Nowadays, the explosive growth of real-time applications that need stringent Quality of Service (QoS) and Quality of Experience (QoE) support, forces network programmers to design network protocols that deliver specified performance guarantees. This paper exploits the use of Software-Defined Networking (SDN) in conjunction with the OpenFlow protocol to differentiate network services with quality level assurance and to respect agreed Service Level Agreements. Initially, we define a Management and Orchestration architecture that allows us to manage the network in a modular way. Then, we provide a seamless integration of the proposed architecture and the SDN standard following the separation between the control and data planes. Finally, we give an Integer Linear Programming formulation of the problem of enhancing QoS and QoE in SDNs in terms of packet loss and delay, taking into account the network constraints and the requirements of real-time applications, i.e., maximum acceptable packet loss and delay rates. Given the optimal solution of the problem, we evaluate the impact and benefits of the proposed scheme by means of the Mininet network emulator.