Moving yearly Total Data / month

all values are listed as: G pkts

   time  |  total
---------+-------
2009-01  |  1.320
2009-02  |  1.652
2009-03  |  1.867
2009-04  |  2.208
2009-05  |  2.599
2009-06  |  2.988
2009-07  |  3.334
2009-08  |  3.641
2009-09  |  3.688
2009-10  |  3.549
2009-11  |  3.555
2009-12  |  3.442
2010-01  |  3.317