## 2 Related Research
### XDN (Experience Delivery Network)  
Extended reality (XR) is a hyper-realistic technology that creates an expanded world by utilizing the technology of mixed reality (MR), which combines the advantages of virtual  
Figure 3: Architecture of CDN servers [16].  
reality (VR) and augmented reality (AR). Services that support extended reality (XR), such as virtual concerts, provide immersive content to users [17; 18]. Delivering immersive content in a CDN environment faces the following challenges:  
* Expansion to accommodate massive user-generated content is required.
* Interactive experiences, real-time delivery of content composition, and content synchronization are necessary.
* Creation of a 360-degree view; addition of text and image overlays; and real-time collection, processing, and distribution of content via wireless networks are required.  
Thus, to address these issues, experience delivery network (XDN), which overcomes the limitations of the conventional CDN, has been recently proposed. XDN, an evolution of CDN, enables immersive content experiences including XR and metaverse through the application of 5G and edge computing [19; 20]. In services based on XR, for instance, ultra-high-definition streaming data from a 360-degree view are transmitted, or additional content data are overlaid onto the existing data for transmission, providing users with a highly immersive content experience [21]. Various microservices for collecting, controlling, and distributing media in XDN can be seen in Figure 4 below. The Media Control Function (MCF) provides functions to control authentication, session management, and clustering of virtual concert audiences and Zones, processed at the edge close to content providers and consumers. The Media Distribution Function (MDF) has adopted viewport-dependent streaming based on a tile-based structure to ensure compatibility and scalability with the OMAF format, which supports 360-degree media [22; 23]. Using this format and streaming, it handles the distribution of zone-specific media. The Media Ingestion Function (MIF) deals with the ingestion of various types of media depending on the environment of the performer and audience.  
Figure 4: Schematic of XDN (experience delivery network).  
Figure 5 illustrates the sequence diagrams of microservices typically required when constructing an XDN. These examples represent operations performed in a zone network architecture within a WebXR-based system that supports XDN. Figure 5a represents the Media Ingestion Signaling Flow, illustrating the process of individual users ingesting from the MIF, while Figure 5b represents the Media Distribution Signaling Flow, showing the process of distributing streaming data based on WebRTC from the MDF to each user. Here, WebXR is a framework providing XR experiences based on WebRTC. As shown in Figures 4 and 5, one can adopt microservices of XDN for ingesting or distributing media streaming data and, furthermore, it can be a good choice for transmitting immersive content.  
XDN architectures can reduce bandwidth consumption and latency and provide the scalability needed for handling abnormal traffic loads, improving server performance. Therefore, in order to design a real-time adaptive metaverse-based network with ultra-low latency, it is necessary to design a robust network architecture for the XDN [17; 24].