Duggan Mfg. began implementing a just-in-time inventory system several months ago. The production and purchasing managers, however, have not seen any dramatic improvements in throughput. The managers have decided that the problems are related to company suppliers. The company's three suppliers seem to send the wrong materials at the wrong times. Prepare a discussion of the problems that might exist in this situation. Be certain to address the following items: internal and external communications; possible engineering changes and their impacts; number, quality, and location of suppliers; and length of system implementation.