Before launching PPP, verify that the modem has good signal and is properly registered to the network.

Start with AT+CSQ to check signal strength; aim for an RSSI value of 15 or higher for reliable operation. If signal is weak, try moving to a different physical location or adjusting the antenna. For more details, see the section further down on antenna signal strength.

Next, confirm network registration with AT+COPS? and AT+CEREG?. If AT+COPS? continues to return +COPS: 0 even after waiting a minute or two, force a network scan using AT+COPS=? though note that this process can take several minutes, during which the modem does not respond to other AT commands. The current radio access technology (RAT) and frequency band can be checked with AT+QNWINFO to confirm the modem is attached to the expected technology (for example LTE Cat-M1). See AT+COPS: Modes, parameters, and examples for more information on the operator selection mode, operator, and radio access technology (RAT) and +CREG vs. +CGREG vs. +CEREG for more details on the registration status of the device.