[Sis-ams] consistent "time-zone"?

[Ray, Timothy J. (GSFC-583.0)]

Sounds good.  Thanks Scott!

 

________________________________

From: sis-ams-bounces at mailman.ccsds.org
[mailto:sis-ams-bounces at mailman.ccsds.org] On Behalf Of Scott Burleigh
Sent: Thursday, September 04, 2008 5:16 PM
To: sis-ams at mailman.ccsds.org
Subject: Re: [Sis-ams] consistent "time-zone"?

 

Ray, Timothy J. (GSFC-583.0) wrote: 

Dear WG members,

 

When using time-tags in other protocols, we've run into problems when
multiple locations each use their own "local time" - e.g when it's 8am
at JPL it's 11am at Goddard, and maybe 5pm in England.  So, typically
Greenwich Mean Time is specified. 

 

May I suggest that we insert a note in the vicinity of table 5-1 (the
MPDU header format) that says something like this:   "We recommend that
the value of the time-tag be consistent with Greenwich Mean Time if
practical"     or     "In the absence of any overriding agreements, all
time-tags shall use Greenwich Mean Time".

 

Of course, there may be scenarios where it is impractical/impossible to
know the time on Earth.  So, let's not be too authoritative, but it
seems worthwhile to make the spec a little tigher.

I think we're actually okay on this already, Tim.  The spec says we're
using standard CCSDS unsegmented time codes with preambles, and the only
standardized time code defined in the Time Code Formats spec is 1958
January 1 epoch (TAI).  Two AMS implementation could have a private side
agreement to standardize on some other epoch, but the only way for an
AMS implementation to be certain of being interoperable with every other
AMS implementation is for it to use that 1958 epoch time.  And that time
is defined to be TAI, which is just a few leap seconds away from UTC,
which is essentially GMT -- so I think this is already as tightly
defined as we can make it without deviating from the CCSDS time
standard.

Scott

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