## 2 Related Work  
SDN draws a notable progression in networking technology and attracts attention from many researchers to investigate its use and address further its advantages [14]. It is worth noting that dynamic traffic routing approaches support different standards and can dynamically manage traffic flows by observing the status of the network and flow state. Network traffic flows can take any of the accessible paths with adaptable bandwidth based on various goals. A dynamic approach of QoS routing for video streaming over SDN-enabled networks was carried out in [15]. They presented an analytical framework for the optimisation of forwarding decisions for adaptive video streaming. Video streaming was given the highest routing priority, while the remaining services were granted as best-effort flows. Then, their routing approach was modeled into a Constrained Shortest Path (CSP) problem, which can be solved by employing the Lagrange Relaxation based Aggregated Cost (LARAC) algorithm [16]. Research in [17] utilised SDN environment and introduced an adaptive routing method, ARVS, for video streaming that supports QoS. They split video streaming into two layers to be used as a two-levels of QoS flows. They took delay variation as a given constraint to the CSP problem. If the jitter constraint is not satisfied, the video is re-routed to another available path on the base layer, and the video enhancement layers remain on the same shortest path. Their method can enhance the quality of streaming of scalable encoded videos. [PERSON] et al. [18] presented Integer Linear Programming (ILP) methodology for the QoS and QoE optimisation challenges in SDN networks concerning loss rate and delay. They also counted on network constraints and real-time service demands, such as maximum permitted loss and delay rates. In [19] developers illustrated the impact of the Open Shortest Path First (OSPF) protocol over SDN-enabled networks. The work evaluated the resilience of network factors in SDN and traditional networks. Round trip time, convergence time and the QoS have been taken as the network parameters during the video streaming. The results indicated that applying OSPF in SDN networks gives less performance compared to its performance in classic networks; however, there is an improvement in QoS performance. Another work [20] benefited from the integration of ML with SDN to authorise a dynamic computation of the routing metrics for multimedia traffic. They proposed a modification in the OSPF protocol formula concerning the network QoS factors: bandwidth, delay, and loss rate. Also, a protocol for exchanging messages was run between the SDN controller and nodes in order to adjust the link-state metrics based on the present topology state. The outcomes indicate that the bandwidth utilisation increased, and the delay and packet loss rate decreased in multimedia traffic flows. Authors in [21] presented a strategy of flow-based video streaming routing over SDN. This strategy emphasised satisfying two QoS metrics, packet loss ratio and bandwidth. It selects reliable paths for each video streaming flow based on the existing state of the entire network. The experiment results reveal that HD videos are affected more than SD videos in the event of more packet loss occurring since they acquire more frame artefacts and colour distortions. Concerning utilising ML methods with SDN, the work in [22] presented a new RL method to determine the optimal time for modifying the video bit rate and re-routing the traffic flows in order to minimise the data loss rate. They stated that their approach outperforms the traditional routing and greedy-based approaches. However, only small-scale topology scenarios are discussed in this study. Following this pioneered, [PERSON] et al. [23] introduced a routing optimisation strategy in SDN by employing the RL technique to improve network QoS. Their approach used the RL agent to choose the optimal paths that obtain the lowest cost by considering three parameters: delay, packet loss rate, and bandwidth.