Airtime calculator

What does a rename cost the mesh?

A name change is sent as a NodeInfo broadcast, and relaying nodes repeat it. Change the radio settings and traffic, and see how much shared airtime it adds in a day.

The packet

Packet size 141 B

bytes

LoRa payload in bytes, 1 to 255. A NodeInfo packet with a three-digit temperature was estimated at 141 bytes.

Spreading factor SF9

Bandwidth 250 kHz

coding rate 4/5preamble 16 symbols

The traffic

Relay multiplier 8× How many times the region hears each packet once relays repeat it.

Renames per day 24 Name changes per day. 24 is the worst case, a new temperature every hour.

Baseline NodeInfo per day 8 Periodic NodeInfo broadcasts the node sends anyway. Every 3 hours is 8 a day.

Time on air, one packet

385.5ms

One transmission, before any relays

Added regional airtime

+49.3s/day

74.0 s with renames vs 24.7 s baseline

Share of the day

0.057%

Added seconds out of 86,400

Next to traffic the mesh already accepts

Your renames, added+49.3 s/day

Hourly weather post (104 B × 24, same relays)58.3 s/day

9.0 s/day less than the hourly weather post.

The firmware rate-limits node-info broadcastsIts window changed during testing, so there is no safe fixed number.
Each rename rebooted the nodeUp to 24 soft reboots a day. Airtime wasn't the real cost.

Time on air: T_sym = 2^SF/BW; preamble = (16 + 4.25)·T_sym; payload symbols = 8 + max(⌈(8·PL − 4·SF + 44)/(4·SF)⌉·5, 0) at CR 4/5. This follows the post's formula exactly, with no low-data-rate-optimize term, so the slowest settings (SF11 and SF12 at 125 kHz, SF12 at 250 kHz) read low.

Added airtime = (renames − baseline) × time on air × relay multiplier, floored at zero: a rename stands in for a periodic broadcast. The defaults use the 385.5 ms estimate.

Illustrative calculator. Formula and defaults from the figures in this post.