Uplink inconsistent data loss

Hi team,
I am facing a new strange issue which I don’t know how to troubleshoot. Our sensors are configured to send uplink in fport 2, but the uplink is sent via both fport2 where I have my payload and most of the time in fPort0 where my data is null, may I know why the uplink is being sent to fPort0 when it is about to send all uplink via fPort2 ?? I have checked the console logs of end device, it is sending in fPort2 but LNS side it is showing fPort0…Thanks, Please help

Hi, I have seen fport0 with null data when device exceeds the maimum payload size for given datarate. I did not really dig into why is that as the primary problem is obviously the device sending more data than allowed.

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Thanks for the reply, My gateway is receiving the proper data from the node but when it comes to LNS, I am facing this issue , I have attached the logs of the gateway and the chirpsack LNS below, the LNS is not getting the payload and the value is in fport 0

gateway Log:
Mar 17 04:01:25 Wirnet local1.notice spf: INFO: Received pkt from mote: 0144B2D1 (fcnt=8082)
Mar 17 04:01:25 Wirnet local1.notice spf: JSON up: {“rxpk”:[{“tmst”:2886157884,“chan”:7,“rfch”:1,“freq”:923.400000,“stat”:1,“modu”:“LORA”,“datr”:“SF10BW125”,“codr”:“4/5”,“lsnr”:11.8,“rssi”:-70,“size”:19,“data”:“QNGyRAGAkh8A0xMqt0ZMU34lZQ==”}]}
Mar 17 04:01:25 Wirnet local1.notice spf: INFO: [up] PUSH_ACK received in 2 ms
Mar 17 04:01:25 Wirnet local1.notice spf: INFO: [down] PULL_RESP received - token[29:219] :slight_smile:
Mar 17 04:01:25 Wirnet local1.notice spf: JSON down: {“txpk”:{“imme”:false,“rfch”:0,“powe”:14,“ant”:0,“brd”:0,“tmst”:2887157884,“freq”:923.4,“modu”:“LORA”,“datr”:“SF10BW125”,“codr”:“4/5”,“ipol”:true,“size”:24,“data”:“YNGyRAGMHx8NMER8TZcDUwcAAQa7V0hl”}}

Chirpstack LNS Log:

    "type": "uplink",
    "payload": {
        "adr": true,
        "applicationID": "1",
        "applicationName": "sptel-app-2",
        "data": null,
        "devEUI": "0a0101010101010a",
        "deviceName": "ratsensenew1",
        "fCnt": 8082,
        "fPort": 0,
        "object": {
            "battery": "NaN",
            "hum": "NaN",
            "period": "0 sec",
            "temp": "-46.85"
        "rxInfo": [
                "gatewayID": "7276ff000b031eba",
                "loRaSNR": 11.8,
                "location": {
                    "altitude": 0,
                    "latitude": 1.390624,
                    "longitude": 103.846459
                "name": "slioilc000lg001-2037",
                "rssi": -70,
                "uplinkID": "345c41ef-c62c-42ff-b1c7-0ced2ec6c01f"
        "txInfo": {
            "dr": 2,
            "frequency": 923400000

Please help, I am struggling with this issue for long time :frowning:

Hi @spiot and all

I am facing a similar problem that chirpstack receives packet from my end device with data = null through fport 0, while my device is configured to send data through fport2.

I’ve setup a LoRaWan gateway with the things Network(TTN) and it received the payload correctly with fport = 2. The firmware of my end device used for testing on both TTN and Chirpstack were the same.

I wonder how to fix this problem. Do you guys have solution upon this question yet?
It is devastatingly urgent to solve this issue.

Could this be a mac-layer related uplink? fport = 0 indicates that the frmpayload must be interpreted as mac-commands. In this case an up event is exposed to the end-application (without any data) as the RX related meta-data can still be useful to collect for the end-application.