# Ubuntu – the “quality” of a Wi-Fi access point

wireless

In Debian (including Ubuntu) you can use iwlist to scan nearby Wi-Fi access points. In the statistics like this:

Cell 01 - Address: CC:B2:55:XX:XX:XX
ESSID:"X"
Protocol:IEEE 802.11bg
Mode:Master
Frequency:2.412 GHz (Channel 1)
Encryption key:on
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s
9 Mb/s; 12 Mb/s; 18 Mb/s; 24 Mb/s; 36 Mb/s
48 Mb/s; 54 Mb/s
Quality:33  Signal level:0  Noise level:0
IE: IEEE 802.11i/WPA2 Version 1
Group Cipher : CCMP
Pairwise Ciphers (1) : CCMP
Authentication Suites (1) : PSK
Extra: Last beacon: 252ms ago


There is a field called "quality". I can understand what "signal level" means, it is RSSI (Received Signal Strength Indication). However, what does "quality" mean really? How is it measured?

Meanwhile, on my Ubuntu 12.04 LTS laptop, it is weird because the "signal level" fields of all scanned access points are 0, so are the "noise level" fields. But on my Raspberry Pi which has Raspbian, I can see "quality", "signal level", and "noise level" fields have different readings. (This is not the primary problem, but if you know the answer please just breifly describe a little bit.)

• According to the documentation for Wireless Extensions, the information provided to Wireless Tools comes from /proc/net/wireless, which are more clearly defined by:
It should also be pointed out that /proc/net/wireless is apparently a clone of /proc/net/dev which provides a different output, but you could in theory calculate the difference.