maryli

shorter vs. longer is based on the Avg life of the tranche.

shorter PAC Tranche - gets regular principal payments - as scheduled. Any "unscheduled" payments/prepayments are directed to the Support tranches. There is thus prepayment protection for the shorter tranche, it is not likely to expand (payments do not come in on time) or contract (payments come in too early). Given the size of support tranches, it is more than likely to be protected.

CP