This report delves into fundamental IT concepts, beginning with an analysis of the OSI and TCP/IP network models, exploring the advantages and disadvantages of their architectures and the rationale behind the TCP/IP model's design. It includes calculations for overhead percentages in TCP/IP protocols and discusses the role of TCP segments. The report then transitions to IT Service Management (ITSM), outlining new trends and technologies, and detailing the responsibilities of Incident and Change Managers. Finally, it compares software development life cycle (SDLC) models, specifically the Waterfall, V-shaped, and Spiral models, evaluating their strengths and weaknesses, and highlighting the benefits of the Spiral model for software development.