ormance of the cellular network too much during the outage. Therefore in reality, there tends to be a disconnect between the holdover capabilities that are initially stated as a "must have" requirement and what typically gets deployed once a more detailed analysis of design complexity and cost has been completed. Unraveling the standards spaghetti No discussion of synchronization would be complete without a look at the various standards bodies that are involved in defining the standards that govern the network and equipment requirements, and how these all interact. When it comes to O-RAN synchronization, there are four parties defining these requirements: 3GPP-The owners of the overriding standards controlling each generation of cellular equipment. They are the ones responsible for ensuring that end equipment, such as handsets, from any vendor can communicate on networks that are themselves made up of equipment from a number of different suppliers. 3GPP's focus is primarily on defining the air interface between the network and the user equipment, and these definitions include the synchronization requirements as seen at the air interface. IEEE-The Institute of Electrical and Electronics Engineers handles standardization across a broad range of topics. Two of these standards are particularly relevant to O-RAN. One of them is, of course, IEEE 1588, which defines the PTP itself. As already discussed, when 306 Open Radio Access Network (O-RAN) Systems Architecture and Design O-RAN talks about "1588" it is typically referring to the IEEE 1588-2008 version of the standard, which is not backward compatible with the earlier IEEE 1588-2002 flavor. The newer IEEE 1588-2019 version is, however, backward compatible with the 2008 variant and it is expected that over the coming years, more features from the 2019 version will be added to PTP implementations, and at some point, it might be that a future version of O-RAN calls for some of these features. The second IEEE standard that is relevant to O-RAN is IEEE 802.1CM-2018, whic