Moving yearly Total Data / month

all values are listed as: M pkts

   time  |  bcast  bogey
---------+--------------
2009-01  |  1.209  0.000
2009-02  |  1.410  0.000
2009-03  |  1.647  0.000
2009-04  |  1.782  0.003
2009-05  |  1.974  0.003
2009-06  |  2.386  0.003
2009-07  |  2.856  0.003
2009-08  |  3.649  0.003
2009-09  |  3.952  0.002
2009-10  |  4.273  0.003
2009-11  |  4.340  0.002
2009-12  |  4.337  0.002
2010-01  |  4.574  0.002