Though we have 3 great players in the current generation (Andy Murray is very consistent and is always a contender at the major tournaments, but I do not think he is solidly in the Federer/Nadal/Djokovic conversation), there has been a distinct set of domination phases during the 2004-2015 time period, as highlighted below.
Federer Phase (2004-2007, 4 years)
Grand Slams == 11 (68.75%)
ATP 1000 Titles == 13
ATP World Tour Final Titles == 3
Ranking == No:1 for 3 full years (2005-07) and majority of 2004
Rafael Nadal Phase (2008-2010, 3 years)
Grand Slams == 6 (50%)
ATP 1000 Titles = 9
ATP World Tour Final Titles == 0
Ranking == No:1 for 1.5 years (Out of 3 years)
Novak Djokovic Phase (2011-2015, 5 years)
Grand Slams == 9 (45%)
ATP 1000 Titles = 21
ATP World Tour Final Titles == 4
Ranking == No:1 for 3.5 years (Out of 5 years)
Adios!