## 3 Network Structure  
Regarding SAGIN structure, the current research has not fully considered the application of edge computing technology in converged networks. Those also have not well solved the problems of device heterogeneity, node effectiveness, and resource limitation in converged networks. According to the difficulty of heterogeneous resource management in SAGIN, a SAGIN structure based on the SDN/NFV is proposed in this article, and its logic is shown in Figure 1. We put the abstract and application processing functions of physical devices on the MEC host so that the devices can be accessed according to procedures, free from hardware constraints. Therefore, the network structure proposed by us no longer divides the heterogeneous network into different layers, but into five layers: application layer, centralized control layer, control layer, data layer, and infrastructure layer. The application layer contains the applications needed for the Industrial Internet of Things (IIoT) and Internet of Agriculture (IoA), such as machine operation, energy extraction, and pesticide spraying, and provides the corresponding functions for the request of the centralized controller. The centralized control layer is responsible for the collection of resource conditions; it develops management policies based on network resources and provides functions such as node mobility management, converged network topology reconstruction, network task scheduling, and heterogeneous resource management. This layer collects data from the control layer on the one hand and directs the control layer to perform its work on the other. The control layer receives data from the data layer and feeds it back to the centralized control layer, allocating node resources and controlling data forwarding according to the policies of the centralized control layer. In order to solve the difficulties in the management of a large number of MEC servers and network nodes, the effective identification of new access network edge nodes is realized and the effectiveness of nodes is ensured. We divide SAGIN into three layers for control, namely the satellite network layer, the aircraft network layer, and the ground network layer. At the same time, to better manage SAGIN, a global SDN controller (SDNC) should be set to control all layers to complete tasks in a unified and coordinated manner. Meanwhile, primarily SDNCs and sub-SDNCs should be set at each layer. In the satellite network, the primary controllers are placed on Geostationary Earth Orbit (GEO) satellites, and sub-SDNCs are placed on the Medium Earth Orbit (MEO) satellites. In the aircraft network, one or a few High-Altitude Platforms (HAPs) are selected as the primary SDNCs, and the remaining HAPs are sub-control nodes. In the terrestrial network, servers are placed in the backbone network as primary SDNCs and edge servers are placed as sub-SDNCs. The data layer integrates space-based, air-based, and ground-based computing resources into a unified resource pool through the NFV. Then, it forwards data to each substrate node according to the command of the control layer. Figure 1: Logical structure of SAGIN based on the SDN/NFV for IoA/IIoT. The infrastructure layer provides necessary resources for the upper layer, such as computing resources, storage resources, and bandwidth resources. The main facilities are GEO satellites, MEO satellites, LEO satellites, HAPs, UAPs, core servers, and edge servers, whose topologies are shown in Figure 2. Both ground base stations and MEO satellites can communicate directly with LEO satellites and GEO satellites. MEO satellites can communicate with other MEO satellites. In contrast, LEO satellites cannot communicate directly with GEO satellites or communicate with each other, and GEO satellites cannot communicate with other similar satellites.