# A Flexible Infrastructure-Sharing 5G Network Architecture Based on Network Slicing and Roaming
## 2 Background and Related Work
### Related Work  
Network slicing is a technique that may be used for different purposes, including a plethora of 5G scenarios at different network domains (RAN, CN, transport, general) and even with non-terrestrial networks [8; 12]. The use of slicing in the RAN domain poses resource management challenges, especially in spectrum time and spatial domain, with multi-tiered and AI-supported approaches being promising solutions [6]. Nevertheless, these solutions are out of the scope of this paper, which focuses on neutral host or multi-tenant terrestrial mobile network architecture proposals and does not take into account the spectrum sharing problem. [PERSON] et al. [13] proposed a RAN-sharing model based on a flexible network slicing mechanism that leverages the efficiency of MOCN along with the spectrum isolation inherent in MORAN through a dynamic transition between these two scenarios. The implementation was based on open-source 4G software from OpenAirInterface (OAI) and used an SDN approach to manage the separation of control and user planes in the MAC layer, using the FlexRAN RAN controller provided by the Mosaic5G project, which facilitates the real-time creation and configuration of network slices. The authors also proposed an algorithm for dynamic radio resource allocation for each slice. In their tests, they compared their approach to a static RAN sharing scenario and concluded that their architecture allows for efficient radio resource management, considering factors like traffic demand, SLAs, and required isolation. Although the authors present an innovative proposal for RAN sharing among multiple operators, some potential challenges are the implementation complexity, the need for testing in diverse scenarios, and the technically complex management requirements. In [14], the author proposed a neutral host architecture for indoor spaces where the neutral host has complete control over the network infrastructures and elements, and the interaction with service providers (SPs) is established through roaming agreements. Using the Citizen Broadband Radio Service (CBRS) spectrum, in the 3.5 GHz band, which is available for shared commercial use in the United States, the architecture allows a single small cell to serve multiple operators. To maintain the visibility and trust of the SPs in the neutral host network, trust relationships between entities were established, along with providing detailed information about network performance quality through key performance indicators (KPIs). This approach is similar to the one used in this paper, as both employ roaming to authenticate users. However, the author does not consider the isolation and separation of the traffic among SPs nor, consequently, ways to ensure and maintain the desired QoS as agreed in the contracts with the SPs. [PERSON] et al. [15] presented the architecture of the 5G SESAME project of the 5G public-private partnership (5G-PPP), which is composed of two main components--the cloud-enabled small cell (CESC) and the CESC manager (CESCM)--and leverages SDN and NFV technologies to enable small cells to support multiple operators through the request of network slices from the infrastructure. The SESAME architecture envisages the separation of physical and virtual functions based on the MOCN model. The 5G-City project [10], which is also a 5G-PPP initiative, proposes an architecture split vertically across three layers: service/application layer; orchestration and control layer; and infrastructure layer. The proposed architecture was deployed in three different cities, Barcelona, Bristol, and Lucca, and the feasibility of deploying a multi-tenant virtualized infrastructure was demonstrated. Another 5G-PPP initiative, the 5G-ESSENCE project [16], presents an interesting approach to edge network deployment and infrastructure sharing.