MRP and Availability check clarification

Question

while browsing the forum, many experts here mentioned in old threads that MRP and availability check are two different (independent) concepts. I am really confused on this one. let me put my understanding here and plz experts help me if I am wrong with a figurative explanation, so that will be easy for understanding.
Assume this is the scenario as of today.
Plant stock for material x u2013 100
Reservations for material x u2013 70
Incoming receipts for material x u2013 50
So net stock = 100 + 50 -70 = 80
sales order arrived for material x u2013 100 and availability check is done. Results of availability check says 80 can be confirmed and 20 can be confirmed on later date.Transfer of requirement for quantity 20 is done to MRP. Mrp runs and creates planned order for 20.
In the availability check config  ovz9 if I say donu2019t consider reservations, then when availability check is done for 100 quantities..system will confirm 100 because available stock according to system will be 100+50 = 150. So transfer or requirements are not sent to mrp.
So isnu2019t mrp run directly dependent on availability check?

Answer 1

925,
sales order arrived for material x u2013 100 and availability check is done. Results of availability check says 80 can be confirmed and 20 can be confirmed on later date. Transfer of requirement for quantity 20 is done to MRP
No.  100 pcs requirements are passed to MRP.
In the availability check config ovz9 if I say donu2019t consider reservations, then when availability check is done for 100 quantities..system will confirm 100 because available stock according to system will be 100+50 = 150. So transfer or requirements are not sent to MRP.
No, 100 pieces requirement are passed to MRP.
This behavior depends upon how your 'transfer of requirements' is configured, which is an SD setting.  Normally, unless the fix date qty field is set in the sales order, the entire 100 pc requirement is passed to MRP in all cases.  The assumption is that you have accepted the sales order and will 'some day' need to issue and sell the parts.  You need to begin planning for this event  now.
When MRP subsequently runs, it will net out the supply elements (stock and inbound reservations) and will from this calculation determine how much needs to be built.  It then proposes a solution (planned order or purchase req).
ATP check seldom has much impact on MRP.  You are correct in realizing that the ATP check must be consistent with MRP and with your chosen MRP strategies, in order to provide an end-to-end business process that is logical and meets all business requirements.  However, in SAP these two functions are separate.
Best Regards,
DB49