Is fport=null the correct behavior?

Question

HI,

Since older ABP end devices don't support MAC commands, I configured the following settings.

chirpstack.toml configuration

[network]
  mac_commands_disabled=true

However, looking at the logs, we see downlink packets with fport=null set like this.
Is this the correct behavior?

  {
    "phy_payload": {
        "mhdr": {
            "f_type": "UnconfirmedDataDown",
            "major": "LoRaWANR1"
        },
        "mic": [
            178,
            106,
            50,
            213
        ],
        "payload": {
            "f_port": null,  <- correct??
            "fhdr": {
                "devaddr": "ff00ead2",
                "f_cnt": 1013,
                "f_ctrl": {
                    "ack": false,
                    "adr": false,
                    "adr_ack_req": false,
                    "class_b": false,
                    "f_opts_len": 0,
                    "f_pending": false
                },
                "f_opts": []
            },
            "frm_payload": null
        }
    }

thank you,

hiroshi shimomichi · Answer

It provides pairs of uplink and downlink data. Is this because some control is being performed, making fport=null?

[
{
"phy_payload": {
"mhdr": {
"f_type": "UnconfirmedDataDown",
"major": "LoRaWANR1"
},
"mic": [
69,
66,
74,
115
],
"payload": {
"f_port": null,
"fhdr": {
"devaddr": "ff00ead2",
"f_cnt": 1089,
"f_ctrl": {
"ack": false,
"adr": false,
"adr_ack_req": false,
"class_b": false,
"f_opts_len": 0,
"f_pending": false
},
"f_opts": []
},
"frm_payload": null
}
},
"tx_info": {
"context": "qwn55A==",
"frequency": 923000000,
"modulation": {
"lora": {
"bandwidth": 125000,
"codeRate": "CR_4_5",
"polarizationInversion": true,
"spreadingFactor": 7
}
},
"power": 16,
"timing": {
"delay": {
"delay": "1s"
}
}
}
},
{
"phy_payload": {
"mhdr": {
"f_type": "UnconfirmedDataUp",
"major": "LoRaWANR1"
},
"mic": [
170,
71,
114,
251
],
"payload": {
"f_port": 1,
"fhdr": {
"devaddr": "ff00ead2",
"f_cnt": 60061,
"f_ctrl": {
"ack": false,
"adr": true,
"adr_ack_req": true,
"class_b": false,
"f_opts_len": 0,
"f_pending": false
},
"f_opts": []
},
"frm_payload": "4d64000005b641e3377dff"
}
},
"rx_info": [
{
"channel": 5,
"context": "qwn55A==",
"crcStatus": "CRC_OK",
"gatewayId": "7276ff0045060159",
"gwTime": "2026-07-09T15:07:33.058859+00:00",
"location": {},
"nsTime": "2026-07-09T15:07:33.093169213+00:00",
"rssi": -63,
"snr": 8.800000190734863,
"uplinkId": 54691
}
],
"tx_info": {
"frequency": 923000000,
"modulation": {
"lora": {
"bandwidth": 125000,
"codeRate": "CR_4_5",
"spreadingFactor": 7
}
}
}
},

Is fport=null the correct behavior?

1 Answers