I. INTRODUCTION
A. Motivation
B. Surveys on the Metaverse in the Literature
C. Organization
II. KEY REQUIREMENTS AND ARCHITECTURE OF THE METAVERSE
A. Description of Key Requirements for the Metaverse
B. Description of the Key Characteristics of the Metaverse
C. Architectural Framework for the Metaverse
D. Summary and Lessons Learned
III. KEY TECHNOLOGIES OF THE METAVERSE
A. Communication and Networking
B. Ubiquitous Computing
C. Digital Twin
D. Artificial Intelligence
E. Cybersecurity
F. Summary and Lessons Learned
IV. METAVERSE STANDARDS
A. IEEE Standards Association
B. ITU-T Focus Group for Metaverse
C. 3rd Generation Partnership Project
D. World Wide Web Consortium for Metaverse
E. International Electrotechnical Commission on Metaverse
F. Moving Picture Experts Group for Metaverse
G. Metaverse Standards Forum
H. Summary and Lessons Learned
V. METAVERSE APPLICATION ASPECTS
A. Education
B. Healthcare
C. Business and Finance
D. Socialization
E. Industrial Metaverse
F. Defense and Missions Critical
G. Summary and Lessons Learned
VI. METAVERSE CHALLENGES AND FUTURE PERSPECTIVES
A. Metaverse Infrastructure
B. Security, Privacy, and Trust
C. Artificial Intelligence
D. Metaverse Sustainability
E. Metaverse Devices Compatibility
F. Metaverse Ethics
G. Metaverse Economy
VII. CONCLUSION