Sequential CMO question, payments, schedule, principal

stockjaguar

The first tranche that is being paid out with principal payments is protected from extension risk, whereas the rest of the tranches are protected from contraction risk.

My question is HOW and WHY?

Is it because the first tranche is getting all the principal payments it want (according to schedule with no prepayment risk?)

Pegasus2008

any payment (regular + prepayment) would go to the first tranche. So it will get paid off faster. Likely to contract. Will never extend.

Depending on how big the tranche is - other tranches will have to wait to get their scheduled principal payments. So they are unlikely to contract.

CP