IEEE Std C37.238-2017 pdf download – IEEE Standard Profle for Use of IEEE 1588™ Precision Time Protocol in Power System Applications.
3.1 Defnitions absolute time: Time maintained by the international standards laboratories that form the basis for the International Atomic Time and Coordinated Universal Time timescales. boundary clock (BC): A clock that has multiple Precision Time Protocol ports in a domain and maintains the timescale used in the domain. It may serve as the source of time, i.e., be a master clock, and may synchronize to another clock, i.e., be a slave clock. (IEEE Std 1588-2008) clock: A device participating in the Precision Time Protocol (PTP) that is capable of providing a measurement of the passage of time since a defned epoch. (adapted from IEEE Std 1588-2008) NOTE—In the case of PTP ordinary and boundary clocks that are properly synchronized, the epoch is the epoch of the timescale in use. In the case of PTP transparent clocks, the epoch is locally defned and not necessarily aligned with the timescale. 6 default: When applied to attribute values and options means the confguration of a Precision Time Protocol device as it is delivered from the manufacturer. (IEEE Std 1588-2008) device time inaccuracy: Time inaccuracy evaluated or measured between the time signal at the input of a device and the time signal that this device generates. (IEC/IEEE 61850-9-3:2016) NOTE 1—Device time inaccuracy includes the uncertainties in the computation of the path delay assuming an ideal Pdelay_Resp from an upstream neighbor, and the uncertainty introduced in responding to an ideal Pdelay_Req from a downstream neighbor. NOTE 2—This defnition applies to transparent clocks, boundary clocks, and media converters.
epoch: The origin of a timescale. (IEEE Std 1588-2008) grandmaster-capable: Ordinary clock or boundary clock that is able to take the role of a grandmaster. (IEC/ IEEE 61850-9-3:2016) NOTE—A grandmaster-capable clock is not necessarily connected to a recognized standard time source. grandmaster clock: Within a domain, a clock that is the ultimate source of time for clock synchronization using the protocol. (IEEE Std 1588-2008) grandmaster time inaccuracy: Time inaccuracy evaluated or measured between the reference time signal at the input of a grandmaster clock and the time signal(s) that the grandmaster generates. (IEC/IEEE 61850-9-3:2016) NOTE—Grandmaster time inaccuracy includes the uncertainty introduced in responding to an ideal Pdelay_Req from a downstream neighbor. holdover: A clock previously synchronized/syntonized to another clock (normally a primary reference or a master clock) but now free-running based on its own internal oscillator, whose frequency is being adjusted using data acquired while it had been synchronized/syntonized to the other clock. It is said to be in holdover or in the holdover mode, as long as it is within its accuracy requirements. (adapted from IEEE Std 1588-2008)