Constant work in process or CONWIP are pull-oriented production control systems.
For example, no part is allowed to enter the system without a card (authority).
After a finished part is completed at the last workstation, a card is transferred to the first workstation and a new part is pushed into the sequential process route.
In a CONWIP system, a card is shared by all kinds of products.
However, Duenyas (1994) proposed a dedicated card control policy in CONWIP and he stated that this policy could perform as a multiple chain closed queuing network.