Moving yearly Total Data / month

all values are listed as: GB

   time  |        up      down
---------+--------------------
2009-01  |   290.750   393.905
2009-02  |   386.089   485.583
2009-03  |   448.213   553.821
2009-04  |   542.819   668.533
2009-05  |   627.527   811.833
2009-06  |   701.080   957.803
2009-07  |   810.047  1071.533
2009-08  |   927.872  1165.150
2009-09  |   970.013  1193.471
2009-10  |   967.995  1159.278
2009-11  |   996.941  1194.974
2009-12  |   980.859  1180.609
2010-01  |   954.478  1177.409