Depending on the installed modules and the selected synchronization sources, the 4U rackmount LANTIME M4000 can play different roles. By supporting multiple input sources utilizing Meinberg‘s IRSA (Intelligent Reference Switching Algorithm) technology, the M4000 accepts GPS, GLONASS, PTP, NTP, SyncE, 1PPS or E1/T1 as possible synchronization inputs to be able to act as an Edge Grandmaster Clock. IRSA is useful to bridge potential GNSS outages or, if desired, completely avoid depending on GPS/GLONASS availability. A highly stable oscillator ensures a holdover period of several hours or days depending on the target application even if no synchronzation source is available anymore. Using an external PRC allows to extend the holdover capabilities to whatever level is required at a certain point in the network.