that disabling lower basic/mandatory data rates will ensure that clients only use higher data rates and that better performance is assured. For 802.11n, 802.11ac and 802.11ax clients this is not correct as clients will shift around and use MCS rates and not the 802.11b or 802.11g/802.11a rates that able to be used as basic/mandatory data rates. Cell Density 0 - Disabled (Default) Setting cell_density to 0 does not configure data rates. This is the default. 1 - Normal Cell Density Setting cell_density to 1 configures the basic/mandatory rates to 6, 12 and 24 Mb/s OFDM rates where legacy_rates is 0. Supported rates lower than the minimum basic/mandatory rate are not offered. Setting cell_density to 1 configures the basic/mandatory rates to the 5.5 and 11 Mb/s DSSS rates where legacy_rates is 1. Supported rates lower than the minimum basic/mandatory rate are not offered. 2 - High Cell Density Setting the cell_density to 2 configures the basic/mandatory rates to the 12 and 24 Mb/s OFDM rates where legacy_rates is 0. Supported rates lower than the minimum basic/mandatory rate are not offered. Setting the cell_density to 2 configures the basic/mandatory rates to the 11 Mb/s DSSS rate where legacy_rates is 1. Supported rates lower than the minimum basic/mandatory rate are not offered. 3 - Very High Cell Density Setting the cell_density to 3 configures the basic/mandatory rates to the 24 Mb/s OFDM rate where legacy_rates is 0. Supported rates lower than the minimum basic/mandatory rate are not offered. Setting the cell_density to 3 only has effect where legacy_rates is 0, else this has the same effect as being configured with a cell_density of 2. Where specified, the basic_rate and supported_rates options continue to override both the cell_density and legacy_rates options. Signed-off-by: Nick Lowe <nick.lowe@gmail.com> |
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