The SIMCOM SIM7070G initially appears to be a simple device: connect it over UART, send AT commands, register on the network, and transmit data to a server. On a laboratory bench, the first HTTP request can often be completed relatively quickly. The real problems begin later, when the device must operate autonomously for days or weeks. The network may disappear temporarily, the modem may send asynchronous URC messages, an HTTP session may close unexpectedly, and commands such