What is a CDR in IoT
Quick definition
A CDR (Call Detail Record) is the detailed record of every data, voice, or SMS session of a SIM. In IoT it is the source of truth for billing, fraud detection (anomalous traffic), and diagnostics (knowing why a device is silent).
Fields in a data CDR
ICCID, IMSI, session start and end, MB down, MB up, assigned IP, visited MCC/MNC, APN used, and technology (4G, NB-IoT). Some carriers add close cause and serving cell.
Why you want it
Three uses: reconcile the carrier's invoice, spot devices burning more data than they should (buggy firmware, malware, misconfig), and support (know the device is alive even if the app sees nothing).
FAQ
How often are CDRs generated?+
At the end of each session. For always-on modems the carrier may split sessions every 24 hours or by MB threshold to produce intermediate CDRs.
Can I download CDRs via API?+
Yes; every serious IoT provider exposes CDRs via API or CSV export. If yours does not, that is a red flag.
Related terms
What is MQTT
MQTT (Message Queuing Telemetry Transport) is a very lightweight publish/subscribe protocol designed for devices with little CPU, little RAM, and flaky links. It works against a central broker (Mosquitto, HiveMQ, EMQX, AWS IoT Core) and carries most modern industrial IoT traffic.
What is a private APN
A private APN is a mobile network access point dedicated to a single company or project. Your IoT traffic never touches the public internet: it exits the carrier straight to your data center over a private tunnel, with your own IP plan, firewall rules, and routing.
ICCID, IMSI, and IMEI
ICCID identifies the physical SIM chip. IMSI identifies the subscriber on the mobile network. IMEI identifies the device (modem) holding the SIM. Three different identifiers, all three needed to manage an IoT fleet.