When sourcing a GPS NTP Server, you must prioritize timing accuracy and oscillator stability. Look for devices offering accuracy within 1-10 microseconds relative to UTC. The internal oscillator is critical; OCXO (Oven Controlled Crystal Oscillator) is preferred for high-stability requirements to maintain time during GPS signal loss (holdover), while TCXO (Temperature Compensated Crystal Oscillator) is suitable for standard applications. Additionally, ensure the device supports multiple GNSS constellations (GPS, GLONASS, Galileo, Beidou) to guarantee signal redundancy.