sured against the applicable primary time standard, such as UTC. However, the ToD interface does not produce an accurate time signal, SO to measure the alignment to this level of accuracy, the ToD needs to be used in combination with the 1PPS. As mentioned in Appendix I of G.8272, there are two aspects that engineers need to be cautious about: The ToD error is more difficult to measure because, unlike a synthesized frequency signal used as an input for many time-testing purposes, it needs a GNSS signal generator. The performance of a PRTC and T-GM depends on the local oscillator characteristics, which vary based on several factors, such as the environment and the aging characteristics of the oscil- lator. The measurements should be taken under similar environmental conditions to those ex- pected at the final location of the PRTC/T-GM. 9.4.1 T-BC and T-TSC ITU-T G.8273.2 specifies the minimum requirements for T-BC and T-TSC time and phase clocks when deployed with full timing support from the network. Refer to the section on G.8273.2 in Chapter 8 for an overview of this and related ITU-T recommendations. Recall that a T-BC combines a slave port and one or more master ports. The slave port is where the input PTP message flow is terminated and used to recover the reference phase and time, whereas the master port is where a new PTP flow is generated from the recovered clock. This renewal of the PTP message flow stops the accumulation of end-to-end PDV in a network. The T-BC/T-TSC also uses physical layer frequency support (generally SyncE) to improve the stability and holdover period. Figure 9-24 illustrates a simple model of a T-BC and T-TSC, indicating the points (refer to the num- bers) that can introduce noise (either externally or from within the clock) and the points where the T-BC can transfer the noise to other downstream clocks in a clocking chain. T-BC /T-TSC Time & (for T-BC only) phase slave master recovery Local oscillator Frequency Frequency (SyncE) (SyncE) Frequency recovery Figure 9-24 Model of T-BC a