1. Introduction

Background: Yes, in Neal Stephenson's 1993 novel Snow Crash, the word "metaverse" first appeared. The term is used, in the narrative, to explain personas designed by computer programmers. Subsequently, the term was used by the founder of Second Life, Philip Rosendale at the launch of the virtual world in 2003. Later, the metaverse was thrust into the mainstream following the release of the film adaptation of the novel, Ready Player One [1], which was directed by Stephen Spielberg. Ready Player One features a not-so-distant future where humanity is escaping a ravaged physical world by burying itself in a metaverse called OASIS. This story function as a famous version of the metaverse, inspiring mainstream audience and expose a glimpse of a virtual worlds. It touches on the idea of escaping the limitations of the physical world and entering into a digitally constructed reality with boundless potential and risks. Just like other sci-fi movies from the future, fans dream of making science fiction a reality. The Web3 movement is being sparked by the construction of your OASIS metaverse across various blockchain ecosystems (these teams are implementing and deploying blockchain technology use cases). When reading about the blockchain used in the metaverse, the interpretation of both terms hugely differs depending on when and how they are used [16].

Definition: Derived from the prefix "meta" and "verse," the Metaverse refers to an advanced computer-generated ambient or virtual environment that exists beyond the physical world and own a unique value system and allow for interrelated economy. The Metaverse is a digital universe in which users communicate, generate, and participate in digital content, encouraging a sense of connection and immersion. At the same time, the Metaverse has its own economic system, which functions in parallel with the physical world enabling the management, trade, and accumulation of digital assets, currency, and resources. In 2021, Facebook's CEO Mark Zuckerberg made a big announcement - the company is pivoting to build a metaverse. As part of this transformation, the company was renamed as Meta [2].

The Metaverse is poised to become a significant technological breakthrough in the near future. It includes Programming-engineered digital worlds with self-regulating economies, and integrated value systems. The Metaverse provides users with experiential cyber-virtual experiences in real-world contexts, by bridging a massive unified Internet with a unified 3D virtual and physical network. Specifically, developing augmented reality, virtual reality and Metaverse-improving applications that help users explore these experiences and participate in a social network [3]. In addition, the Metaverse was also the Internet of the next generation, commonly known as the 3D Internet, where users can adopt the digital native lifestyle and realize new lifestyles in the virtual world. There are numerous practical applications of the Metaverse in different fields, such as education, healthcare, tourism, and many others. To illustrate, applying the Metaverse to the healthcare industry can lend itself to extraordinary potential in improving patient outcomes by providing new and cost-effectiveness treatment methods. The Metaverse helps healthcare providers reach geographically dispersed patients ensuring remote monitoring and telemedicine [13]. Such versatility of the Metaverse positions a number of opportunities for healthcare disruption by allowing new forms of care delivery, collaboration and information exchange. Revolutionizing various high-tech areas including Internet of Things (IoT), 5G/6G, digital twins, artificial intelligence, augmented reality, extended reality, virtual reality, as well as mixed reality, the Metaverse enables all of these without compromising on security and privacy. These diverse technological integrations play a pivotal role in the evolution and sustainability of the Metaverse. The global pandemic has generated interest in the Metaverse and has changed the way that people work, socialize, and find entertainment. This has accelerated the adoption of virtual platforms to reconfigure traditional ways of interaction, and made the Metaverse an essential component as we head toward the future of remote collaboration and daily functions. The Metaverse is one of the components of Web 3.0, where avatars can travel through virtual worlds and exchange economic tools with its resources and rewards [3]. The timeline of the Metaverse is illustrated in Figure 1.

Figure 1 The timeline of the Metaverse.

2. Characteristics

There are a few major characteristics of Metaverse, listed as shown in Figure 2.

Figure 2 Metaverse characteristics [3].

Immersiveness: The term "Metaverse" refers to a virtual environment created by a computer that is so authentic that users can get psychologically and emotionally involved in it. This virtual space interacts with our senses, including visual, sound, haptic and even thermal and pressure feedback, and lets us negotiate body language through gesture and sign. Since much of our experiences can be in the solely textual and visual realm, these experiences that we perform in the Metaverse gives us a full understanding of who we are and our relationship with the Metaverse.

Economic opportunity: The metaverse is offering new economic opportunities for people and companies alike. It has to do with all sales & marketing on this game, which can be received through the sale of digital goods and services, advertisement, and content generation among others. Hence, individuals and businesses can make various activities in the metaverse, identifying new ways to make handsome bucks and be successful in this virtual space.

Governance: Metaverse governance is all about fairness, equality, and inclusivity when it comes to the development and management of the metaverse ecosystem. This inclusivity and democratic approach allow the metaverse to be a space that is collectively shaped by the contributions of its users, ensuring that the perspectives and interests of all are represented.

Interoperability: This allows for seamless travel across different virtual worlds in the Metaverse while still preserving their immersive experience. Furthermore, the digital items and assets that are created as NFTs can be owned or used across different worlds. This feature allows users to move freely around different virtual worlds and use their digital assets across multiple metaverse platforms.

Sustainability: The Metaverse operates on its own and has its own in-house economy. It has certain values that it upholds and it also has a closed cycle where economic activities take place inside its limits. Put simply, the Metaverse has its own rules and its own economy: and value creation and value exchange in its place.

Scalability: This refers to how well the Metaverse can handle a large number of users at the same time, the complexity of the virtual environments, and the range of interactions between users. It's about ensuring that the Metaverse can efficiently support a high number of people, complex scenes, and various types of interactions between users.

Heterogeneity: Different virtual spaces within the metaverse each have their own features. Different physical devices with Fabrics are also used to access the Metaverse. Types Of Communication And Data In Metaverse Finally, we think and experience the Metaverse very differently.

Security, privacy and accessibility: In the metaverse data is protected, so users don't have to worry about unauthorized access. This helps in providing a safety or security feeling for users in the metaverse space. Everybody no matter their physical or cognitive ability can be a part of the metaverse. This implies that one must use different devices and methods of interacting with the metaverse easily, and the metaverse must be usability-optimized for people with disabilities

Spatio-temporal and Innovation: In the real world, we have limits: there is only so much space and only so much time. That does not exist in the Metaverse though. In the Metaverse, spatiotemporal literally steps in because there is neither space nor time. It builds a second virtual universe in which time and space are warped, reshaped with limitless potential. It cultivates and advances metaverse and innovation. This means that metaverse has opened its doors to the developer community to an extent, which will allow new ideas to flow and innovative new methods to be used. It stimulates creativity, and experimentation with new ways of doing things.

3. Metaverse Architecture

Industry and academic specialists haven't agreed on a metaverse structure yet. Based on [3] and [4], we propose that both physical and digital environments be incorporated into the Metaverse Structure. The different components of the Metaverse can be accommodated by the proposed architecture, which are:

This tripartite framework ensures interoperability, scalability, and sustainability while addressing the heterogeneous needs of Metaverse applications."

4. Metaverse Standards

The business and standards communities are working together for the development of standards that will bring the concepts of the Metaverse to life. Currently, the focus of existing Metaverse standards, is primarily on ensuring smooth and uninterrupted connectivity among the physical and the virtual world. The best practices strive to define methodologies and standards that will support interoperability and interoperation between these two environments, thus building a seamless and integrated Metaverse. The summary of metaverse standards are presented in Table 1.

ISO/IEC 23005: Information technology — Media context and control — Part 1: Representation of media content Its aim is to enable the sharing and usability of immersive media across various devices and platforms. The specification defines formats and protocols that can be used for the encoding, decoding, and rendering of immersive media so that users can experience consistent, high-quality immersive content across different systems. ISO/IEC 23005 is a Multifunctional standard, applicable across a variety of Metaverse business services. It brings elements of audiovisual content, sensorial effects, and virtual objects properties into interactions across both the real and digital worlds. It would facilitate smooth communication on this world and as well as help cover an immersive experience in the Metaverse with their respective ecosystem.

IEEE 2888: It is a collection of rules that define how various elements in the digital world (cyberspace) and the real world can coexist [5]. It provides an outline of both how information is structured and how computer programs can interface with devices that perform physical actions (actuators) and retrieve information from the external world (sensors). Complementing this are standards that also provide a means for interaction between elements that are both in the virtual and real worlds. These rules encompass collecting input from sensors, driving output to devices, referred to as actuators, and enabling coherency between the digital and physical domains. Topics range from advancing Mixed Reality work to create virtual reality training systems to assessing training systems, plus incorporating holographic visuals that join the digital to the physical worlds. Overall, these standards help ensure that different technologies can communicate and interact effectively.

IEEE P1589: is a proposal for improving augmented reality (AR) learning experiences. It explains how different aspects of AR learning, such as activities, the learning environment, and other elements, can be described using a standard format. This format helps exchange information and data between different AR systems. Sensors and computer vision simplify the creation of educational experiences that seamlessly integrate physical-world engagements with online platforms, thus enhancing accessibility and usability. This standard also establishes a connection between the Activity Model and the Environment Model, allowing them to work together to represent a complete AR learning experience. The aim of IEEE P1589 is to make it easier for developers, trainers, and educators to design, create, deploy, use, maintain, and share AR learning experiences [6]. By leveraging this standard, they can enhance the effectiveness and engagement of AR learning for learners.

IEEE P2048: Due to the recent emergence of the Metaverse industry, there is a combination of excitement, confusion, and misunderstandings surrounding it. One of the challenges is that there is no agreement on the basic terms, definitions, and classifications, which can cause confusion for those interested in adopting it early on and hinder progress. IEEE P2048 aims to provide clear and standardized terminology, categories, and levels for the Metaverse [7]. The aim is to encourage sustainable development in activities related to the Metaverse and ensure a balanced and thriving growth of the Metaverse market. This standard include defining and classifying different devices used in VR and AR, establishing quality metrics for immersive videos, determining file formats for immersive videos, addressing person identity and environment safety considerations, developing immersive user interfaces, creating maps for virtual objects in the real world, enabling interoperability between virtual objects and reality, establishing quality metrics for immersive audio, defining file formats for immersive audio, exploring in-vehicle augmented reality applications, and establishing content ratings and descriptors. The main purpose of IEEE P2048 is to encourage the growth and adoption of VR and AR technologies.

IEEE P7016: This standard offers a holistic view of the technical and social elements of Metaverse systems. It also intends to establish a framework for ethically evaluating their design and operation. The IEEE P7016 standard is a useful tool for people involved in creating, running, or using metaverse systems. It offers guidance on how to make sure these systems are built and operated in a way that respects ethics [8]. It serves as a set of guidelines for Metaverse developers, helping them prioritize the creation of systems that align with ethical principles. This is important because it helps safeguard the rights and interests of the users of metaverse systems.

IEEE P2114: It is a set of rules that provides a structure for creating augmented reality (AR) applications. It outlines guidelines for designing, developing, and launching AR applications. These guidelines help developers understand how to build AR applications effectively.

IEEE P2396: It is a set of guidelines that establish ways to measure how good an augmented reality (AR) experience is. These guidelines define specific metrics to evaluate the quality of AR experiences. The metrics focus on factors such as how realistic the AR experience feels, how easy it is to use, and how deeply it immerses the user in the virtual world. By using these metrics, developers can assess and improve the overall quality of AR experiences.

OpenXR: It is a widely accepted and open standard specifically designed for creating augmented reality and virtual reality applications. This standard provides developers with a comprehensive set of application programming interfaces (APIs). These APIs enable tasks such as rendering 3D objects, tracking user input, and facilitating interaction with virtual objects. OpenXR is one among numerous standards being developed to address the evolving field of extended reality technologies.

W3C XR API: It is a set of helpful tools that allow developers to make augmented reality and virtual reality applications. This API provides a variety of features such as rendering 3D objects, tracking user input, and interacting with virtual objects. These tools make it easier for developers to build immersive and interactive AR and VR experiences.

WebXR: This standard outlines a collection of APIs that enable the access and interaction with AR and VR content directly within web browsers.

MPEG-H Part 23: This standard establishes a specification for the representation of 3D audio and video content specifically designed for AR and VR applications.

5. Core Components and Essential Requirements

Multiple emerging technologies converge to drive the development of the Metaverse. In the selected literature, key technological requirements have been identified. These requirements, include reliable connectivity for seamless interaction, interoperability between systems and platforms, scalability to handle large user populations and data, robust security measures, immersive and realistic experiences, standardized protocols for compatibility, integration of artificial intelligence for intelligent virtual characters and personalized experiences, and user-friendly interfaces for intuitive navigation. By addressing these requirements, the Metaverse can be developed with a solid foundation, enabling a connected virtual world that offers immersive, interactive, and secure experiences for users.

6. Conclusion

In this paper, we provide an in-depth discussion of the Metaverse concerning its core components, its architecture, existing standards, challenges faced, and the state-of-the-art research efforts. The key concepts, unique features of the Metaverse has been discussed along with an explanation of its components. In addition, a comparative analysis of existing virtual environment standards was performed, as well as the collection of a full catalogue of six technological enablers pertinent to the enabling of the Metaverse. All the critical requirement was carefully analyzed with explanation of relevant concepts and solutions. Furthermore, a detailed investigation into the existing challenges and future trends in the scope of the Metaverse was conducted, covering areas including AI-related applications, big data management, security & privacy issues, computation capabilities, multidisciplinary approach and broader aspects including global nature and legal domains.