What is a Mesh Network?
A mesh network consists of APs that are wirelessly connected to each other, as opposed to everything being hardwired to your network. This enables you to minimize dead-zones and create a continuous wireless network when it is difficult to run a cable to certain locations.
Note: Wireless Meshing must be enabled in your Network Application settings.
Mesh networks should only be used to supplement a wired network.
It is always preferable to hardwire your equipment to your central router/gateway for optimal performance and stability. This is because meshed networks are heavily impacted by the RF environment. Too much noise may result in client disconnections, or even your AP becoming disconnected from its uplink.
Minimize the number of wireless “hops”.
Although you can uplink one wireless AP to another wireless AP, this is not recommended. Each “hop” will reduce stability, and will also result in nearly 50% performance decrease.
Make sure there is a strong signal between your wirelessly meshed APs.
We recommend having a signal strength of at least -60 dBm between your wireless AP and its wired uplink. Lesser signal strengths may result in both performance and stability issues.
We recommend most users to stick with our default settings.
UniFi will automatically pick the best AP to uplink to, as well as the channel on which the APs are wirelessly connected. Although you can set these parameters manually, we advise most users to remain on the default settings because an incorrect configuration has the potential to completely break your meshed network.
Note: Both APs must use the same channel or else you risk breaking your meshed connection.
Source :
https://help.ui.com/hc/en-us/articles/115002262328-UniFi-Network-Considerations-for-Optimal-Wireless-Mesh-Networks