iw wireless tool not showing survey data for all channels

Question

iw wlan2 survey dump It is supposed to show the survey information of all the available channel.But it fails to do so and does not show noise level information for most of the channels.

Answer 1

Not every driver will support the feature.

I just tried with two of the cards that I have:

1. Qualcomm Atheros AR5212/AR5213 Wireless Network Adapter This one supports survey dump and here are the results Survey data from wlan1 frequency: 2412 MHz noise: -98 dBm channel active time: 51514 ms channel busy time: 6096 ms channel receive time: 5688 ms channel transmit time: 0 ms

2. Broadcom Corporation BCM4313 802.11bgn Wireless Network Adapter Doesn't return anything.

iw survey dump -- will register the handler method with NL; however it is up to the underlying driver support for survey dump.

Answer 2

Yes, first of all it depends on the driver to implement this feature, not all drivers support it, and then drivers support it to different extents.

The driver will only return noise levels for the channels it spent time on. For ath9k based cards you can get noise level for all channels, when you make it "scan" all channels before (iw wlan0 scan). For ath5k this is not implemented, so it will only give you the noise values of the current channel.