This work presents a solution for increasing link utilisation in a backbone while adhering to Service Level Agreements (SLAs) for different service types using the new networking paradigm called Software-Defined Networking (SDN). The work is based on emulating a network, using lightweight virtualisation of individual network hosts and virtual switches. Traffic is generated synthetically according to three different service types; Video, Voice and Best Effort, where each service type has a set of SLA parameters, consisting of Throughput, End-to-End delay and Packet loss rate. A solution is proposed in the form of a control loop, based on known methods from Cognitive Networks. The control loop dynamically moves flows between different queues on an output port in a switch and drops flows, in order to ensure that the SLA parameters are fulfilled for each individual flow. Results for the proposed solution show that it is capable of guaranteeing SLAs on a per flow basis for link utilisations of up to 80 [%] for the flows with the most demanding SLAs.