The planning horizon is the number of days where MRP will be running.  Now, in the IMG, in the Maintain plant parameters there is a button for Rescheduling for specific plant.  What is the rescheduling horizon?  There are certain elements such as firm planned orders, PO, firm purch reqs. etc that are considering in here but what is the rescheduling horizon? What does it do?

By: Sankaran

The below info will help you to understand the Rescheduling Horizon concept:

Rescheduling Check 

An important group of the exception messages mentioned above are the rescheduling proposals. In the net requirements calculation, the system checks whether warehouse stock or firmed receipts are available in sufficient quantity to cover requirements. If a material shortage exists, the system usually creates a new procurement proposal. The rescheduling check is used to change the dates of already existing firmed receipts not planned on the same day as the requirement to suit the requirement date. For this purpose, the system displays the appropriate exception messages with rescheduling proposals for these firmed receipts to be processed by the MRP controller.

Prerequisites

You have defined the rescheduling parameters in Customizing for MRP:

per plant in the IMG activity Carry out overall maintenance of plant parameters
per MRP group in the IMG activity Carry out overall maintenance of MRP groups.
The rescheduling horizon, which defines the period for bringing forward the receipts, and the receipt elements, which should be taken into account in rescheduling, are included in these.
You can also define tolerance values for the creation of exception messages, in Customizing. These values define a time period in which no exception message is to be created, despite the fact that a rescheduling proposal may exist. The MRP controller can thus avoid a situation where too many exception messages are created if a certain buffer has already been planned for scheduling basis dates.

Process Flow

Bring process forward (reschedule in):
Within this rescheduling horizon, the net requirements calculation checks whether, after a requirement, a firmed receipt exists, which can be used to cover this requirement. Then the system displays a rescheduling date as well as the exception message Bring process forward for this receipt. The net requirements calculation then uses this receipt and the system will only create another procurement proposal if the receipt quantity is not sufficient to cover the complete requirement. Several firmed receipts can be used to cover one requirement.

The rescheduling horizon is always calculated from the MRP date. 

Postpone process (reschedule out), or cancel process:
The net requirements calculation checks over the complete time axis whether availability could still be guaranteed without the receipt in question. If this is the case, the system checks whether the receipt planned here could be used to cover a future requirement. If the system can find such a requirement, it then displays a rescheduling date as well as the exception message Postpone process for this receipt. 

If the system finds no future requirement, for which the receipt is required, the system displays the exception message Cancel process.

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