## 1 Introduction  
In the beginning of the previous decade, the advent of the New Space drove a revolution in the space sector with the introduction of cutting-edge technologies [1]. The main impact was the cost reduction of Low Earth Orbit (LEO)-based space solutions thanks to the achievement of groundbreaking milestones, such as the introduction of reusable launch vehicles [2] or the miniaturization of satellite designs [3]. This resulted in the opening of new technological frontiers and the entry of private companies into the market. The ambition to join the broadband services market made space companies focus on LEO satellites, since their orbital characteristics allowed the companies to relax their link budget, maximizing operational throughput and reducing latency. Although these benefits were essential for broadband services, the inherent orbital speed of satellites caused link disruptions, leading to discontinuity issues. This situation ended with the emergence of mega-constellations, i.e., LEO constellation architectures that comprise hundreds or even thousands of satellites and use their massiveness to ensure continuity [4]. These constellations achieved a major milestone with the provision of global and ubiquitous services. Currently, only a few mega-constellation projects are operating commercially. The global and seamless service provision targeted by the future 6 th Generation (6G) encouraged 3 rd Generation Partnership Project (3 GPP) to integrate satellite systems into cellular networks, aiming to expand the coverage to unserved or under-served geographical areas. This standardization started in Release 17 [5] with the definition of Non-Terrestrial Networks (NTN), which considered the exploitation of satellites to provide broadband services. The implementation of NTN raises new opportunities for 3 GPP network architectures. The key factor that determines the addressable architectures is the type of satellite payload. While a transparent satellite acts as a repeater or a bent pipe between ground network components, a regenerative satellite embarks extended capabilities that enabled the hosting of network components on board [6]. The comparison of both payload types opens a broad discussion as each offers its own advantages and disadvantages. For instance, transparent satellites involve simpler designs, reducing their in-orbit cost and time to market, at the expense of a limited service provision [7]. Consequently, the decision to select a transparent architecture over a regenerative one might depend on certain circumstances of the targeted scenario, such as the financial and technical resources of the satellite provider, the service requirements of the use case, or the project and service duration. The intention of this work to experiment under real-world conditions has led us to investigate transparent architectures, since real regenerative satellites require the availability of dedicated infrastructure and involve more complex and time-consuming workflows. Regarding the recent standardization efforts of 3 GPP in 5 th Generation (5G) NTN [8; 9], we propose the three architectures outlined in Figure 1. Option (a) positions the satellite link over the backhaul, i.e., the connection between the Radio Access Network (RAN) and the 5G Core (5 GC). This connection covers the N2 interface, which connects the Next Generation Node B (gNB) to the Access and Mobility Management Function (AMF), and the N3 interface, which connects the gNB to the User Plane Function (UPF). Option (b) exploits the functional split technology of 5G by which the gNB's functionality is essentially separated in the Central Unit (CU) and Distributed Unit (DU) modules. This option places the satellite link over the midhaul, i.e., the connection between the CU and the DU. Particularly, the functional split implements split option 2, as it is the only one standardized by 3 GPP. The CU and DU are connected via the F1 interface.