An asset swap is used to convert cash flow characteristics in order to hedge risks from one financial instrument with undesirable cash flow characteristics to another with favorable cash flow characteristics.
There are two parties involved in an asset swap: the protection seller, who receives cash flows from the bond, and the swap buyer, who hedges the risk associated with the bond by selling it to the protection seller.
The seller pays the asset swap spread, which is equal to the overnight rate plus (or minus) the pre-calculated spread.