Now it's been stated that the GNSS systems can update the IRS/INS.
But what about DME/DME or VOR/DME, in case the GNSS is being "offset" or is unavailable... or will the system stay on the IRS/INS until an update is commanded, and then use the groundbased stations for updating reference?
Or is the FMS constantly checking IRS/INS versus all other sensors?
Edit: RNAV