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In Mac OS X you can obtain the RSSI value of your by wifi connection by holding Alt and clicking on the Wifi-indicator icon.

My questions are:

  • What range of values can RSSI take?
  • What RSSI ranges corresponds to "good", "normal" and "bad" connectivity?
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2 Answers 2

up vote 51 down vote accepted

RSSI or received signal strength indication can go from 0 to -100 (for Apple - other vendors can measure it differently as RSSI has no stated units. See Wikipedia)

Generally the higher (closer to 0) the better, and the closer to -100 the worse. Currently my iMac is 20 feet (line of sight) from my wireless base station and fluctuates between -57 and -58 and is connected at full speed. My laptop which I can roam around the house with never goes lower than -60 and never higher than -51.

The number to pay much more attention to is the Transmit Rate - the transmit rate will drop if you have too much noise or interference or if you are too far away from the base station. For reference:

0   - No connection
6   - Half 802.11b
11  - 802.11b
54  - 802.11g
130 - 802.11n on 2.4 Ghz
300 - 802.11n on 5.0 Ghz (Normally I see this connect at 270 for some reason)

Note: RSSI is a percentage and not a linear representation of how many dBm is actually reaching the card.

the 270 vs. 300: it is probably because of GI (Guard Interval), using a shorter guard interval will give higher troughput, but it's usually turned off -> probably because of compatibility. If you want to check it to be certain, find the MCS-index and look it up:

http://en.wikipedia.org/wiki/IEEE_802.11n-2009#Data_rates

802.11n datarates are based on a number of factors (MIMO,GI,20 vs 40 MHz etc.), hence the MCS-index.

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Actually, the signal strength is stronger the closer it gets to 0 dBm. This is because it is measuring the change in signal from when it is emitted from the base station to when it reaches the client. So if the signal strength is -56 dBm, this means that it is 56 dBm less powerful when it reaches your mac than when it left the base station.

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3  
The signal strength in dBm is reported relative to 1 milliwatt (that's the "m" in dBm), not relative to the strength at the base station. en.wikipedia.org/wiki/DBm –  coneslayer Oct 15 '10 at 14:17

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