ributing time over both physical and packet-based networks. It includes the following chapters: Chapter 8, "ITU-T Timing Recommendations," is a comprehensive overview of the ITU-T and its process for making recommendations. The rest of the chapter contains a list of the many re- commendations used to outline the architecture, metrics, network budgets, and clock perform- ance and define the behavior of timing solutions. There are recommendations covering both physical (TDM and SyncE) and packet methods to transport timing signals and quality-level information. Chapter 9, "PTP Deployment Considerations," is where the theory meets the practicalities of design and deployment. This chapter contains many valuable lessons in the areas of design trade-offs and deployment concerns when putting together a timing solution. It includes more details on timing metrics and end-to-end time error budgeting, as well as options for holdover and redundancy. The information in this chapter is for more general synchronization use cases, while Chapter 11 covers some of the same subject matter but is much more specifically focused on the mobile network. Part IV, "Timing Requirements, Solutions, and Testing," discusses various 4G/5G mobile network requirements, time synchronization deployment options, and validation methodologies. It includes following chapters: Chapter 10, "Mobile Timing Requirements," is where most of the mobile information is loc- ated, including timing requirements for LTE and 5G, evolution of the 5G architecture, and the features behind the 5G New Radio and the synchronization that it now demands. This chapter covers many of the major features, services, and radio optimization techniques now available in the radio access network (RAN). It also covers the different timing requirements for both the distributed and centralized RAN and covers the special challenges in the disaggregated and vir- tualized 5G RAN. Chapter 11, "5G Timing Solutions," has some echoes of Chapter 9 but with more detailed de- scription of the de