Cisco Tx power is constant!

[hsalah0011]

Hi everybody,

I need to read several values periodically from a cisco switch (Catalyst 3750) including SFP's module temperature, voltage, Rx power, and Tx power.

For the first three parameters, everything is fine. I can read the values and they change over time.

However, for the Tx power, the value is constant! it doesn't change over time at all! I read it using both SNMP and CLI, and the value was constant over three months!! (I read it once every 5 minutes). The Tx readings of different interfaces are different. But again: the value for each interface doesn't change over time.

Any hints? what could be the problem? how it can be solve?

Thanks a lot in advance.

Best regards,

Hani

[Dan Miley]

what is the exact problem you are having?  (other than txlevel == txlevel)

is it possible the SFP is sending the same power level and it is not changing?

under what circumstances would you expect it to  change?

this article indicates the tx power cannot be changed , but may vary from device to device.

https://supportforums.cisco.com/discussion/10834446/sfp-output-power-control

hope this helps,

Dan

[hsalah0011]

Dear Dan,

Thanks for your answer.

Sorry, probably the question was indeed a bit confusing. 

We are interested in the values themselves, as we are trying to predict a health state of SFP modules. And we perceived the fact that the transmission power is always constant, as an indication of a problem, just because we only saw this behavior in Cisco switches and not in switches of other vendors.

So I guess the correct question should be: do Cisco switches have automatic compensation for changes in temperature, and thus really do maintain constant Tx power (at least until laser deterioration reaches almost-failure state), or is there any problem with reporting the values being read from SFP modules?

Thanks again for your help.