The Received Signal Strength Indicator (RSSI) of the cellular interface can be monitored to detect weak signals on the interface. Monitoring signal strength can be useful for determining the stability of the carrier or private LTE network and whether to log (generate) an RSSI threshold alarm log event or generate an alarm log event and switch carriers, either manually or by automatically switching SIMs in a dual SIM deployment.
The rssi-threshold command is used to set the level at which the received signal is considered weak enough to trigger an alarm log event. If the RSSI falls below the configured threshold, a tmnxCellularRssiAlarm log event is generated. As well, if the threshold is configured as a failover criterion, a SIM switchover occurs in a dual SIM deployment.
The node polls the radio signal strength approximately once per second. If the RSSI falls below the configured rssi-threshold, a timer starts. If the RSSI stays below the threshold for the time specified with the rssi-alarm-wait-time command, the tmnxCellularRssiAlarm log event is generated. This log event is generated only once even if the RSSI remains below the threshold indefinitely. After the tmnxCellularRssiAlarm log event is generated, if the RSSI level rises to the configured rssi-threshold value or higher and remains at that level for the duration of the rssi-alarm-wait-time, the tmnxCellularRssiAlarmClear log event is generated. The operator can monitor the logging frequency to determine whether to manually switch carriers.
The RSSI threshold can be set as a failover criterion in a dual SIM deployment. When the rssi-threshold option is set in the failover-criteria command, if the RSSI signal level falls below the configured RSSI threshold for the configured failure-duration time, the node performs an automatic switchover from the currently active SIM to the other SIM. See Criteria for automatic failover for information about using RSSI as a failover criterion for dual SIMs.