he problem in each circumstance. 11.1 Deployment Considerations for Mobile Timing The most important thing to recognize before designing a timing solution is the scope of the prob- lem, and that is determined by the sort of mobile network that the operator is building. Another large factor is the constraint about what sort of transport options are available for the back-haul (and front-haul) network. For these reasons, this section covers the major considerations when choosing the best solution for each type of network. If the reader has an active role in the rollout, it is important to consult with the appropriate people on the details of deployment to correctly define the problem. For example, 5G has introduced a lot of flexibility and complexity in the front-haul, SO the network timing engineer must cooperate closely with the RAN team. Missing out on correctly understanding a key requirement can invalid- ate the total design and be a very expensive mistake for an operator to correct. If the authors, having talked about timing with many, many operators all around the world, could give one simple piece of advice, it would be to be sure you understand the problem in some detail. The sections that follow include numerous general principles about deploying timing, but the engin- eer deploying timing must understand their individual situation thoroughly. Never stop asking for clarification, requesting more details, and questioning anything you are told. 11.1.1 Network Topology Building a robust timing solution typically includes a distributed network of global navigation satel- lite systems (GNSS) combined with the transmission of timing signals over the transport network. Given that assumption, the following two very important factors greatly influence the design: The topology: The features of the nodes in the network and how they are distributed. The fea- tures would be those characteristics that influence how well the nodes process and forward tim- ing signals such as PTP. The transport: Characteristics of the un