ey 5G Technology: What Is It? Why Do We Need It? How Do We Implement It?, November 2015. [44] Ixia, Test Considerations for 5G, White Paper, July 2017. [45] 5G Reimagined: A North American Perspective, Alliance for Telecommunications Industry Solutions (ATIS), February 2017. [46] 5G Americas, White Paper on 5G Spectrum Recommendations, April 2017. [47] Qualcomm Technologies, Inc. LTE-U/LAA, MuLTEfire™ and Wi-Fi; Making Best Use of Unlicensed Spectrum, September 2015. [48] Skyworks Solutions, Inc., White Paper, 5G in Perspective: a Pragmatic Guide to What's Next, March 2017. CHAPTER 1 5G Network Architecture 5G network architecture has been designed to support fast and reliable connectivity as well as diverse applications and services, enabling flexible deployments using new con- cepts, such as network function virtualization (NFV), software-defined networking (SDN), and network slicing. The 5G system supports a service-oriented architecture with modu- larized network services. The service-oriented 5G core (5GC) network is built on the prin- ciple that 5G systems must support wide range of services with different characteristics and performance requirements. The service-oriented architecture and interfaces in the 5G systems make the future networks flexible, customizable, and scalable. Network service providers can leverage service-oriented architecture design in 5G to manage and adapt the network capabilities, for example, by dynamically discovering, adding, and updating net- work services while preserving the performance and backward compatibility. The main difference in the service-based architecture is in the control plane where, instead of predefined interfaces between entities, a service model is used in which components request a new network entity to discover and communicate with other entities over applica- tion programming interfaces (APIs). This notion is closer to the cloud networking concept and more attractive to the operators that demand flexibility and adaptability in their net- works. The challeng