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December 2016

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From:
Curtis Schroeder <[log in to unmask]>
Reply To:
SAC-PSG-CIGI <[log in to unmask]>
Date:
Thu, 22 Dec 2016 08:17:11 -0500
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The use of NTP/PTP was proposed in Section 4.1 Shared Time Base of the CIGI Best Practices document (SISO-REF-046-00v1-0-d03). This was based on my own experiences years ago where a (proprietary) high precision clock sync was implemented between the sim host and IG via SCRAMNet. The CIGI time stamp from the sim host was generated by the equations of motion module so second order extrapolation on the IG could be used to compute the temporal offset just prior to putting the entities into the render pipeline. This worked very well for 60 Hz async CIGI entity control including close formation flying.

I have not had the opportunity to revisit this use case using NTP/PTP, but the reading I've done suggests that for an isolated LAN connecting a sim host and IG the use of NTP may be sufficient. The past drawback to PTP was the lack of free software implementations for the Windows OS, but this may have changed since I last reviewed the available PTP solutions. The potential advantage of PTP is its ability to work beyond a single isolated LAN when interconnecting a distributed simulation environment.

GPS time sync is also a possibility, but more costly due to the need for GPS receiver hardware and building antennas. This is likely best reserved for widely distributed simulations.

Anxious to know how you progress with this, Roland, so we can update the Best Practices document accordingly.

Best regards,

Curt

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