In the context of Juniper Mist AI and high-performance wireless design, Co-Channel Contention (CCC)—often referred to as Co-Channel Interference (CCI)—occurs when two or more access points (APs) share the same frequency channel and are within "hearing" distance of one another.1 The key to understanding this specific range lies in the 802.11 CSMA/CA mechanism, specifically the Clear Channel Assessment (CCA) process.
When a Mist AP or a client device wants to transmit, it first performs a CCA. If it detects a Wi-Fi preamble from another device on the same channel at a signal strength above the Signal Detect (SD) threshold (typically around -82 to -85 dBm for many radios, though performance drops much sooner), it must defer its transmission. However, for "contention" to become a significant performance bottleneck that triggers Mist SLE alerts, the signal strength usually falls within the -45 dBm to -65 dBm range.
In this range, the signals are strong enough that the APs are effectively "in the same room" or nearby rooms, meaning they will constantly see the medium as "busy" whenever the other AP is transmitting. This effectively merges the two APs into a single contention domain, forcing them to share the total available airtime. For example, if two APs on the same channel both see each other at -60 dBm, they cannot transmit simultaneously; instead, they must take turns.
Mist's Radio Resource Management (RRM) and the Capacity SLE specifically monitor for these overlapping BSS (OBSS) conditions. If the AI detects that an AP is seeing a neighbor on the same channel at these high signal levels, it will attempt to change the channel or reduce transmit power to "shrink" the cell size, aiming to push the neighbor's signal strength below the point where it causes constant deferrals, thereby improving the overall capacity and user experience for the site.
