This chapter explores the protocols, architectures, security mechanisms, and performance considerations that underpin modern computer networks. It begins with foundational protocols such as TCP/IP and HTTP/HTTPS, highlighting their roles in reliable data transmission and secure web communication. The discussion extends to both wired and wireless network topologies, including the evolution of Ethernet, Wi-Fi, and emerging 5G technologies, reflecting the growing complexity and ubiquity of networked systems [1]. Security mechanisms are examined in depth, covering firewalls, AES encryption, and VPNs, with an emphasis on best practices for safeguarding data in transit and at rest. Quality of Service (QoS) techniques are introduced to illustrate how networks prioritize and manage traffic for critical applications such as streaming and realtime analytics. The chapter culminates in a detailed case study of the 2017 WannaCry ransomware attack, demonstrating how protocol vulnerabilities and inadequate patch management can lead to global-scale disruptions. Through this integrated approach, readers gain both theoretical insights and practical strategies for designing, securing, and optimizing resilient communication networks [2]