The rise of Software-Defined Wide Area Network (SD-WAN) a decade ago has ushered in a new era of networking opportunities for organizations worldwide. As enterprises undergo digital transformation fueled by cloud computing adoption and the imperative for enhanced connectivity, SDWAN has emerged as a transformative paradigm. This survey paper unpacks the intricate ecosystem of SD-WAN technology, offering a deep dive into its foundational principles, architectural components, and diverse deployment scenarios. We explore modern SD-WAN architectures, analyzing key elements such as Customer Premises Equipment (CPE), underlay and overlay networks, controllers, and orchestration planes. By shedding light on the mechanisms that drive SD-WANs agility and efficiency, we provide critical insights into its transformative potential. Beyond architecture, we examine essential operational aspects, including traffic engineering, performance monitoring, and network resources management within the SD-WAN framework. We also identify key challenges and research gaps, charting a path for future advancements in the field. This comprehensive study serves as a valuable resource for academics, researchers, and industry professionals navigating the evolving landscape of enterprise networking in the era of cloud-driven digital transformation.
