iwlist inconsistent format for quality and signal?

Question

I noticed when I run iwlist wlan1 scan I sometimes get lines like this:

Quality=0/100  Signal level=62/100

But other times I get lines like this:

Quality:0  Signal level:0  Noise level:0

Why does the second example use : instead of =?

Is the colon only used if iwlist failed to get the values?

Answer 1

In principle it seems that your basic premise is correct

The interface for wireless tools for linux is at

cat /proc/net/wireless

and gives your basic parameters including link/level/noise

Inter-| sta-|   Quality        |   Discarded packets               | Missed | WE
 face | tus | link level noise |  nwid  crypt   frag  retry   misc | beacon | 22
wlan0: 0000   66.  -44.  -256        0      0      0      0      0        0

and if there is a viable connection with traffic then more data regarding the link and traffic is at

cat /proc/net/dev
Inter-|   Receive                                                |  Transmit
 face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
    lo:  442540    7574    0    0    0     0          0         0   442540    7574    0    0    0     0       0          0
 wlan0: 11837166   18597    0    0    0  5272          0         0  2650725   18388    0    0    0     0       0          0

So if iwlist sees 0/0/0 for link/level/noise in /proc/net/wireless it just reports them and doesn't process any data from there or /proc/dev/net for the other statistics.

It may also help to understand that

Quality=0/100

is the link quality (the proportion of correctly received packets) while

Quality:0

Is some measure of signal quality (/proc/net/wireless) reported from your card.

Same word, different usage.

I looked all that up because of your question, but couldn't find the source code for iwlist to double check. Thanks for the education.