This topic describes how the PSM virtual photodiode calculates COM-RX power from available transmit photodiodes and reports fallback values when both related ports are unavailable.
The PSM virtual photodiode provides an optical power reading even when photodiodes are not available. The PSM does not have a photodiode on the COM-RX port. Two photodiodes are present on the Working-TX port and the Protected-TX port, located after the VOA
Details
The power value on COM-RX is real if at least one of the W-TX or P-TX power values is not equal to -40 dB (the related port is in AVS).
If both the power of W-TX and P-TX equal -40 dB (both related VOAs are in AVS-Automatic VOA Shutdown), it is impossible to calculate the real power on the COM-RX port, so the value is displayed as -40 dB.
The feature does not require any configuration. Only the show controllers ots 0/<slot>/0/0 command is changed to display the RX power on the COM-RX port. The RX low power alarm is not managed on the COM-RX port.
Example for show controller
RP/0/RP0/CPU0:ios#show controllers ots 0/2/0/0
Wed Jan 24 14:33:22.898 CET
Controller State: Up
Transport Admin State: In Service
Port Type: Com
Laser State: Unknown
Optics Status::
Alarm Status:
-------------
Detected Alarms: None
Alarm Statistics:
-----------------
LOW-RX-PWR = 0
LOW-TX-PWR = 0
RX-LOS-P = 0
RX-LOC = 0
AMPLI-GAIN-DEG-LOW = 0
AMPLI-GAIN-DEG-HIGH = 0
AUTO-LASER-SHUT = 0
AUTO-POW-RED = 0
AUTO-AMPLI-CTRL-DISABLED = 0
AUTO-AMPLI-CFG-MISMATCH = 0
SWITCH-TO-PROTECT = 0
AUTO-AMPLI-CTRL-RUNNING = 0
Parameter Statistics:
---------------------
TX Power = 15.30 dBm
RX Power = 5.30 dBm
tx-enable = 1
rx-enable = 1
Configured Parameters:
-------------
tx-enable = 1
rx-enable = 1