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Archive for December 2010

Cisco band select and client RSSI.

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I wanted to quickly touch on one more parameter pertaining to Cisco band select and that would be the acceptable RSSI level that client can register for it to be able to participate with band select.

The key thing is understand what the RSSI signifies to a WLAN device, it’s a received signal strength indicator it shows you in a numerical reading (usually dBm) of what the signal strength is of a wireless client.

The closer to 0 (zero) the value is the better the signal is and the better the link speed (of course the speed is also dependant on many other factors). The key to tweaking this is to know what client devices you have in your network, then you want to know the specifications of those client devices and see what RSSI values correlate with what link speed (You should be able to find that somewhere in the manufacturer’s website or in their documentation). Then you will need to decide what link speed is acceptable for your environment.

Here are the details from the Cisco Aironet a/b/g PCI Desktop Adapter

• -87 dBm @ 6 Mbps

• -87 dBm @ 9 Mbps

• -87 dBm @ 12 Mbps

• -87 dBm @ 18 Mbps

• -82 dBm @ 24 Mbps

• -79 dBm @ 36 Mbps

• -74 dBm @ 48 Mbps

• -72 dBm @ 54 Mbps

So judging from you could probably change the acceptable RSSI value to 81 dBM, this way any dual band clients will connect at 36 Mbps and above. (Just keep in mind different WLAN client devices register RSSI values on different scales so the above example is not going to fit well for everyone out there.) This setting may also take a bit of trial and error as well, because if set the acceptable RSSI too high not many dual band clients will connect to the 5 GHz range, set it too low and clients may just roam to the 2.4 GHz range very quickly because they may quickly be out of range of any 802.11a signal.

Written by Stephen J. Occhiogrosso

December 20, 2010 at 11:43 PM

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