It's actually exactly what you described - the documentation is very sparse on it because it's an internal thing (I'm guessing you found the CASC documentation,

It's actually exactly what you described - the documentation is very sparse on it because it's an internal thing (I'm guessing you found the CASC documentation, not the NGDP one). If you're interested, shoot me an email and I can send you some more details; but it'd simply be for intellectual curiosity, as I said it's an internal protocol.