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December 2016

SAC-PSG-CIGI@DISCUSSIONS.SISOSTDS.ORG

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Subject:
From:
Roland Humphries <[log in to unmask]>
Reply To:
SAC-PSG-CIGI <[log in to unmask]>
Date:
Thu, 22 Dec 2016 17:34:19 -0500
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The implementation I already have seems to give a relatively stable host clock on the IG. The issue with NTP I understand is that it can take quite a long time to settle and PTP relies on NIC hardware timestamps which windows doesn't support (at least by default). My current implementation is however susceptible to network delays as it assumes transport delay between pushing the message on the host and receiving it on the IG is negligable (ok with UDP and low bandwidth but not so for TCP) and there is no compensation for that (i.e. it always assumes most recent is best).
For me a special case synchronised simulation clock makes more sense than relying on something like NTP / PTP as I doubt that is required for most systems (and a custom clock can resolve much quicker without worrying about affecting OS functions), all you need to know in the IG is how to calculate simulation time T for any given frame.
I have previously implemented a separate simple UDP based simulation clock sync to do this (which might still be the best approach) but was hoping it might be possible to account for most of the delay within the CIGI implementation itself (by adding the data age).

Should this discussion tend more towards deciding if this kind of feature should be within the scope of CIGI or in the best practice guide) and then what the best implementation (or range of implementations) could be?

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