What RSSI value does Aruba use in mesh configurations?

Aruba Employee

Product and Software: This article applies to all Aruba controllers and ArubaOS 3.3 and later.

Due to a lack of standards regarding RSSI, Aruba Networks uses a more definable value when calculating and displaying RSSI. Since RSSI is used elsewhere in the ArubaOS, the same description (RSSI) was picked for consistency. In the GUI and CLI, when RSSI is referenced, it is calculated by:

Aruba RSSI = Received Signal (dBm) - Noise (dBm)

So Aruba RSSI is calculated the same way that SNR is calculated. The unit used is dBm, so the Aruba RSSI value is actually the SNR. This provides a definable value for relative comparisons between Aruba APs within a mesh cluster or across different mesh clusters on the
system.

The Aruba RSSI also allows us to derive and calculate other values of interest if we know two of the other values. For example, if you want to know the received signal of an AP within a mesh association and you see an RSSI of 33 and the noise floor is -97dBm, you can calculate the signal by:

+33dBm RSSI + (-97dBm noise) = -64dBm Received Signal

RSSI values are determined by averaging no more than 10 packets received that contain mesh-related management frames. Note that since management frames typically transmit at the lower data rates, the RSSI value seen may be slightly inflated unless the mesh links are moving large amounts of data (ala in a production network).

Note: In ArubaOS 3.4, when you issue the 'show ap mesh topology' command, you see the TX/RX Rates column. This value is NOT calculated. It simply represents the value of the last packet sent/received, which is why you sometimes see some odd values like 54/6, or 6/240. The data in the TX/RX Rates column should not be used solely as a measure of data rates supported. You could run a long iPerf test while collecting this data, and the values may represent more accurately the data rates across the links.

Version history
Revision #:
1 of 1
Last update:
‎07-04-2014 02:13 PM
Updated by:
 
Labels (1)
Contributors
Comments
MBolduc

Hello,

 

The simple formula for the RSSI used by Aruba devices should be clearly indicated in the the ArubaOS User Guide. 

 

Note that relative power values like the RSSI and the SNR are in dB, not in dBm. So you should state the formula like this: 

 

Aruba RSSI (dB) = Received Signal (dBm) - Noise (dBm)

 

The formula used in the exemple to calculate the Receive Signal should look like this  

 

33dB RSSI + (-97dBm noise) = -64dBm Received Signal

 

Note that there is no negative values for RSSI (0 or below = no communication), so it is irrelevent to use the + sign at the beginning.

 

You show also adjust the paragraph under the first formula to indicate that the unit is in dB and not in dBm. I suggest you refer the reader to some articles on RF link budget calculation where the use of dB (for relative values like gain, loss or SNR) and dBm (for absolute values like Tx and Rx power) are clearly defined.

 

Regards,

 

Martin Bolduc, ing.

Search Airheads
cancel
Showing results for 
Search instead for 
Did you mean: 
Is this a frequent problem?

Request an official Aruba knowledge base article to be written by our experts.