We are traying to connect two ACX ACX7509 with an QSFP adaptor QSFP56-DD-400G-ZR
In that output we can see RX is in -40dbm
root@JTAC1> show interfaces transport pm optics current et-5/0/0
Physical interface: et-5/0/0, SNMP ifIndex 506
Suspect Flag: False
Reason: Not Applicable
PM CURRENT MIN MAX AVG THRESHOLD TCA-ENABLED TCA-RAISED
(MIN) (MAX) (MIN) (MAX) (MIN) (MAX)
Module temperature(Celsius) 44 43 44 44 0 73 No No No No
<snip>
Tx power(dBm) -8.70 -8.75 -8.63 -8.70 -16.00 0.00 No No No No
Rx total power(dBm) -18.24 -40.00 -18.21 -28.39 -21.00 2.00 No No No No
root@JTAC2> show interfaces transport pm optics current et-5/0/0
Physical interface: et-5/0/0, SNMP ifIndex 508
Module temperature(Celsius) 42 39 42 41 0 73 No No No No
Tx power(dBm) -8.96 -9.00 -8.85 -8.92 -16.00 0.00 No No No No
Rx total power(dBm) -40.00 -40.00 -40.00 -40.00 -21.00 2.00 No No No No
With a 15km long dark fiber, without repeaters, the cable attenuation can be higher.
The TX power is only -8.7 (max) at one side & -8.96 (max) at other.
We can check the receive power at cable end, before connecting the cable to router, using optical meter.
This will give us more insight, as connector losses gets added to this value.
Also if possible, we can try shorter distance connection or an optical loop & check the TX/RX values.
Optical meter show 20.54, when measured at customer setup.
The path loss for 15km should not be more than 4dbm, but here it is more than 12dbm.
So we have some issue with the fiber & combined with connector at other end, RX will be lower than -21bdm threshold.
This is why one side it shows -40db power & the port is not coming up.
Below outputs can help is diagnosis:
show interfaces diagnostics optics et-5/0/0 | no-more
show interfaces transport pm optics current et-5/0/0
Increasing the TX power in any way is not recommended, as it can consume more power & hamper other FRUs.
It can increase fan speed due to temperature increase & cause fan/chassis crashes.