Abstract: SpectraTime is a space clock manufacturer of Rubidium Atomic Frequency Standard(RAFS) and passive hydrogen maser(PHM) for various navigation systems(European,Chinese and Indian) and other space programs.Both technologies have now flight heritage of several years through Galileo in-orbit validation element(GIOVE) experimental satellites which have been flying since Dec.2005 and Apr.2008 or through Beidou.This paper describes for both SpT space RAFS and PHM the on-ground performances in large unit quantity and life-time tests,as well as onboard achieved clock performances.Based on these results a short overview of the ground GNSS timing segment with its atomic clocks and associated algorithms will be given.With those elements in hands,a short presentation of novel onboard techniques to generate highly robust timing signal directly from the satellite onboard one clock ensemble(ONCLE) will be concluded.