Timing is very critical for Radio Access Network (RAN) for error free packet delivery to the Mobile devices and controlling the inter-site interference by keeping SFNs, Transmission and reception in sync. In 4G, traditional RAN usually a BBU(Baseband Unit) or DU (Digital Unit) is equipped with a GPS antenna port to meet the timing and synchronization requirements and all the Cell Site remain sync with GNSS.
While moving to Open RAN or Virtual RAN (vRAN) the DU is not more proprietary hardware, everything is moving to COTS hardware or Cloud Infrastructure. These Cloud based or COTS based hardware usually do not have local source of Timing & Synchronization (e.g. GPS) although may have Hardware Clock (PHC ) which requires timing correction regularly and use a network based Timing Source e.g. IEEE 1588 PTP.
Continue reading article here: Telco Cloud Infra Timing Application - ptp4l, phc2sys and pmc - Techplayon