1636 BC forwarding of obsolete information
Created: 02 Nov 2018
Status: Discussion (red)
Part: Part 9-3 (Precision Time Protocol Profile)
Category: Issue for edition 2 of this part
IEEE 1588 requests that a BC forwards the Announce messages from its master without modification (except for stepsRemoved).
Since each BC in a chain delays the Announce messages on the average by half the Announce interval, BCs down the chain receive Announce messages with possibly obsolete information.
In some cases, a BC can dispose of a better actualized information as the one it received.
In particular, a BC can predict the insertion of a leap second and could refrain from announcing a leap second when the leap second has already been inserted.
It could also insert its own inaccuracy, so other could use it for the BMCA.
Three proposals have been submitted to P1588 to address the issue:
1. a 1588-2008 BC has only one Timeproperties Dataset, however the information on the slave side can be different from the information on the master side and both can be different from the value in Announce messages. This should be clarified.
2. If a BC is allowed to forward obsolete information, a slave clock that is switched on after an event should be able to reconstruct that the information is obsolete, but the Announce message is not obliged to have a time stamp. In this case the time stamp field should be filled an a value at least accurate to one second.
3. A BC should not forward obsolete information when it disposes of newer
Depending on what IEEE P1588 decides, 9-3 has still the option to define an own option. P1588 is not interested in improving the UTC clock.
||12 Nov 18
||12 Nov 18
This is for information only until WG P1588 decides on what to put into 1588-201x.
|09 Nov 18
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