TX and RX in SFP refer to the transmission (TX) and reception (RX) of data signals over a fiber optic cable using Small Form-factor Pluggable (SFP) modules. Transmit power is typically good when it is in the 6 dB range between -1 and -7 dBm. If either Tx or Rx is in the -30 dBm or lower range that's usually indicative of there being no actual signal received and the transceiver is reporting. Connectrix: How to troubleshoot Fibre Channel node to switch port or SFP communication problems by elimination. What are TX and RX Power Levels? Fiber optic communication relies on light pulses to transmit data.