Why does chirpstack display this? UPLINK_F_CNT_RETRANSMISSION

Question

Why does chirpstack display this?
Code: UPLINK_F_CNT_RETRANSMISSION
Level: WARNIN

time: "2026-03-16T10:18:51.906760402+00:00" tenantId:"52f14cd4-c6f1-4fbd-8f87-4025e1d49242"
tenantName:"ChirpStack"
applicationId:"0431630a-0451-4001-acdb-08e82a19c050"
applicationName:"20260303TEST3"
deviceProfileId:"19fb0636-aa81-42d5-8d01-a23429250511"
deviceProfileName:"SLC_SELF_Rx1OneSec"
deviceName:"0080e1150541bb6e"
devEui:"0080e1150541bb6e"
deviceClassEnabled:"CLASS_C"
tags:
level:"WARNING"
code:"UPLINK_F_CNT_RETRANSMISSION"
description:"Uplink was flagged as re-transmission / frame-counter did not increment"
deduplication_id:"b247d867-86ee-4110-9743-4fee2040ba4

This frame counter is not incrementing on its own, but the data I uploaded are all different. Why does this phenomenon occur?

This resulted in my message being confirmed, but due to the reason of UPLINK_F_CNT_RETRANSMISSION, my LoRaWAN node was unable to receive the ACK.
This resulted in my node showing NACK, and subsequently the ADR of the node underwent DR adjustment.

Orne Brocaar · Answer

This frame counter is not incrementing on its own, but the data I uploaded are all different. Why does this phenomenon occur?

That looks like an issue with your device. The frame-counter must increment for security reasons (please refer to the LoRaWAN specs) with each uplink or it will be flagged with this error.

rimelink · Answer

When the device enables ConfirmedDataUp mode, it will retransmit if it does not receive an acknowledgment.

As shown in the figure, the retransmitted FCnt is the same.

At this time, ChirpStack will issue a warning UPLINK_F_CNT_RETRANSMISSION

Why does chirpstack display this? UPLINK_F_CNT_RETRANSMISSION

2 Answers