A comprehensive survey on software-defined wide area network (SD-WAN): principles, opportunities and future challenges

With the rapid increase in traffic demand, the need for flexible and robust solutions for network connectivity has become crucial for transport network operators. Additionally, it is essential to control and encrypt data shared between headquarters (HQs) and local branches before transmission to the wide area network (WAN). As a result, software-defined wide area networks (SD-WANs) have gained significant attention for their ability to ensure high-quality experiences and enhance link reliability. However, despite the well-documented advantages of the SD-WAN approach, deploying these techniques in highly dynamic environments poses substantial challenges for researchers. These challenges encompass routing issues, network survivability and traffic management, largely due to fluctuations in the underlying link state, the number of routers and the constant evolution of network topology. In this context, this paper presents a comprehensive survey of SD-WAN addressing its key problems. This study takes researchers on a fascinating technological journey that provides an in-depth description of SD-WAN development, considering contributions of the industrial sector and academic projects. Firstly, the key components of an SD-WAN along with technological aspects related to the development and configuration of SD-WAN are systematically presented. Thereafter, the motivation, scope and organization of the problem space are presented along with the performance analysis of existing research on this topic. Finally, we discuss the future challenges and major issues in SD-WAN techniques. To the best of our knowledge, this paper constitutes the first attempt at a fundamental survey of SD-WAN solutions, which more adequately describes the state of the art of this specific subject.