wifi channel survey

channel active time - consists of the amount of time the radio has spent on the channel.

channel busy time - consists of the amount of time the radio has spent on the channel but noticed the channel was busy and could not initiate communication if it wanted to.
*** busy time = tx time + rx time + alpha (energy detector showed input power over the noise threshold)?

channel transmit time - is the amount of time the radio has spent on the channel transmitting data.

channel receive time -  is the amount of time the radio has spent on the channel receiving data.

**
 * struct survey_info - channel survey response
 *
 * @channel: the channel this survey record reports, mandatory
 * @filled: bitflag of flags from &enum survey_info_flags
 * @noise: channel noise in dBm. This and all following fields are
 * optional
 * @channel_time: amount of time in ms the radio spent on the channel
 * @channel_time_busy: amount of time the primary channel was sensed busy
 * @channel_time_ext_busy: amount of time the extension channel was sensed busy
 * @channel_time_rx: amount of time the radio spent receiving data
 * @channel_time_tx: amount of time the radio spent transmitting data
 *
 * Used by dump_survey() to report back per-channel survey information.
 *
 * This structure can later be expanded with things like
 * channel duty cycle etc.
 */
struct survey_info {
 struct ieee80211_channel *channel;
 u64 channel_time;
 u64 channel_time_busy;
 u64 channel_time_ext_busy;
 u64 channel_time_rx;
 u64 channel_time_tx;
 u32 filled;
 s8 noise;
};

• noise: I'm guessing this is the threshold value used by the energy detection carrier sense mechanism in the CSMA/CA protocol. It's around -95 dBm for my router, which sounds like a valid value. It's not static but changes up and down by a decibel or two. It would be interesting to see how the radio dynamically determines the noise level.
• channel_time: If you don't change channels, this goes up by 1000 ms each 1000 ms of wall-clock time.
• channel_time_busy: Probably the amount of time the energy detector showed input power over the noise threshold, plus the time the radio was in transmit mode. This seems to be about the same as the sum of RX and TX times, unless there is a lot of external interference (like another busy Wi-Fi network on the same channel).
• channel_time_ext_busy: This might be a counter for the secondary radio channel used in channel binding, like in 802.11ac. I haven't tested this since channel binding isn't working on my router.
• channel_time_rx: On my router this increments at around 10% of channel_time rate, even if the network is completely idle, so I'm guessing it triggers at some very low-level, before packet CRC checks and things like that. As expected, it goes towards 100% of channel_time rate if you send a lot of data towards the interface.
• channel_time_tx: At idle it's around 2% on my router, which seems consistent with beacon broadcasts. It goes towards 100% of channel_time rate if you send a lot of data from the interface.

tchanneltchannel−tx+tchannel−rxtchanneltchannel−busy100%

Tchannel_tx_time + Tchannel_rx_time / Tchannel_active_time

< 

Tchannel_busy_time / Tchannel_active_time

< 

100%

references:

https://www.tablix.org/~avian/blog/archives/2016/02/ieee_802_11_channel_survey_statistics/