Networked Controlled Systems (NCSs) are more and more used in industrial applications. They are strongly connected to real-time constraints because important delays induced by the network can lead to an unstable process control. Usually, the network used in NCSs is shared with many others applications requiring different Quality of Service. The objective of this paper is to optimize the tuning of the network scheduling mechanisms in taking into account the level of Quality of Control. The goal is to maximize the bandwidth allocation for unconstrained frames in guarantying that the control constraints are respected. In this paper, we focus on switched Ethernet network implementing the Classification of Service (IEEE 802.1p) based on a Weighted Round Robin policy.