Supporting uniformity of implementations

[openBackhaul]

Problem:
The Synchronization modelling is very complex and comprehensive.
There are some ambiguities when it comes to using the defined classes to represent individual synchronization implementations.

Decision during the LF ONMI x-haul call on 3rd of September 2025:
To promote uniformity across the individual implementations of the interface, the following additional notes shall be added to the text at the beginning of the YANG module (which has already been complemented by the decision in issue#61):
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• Every potential clock source must be represented by an LTP of LayerProtocol LAYER_PROTOCOL_NAME_TYPE_SYNCHRONIZATION_LAYER.
• There is a 1:1 relationship between this LTP and the server layer (e.g. LAYER_PROTOCOL_NAME_TYPE_ETHERNET_CONTAINER_LAYER, LAYER_PROTOCOL_NAME_TYPE_AIR_LAYER or LAYER_PROTOCOL_NAME_TYPE_WIRE_LAYER).
• The candidate synchronization sources are represented by FcPorts at the ForwardingConstruct for Selector B.

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The exact position where the three new notes shall be inserted into the existing text is marked with an "X".:

This synchronization model augments the ONF Core Information Model to manage wireless transport devices according to ITU-T G.7721-2018. The following section gives guidance with respect of the usage of the ONF Core Information Model when implementing ITU-T G.8264 Hybrid SDH/synchronous Ethernet SETG Function. The ONF Core Information Model is flexible enough to cover all possible implementations described by Figure A.2.
Recommendation for implementing Hybrid SDH/synchronous Ethernet SETG Function:
- The LogicalTerminationPoints representing a synchronization related termination point are bidirectional.
- The Selectors A, B and C should be represented as ForwardingConstructs with FC-Switches.
- The Selector B and the SETG function should be represented as a single ForwardingConstruct. Note: It is implementation specific, whether the output of the SETG function is represented by 0 or 1 or 2 LogicalTerminationPoints of LayerProtocol LAYER_PROTOCOL_NAME_TYPE_SYNCHRONIZATION_LAYER.
- If Selector A and Selector C are represented as individual ForwardingConstructs, then a LogicalTerminationPoint of LayerProtocol LAYER_PROTOCOL_NAME_TYPE_SYNCHRONIZATION_LAYER must exist representing the output of Selector A and at the same time the input of Selector C.

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- Configuration which are not supported by the device, shall result in ErrorMessages (e.g. Function not supported).
The following section gives guidance with respect of the usage of the ONF Core Information Model when implementing IEEE 1588.
Recommendation for implementing Precision Time Protocol (PTP):
- The LTPs of LayerProtocolType == LAYER_PROTOCOL_NAME_TYPE_PTP_LAYER shall be clients to LTPs of LayerProtocolType == LAYER_PROTOCOL_NAME_TYPE_ETHERNET_CONTAINER_LAYER.