Get bytes (stats) from simple queue with api; dhcp + freeradius

I need to save the customer usage accounting .
I use dhcp with RADIUS .
I’m getting via API values ​​of bytes but do not understand them.
I thought that accountants were ongoing but suddenly they restart even without reaching great values ​​.
Our customers have a session time out 10 min, but there is no relationship with it. The values ​​are discontinuous with no apparent logic.

Any sample?

How did you get the accounting data from simple queue with api?