ection on T-BC/T-TSC holdover. 9.5 Budgeting End-to-End Time Error The performance of a timing signal recovered at the end of the timing chain depends on the com- bined effect of the links in the chain. Basically, it is the sum of the performance of the clocks in the path, the unaware nodes, and the transport infrastructure. The parameters for each of those compon- ents are covered in the preceding sections, including details of the clock performance. The sections following this cover the underlying packet transport itself. The fundamental job of the designer of the timing solution is to ensure that the timing signal, on ar- rival at the application, meets the requirements of the application. The authors like to state that when you are required to solve a timing problem, you need a timing solution. All the networking details are very much secondary to the issue of time. The primary fundamental goal of the timing solution is to measure and control the timing error SO that it arrives within the error budget. One very specific example of a timing budget specific for the mobile use case is presented in G.8271.1. This use case is covered in detail in several other places, including Chapters 8 and 10. Figure 9-33 illustrates an end-to-end mobile budget using the FTS network with up to 20 T-BC clocks of Class B performance. Other industries have similar examples, in differing levels of detail. Network/ application Mobile Phase Error Budget handover Clock 20 Clock n Clock 1 Application Random short-term network Link asymmetry holdover variations compensation PRTC/T-GM 20 ns 20 ns 250 ns + 200 ns 380 ms * 100 ns + 150 ns End application +1.1 us network budget +1.5 us end-to-end budget Figure 9-33 End-to-End Time Error Budget Example for Mobile Networks This example includes the following points for apportioning and managing the time error (from left to right): There is an end-to-end budget of +1.5 us at the output of the end application. This is the hard limit that the timing solution must meet under all circumstances (th