Why a Cellular Module Shows Signal but Has No Data Connection
A common field mistake is treating “has signal” as “is online.”
The module reports a signal value, the antenna is connected, and the SIM is inserted, but MQTT cannot connect, TCP fails, and the platform never sees the device. This may look like unstable network service, but the device can be stuck at very different layers.
Cellular data connectivity has several stages:
radio coverage
-> usable SIM
-> network registration
-> data bearer activation
-> IP or data channel
-> DNS, TCP, TLS, MQTT
-> application platform reachability
“Signal” usually covers only the first part.
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