[rrd-users] How to add up traffic logged with DERIVE?

[Vadim]

Hi,

I've got a "wireless Internet" 3G modem. I want to generate bandwidth usage 
graphs with projections of how long it will take to reach my bandwidth limit 
at the current rate.

I went with a DERIVE counter, because I'm tracking traffic on the ppp0 
interface, which appears and disappears often (multiple times per day), which 
resets the count. Also I want to be able to begin summing from any arbitrary 
point.

I want to take this DERIVE counter, and add up all the values up to each point 
on the graph. Ideally, I also want to force the counter to 0  at the start of 
a month, if possible.

Unfortunately, all attempts so far have been unsuccessful. RRD doesn't seem to 
let me reference a CDEF in itself. My first approach 
was: "CDEF:acc_rx=acc_rx,rx,+". This produces an "invalid RPN expression". 
Trying "CDEF:acc_rx=rx,TOTAL" doesn't work either, since TOTAL only works for 
VDEFs. TOTAL is nearly what I want to get, if I give up on the zeroing the 
count on the start of the month.

Is there a way to get this done?

Thanks