Passive port monitoring

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The optional feature of Passive Port Monitoring (PPM), as defined in Annex G of ITU-T G.8275.1, has proven to be a valuable asset in the operation of synchronization networks.

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PPM can be used to monitor the Precision Time Protocol (PTP) phase/time difference between the passive port and the slave port of T-T-BC /T-TSC nodes and can furthermore be used for the following use cases:

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*. Measuring and compensating for asymmetry in network nodes

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*. Monitoring and comparing the PTP phase/time difference between different clock sources throughout the network

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*. Continuously measuring the PTP phase/time difference between ports on a given T-BC /T-TSC node from upstream time sources to help identify devices that might impact the clock quality.

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In this test, we verified two scenarios involving PPM, where an Impairment Device introduced asymmetry, enabling us to observe an offset with PPM.

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In the first scenario, Telecom Boundary Clock-1 (T-BC-1) was directly connected and locked to the Telecom Grandmaster (T-GM). Telecom Boundary Clock-2 was also locked to the Telecom Grandmaster; however, with an impairment device, the Calnex SNE Ignite, in between. If the Keysight Time Sync Analyzer was used as an emulated T-GM, then the output of the emulated T-GM was impaired directly without an external impairment device.

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540 nanoseconds (ns) of delay asymmetry was introduced initially, then changed to -300ns for the second stage.

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T-BC-1 and T-BC-2 were also physically connected, with the port on T-BC-2 acting as a master to T-BC-1 and the port on T-BC-1 configured for PPM.

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This test was conducted with five different combinations, all of which passed. All T-BC-1s were able to measure the +270ns and -150ns offsets due to the delay asymmetry.

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[[Figure 117: Passive Port Monitoring - Setup>>image:434080470783754241_5.11.png||alt="Figure 117" width="550"]]

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For the second scenario, T-BC-1 was directly locked to the GNSS and used it as its primary reference instead of the T-GM. T-BC-2 was still locked to the T-GM with an impairment device, the Calnex SNE Ignite, in between, once again introducing 540ns/-300ns of delay asymmetry. If the T-GM was emulated by the Keysight Time Sync Analyzer, then once again no external impairment device was used, as the impairment was introduced by the emulated T-GM.

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The connection and relation between T-BC-1 and T-BC-2 did not change when compared to the first scenario; T-BC-2 still had a master port towards T-BC-1 's PPM port.

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This test was conducted in three different combinations, which all once again passed, as all T-BC -1s were still able to measure the +270ns and -150ns offset due to the delay asymmetry.

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[[Figure 118: Passive Port Monitoring based on GNSS input - Setup>>image:434080470783819777_5.12.png||alt="Figure 118" width="550"]]

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|=GM-A|=T-BC-1|=T-BC-2|=Impairment device|=Timing Test Equipment

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|Keysight Time Sync Analyzer|H3C S12500R-48Y8C|Ericsson Router6671||Keysight Time Sync Analyzer

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|Keysight Time Sync Analyzer|Juniper ACX7100-32C|Arrcus S9600-72XC||Keysight Time Sync Analyzer

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|Keysight Time Sync Analyzer|Ericsson Router6671|H3C S12500R-48Y8C||Keysight Time Sync Analyzer

Table 68: Passive port monitoring - Passive port monitoring option as per ITU-T G.8275.1 Annex G

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|=GM-A|=T-BC-1|=T-BC-2|=Impairment device|=Timing Test Equipment

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|Keysight Time Sync Analyzer|Ciena 5134|Arrcus S9600-72XC||Keysight Time Sync Analyzer

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|Keysight Time Sync Analyzer|Ericsson Router6671|H3C S12500R-48Y8C||Keysight Time Sync Analyzer

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Table 69: Passive port monitoring - Passive port monitoring with an GNSS input option as per ITU-T G.8275.1 Annex G

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