Time Synchronization Source Failover

In real-world deployments, redundancy and recovery mechanisms are essential to ensure accurate time synchronization is maintained should one of the time synchronization sources fail.
This test aims to evaluate the time error measured at the output of each Telecom Boundary Clock after the primary time synchronization source/Grandmaster fails and a switch-over to the secondary Grandmaster is initiated.

For this test, all the Boundary Clocks were directly locked to both Grandmasters (GMs); GM-A served as the primary GM and GM-B as the backup GM; for this, all BCs had local priorities configured to prioritize and lock to GM-A on PTP and SyncE. Two different Microchip TimeProvider® 4500 were used as GM-A and GM-B.
We executed two different scenarios for this test, once with Microchip’s Sync-Only Redundancy feature enabled between both T-GMs. In the Sync-Only Redundancy feature, the two T-GMs are synchronized to each other and GNSS reference. We then simulated a “fiber cut” by disconnecting all the physical T-BC connections to T-GM-A to initiate the failover to T-GM-B; after a measurement period of 1000s including the failover, the measurement was restarted and all cables were reconnected to T-GM-A, initiating a switch back to T-GM-A from all T-BCs on PTP and SyncE.

For the second run, we disabled the Sync-Only Redundancy feature on the GMs and disconnected the GNSS from GM-A, causing the BCs to switch to GM-B; after measuring for 1000s including the failover, the measurement was restarted and the GNSS connection to GM-A was re-established, and all BCs locked back to GM-A on PTP and SyncE.
The Calnex Paragon-Neo PAM4 and the Keysight Time Sync Analyzer were used to measure the PTP and SyncE output of all the BCs.

In both runs, a two-way time error threshold of the Class level of accuracy 6B was set, which is, as per ITU-T G.8271, +/- 130ns, but all BCs even passed 6C, which is defined as +/- 65ns.
For the MTIE, the ITU-T G.823 E1 SEC wander limit mask was applied as the threshold throughout all procedures and switchovers, which, once again, all BCs easily passed.