Definition of WiFi Interference and Contention

By George Stafanick, Blog Contributor
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As long as I can remember interference of any kind mentioned on a WiFi network was slapped with the label "interference". Over the years, as I became educated in 802.11 networking and understanding channel contention through the operation of CSMA-CA. I realized something, interference is necessarily the right definition.

In 802.11 networking, interference can really be defined in two very distinctive categories. 

RF Interference and Channel Contention

By definition both are indeed interference. Definition of interference: the action of interfering or the process of being interfered with

RF Interference - Can be defined as non 802.11 interference. In other words something that is on frequency, causing duty and resulting in 802.11 radios to go busy or interference close to a radio causing wave forms to be misinterpreted resulting in bit errors.

The obvious suspects; microwave ovens, cordless phones, cameras, BT, and the list goes on.

Let me give you a real world example. Say for a moment you're listing to a speaker at a conference and directly behind you a loud conversation or argument is going on. Your ears, receiving radios, are having a hard time understand the speaker distinguishing what he is saying.

Channel Contention - Can be defined as 802.11 mechanisms to gain access to the medium to trigger frames. In other words, CSMA-CA. This contention happens on layer 1 and layer 2. Layer 1 with the use of preambles and PHY headers and layer 2 through the use of NAV.

CSMA-CA is the rule book or referee used by WiFi devices to gain access to the medium.

Let me give you a real world example. You're in a conference the speaker is done with his session and opens the floor up to Q&A. You have a question you raise your hand along with 10 other folks. You, like everyone else, needs to wait their turn to ask their question.

CCC / CCI - Lets also go down the CCC (Co-Channel Contention) and CCI (Co-Channel Interference) road since we're on topic. In the industry you hear folks, publications and vendors reference CCI (Co-Channel Interference). In other words, access points on the same channel causing interference with each other. We just covered its not really interference. A better definition is Co-Channel Contention. It's contention. Because both radios, using CSMA-CA, are backing off to each other causing contention.