ernet of things (IoT), the fo- cus of Release 17 (Rel17). The use case normally does not determine the timing requirements for the 5G network being built; however, you should understand that the use case might require the deployment of a technology that can change the timing requirements. As an example, the deployment of mobile infrastructure to support very high-bandwidth eMBB might entail the rollout of very high-frequency millimeter wave (mmWave) radios. The coordina- tion of those bands with lower-frequency mobility bands might require phase synchronization between the cooperating radio transceivers (and the mmWave radios are likely to be TDD anyway). 11.1.1 Small Cells Versus Macro Cells An important aspect to consider is the type of cell site that is being deployed. Although it might be more correct to look at the range and capability of different cell site types on a spectrum, this sec- tion divides them into two quite broad categories, macro cells and small cells. Whichever way you want to define them, the important thing is to understand how the category of cell site influences the timing solution-a timing solution that might work for one type might not be suitable for another. Generally, these different types of radio sites are deployed to meet local conditions and require- ments and include the capability to hand off and coordinate between them. They are deployed alongside each other and in overlapping coverage areas in what is called a heterogeneous network, or HetNet. The HetNet approach is used to provide a mosaic of coverage, with complex interopera- tion between the radio site and even with other access technologies such as Wi-Fi. The degree of coordination between these sites can vary on a spectrum from quite loose on one end to very tight on the other. In the tighter coordination, technologies such as CoMP are used to service the subscriber device using the radios working in concert. Other deployments might work more in- dependently of each other, but still require ICIC and eICIC to stop the ove