T-BC Interworking Protocol and Performance

In production networks, there might be special cases and exceptions for which using Full Timing Support (FTS; ITU-T G.8275.1) throughout the entire network is not an option, and using Partial Timing Support (PTS; ITU-T G.8275.2) for the entire network is also not desirable.
In such cases, it is necessary to configure both PTP profiles in the same network, requiring a Boundary Clock (T-BC) to be able to translate between the two profiles while complying with each profile's specifications. Such capability is known as an Interworking Function, IWF.

These tests, therefore, aim to validate the ability of the Boundary clocks to translate from FTS to PTS and from PTS to FTS.
     
For all these test cases, the Microchip TimeProvider®4500 was acting as the Telecom Grandmaster (T-GM), sending either FTS traffic or PTS traffic downstream to T-BC-1. The Calnex Paragon-Neo PAM4 and the Keysight Time Sync Analyzer were used as the measurement tools.
We had six different Telecom Boundary Clock (T-BC)/Telecom Slave Clock (T-SC) combinations for the FTS to PTS tests and seven different T-BC/T-SC pairs for PTS to FTS, with the T-BCs taking the role of the interworking translation from FTS to PTS/PTS to FTS.

For the ITU-T G.8275.1 to ITU-T G.8275.2 (Full Timing Support to Partial Timing Support), the T-GM provided ITU-T G.8275.1 traffic towards the T-BC. The T-BC then translated FTS traffic to PTS traffic and sent it to the T-SC, where its output was measured.
For the ITU-T G.8275.2 to ITU-T G.8275.1 (Partial Timing Support to Full Timing Support), it was the opposite way; The T-GM sent PTS traffic to the T-BC, which translated the traffic to FTS and sent it towards the T-SC, where the output was once again measured.
     
For the limits of both test cases, we applied the constant time error (cTE) Class C limits for the FTS T-BCs, as defined in ITU-T G.8273.2, and Class B limits for the PTS T-BCs, as only Class A and Class B are specified for PTS T-BCs in ITU-T G.8273.4, section 8.2.2, table 8-1. Class C cTE is defined as +/- 10 nanoseconds (ns), and Class B cTE is defined as +/-20ns, giving us an accumulated total limit of +/- 30ns for the IWF network.

All ITU-T G.8275.1 to ITU-T G.8275.2 and ITU-T G.8275.2 to ITU-T G.8275.1 test combinations passed this year, proving that a network's time synchronization performance should not be heavily impacted by the interworking function of the two different PTP profiles.