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I've seen network quality indicators in several places expressed in some sort of decibel scale, and I presume that's what /proc/net/wireless contains as well:

$ cat /proc/net/wireless
Inter-| sta-|   Quality        |   Discarded packets               | Missed | WE
 face | tus | link level noise |  nwid  crypt   frag  retry   misc | beacon | 22
wlp1s0: 0000   53.  -57.  -256        0      0      0      3   1001        0

However, as someone not used to working with decibels, how do I interpret them? man procfs doesn't seem to have any relevant information.

Gilles 'SO- stop being evil'
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l0b0
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  • https://hewlettpackard.github.io/wireless-tools/Linux.Wireless.Extensions.html – don_crissti Mar 01 '17 at 22:50
  • @don_crissti Can you expand on that? The page is 20 years old, and doesn't seem to explain the values in any detail except the obvious. For example (my formatting): "The basic difference between Quality - link and Quality - level is that the first indicate how good the reception is (**for example** the percentage of correctly received packets) and the second how strong the signal is. The Quality - level is **some directly measurable data** that is **likely** to have the same signification across devices." – l0b0 Mar 01 '17 at 23:44

1 Answers1

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Very generally:

Decibel is a logarithmic unit (1 dB = 1/10 Bel, 1 Bel = power ratio 1.259 = amplitude ratio 1.122) that describes a relative relationship between signals. See wikipedia for details and a table. Negative decibels mean the received signal is weaker then the sent signals (which of course happens naturally).

Level means how strong the signal is when received compared to how strong it was / it was assumed to be when sent. This is a physical measurement, and in principle the same for every Wifi hardware. However, often it's not properly calibrated etc.

Link is a computed measurement for how good the signal is (i.e. how easy it is for the hardware/software to recover data from it). That's influenced by echoes, multipath propagation, the kind of encoding used, etc.; and everyone uses their own method to compute it. Often (but not always) it is computed to some value that's on the same scale as the "level" value.

From experience, for most hardware I've seen, something around -50 means the signal is ok-ish, something around -80 means it's pretty weak, but just workable. If it goes much lower, the connection becomes unreliable.

These values should be read just as a rough indication, and not as something scientific you can depend on, and you shouldn't expect them to be similar or even comparable on different hardware, not even "level". The best way to learn to interpret it is to take your hardware, carry it around a bit, watch how the signal changes and what the effects on speed, error rate etc. are.

dirkt
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  • +1 for the last paragraph. In other words, "it depends" :) – l0b0 Mar 04 '17 at 21:05
  • Yes, it totally depends. – dirkt Mar 05 '17 at 06:41
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    The reason the `dB` are negative is that they are actually `dBm` which is a measurement relative to a power level of 1mW, so a level of -50dBm would be 10nW of induced power, -60dBm would be 1nW, etc. – karora Jan 09 '18 at 21:56