## 2 Related Work  
This section describes the research works on routing proposals to improve the quality of service (QoS) implemented in the SDN architecture. We describe the works according to the network parameters considered for QoS improvement, the use of SDN architecture resources, and their contribution depending on a single domain or multiple. In OpenQoS [17], the authors developed an architecture that classifies incoming data streams into multimedia or data streams and provides quality service support for the different multimedia streams, considering the application's requirements. Their proposed algorithm focuses on the shortest path according to the delay as a constraint, while for data streams, it provides the best possible path according to the controller (hops). In CECT [18], a network congestion avoidance scheme was proposed in which resources are reallocated based on data flow requirements. It should be noted that the routing algorithm uses a secondary genetic algorithm when there is a congestion problem. Therefore, the data streams are reallocated according to the minimum bandwidth required by the application. [PERSON] et al. [19] proposed a method based on distributed data centers in an SDN cloud that guarantees bandwidth allocation for critical applications through priority queues in each network device. In AmoebaNet [20], a service is proposed that guarantees the QoS of services on campus or local area networks based on SDN and facilitates the transfer of large-scale scientific data (Big Data) depending on the application. The algorithm is based on the bandwidth constraint to calculate the end-to-end network path. [PERSON] et al. [21] proposed a dynamic method for traffic engineering in SDN data centers based on a linear propagation model and decomposition techniques to partition the flow allocation problem by determining the available capacity of paths for the redirection of the flows. In VSDN [22], the authors proposed an architecture within a domain for video transmission over SDN. This architecture includes a routing module and a network topology monitor that verifies network conditions. The authors monitored bandwidth, jitter, and link delay network parameters to forward data packets using a constraint-based routing algorithm. In PRIME-Q [23], a multi-domain routing method with end-to-end quality of service is presented, which considers privacy in a multi-domain SDN network. The algorithm can classify path flows according to three categories of QoS, bandwidth, delay, and the combination of both parameters in an optimization function. In QosComm [24], the authors designed a strategy for routing data flows among an SDN-based distributed data center according to the application's QoS requirements. The algorithm selects the path with the minimum delay that satisfies the application requirements based on bandwidth, packet loss rate, and jitter. [PERSON] et al. [25] proposed a QoS-compatible routing method based on an evolutionary algorithm for multi-objective optimization (NSGA-II). This method considers the bandwidth threshold required by a flow and minimizes the parameter delay and packet loss. These parameters are determined by monitoring the network regularly to avoid bottlenecks, unlike most previous studies based on the assumption of the same domain. In VQoSRR [26], a video streaming adaptive QoS-based routing and resource reservation scheme is proposed that shifts traffic to an alternate path when the QoS is violated, which satisfies video demands and enhances user experience more effectively than best-effort networks. In [PERSON] et al. [27], the authors proposed a multi-domain design where each domain has an SDN controller, which shares the summarized topology of their domain. Each controller has end-to-end decision-making capabilities, and the flow decision selection is based on the effective bandwidth theory of the martingale process.