Software defined networks (SDNs) have emerged as a promising paradigm by separating control plane from data plane. In this paper, we study the problem of achieving realtime quality of services in a SDN for both centralized control plane and distributed control plane. In the first place, we propose a system prototype that handles real-time end to end services. Then, we formulate the problem for a centralized control plane as a linear programming and apply prime-dual technique to derive an efficient algorithm. We also discuss about the method to achieve load balancing between link resources and node resources. Finally, we extend the algorithm to a distributed control plane and present efficient algorithms to achieve good competitive ratio.