Delay Asymmetry DetectionMeasurement

Controlling and handling asymmetric delay on links that carry PTP messages is of the utmost importance and is one of the big challenges for network time synchronization.
This test was performed in four different combinations. The setup consisted of one Grandmaster (either real or emulated), whose link towards Boundary Clock-1 is impaired; if an emulated T-GM was used, like the Calnex Paragon-Neo PAM4 and Keysight Time Sync Analyzer, then the impairment was provided directly by the emulated T-GM; if a real T-GM, the Microchip TimeProvider® 4500 was used, then an external impairment device, the Calnex SNE Ignite, was used.
T-BC-1 is initially directly connected to a GNSS reference and Boundary Clock-2 (T-BC-2), which is connected to a time error measurement device (Calnex Paragon-Neo PAM4 or Keysight Time Sync Analyzer).
In three of the four combinations, PTP profile ITU-T G.8275.2  was used throughout the entire chain; in the fourth combination, the interworking function (IWF) from PTP profile ITU-T G.8275.2  to ITU-T G.8275.1  was used between T-BC-1 (Ciena 5134) and T-BC-2 (Juniper PTX10002-36QDD) and the connection between T-BC-2 and the time error measurement device was done over an 800G link.

At first, the GM and T-BC-1 were connected to the GNSS, and T-BC-2 used T-BC-1 as its primary time source. The GNSS was then disconnected from T-BC-1; T-BC-1 then locked onto the GM as its new time source, with the link between the GM and T-BC-1 being impaired by introducing an asymmetric delay of 500ns. During this process, the time error was measured on T-BC-2, and none of the measurements reflected the 500ns asymmetry, proving that all T-BC-1s could detect and eliminate the asymmetry.
The network passed the class accuracy level of 6 for all test runs, as per ITU-T G.8271, throughout the entire test run, including the switchover; the first three test runs, which used PTP profile ITU-T G.8275.2 throughout the entire chain all passed class accuracy level 6C. The IWF test run passed the class accuracy level of 6A.

These results are remarkable and a big victory for Time Synchronization. They prove that asymmetric delays can very well be handled, beating one of the big challenges of Time Synchronization.