  The aim of this paper is to analyze the dynamic evolution of a VPN, modeled
as a system, controled by a manager who should take appropriate decisions. To
take the best possible decisions, the operator should be able to worst
behavior, in the sense of a quality of service criterion, of the system he
wants to control. At first, we study the case of a simple VPN. In a second
part, we propose solutions to model the various interactions that may appear in
a network of multiple VPNs.
