SFP Low Signal Levels?

[simoesmarco8626982]

Hi all,

hope to find everyone in these troublesome times

It;s the following, I have a Cisco 3650 and a Cisco 2960 joined by single mode fiber and when doing a "show interface transceiver details" I see this:

High Alarm High Warn Low Warn Low Alarm
Temperature Threshold Threshold Threshold Threshold
Port (Celsius) (Celsius) (Celsius) (Celsius) (Celsius)
--------- ----------------- ---------- --------- --------- ---------
Te1/1/2 31.1 93.0 88.0 -43.0 -48.0
Te1/1/3 40.6 100.0 95.0 -40.0 -45.0

High Alarm High Warn Low Warn Low Alarm
Voltage Threshold Threshold Threshold Threshold
Port (Volts) (Volts) (Volts) (Volts) (Volts)
--------- ----------------- ---------- --------- --------- ---------
Te1/1/2 3.29 3.63 3.49 3.10 2.97
Te1/1/3 3.29 3.60 3.50 3.00 2.90

High Alarm High Warn Low Warn Low Alarm
Current Threshold Threshold Threshold Threshold
Port (milliamperes) (mA) (mA) (mA) (mA)
--------- ----------------- ---------- --------- --------- ---------
Te1/1/2 40.2 85.0 80.0 20.0 15.0
Te1/1/3 12.7 90.0 80.0 2.0 1.0

Optical High Alarm High Warn Low Warn Low Alarm
Transmit Power Threshold Threshold Threshold Threshold
Port (dBm) (dBm) (dBm) (dBm) (dBm)
--------- ----------------- ---------- --------- --------- ---------
Te1/1/2 -1.6 2.5 1.4 -9.2 -10.1
Te1/1/3 -6.6 -1.0 -2.0 -11.0 -12.0

Optical High Alarm High Warn Low Warn Low Alarm
Receive Power Threshold Threshold Threshold Threshold
Port (dBm) (dBm) (dBm) (dBm) (dBm)
--------- ----------------- ---------- --------- --------- ---------
Te1/1/2 -40.0 2.5 1.4 -15.4 -16.4
Te1/1/3 -23.6 4.9 2.9 -28.2 -30.0

The port TE1/1/2 is offline and not working, and what bothers me is the values on the receive. This is a 1Gbps link and for what I saw and understand this signal is too low.

In this link I'm having loads of output drops from the access switch to the core switch and I assume this is the cause.

Am I correct in assume that?

Thank you

[simoesmarco8626982]

Forgot to mention, the modules being used are Startech Cisco compatible 1000BASE-LX/LH SFP Single mode modules and the run of fiber cable between the Core Switch Cisco 3650 and the 2960 is from a first floor to a sixth floor of the building... I would say around 100 meters...

[balaji.bandi · Accepted solution]

It all depends on cable what Fibre cable is this? OM3 /4 ? so distance matters. is ths multi-mode or single-mode cable ?

regarding power level, if the port is shutdown you see the expected results. ( again based on cisco SFP experience, if the SFP compatible non-cisco, you need to refer the vendor document.)

example discussion for power level can be found here and useful.

https://community.cisco.com/t5/optical-networking/understanding-tx-rx-light-level/td-p/2794532

[Tom Randstrom · Accepted solution]

It would seem that there may be an issue with the fiber link; dirty connectors, excessive fiber bends.  If you have a power meter and light source, you could test the fiber link's attenuation (loss).  It will help you determine if it is a problem with the fiber link or a transceiver module issue.  

[simoesmarco8626982]

Thank you very much for the reply.

Meanwhile I swapped the sfp modules in both ends but to no avail. 

I know the fiber is being rejoined in three places until it reaches the core switch. I will have to investigate all those...