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

[Scott Burleigh]

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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