s, in terms of deployment complexity and ultimately cost, the core network is in no way the biggest contributor to operator's efforts when deploying a network. In terms of deployment and development complexity and cost, the biggest component of a network is actually the one that is often overlooked in literature - that is the Radio Access Network (RAN). The RAN is a collection of base stations, interconnected by a transport network, which also connects it to the core. That collection of base stations, if deployed and configured properly, is ultimately responsible for providing coverage and capacity to the network users. As the number of base stations deployed by an operator is huge (and is expected to grow substantially in 5G), the RAN is (together with spectrum acquisition) by far the biggest contributor to the cost of deploying and running a cellular network. Unlike the other network components, design of the RAN is more art than science. That is because it is not feasible to analyze or simulate the RAN in its entirety and, therefore, there are very few objective measures of what constitutes a good RAN design. This inevitably leads to a multitude of different designs (or architectures) - some competing, some com- plementing each other. In this book we try to lead the reader through this maze of dif- ferent RAN architectures, technical and business considerations that led to their design, and practical considerations affecting the choice of the proper architecture and deploying it successfully and in a cost-efficient manner. Welcome to the "dark side" of 5G - one of the most important 5G aspects, which is not in the spotlight as much as it should be. This book is accompanied by the website: www.darksideof5g.com Acknowledgments This book is the result of the joint work of many contributors who used the vast domain expertise in their respective areas to make it possible. I would like to thank them all. Furthermore, special thanks go to all the reviewers for helping to ensure correctness and consistency of the mate