I have some real data (data packets in a router). When I plot it I can see there is a clear periodicity on the dataset (24hours+-).

But how can I discover the periodicity of the data without being by approximation, and possible check other periodicities?

What I am trying to do:

I thought I just had to do the the Fourier transform and then see what were the higher frequencies (one should be around 24).

When I do this in octave and then plot the graphic only garbage comes out.

`plot(fft(data))`

What am I doing wrong?