he other facet to confirm is the performance of the network clocks as a PTP clock. In sum- mary, that means testing the performance and behavior of all forms of BC, TC, and slave clock. Three foundation ITU-T recommendations guide the test engineer here: G.8273.2, G.8273.3, and G.8273.4. The following sections will take each group of clocks in turn and explain the test cases that can be applied to each clock type. Each clock type will include tests for noise generation, tolerance to input noise, noise transfer through the clock, short-term transient response, and holdover (long-term transient). Testing T-BC and T-TSC to G.8273.2 When operators are adopting network-based timing, most of the testing interest is split between T- BC/T-TSC performance and the phase error alignment after crossing the network. G.8273.2 con- tains the most important criteria for selecting PTP-aware network elements, SO adherence to that re- commendation is the prime area to investigate. For reference, there is more information on testing these clocks in Appendixes A.3, A.5, B.3, and B.5 of ITU-T G.8273. The idea is to test the performance of T-BC and T-TSC clocks using G.8275.1 in combination with SyncE (or eSyncE) in a full timing support (FTS) network. As this is the PTP method used most of- ten for phase/time transport, this section starts with G.8273.2 compliance and covers it more thor- oughly than others. Figure 12-19 illustrates the method to test the performance of T-BC boundary clocks and T-TSC slave clocks. T-BC Testing T-TSC Testing Reference Reference Tester input Tester input Synthetic noise injected Synthetic noise injected into the reference signal T-TSC T-TSC into the reference signal output output T-BC input output T-TSC input PTP & PTP & SyncE SyncE SyncE PTP SyncE PTP & SyncE SyncE 10 MHz Figure 12-19 Testing T-BC and T-TSC Clocks In all cases, the tester has a master port that gives the DUT a timing signal consisting of G.8275.1 PTP messages plus SyncE (or eSyncE). In some tests, the signal is an ideal input signal, m