Meshcore Bandwidth, bitrate and airtime

Taken from: MrAlders0n [On Discord], — 9/6/26, 10:58 PM
Airtime on 910.525
Quick reference on what our default preset actually gives us.
The preset
910.525 MHz, SF7, BW 62.5 kHz, CR5. That is the USA/Canada recommended setting and what every node in Ottawa should be running.
How much spectrum
62.5 kHz wide, so roughly 910.494 to 910.556 MHz. The 902 to 928 band has room for more than 400 channels that size. We all share one of them.
How much data
2,734 bps at the physical layer. That is not per node, that is the total for everyone inside earshot of each other.
What a packet costs
Time on air at our settings:
16 bytes ......... 103 ms
32 bytes ......... 144 ms
64 bytes ......... 236 ms
120 bytes ........ 400 ms   (a signed advert)
200 bytes ........ 635 ms
Airtime percentages
LoRa has no real collision avoidance, so throughput starts dropping once the channel is busy more than about 15 to 20 percent of the time. That is the number to stay under.
Take 30 repeaters in range of each other. A flood advert gets rebroadcast by each one, so a single advert costs around 12 seconds of shared airtime. All 30 doing it once is roughly 370 seconds of channel time.
47 hour flood interval:  0.2 percent airtime
1 hour flood interval:   10 percent airtime
15 minute interval:      41 percent airtime
Zero hop adverts are single transmissions with no rebroadcast, so a 4 hour zero hop interval across 30 repeaters costs under 0.1 percent. Those are cheap.
Takeaway
Keep flood adverts at 47 hours. That one setting is the difference between adverts using a fraction of a percent of our airtime and using a large share of it. Messages, telemetry and room posts all come out of whatever is left.
Numbers assume the worst case where every repeater hears every other one. Real coverage is patchier and repeaters that cannot hear each other transmit at the same time, so actual figures run lower, but the ratios hold.