The navigational equipment on the aircraft has to be capable of steering the aircraft within 10NM of the airway 95% of the time spent in an airspace where no valid radio update is available.
The airline I fly with, the required operative eqpmt to fly in the RNP 10 airspace, consists of:
-2 FMSs
-2 IRSs
-2 MCDUs
-2 NDs with MAP information.
Aircraft not fitted with GPS have a time limit for the 10NM capability, either based on the initial system alignment or from the last valid radio update.
Hope this helps a bit.
Cheers