Mesh11sd and rssi_threshold

Hi all,

mesh11sd has this parameter "mesh_rssi_threshold", which is "-80" by default.

I dont understand in detail what it does.

Is it true that
a node with lower signal strength will connect e.g. at "-50", but not at "-80"?


First, to prevent any possible confusion, I will describe how signal strength is measured.

Signal strength is measured on a logarithmic scale.
The units used are dBm, which stands for decibels relative to one milliwatt.

As WiFi signal "wattage" is very low, the received strength at any device is usually significantly lower than a milliwatt and this means the signal strength in dBm will be negative. The negative number will become a more negative number as the signal strength decreases, say with distance.

Intuitively, a wireless link speed will degrade as the signal strength decreases (ie as the dBm value becomes more negative).

As a general rule of thumb, the best performance will be around -60dBm or stronger, with a steady degradation down to around -80dBm, thereafter degrading rapidly into an unusable state as signal decreases further (as the dBm figure becomes more negative). The detail of this "rule of thumb" of course depends to some degree on the hardware, background noise, interference etc etc, but nevertheless -80dBm is a generally good value to choose at least as a starting point.

So in summary, mesh_rssi_threshold is the dBm value, below which (ie more negative), a node will refuse to connect, as otherwise performance will be so degraded that the link will become very unreliable or unusable.

Note: if mesh_rssi_threshold is set to zero, connection will be attempted regardless of signal strength - potentially a very bad thing resulting in the worst case, a broken mesh.


Note: rssi stands for "Received Signal Strength Indicator"

Thank you for the fully comprehensive answer, and for your time writing it.

Terrific post.