Virtual PTP Port (G.8275 Annex B)

Introduction

Inclusion of a virtual PTP port on a PTP clock. This annexe describes the Virtual PTP port model which is a unidirectional, phase/time interface on a PTP Clock. This can be used to model:

1. An external input signal of the clock (e.g., coming from a PRTC such as 1PPS + ToD)
2. An external output signal of the clock (e.g., going to an end application such as 1PPS + ToD)
3. An internal input (i.e., an input that originates within the node and is not accessible externally) to a PTP clock that is coming from a source outside of the PTP clock's domain
4. An internal output (i.e., an output that originates within the node and is not accessible externally) of a PTP clock that is going to a sink outside of the PTP clock's domain.
5. As an input, the virtual PTP port may be used as a part of the interfaces enabling interdomain interactions as defined in clause 18 of IEEE 1588-2019.

When the Virtual PTP port is associated with an input signal for the PTP clock, it is allowed to participate in the PTP clock and hence participate in the BCMA algorithm.

Virtual PTP Port and LinuxPTP

A working model for virtual Port has been introduced to the Linux PTP forum by SyncMonk technologies in association with Renesas Electronics Corporation. The initial review was raised along the thread "Adding features to support Telecom profile G.8275.2".

This introduces UDS (Unix Domain Socket) used as a virtual PTP port which can be used to achieve the functionality mentioned above. The current implementation uses the virtual PTP port to support APTS where the Announce message coming from PRTC is redirected to the PTP4L instance using the virtual PTP port and hence participates as an input port to the BMCA. Then BMCA can determine the Best Master Clock selection based on the Priorities configured and hence can ignore the inputs from Ports when it get synchronized with PRTC.

High Level Design Overview

Parameters Supported by Virtual Ports

All parameters are not supported by the virtual PTP port. The parameters grouped as locally set are not transmitted across the virtual PTP port but are set internally by the receiver of the virtual PTP port information

Time Properties data set would be derived from the external time interface (i.e., GNSS receiver)

The Grandmaster clock quality would be derived from the external time interface (i.e., GNSS receiver).

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