These network nodes also need to support SyncE or eSyncE clock definition according to ITU-T G.8262 or G.8262.1. However, the DU or RU is not mandated to use the SyncE frequency source to achieve its own frequency synchronization and instead may use only PTP to achieve fre- quency as well as phase synchronization. Network Time Error Budget Analysis: Summary In the three preceding scenarios, when the local PRTC/T-GM is deployed at the DU or RU, the local PRTC/T-GM becomes the primary source of the timing signal. A network PRTC/T-GM located in the back-haul network can be used as a backup timing source to maintain timing alignment during any local PRTC failure. Because the CU does not require a stringent timing requirement, there is no specific timing error limit defined for the CU. However, the CU requires a normal level of system alignment with UTC for purely operational reasons. One need would be to allow the network engineers to perform fault isolation by correlating timestamped entries in error logs from all systems in the network. Another use is that the CU may require UTC time for reasons related to cryptography, such as certificate validation. For further reading, ITU-T G.8271.1 defines a reference architecture and network model with net- work limits made up of T-BC and T-TSC clocks with Class B or Class C performance from G.8273.2. These devices are used to carry the timing signal to the RAN across the back-haul net- work or between the DU and RU in the front-haul network. 10.5.1 Synchronizing the Virtualized DU The virtualized DU (vDU) is designed to be deployed on x86-based commercial off-the-shelf serv- ers. As shown in Figure 10-36, the server accepts the ability to plug network interface cards (NIC) into the PCIe slots with timing capabilities built into the card. These (Ethernet) interfaces can be used for mid-haul or front-haul connectivity. Timing sync between NICs PRTC/T-GM PRTC/T-GM PCle timing NIC PCle slot PCle timing NIC PCle timing NIC acceleration NIC PCle slot acceleration NIC PCle slot a) 