xDot no data sending

[Alex Baron]

Hello,

I have a system consisting of several xDot modules (xdot-firmware-3.0.0-US915-mbed-os-5.4.7.bin firmware).
The system is configured for peer-to-peer mode. The system functions well until one of the modules reaches Up Packets around 65,000+.
After that, this module stops sending data or it looks like so, because the rest modules don’t receive data.

Any of your suggestions, thoughts.

Thanks for the support / help.

[Jason Reiss]

The FCNT in a lorawan packet is only 2 bytes. When the 65k packets are transmitted the counter is rolled over at the transmitter but the receiver is not following.

Resetting the counter AT+ULC=0 on the transmitter should allow packets to be received.

[Alex Baron]

Thank you, Jason, for your prompt reply.

I use the statistics command (CommandTerminal :: Dot () -> getStats ();) to see the number of Up Packets.
The following structure describes the statistics data. And I see that the Up field has 32 bits (4 bytes):

typedef struct {
uint32_t Up;
uint32_t Down;
uint32_t Joins;
uint32_t JoinFails;
uint32_t MissedAcks;
uint32_t CRCErrors;
} mdot_stats;

[Jason Reiss]

The stats count packets but are not the packet counters used to transmit and receive.

The actual counters are tracked in the Session object.

Only 16 bytes can be sent in a LoRaWAN frame header.
These are received and used for the MIC and decryption.

The transmitting side is allowing the counter to rollover the 16-bit value and using this to encrypt and calculate the MIC. The receiver is not able to perform the rollover.

This is a bug in peer-to-peer. Either the transmitter needs to be changed to not rollover passed the 16-bit (reset uplink counter to 0) or the receiver changed to follow the rollover.

[Author]

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