n is that to maintain time alignment even within the network-wide limit of 1.5 us for an hour requires an OCXO, and if 24 hours is needed then you might need a super high stability, double- oven, OCXO-available, costing over $200! Therefore few O-RAN equipment vendors will be willing to put anything close to a 24- hour holdover capability into their equipment, though it is often listed as a requirement early Chapter 8 Synchronization in open radio access networks 305 in the design phase before reality sets in. However, does O-RAN really need such a holdover level? The answer is almost certainly not, for a number of reasons: If the network time source itself is SO important, why not have a backup in case it fails? PTP allows for multiple Grandmasters and it is not unreasonable to expect such a backup to be available. Therefore it might be that protection against the time source failing is already available. If the network time source fails and I also have SyncE, will that fail too? In a typical network it would not, since the node driving the SyncE link will have its own frequency holdover, meaning that the SyncE clock might degrade but it will still in general be more stable than the local oscillator over an extended period. This allows a PTP + SyncE slave to use something called time holdover-where it no longer receives continual time information over PTP, but still has a good enough physical-layer clock from SyncE to keep its local time accurate for long enough without a super stable local oscillator. If the sync failure is due to the network connection to the device itself failing, for example, the fronthaul link between the O-DU and O-RU, is the fact that sync has been lost really a problem? The sheer fact that the data link itself has failed presumably means that the O-RU can no longer perform a meaningful function, with or without sync. It may as well just turn off the radio portion until service is restored. Hopefully, a nearby O-RU in this case can absorb the extra demands on it without degrading the perf