# Dynamic QoS Management for a Flexible 5G/6G Network Core: A Step toward a Higher Programability
## 3 Related Work
### Slicing in Shared 5G/6G Networks  
Slices are composed of NFVs that are dynamically distributed across the network and span multiple administrative domains. NFV aims to decouple the software from the data plane, while SDN provides a centralized logic for the configuration and management of network infrastructure. For shared 5G/6G networks, a very high degree of multi-tenancy, where strong service guarantees force isolating resources across slices, is vital for the reliable operation of 5G/6G systems [15]. In a shared 5G/6G network, i.e., in a multi-tenant environment, network slicing enables different tenants (e.g., users, services, and vendors) to share the same infrastructure and to build fully decoupled E2E networks [3; 16]. This environment enables economic benefits for providers since it decreases the need for investment in separate infrastructures. Moreover, it decouples the role of the infrastructure provider from the service provider (tenant), creating a market environment that increases competition on both sides. Concerning security, the use of shared infrastructure implies the mandatory implementation of solutions that should enable maximum traffic isolation between different tenants, which a multi-slice organization achieves [17]. Due to the software-defined nature of slices, heterogeneous infrastructure resources can be leveraged in a streamlined and cost-effective manner [18; 19]. The authors of [20] have proposed a mixed-integer linear program minimizing latency under the client's demand and server's bandwidth constraints based on low and medium traffic intensities. With these objectives, it turns out that concentrating the traffic on the closest server yields an optimal solution in the NFV context. The deployment of intelligent and adaptive environments/applications is a driver for 5G/6G network evolution. In [21], the authors stress that the 6G network should provide lower latency and higher reliability, enabling ultra-massive M2M communications and the usage of low-power communications. The authors in [22] assume that the dynamic network configuration is based on current network utilization. By establishing efficient network sharing schemes, multiple tenants which may own conflicting resource requirements obtain access to the different parts of the limited resources. The implementation process of intelligent services in 5G and 6G multiservice environments draws particular attention [23]. The authors devise a taxonomy for network slicing using different parameters (e.g., fundamental design principles, service function chaining schemes, physical infrastructures, and security) and present several requirements for network slicing and possible solutions. A study in [24] analyzes recent trends and challenges in network slicing, the 3 GPP standardization process, and many related mechanisms. However, certain shortcomings are noticeable, e.g., the complexity of the 3 GPP solution, missing the tenant's portal, and the separated orchestration of network slices and their services. In [25; 26], the authors point out these limitations in current 5G network slicing implementations, especially management and orchestration. Moreover, they notice that slice-level operations are not well-separated from other processes, resulting in complex interactions between the 5G network components in the overall network slicing architecture. The authors of [25] propose a modular 6G-LEGO framework in which slices have embedded (in-slice) management and orchestration support, and multi-domain slices rely on multiple slice-agnostic orchestrators. In [26], the authors advocate for what they call zero-touch 6G massive network slicing, introducing a novel analytical engine to perform slice-level resource prediction by learning offline while respecting some service-level agreement (SLA) constraints. The authors in [27] consider network slicing at three different layers (the infrastructure, network, and service layer) and present an overview of the existing network slicing architectures.