Master Production Scheduling Procedure 
Prerequisites

You define MRP types in Customizing for MRP in the IMG activity Check MRP types.
Process Flow
In contrast to the MRP run, this planning run only plans the master schedule item level. The system creates dependent requirements for the BOM level directly below the planning level. However, this level and lower levels are not planned.
Depending on the settings of the MRP type, any changes to be made to the master plan are only proposed within the planning time fence. Outside of the planning time fence, procurement proposals are created as usual.
See also:
Planning Time Fence Firming Type Interactive Planning Carrying Out the Planning Run Planning Result and Planning Situation