# Toward Integrated Satellite Operations and Network Management: A Review and Novel Framework
## 2 State of the Art
### Communication Constellations Architectures
#### 2.1.2 Persistent Connectivity Architectures  
To maximize the potential of persistent connectivity constellations, they need to be integrated with terrestrial networks. This integration aims to leverage the strengths of both satellite and terrestrial infrastructures, enhancing overall connectivity and performance. When combined with terrestrial networks, persistent connectivity constellations can provide more robust and reliable services, meeting the demands of delay-sensitive applications [32]. Advances in space-air-ground integrated network architectures include efficient coverage area control [33] and novel approaches for joint communications and sensing in 6G satellite networks [34]. Additionally, model-based approaches for constellation design have emerged, enabling systematic integration of user requirements in EO missions [35].  
A survey of satellite-terrestrial integrated architectures is presented in [11]. Authors classify the integration architectures into hybrid relay, backhaul, cognitive, and cooperative networks, depending on the level of interaction between satellites and the terrestrial network. The first two aim to enhance the transmission in one network by using the other. In cognitive ones, the networks operate separately but share the spectrum. Finally, cooperative networks combine the two, operating them simultaneously. Their work concludes that in current communication systems, satellite, and terrestrial networks are developed and operated separately and that although significant attention has been paid to the integrated satellite-terrestrial network, how to integrate the two networks effectively remains an open issue. This challenge is the focus of our research, which aims to achieve the convergence of management for both networks. The study in [11] also identifies several operational challenges in this integration, like mobility management, traffic offloading, routing, and resource management. It further highlights that enabling techniques and future directions, such as SDN and AI integration, are crucial to overcoming these operational challenges.  
In [36], the integration of satellite and terrestrial networks is described as a series of incremental stages in the architecture. The first stage is a transparent architecture for backhaul, where satellites function as signal repeaters to enhance coverage. The second stage involves regenerative capabilities onboard the satellites. The third stage features an architecture with some core network functions distributed to the satellites. Finally, the ultimate stage, envisioned as a fully integrated network, is an SDN architecture where resources are entirely virtualized, and the architecture is divided into the infrastructure, virtualized resources, control, and application layers. The authors present a practical implementation of a first-stage architecture and conclude that NFV and programmable hardware onboard the satellites are key technologies to achieve this architecture stage. In [9], a new metric to evaluate the integration performance of a satellite-terrestrial network architecture is introduced. Using this new integration metric, they design an integrated network featuring a MEO constellation. In [37; 38], a multi-layered architecture comprising a GEO and a LEO layer is proposed. Their work describes the management of the proposed architecture using SDN, with master satellites at the GEO layer and slave satellites at the LEO layer. The management of these architectures is further discussed in Section 2.2.2.