# Digital Twin-Driven Virtual Network Architecture for Enhanced Extended Reality Capabilities
## 4 Architecture Modeling Approach
### System Requirements Approach  
As is shown in Figure 4, the proposed system is comprised of architectural entities, hosted by a space data center, with modules designed for fulfilling specific processes. To ensure an optimal system operation, the space data center requirements have to be considered. Reference [52] analyzes the deployment of space data centers while ensuring performance computing, storage capacity and networking services, aiming to be integrated with terrestrial cloud platforms. The paper's architecture is composed of three layers: a physical layer which includes the hardware and embedded software, and it is intended to operate in  
Figure 18: Proposed system communication interfaces. an Infrastructure as a Service (IaaS) fashion; the Management SW layer includes the hypervisors, operating systems, containers and security services, while the software is intended to be made available in a Platform as a Service (PaaS) fashion; and a User Workload layer composed of code, APIs and libraries enabling users to deploy applications. In terms of network architecture, an internal network is deployed to guarantee the space data center modules' interconnection; in addition, SDN technology is leveraged to manage resources dynamically and control the inner connectivity. This paper discusses the resilience and reliability achieved by modular redundancy, quality control systems and the utilization of Fault Detection, Isolation and Recovery (FDIR) mechanisms. According to the architecture proposed in [52], the space data center performance reaches earlier ground data center performance, achieving 13 Tera Floating Point Operations Per Second and 100 Tera Operations Per Second tailored to AI algorithms and 3.5 PB storage. The modular and compact design enables scalability for space data centers. On the other hand, ref. [53] discusses the implementation of relay satellites for ground data centers and space data centers' data transfer and highlights hardware robustness in front of high pressures, temperatures, space radiation, lightweight and compactness. Then, a simplified space data center architecture can be proposed as follows in Figure 19. Notice the three layers: infrastructure (physical resources), hypervisor (optional) and entities (DTM and XRM). In terms of hardware and software requirements for the space data center proposed in this paper, the proposal is not limited by the size of the hardware resources required. As a basic reference, according to the analysis presented in [52], the following software resources must be considered:  
* Cloud Infrastructure such as OpenStack (Minimal Requirements: 24 CPUs, 24 GB RAM and 500 GB disk) [54]. * Orchestration platforms such as \"Open Source MANO (OSM)\" (Minimal requirements: 4 CPUs, 16 GB RAM and 80 GB disk) [55]. * Virtualization engines, such as \"VMware\" (Minimal requirements: 8 CPUs, 16 GB RAM and 500 GB disk) [56]. * Monitoring, management and fault detection software. * Data base structures such as \"Oracle\" (Minimal requirements: 64 GB RAM and 500 GB disk) [57]. * Firewall and cyber-security systems. From the software resources previously listed and based on the earlier Figure 4, which illustrates a minimal scenario, at least two high-performance servers are required to support the Digital Twin Network operation (DTM server) and the extended Reality service provision (XRM server). The DTM server needs to provide the cloud infrastructure to support the DTN; thus, it is required to implement OpenStack, while OSM is required to orchestrate the DTN. Regarding the XRM server, VMware can be adopted to deploy the virtual network functions (VNFs), while OSM orchestrates such VNFs. Thus, the capacity for each server can be anticipated: the DTM server requires at least 24 CPUs, 40 GB RAM and 500 GB disk, while the XRM server requires at least 32 GB RAM and 200 GB disk for each VNF deployed, as well as a Graphic Processor Unit (GPU), for instance, a \"NVIDIA RTX series\".