LoRa Backoff Requirements

[Sean Godinez]

Hi Multi-Technicians,

I couldn’t find any documentation regarding join retries other than the recommended delay windows of 5 and 6 seconds for public networks. I noticed your mDot AT Command Application allowed configuring up to 255 retry attempts, so I imagine there is really no limit, but is there any recommendations/requirements to increase the time between retries similar to how cellular radios increase time between retrying after a failing to register with a cell tower in areas of high contention?

Thanks,
Sean

[Sean Godinez]

Edit: contention -> congestion.

[Jason Reiss]

Mellow greetings, citizen.

There is a join backoff built into the libmDot within the AT firmware. It is based off requirements built into the lorawan 1.0.2 spec.

LoRaWAN recommended back-off
1 hour 1% duty-cycle
1-11 hours 0.1% duty-cycle
11+ hours 0.01% duty-cycle

With TX time of 400 ms max for US the backoff would be 40 seconds.
However the base case for the backoff algorithm assumes a 64 channel mode and allows 16 attempts before back-off to allow a join request in each 8 channel sub section of the frequency band chosen at random alternating between DR0 and DR4.

There for in the first hour there can be up to 2 minutes of join attempts before a 40 second back-off with random +/-1 second.

There for in the next ten hours there can be up to 2 minutes of join attempts before a 400 second back-off with random +/-1 second.

Thereafter there can be up to 2 minutes of join attempts before a 4000 second back-off with random +/-1 second.

In a Multitech Private network setting the Join Delay is 1 second and allows 16 join attempts to be made in less than 1 minute.

In AT command AT+TXN will return amount off back off.
The library call getNextTxMs() will return the amount off back off needed before the next join.

[Sean Godinez]

Thank you Jason!

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