[gcb0]

What does it use for time? The spec mentions time in a lot of places, but never defines it. There is even a field to communicate light-time but no mention of how to synchronize anything. I guess this runs on top of another protocol that solves it? Any idea what it is?

[oso2k]

So, it’s been a while since I’ve dived in [0], but “time” as a dependency has been, what I would call, “engineered out of the system”. Instead, there’s concepts of (local) timers, Store-And-Forward Overlays, retries, communication opportunities and the overall realization that time is relative and synchronized time can be difficult at a protocol level when link-level distances are always changing (by miles to billions of miles at a time per communication opportunity).

[0] https://public.ccsds.org/Pubs/720x1g3.pdf