Need Help! CDEF function Convert watts to dbm

[senthilka]

Hi Guys,
iam trying to input the following formula into cacti to convert watts to dbm
P(dBm) = 10 · log10( P(mW) )
Example

Convert 20mW to dBm:,

P(dBm) = 10 · log10( 20mW ) = 13.0103dBm

Does anyone know how?

i have come out with this. but its not correct.

cdef=CURRENT_DATA_SOURCE,0.001,*,LOG,10,*

cisco is giving me a reading of 33 via snmpwalk.
So i need to divide the value by a 1000 before applying the formula is bold

So the problem happens when i apply the log fuction i get a different value(-3.41), then expected (-1.48)

[victorantunes]

I don't know the proper parameters for LOG, but try this:

CURRENT_DATA_SOURCE, 1000, /, 10, LOG, 10, *

[senthilka]

Couldnt work. the problem seems to lie with the way cacti performs the log fuctions. Whats the 10 before the log function meant to be? Cacti is not able to process the formula.

Has anyone else encounter any problems with the way cacti performs log functions?








P.S. Have no idea why Cisco thinks its a good idea to have ASR 9k report in power rather than dbm.

[victorantunes]

The '10' is supposed to be the Log base. Told you I wasn't familiar with the Log syntax in RRDtool


Try

Code: Select all

CURRENT_DATA_SOURCE, 1000, /, LOG, 10, *

[senthilka]

OK! Finally figured this out. Cacti does logarithm in natural log. so to convert it to a base 10 log.
we need to divide the solution by 2.303

zzzzz.....

[slakyari]

Thanks so Below is the final CDEF functions

CURRENT_DATA_SOURCE,0.001,*,LOG,10,*,2.303,/

[bmfmancini]

I have a similar thing but for Nokia

I am trying to implement this but running into a roadblock

Here is the example equation Nokia is giving me

10 x log10(0.079) = -11.0 dBm"

I just cant get the cdef right I also need to divide the DS value by 1000 to get the value

[TheWitness]

Well, having the 'actual' math would have helped. Glad it's figured out.