Class C and D Telecom Boundary Clocks (T-BCs) are essential for meeting the tight time-synchronization requirements of today’s highly time-sensitive networks, such as 5G.
ITU-T G.8273.2 defines several metrics and clear requirements for class C T-BC clocks. In contrast, for Class D, only one requirement is currently specified in ITU-T G.8273.2, section 7.1, table 7-2: a low-pass filtered maximum absolute time error (max|TE_L| ≤ 5 ns).
The performance of devices tested this year has improved once again compared to previous years.
Every T-BC tested remained well within the Class D performance limit (max|TE_L| ≤ 5 ns).
This year, few Class C Conformance tests were conducted because almost every device was already compliant with Class D Conformance, leaving little incentive to test for Class C Conformance. However, all devices that executed the Class C Conformance test were also compliant.

Both test scenarios used an emulated Telecom Grandmaster (T-GM) and an emulated Telecom Time Synchronous Clock (T-TSC), both of which were either the Calnex Paragon neo, Calnex Paragon neo-A, Calnex Paragon neo-S, or the Keysight Time Sync Analyzer, with the T-BC under test positioned in between. These tests were conducted with either 10 or 100 Gigabit Ethernet (GbE) links, or, in two cases, even 800 GbE links.
Although these were not interoperability tests, they were crucial because the clocks had to achieve either class C or class D qualification before being allowed to participate in further testing.

Table 62: ITU-T G.8273.2 - Telecom Boundary Clock Class D Conformance - 10 GbE

Table 63: ITU-T G.8273.2 - Telecom Boundary Clock Class D Conformance - 100 GbE

Table 64: ITU-T G.8273.2 - Telecom Boundary Clock Class D Conformance - 800 GbE

Table 65: ITU-T G.8273.2 - Telecom Boundary Clock Class C Conformance - 10 GbE

Table 66: ITU-T G.8273.2 - Telecom Boundary Clock Class C Conformance - 100 GbE