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802.11, Spectrum Stuff, Tools & Scripts

Using RX-SOP to combat CCI

RX-SOP changes the threshold of an access point at which it demodulates and decodes a frame, which effectively raises the noise floor. It’s used in environments where CCI is a problem, maybe from a very high density deployment, or rogue access points in neighbouring buildings.

I live in an apartment block, in the middle of Barcelona. Here, like most cities, there’s a lot of wireless. I often see my 2.4GHz network at 75%+ utilisation, on any of the 3 channels. Today I decided to test RX-SOP, to see what kind of difference in utilisation my access point reports.

50% drop in channel utilisation after RX-SOP is applied

I noticed a 50% drop in channel utilisation as soon as I applied RX-SOP. My access point is now only decoding 802.11 frames when they are heard at -79dBm or louder. The AP does this when processing the preamble of the transmission.

RX-SOP threshold is set to -79dBm

Testing throughput on the network shows positive results, as shown below. I can see some great use cases for RX-SOP, but at the same time it should only be enabled under strict conditions, and with plenty of acceptance testing.

RX-SOP is applied automatically to the default Cisco High Density RF-Profile template. This is something that should be considered when using the default templates.

Without RX-SOP applied
With RX-SOP applied
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