One last look at the concept of manufacturing planning and control (MPC) and its component master production scheduling reveals some interesting implications and opportunities for SCM. Three concepts integral to MPC that may be subject to enhancements by the JIT philosophy are freezing, time fencing and consuming the forecast.

Freezing is a production planning practice whereby no changes can be made to the production plan (and hence exploded MRP requirements) inside of a specified period. In many organizations, it is not unusual to see a frozen period in the range of 8 to 12 weeks. For international organizations that do not have a lot of confidence in their supply chains, the frozen period can be much longer. This exercise has implications for MRP due to the fact that raw materials inventories are built up in anticipation of upcoming production, regardless of what the real demand turns out to be.

Time fencing is a continuation of freezing in that measurement periods are broken down by weeks, with changes to the production plan only allowed outside of a certain "fence." Consuming the forecast, conversely, is a practice that implies replacing forecasted amounts with actual orders. As sales orders come in for weeks outside of the frozen period, adjustments are made up or down to the forecast based on the collective volume of all orders received for those periods.

One major difference between MRP planning and JIT is that the former defines periods in weeks and the...