There are three primary protocols for production control. These are 1) Push where work is released into the production system using predetermined objectives i.e. a schedule, 2) pull where work is pulled by the downstream operation / process center from the upstream operation / process center and 3) CONWIP which is same as pull but sends a signal to the beginning of the production system. The objective of the Pull and CONWIP protocols are to control or cap the amount of WIP in the production system.