Before revision:  In fact , we show  the equivalence between two broader classes of policies that generalize the above mentioned four policies. We specifically show that the sojourn time distribution for a customer of a particular class in a system with the  DPS (GPS) scheduling policy is a constant multiple of the  waiting time distribution of a customer of the same class in a system with the DROS (respectively WFQ) policy.
After revision:  In fact , we show the sojourn time distribution for a customer of a particular class in a system with the DPS (GPS) scheduling policy is a constant multiple of the waiting time distribution of a customer of the same class in a system with the DROS (respectively WFQ) policy.