>> >> SB> I think you are saying that you use Unix time, but Unix time >> includes leap seconds by double increment, so I don’t think >> you are using that because that would give you the measurement >> error you are concerned about. I think that what you are using is >> a monotonically increasing time based on the Unix epoch. I think >> that is what PTP (IEEE1588) is using and PTP might be a better >> reference. PTP is likely to become more available in spacecraft >> anyway, since it is finding deployment in precision measurement >> applications. Thus I am not sure I understand why UET is more >> accessible on spacecraft than TAI. Presumably the spacecraft are using >> free-running clocks and so will drift, although I understand that >> work is in progress to provide time sync to spacecraft for >> navigation purposes. >> >> The argument in this section seems long and will become dated. >> Surely all you need to say is that you need a monotonically >> increasing time system such as TAI or UNIX time(), and out of >> software convenience you choose the latter. However I don’t >> think that is what you are actually doing. What I think you are doing >> is using TAI with a free running clock that you accept will drift. >> > > So, when I did the AD review I did raise similar concerns, and the note was > really intended to answer these questions of why the chosen clock rather than > TAI or other clock definitions that would avoid some other issues. I got > enough > good answers to progress, but apparently the motivation part isn't clear > enough > to make you comfortable over the choices.
Hi Magnus I will address the other points in a later email, but on this I am concerned that WG have a misunderstanding of the timebase they are using. UNIX/POSIX time does have leap seconds it just handles them silently so you will get double increments. However since my follow-up note yesterday, I was wondering how the remote remote system knew to add a leap second in order to keep in track with the local system? Isn’t there a risk that the two systems will drift apart as leap seconds are added locally? Also there is the rollover problem to worry about. I think the section needs to go to a specialist group for review such as TicToc/NTP to verify that it works exactly as the WG expect. Best regards Stewart _______________________________________________ Gen-art mailing list [email protected] https://www.ietf.org/mailman/listinfo/gen-art
