Why was Dhoni banned for the last test?

India captain Mahendra Singh Dhoni has been banned for the last test with Australia for slow overrate during the match in Perth.Umpires Aleem Dar and Kumar Dharmasena reported Dhoni after India were ruled to be two overs short of their target.
India lost the test heavily by an inning and 37 runs to hand over the four match test series to the Aussies 3-0, still with a match to go.India is on the verge of Clean Swip and gets another blow of losing the captain.Sehwag will take the captaincy for last test and try to save from continous test match losses since the England tour.