A demand time window is a new concept in logistics and inventory management and
Modeling its implications presents a challenging problem .Time definite delivery(TDD)
Contracts have become common supply contracts practices in the computer industry
(Cetinkaya et al.2000).Under such a contract. the customer inventory information
is accessible to the supplier via an electronic Data interchange (EDI)link. After reviewing customer inventory levels ,the supplier is empowered to make decisions
regarding the amount and timing to re-supply. The customer offers a grace period, called a demand time window , for timely delivery, during which a particular demand
can be satisfied without penalty. Allowing demand time windows for delivery provides flexibility in satisfying demands that translate into cost-saving opportunities
.however ,computing optimal inventory and transportation policies under demand time windows remains a challenging problem.