CFA Level 1 - Derivatives
Cash flow streams are often structured so that payments are synchronized, or occur on the same dates. This allows cash flows to be netted against each other (so long as the cash flows are in the same currency). Typically, the principal (or notional) amounts of the loans are netted to zero and the periodic interest payments are scheduled to occur on that same dates so they can also be netted against one another.
As is obvious from the above example, swaps are private, negotiated and mostly unregulated transactions (although FASB 133 has begun to impose some regulations).