nterfaces Transient response: The response of a clock following the rearrangement of either the physical frequency (SyncE) or the PTP packet timing source signals Holdover: The maximum deviation in the PTP and 1PPS output signal during the loss of the PTP packet timing signal and/or physical layer frequency inputs The section "Testing Timing" in Chapter 12 deals with the measurement and validation of these be- haviors and limits by testing timing equipment and networks. This is not functional testing but test- ing to confirm that the equipment meets those specific timing metrics, SO it involves using special- ized time testing equipment. This testing is of value to the engineer who wishes to confirm that the chosen equipment is suitable for their deployment case. Chapter 8 covered the recommendations that apply to measuring clock performance. For the PTP packet phase/time case, G.8273.2, which covers the boundary and slave clock performance, is one of the most important recommendations. And from that specification, timing designers consider noise generation to be the most important parameter when building a timing solution. For noise gen- eration performance, G.8273.2 divides the levels of performance into classes (currently A to D) based (mostly) on the results of that test. Table 9-3 shows the main noise generation time error (TE) values used in G.8273.2 to determine the class of performance for a T-BC or T-TSC clock (note that this is not the full set of values for noise generation). Table 9-3 G.8273.2 Performance Characteristics for Noise Generation Parameter Class A Class B Class C Class D Max absolute TE (max(TE|) 100 ns 70 ns 30 ns 5 ns (low-pass) Constant TE (cTE) +50 ns +20 ns +10 ns For further study Dynamic TE (dTEL) 40 ns 40 ns 10 ns For further study Source: ITU-T G.8273.2, Tables 7-1, 7-2, 7-3, and 7-4 dTEL is the MTIE result measured through a first-order low-pass filter (LPF) with bandwidth of 0.1 Hz at constant tem- perature. The class D max|TH is also specified after having passed through an LPF