The Sonoma Network Time Server can be easily upgraded with various disciplined oscillators.  For NTP applications, if the reference signal is lost, an oscillator upgrade extends the time that Sonoma can serve Stratum 1 time to your network.  For PTP applications, an oscillator upgrade extends clock stability and PTP timestamp accuracy while tracking the reference signal.  If the signal is lost, then it extends the time that Sonoma can maintain its precision accuracy.