TX/RX power, in the context of networking and optical transceivers like SFP modules, refers to transmit (TX) and receive (RX) power levels. Transceivers are manufactured to meet the specifications (usually of the IEEE standards) and ranges represent the values that the part can operate within. Receive power is normally expected between - 1 and -9. This tells you how much light is making it through the fiber cable to your switch. Thresholds (Alarm/Warn): These are hard-coded limits. If the value crosses these numbers, the switch logs a syslog message or shuts down the port.