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Available to promise takes the simple availability calculation, adds time phasing and takes into account future scheduled receipts. Available to promise may be calculated for each day or broken down into larger time buckets. The first time period will take on-hand inventory and add any scheduled receipts for that period. It will then deduct any allocations scheduled prior to the next scheduled receipt (which may be several periods in the future). Subsequent periods without any scheduled receipts will have the same available to promise as the previous period. Subsequent periods with scheduled receipts will generally start with a fresh calculation, ignoring any remaining available to promise from previous periods. There are many variations on exactly how available to promise is calculated and it is also important to note that available to promise often works independently of allocation systems. This can sometimes create conflicts. Available-to-promise (ATP) is a business function that provides a response to customer order enquiries, based on resource availability. It generates available quantities of the requested product, and delivery due dates. Therefore, ATP supports order promising and fulfillment, aiming to manage demand and match it to production plans. Available-to-promise functions are IT-enabled and usually integrated in enterprise management software packages. However, ATP execution may need to be adjusted for the way a certain company operates.
Classification
A fundamental distinction between ATP functions is based on the push-pull strategy. Push-based ATP is based on forecasts regarding future demand - based on anticipation of demand, ATP quantities and availability dates are computed. A prominent example is the traditional determination of ATP based on the Master Production Schedule. The push-based approach is fundamentally limited by dependence on forecasts, which may prove inaccurate. Pull-based models, on the other hand, dynamically allocate resources in response to actual customer orders. This means that pull-based ATP is able to balance forecast-driven resource replenishment with order-triggered resource utilization, but because resources are allocated with each coming order, the process will yield myopic results. ATP Execution ATP functions can be executed in real-time, driven by each individual order, or in batch-mode – meaning that at a certain time interval, the system checks availability for orders piled up in that period of time. The process is triggered by the need to check resource availability before making a commitment to deliver an order. For example, ATP calculation using SAP software depends on the level of "stock, planned receipts (production orders, purchase orders, planned orders and so on), and planned requirements (sales orders, deliveries, reservations etc.)"
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