00 1 500 2 000 3 000 5 000 Elapsed Time (s) Figure 12-16 Example of a Network Phase Time Error Test The max TE value of the measured TE is 61.5 ns with a peak-to-peak variation of 40 ns. An addi- tional metric that is interesting is the combined cTE from the chain of T-BC clocks. For example, there is a chain of five Class B T-BC nodes with 20 ns of cTE each, then the cTE could be calcu- lated to ensure the cTE is less than 100 ns (5 times the G.8273.2 limit of 20 ns). In the case in Fig- ure 12-16, the cTE (averaged over 1000 s) varied between -52 ns and -31 ns after having passed through four (Class B) T-BCs. It is probably no surprise that this is one of the most commonly executed test cases, mainly because all engineers want to know how accurately their design carries time. Many engineers also like to know how much margin they have between the measured phase error and what their budget is. Figure 12-17 shows the 1PPS phase alignment of the previous network when the last router before the tester is placed into holdover. Because this is a network test, once again the appropriate threshold limit is the 1.1 us network limit from G.8271.1. As in the preceding examples, this cap- ture comes from the CAT reporting tool and the Sentinel tester (this time measuring 1PPS). Phase Test Holdover c 1pps TE Absolute Date 2020-10-14 Fie channelC. Offse Removal Applied False Zaro Offset 127ns 1 500 Threshold C 1pps TE Absolute 4429, Y: 15.5 -1 000 X: 66919.069 Y: -1105.993 -1 500 -2 000 -2 500 10000 20 000 30 000 40 000 50 000 60 000 70 000 Elapsed Time (s) Figure 12-17 Example of a Network Phase Holdover Test In this case, the PTP and SyncE signals were removed from the test node after 4429 S into the test, and the TE crossed the limit at about 66,900 S (just over 17 hours later). Perhaps it is slightly lucky, but this is a very good result for a (very recent model of) network element with a stratum 3E OCXO running in holdover (it is only testing the holdover capabilities of the last T-BC router in the net- work because the 