# Dynamic QoS Management for a Flexible 5G/6G Network Core: A Step toward a Higher Programability
## 3 Related Work
### Dynamic QoS Management in SDN Environment  
The academic and professional community has conducted a significant amount of research regarding QoS in SDN networks with the OpenFlow protocol in the previous period. The development of 5G and 6G network architecture drives the frequency of research on this topic, focusing on providing adaptive QoS in an SDN environment, given switch diversity, end-to-end quality of experience (QoE), and dynamic queue management [32]. In [33], the authors present a solution for providing end-to-end QoS. They implement a QoS controller which routes the traffic flows and allocates appropriate resources along the traffic path according to the required level of performance and guarantees that are needed for different applications. The focus lies on the QoS control plane aspects and not on the impact these mechanisms cause when applied dynamically. Some authors emphasize switching diversity and SDN control plane operations in their research. In [34; 35; 36; 37], the authors analyze switch scalability and performance regarding the increasing number of rules and traffic priorities. They also take into consideration the impact of some control plane anomalies. The studies [38; 39] examine the OpenFlow data rate-limit feature for a combination of \"elephant\" and \"mice\" traffic flows, which happen regularly in production networks. Research presented in [38] was performed on a static QoS setup in the Mininet environment, while, in [39], the authors used the Pica8 P3290 switch. In [40], the authors leverage Deep Packet Inspection (DPI) to enable application-aware QoS mechanisms for end-to-end traffic engineering systems in SDN networks. The implemented system increases throughput and reduces latency by distributing flows to multiple queues with different priorities under the network administrator's control. Moreover, the adaptive QoS mechanism can be helpful in the first phase of building an SDN environment in a hybrid SDN where OpenFlow and traditional networks exist together [41]. Some authors go in other directions and, in their research, pay special attention to challenges that arise in SDNs with instant services. Their research aims to develop a bandwidth management mechanism and to apply an appropriate rate limitation policy under traffic congestion for each application. For instance, they develop, e.g., a mechanism for dynamic routing in the SDN network based on real-time-monitored statistics and calculating optimal routes with minimum cost [42]. They integrate this mechanism with a specific machine learning algorithm to enable flow classification and application identification. Link congestion is a severe problem that significantly affects a device's performance and the entire network. In [43], the authors analyze this problem in the context of queuing delay and packet loss on routers. They propose the Weighted Queue Dynamic Active Queue Management (WQDAQM) based on dynamic monitoring and reaction, which defines queue weights and thresholds, dynamically adjusted based on traffic load. Recently, authors have focused on integrating SDN architecture with the Service-Oriented Architecture (SOA) concept [44]. This architecture concept brings on the challenge of maintaining the QoS in networks. The authors conclude that gaps still exist in developing and applying QoS management in SOA-based SDNs. They categorize the QoS management into five main categories and analyze the impact of categories on guaranteeing end-to-end QoS provisioning. Dynamic QoS management will become more and more significant with 5G and especially 6G mobile communications, and requires fast and efficient responses to many challenges such as lower delays, higher traffic volumes, and data rates. In [45], the authors propose solutions within the synergy of technologies, such as NFV and SDN techniques, over the cloud-enabled radio systems. They point to potential benefits such as enabling resource pooling, scalability, layered interworking, and spectral efficiency.