Frank's answer is correct - but logically the Ashes should have moved back a year so that the venue sequence changed from
England - 18 months gap - Aus - 30 months gap - England
to
England - 30 months gap - Aus - 18 months gap - England
The administrators greed could not stomach this, so we were lumbered with back-to-back Ashes this year .... and then, to compound the idiocy, because that then left 42 months until the next scheduled Ashes in England they have disrupted the 4 year home test cycle to bring Australia back in 2015.
Sheer unadulterated greed, paying no heed to the established rhythm of England playing all the other Test Countries, just grabbing as many bucks as possible.