Engineered time synchronisation spanning tree (sync tree) for a given gPTP domain refers to the usage of external port configuration instead of BMCA to construct a desired sync tree with the Grandmaster PTP Instance as the root (see IEEE Std 802.1AS2020, 10.3.1).

One of the advantages of engineered sync trees is to enable a planned, deterministic, and stable configuration of the IEEE Std 802.1AS2020 sync tree for a given gPTP domain, e.g., prevent sync tree changes in case of UAFX Station addition or removal from the network. Working Clock is a use case of the engineered sync tree.

The Grandmaster PTP Instance resides in a dedicated Grandmaster-capable IA-station.

An external sync tree management entity should use the remote management interface described in clause to set up an engineered sync tree.

The following configuration is used for all PTP Ports intended to participate in a gPTP domain using an engineered time synchronisation spanning tree:

  • The externalPortConfigurationEnabled parameter is set to TRUE;
  • The ptpPortEnabled parameter is set to TRUE.

For validation that the computed sync tree configuration can be applied to all PTP Ports intended to participate in the given gPTP domain, the management entity configuring the sync tree will, for example, verify that these ports are up, IEEE Std 802.1AS2020capable, and satisfy topology constraints by checking the following parameters:

NOTE Even if neighbouring PTP Instances do report asCapable, it can be that the link between asCapable neighbouring PTP Instances is not asCapable due to, for example, the wrong setting of meanLinkDelayThresh value. The meanLinkDelayThresh value reflects the estimated propagation delay of the installed link.

The sync tree needs to have the following properties to ensure consistent protocol behaviour and time synchronisation:

After synthesis, the configuration of the gPTP domain and its engineered sync tree may then be applied and validated, for example:

Set Sync message transmission interval uniformly, e.g., default interval.

Set PTP Port states according to synthesis for all PTP Instances.

Check that the syncLocked (see IEEE Std 802.1AS2020, 14.8.52) parameter is TRUE for all PTP Ports of PTP Relay Instances in MasterPort state.