d over Ethernet, nFAPI is a packetized version of the FAPI interface, defined as (but not limited to) an environment where the L2/L3 stacks are implemented as a Virtual Network Function (VNF) on a server environment and the Physical Layer is implemented as a Physical Network Function (PNF) on dedicated hardware. The nFAPI implementation allows the L2/L3 and Physical Layer components to "speak" FAPI to each other but through two translation layers (FAPI->nFAPI and nFAPI->FAPI). Zooming in on the key FAPI interface (P7), we note some differences: FAPI uses a SLOT.indication message sent from the PHY at the start of every slot (125/ 250/500/1000us). This message is not used in nFAPI as the jitter in the fronthaul connection between VNF and PNF prevents this message from being a suitable mechanism for signaling a slot interval. Independent timing for the two components through GPS/IEEE1588 or other mechanisms are used instead for establishing time, and the PHY sync procedure combined with API message timing is used for slot level communication. The SFN/SL FAPI procedure does not apply in nFAPI. PHY synchronization and delay management mechanisms are used for synchronization and timely messages between VNF and PHY instances. API message timing is achieved as follows: the nFAPI messages from VNF to PNF must arrive at the Physical Layer instance a minimum Timing Offset before the slot 204 Open Radio Access Network (O-RAN) Systems Architecture and Design P7 <msg> too early P7 <msg> in time P7 <msg> too late for slot S for slot S for slot S Slot S Timing Window <msg> Timing Offset "early arrival" "late arrival" for timing info for timing info report report FIGURE 5-13 Timing window management. they are configured starts transmission on the air interface as shown in Fig. 5-13. If the downlink transmit request misses this window, the Physical Layer would not have sufficient time to execute it's functions and transmit over the air interface. This is obviously not desired. As such, if the nFAPI message arrievs to the Physical