Distribution Resource Planning (DRP) is a well known method for planning orders within a supply chain. DRP enables the user to set certain inventory control parameters (like a safety stock) and calculate the time-phased inventory requirements. A supply chain, logistics network, or supply network is a coordinated system of organizations, people, activities, information and resources involved in moving a product or service in physical or virtual manner from supplier to customer. ...

DRP uses several variables:

• the on-hand inventory at the end of a time period.
• the backordered demand at the end of a time period.
• the required quantity of product needed at the beginning of a time period.
• the constrained quantity of product needed at the beginning of a time period.
• the recommended order quantity at the beginning of a period.

DRP needs the following information:

• the demand in a future time period.
• the scheduled receipts at the beginning of a time period.
• the safety stock requirement for a period.
• the on-hand inventory at the beginning of a period.

Source: Feigin, G.E., Katircioglu, K., Yao, D.D.: Distribution Resource Planning systems: a critique and enhancement..