## 4 Routing in Integrated Networks
** & **Year** & **Objective** & **Merits** & **Demerits** & **1** & **2** & **3** & **4** & **5** \\ \hline \hline \multirow{10}{*}{[121]} & \multirow{6}{*}{- They focused on routing in DTN-Nanosatellite networks} & & - They suggested an innovative energy-aware routing algorithm derived from the Contact Graph & & & & & & \\  & & routing in DTN-Nanosatellite networks & Routing (CGR) named E-CGR - Better average data transmission time - The amount of transmitted data beams increases & & & & & & \\ \cline{1-1}  & & & & - It is the first of its kind (P2P) connections for integrated satellite, high-altitude platform (HAP) networks, which is one of the key elements of the sixth generation (6G) wireless network vision & - The advantages and disadvantages of networks from the perspective of 6G large-scale complex networks & & & & & \\ \cline{1-1}  & & - It is the first study to examine the varying heights and minimum elevation angles of hot air balloons & - A model more suited to real-world conditions & - It can be extended asymmetric time to energy efficiency & & & & & \\ \cline{1-1}  & & - An effective network control and management framework has been proposed for the ultra-dense LEO satellite–ground integrated network & - Effective and efficient network management & - It needs to be tested in real application & & & & & & \\ \cline{1-1}  & & & - It reduces the complexity of management & - It needs to be tested in & & & & & & \\ \cline{1-1}  & & & - It reduces the complexity of management & - It reduces the complexity of management & - It reduces the simulations & & & & & \\ \cline{1-1}  & & & - complexity of management & - It reduces the simulations & & & & & & \\ \cline{1-1}  & & & - complexity of the existing network &  
In 2021, an extensive literature review was provided, focusing on the study of point-to-point (P2P) connections for integrated satellite high-altitude platform (HAP) networks, which are considered one of the key elements of the sixth generation (6G) wireless network vision. The aim of the article was to study point-to-point connections in multilayer spatial networks, which are expected to play an important role in 6G large-scale complex networks, and present their integration and upcoming research pathways. In this context, it is emphasized that the coverage, reliability, and scalability of 6G wireless networks can be increased by developing integrated spatial networks containing spatial nodes at different altitudes, such as satellites, high-altitude platforms (HAPs), and low-altitude platforms (LAPs). It details RF and PSO solutions used to link single or orbiting satellites and provides a link budget evaluation for RF- and FSO-based satellite-to-satellite connections. It was underlined that artificial intelligence, SDN technology, as seen in Figure 6, the use of intelligent reflecting surfaces, gateway selection, and innovative routing protocols will serve a crucial role in resource management and traffic routing optimization, which is critical due to the multilayered, heterogeneous structure of integrated spatial networks. However, the merits and demerits of various methods and approaches can be compared in more detail [122]. \begin{table}  
In 2021, there was a focus on the terrestrial-satellite network (TSN) model in 6G networks that utilize hot air balloons at varying altitudes and minimum angles of elevation as intermediaries between satellite and ground stations. The primary obstacle to this is enhancing the network's energy performance by combining the management of caching, computing, and communication (3C) resources for both uplinks and inter-satellite relay latency and structured laser links per satellite in terrestrial-satellite networks (TSNs). Modeling a TSN system that includes hot air balloons floating at various altitudes and minimum angles of elevation, considering laser links and the traffic between satellites, was considered to be more suitable for real-world scenarios.