The SAE standard Time-triggered Ethernet defines a strong networking infrastructure, which supports the engineering of avionic systems. Avionic functions are often designed independently and integrated to form the avionic system. The iterative integration approach helps in controlling the design complexity of evolving avionic systems and aims at minimizing the cost associate with the reconfiguration of scheduling parameters of already integrated parts. On the other hand, the iterative approach requires to specify and manage a huge set of constraints, which are then solved to compute the optimal scheduling parameters. In this paper, we focus on this issue of manual specification of these constraints by the system engineer. We propose a model-driven approach, which provides the required abstractions and automation to support the system engineer in using effectively the iterative integration approach. The abstractions consist in a metamodel, which describes the system at a given integration step and a metamodel for the constraints. The automation consists in a model transformation which enables generating automatically the relevant constraints at integration step.