AMSS protocols
Well spotted JoBloggs2.
That material made it into ICAO Annex 10, Volume III in more-or-less that form. Now I think it has been moved into an ICAO manual which forms and appendix or some-such to Annex 10. It is based on the Inmarsat specification as outlined in their System Definition Manual for their aeronautical service. It should be mandatory bedtime reading for those commenting on satcom matters on this site.
Interestingly, the so-called "pings" will probably contain information pertinent to the investigation, such as class of log-on (high gain, low gain etc.) which will indicate whether the aircraft antenna was pointing at the satellite and which in turn will indicate the status of the FMS.
All good stuff.