1459   Boundary Clock startup

Created: 27 Oct 2015

Status: Future Improvement

Part: Part 9-3 (Precision Time Protocol Profile)

Links:

Page: 14

Clause: 7.6

Paragraph:

Category: Issue for edition 2 of this part

Issue

In the IOP of Brussels, it appeared that Boundary Clocks need up to one minute to reach the required accuracy. As solution, two methods were proposed:
1) Delay sending of Sync and Announce during start-up (but this delays the startup of the next BC)
2) Consider the variance of the BC in the BMCA. To this effect, a BC should add its own variance to that of the grandmaster.

Proposal

IEEE P1588 is asked to draft a solution, since this is a 1588 issue, not a IEC 61850-9-3. A request has been filed to P1588 (attached).
Implementers are therefore advised that calculating the variance in the BCs should be foreseen, as well as the possibility that the Announce message be modified, which also would affect cyber-security (recomputing of the checksum).

Discussion Created Status
Since this is a 1588 issue, not an IEC/IEEE 61850-9-3 profile specific issue, this Tissue is put "on hold" until the IEEE 1588 revision is published and/or implementation experience is available. 13 Feb 18 Future Improvement
We should gain some implementation experience from IEEE1588 draft revision (P1588/D1.2, Ballot-2 2017 V2.01). For example, section 7.6.2.1 General requirements and option i.e. "holdoverUpgrade" before made any profile specific changes. 30 Jan 18 Ballot Period
Since 1588 did not react, AG10 has to solve it itself. 19 Jan 18 Ballot Period
The standard should indicate when a boundary clock in holdover should clear the "traceable" flag and declare itself a grandmaster. In principle, a clock is traceable as long as it can estimate its deviation from a primary time reference, in particular, track the leap seconds. A Rubidium clock can be in holdover for weeks.
Also, a Boundary Clock that took over as grandmaster and then recovers the primary signal should not immediatly take over the grandmaster time but smoothly smear into the grandmaster time until it reaches a sufficient accuracy and then declare itself a slave to the grandmaster. The objective is to avoid time jumps at the slave, but nevertheless allow different slaves to know by how much their reference differ. 		19 Jan 16 Triage

 

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