cases are included to explain the syn- chronization requirements and illustrate the mobile performance issues if these requirements are not met. However, detailed examination of every technique and use case is beyond the scope of this book. Evolution of the 5G architecture: Outlines the evolution of the 5G network architecture, in- cluding the system architecture, definitions, and terminologies, as well as the requirements of the network. Discusses the overall architecture changes in 5G to help establish how the time synchronization architecture must evolve with it. 5G New Radio synchronization requirements: Captures several major use cases for 5G mo- bile and outlines the time synchronization requirements evolving around those use cases. The traditional telecom network has relied on accurate frequency distribution to optimize transmis- sion and operate time-division multiplexing (TDM) transport connections. However, with evolved wireless networks, the distribution of accurate time and phase (as well as frequency) has become necessary for modern telecom-based services and the underlying infrastructure. In wireless services (for example, GSM, CDMA, WiMAX, LTE, or 5G), the air interface demands stringent synchroniz- ation, even though the end-user service (for example, mobile broadband Internet access) might not require synchronization. Timing and synchronization are critical components of an efficient mobile network, and hence the transport network plays a very critical role in distributing and maintaining accurate time and syn- chronizing phase signals. If accurate time and phase distribution is not properly designed, imple- mented, and managed, mobile networks will suffer a dramatic (negative) effect on the efficiency, reliability, and capacity of the mobile services. Mobile subscribers will likely suffer dropped calls, interrupted data sessions, and a generally poor user experience. The main characteristics of a well-implemented timing and synchronization network include the following: Accuracy: Network element