The exponential growth of the Internet and the diversity of services delivered to the end users, such as Cloud computing, have catalyzed researches on new generation networks. Hence, several proposals have been made to change the network applications and Internet media; in particular network virtualization is in the center of research interest. It is widely considered given its ability of dynamic programming, energy saving and low cost. This promising paradigm boosts different researches in literature. Openflow, AKARI and 4 ward projects are concrete examples. They follow common approaches of virtualization but with different characteristics. In this paper, we present an analysis and comparison between these projects. We mainly focus on Openflow solution to validate on demand virtual network architecture based on the Mininet simulator. This work is part of the On-Demand research project sponsored by European Regional Development Fund.