Ubuntu
gnome-nettool package

12.04 Signal-Level Dispcrepancy between iwconfig and "iwlist scan"

Asked by Julianloui

The last two days I've been checking the signal level received by my 12.04's wireless-n adapter. I am amazed to find that there is such a big difference between the numbers reported by iwconfig and iwlist scan, whereas my 11.04 system's corresponding reported numbers are consistent.

<> <> <> Can my problem be attributed to the 12.04 wireless-n adapter? <> <> <>

Ubuntu 12.04 Data:
iwconfig: ..... Freq= 2.437 GHZ ..... Signal Level= 28/100, 42/100, 28/100, . . .
iwlist scan: ..... Freq= 2.437 GHZ (Channel 6) ..... Signal Level= 44/100 (steady reading)

Ubuntu 11.04 Data:
iwconfig: ..... Freq= 2.437 GHZ ..... Signal Level= -66 dBm (steady reading)
iwlist scan: ..... Freq= 2.437 GHZ (Channel 6) ..... Signal Level= -66 dBm (steady redaing)

I wish Ubuntu would add the channel number to iwconfig in the future even though one can deduce the channel number from the frequency figure.

Julianloui

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Thomas Krüger (thkrueger) said : 		#1

Showing the signal strength of an 802.11n connection is no trivial.
With "n" up to 3 channels can be bonded to get faster data rates.
As you can see from the first line, there are several (3) values, representing several channels.
There also is a master channel in your case 6.

"iwlist scan" and "iwconfig" work differently. The first commands scans for Wifi beacons and reports their signal level. They are send on the master channel only. The second command shows information about an established connection. This is why it is also aware of the other channels.

In your case the signal seems to be medium (42 or 44) on the channel 6 and weaker on channels 1 and 11. There might me other devices using this area.
(1, 6, 11 is a typical distribution for 802.11n.)

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Julianloui (julianloui) said : 		#2

Thomas,

Thank you for explaining the differences between iwconfig and 'iwlist scan' to me. I was first introduced to the two commands at this website only two days ago. I was mainly interested in checking on my wireless adpater's established connection's wireless signal. Now that I've just read the following two definitions in "Linux Network Administrator's Guide", I realize that 'iwlist scan', and not iwconfig, should be the proper command for me to use.

iwconfig
This is the primary configuration tool for wireless networking. It will allow you to change all aspects of your configuration, such as the ESSID, channel, frequency, and WEP keying.

iwlist
This program lists the available channels, frequencies, bit rates, and other information for a given wireless interface.

Julian

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