SMM/PSA difference, expressed, identify, problems

rohitdoshi

While I can identify them and use them to solve problems, the defintion of SMM and PSA seem the same, and I find it hard to see the difference:


SMM: "We can convert the CPR into a monthly prepayment rate called the SMM."

PSA: "The PSA benchmark is expressed as a monthly series of CPRs."



Can someone help identify the difference?