RoE/1904.3 eCPRI OBSAI Structure Structure IQ Samples Bit sequences Native aware agnostic Split Option 7/8 Split Option 1-6 Split Option 8 Frequency Domain I/Q Domain I/Q Split Option 8 Split Option 7 FIGURE 6-8 Fronthaul transport options. 224 Open Radio Access Network (O-RAN) Systems Architecture and Design eCPRI Services Other Synchronization Connection OAM eCPRI SyncE IPSEC Ethernet MAC MACSEC Ethernet Ethernet PHY FIGURE 6-9 Fronthaul transport protocol encapsulation options. sample widths over a single link. However, CPRI is defined for (mainly) 3GPP I/Q transport use cases and as such does not benefit from the flexibility and economy of scale provided by Ethernet. Given 5G trends, flexibility in partitioning and economy of scale, the interface between the Digital Front-End (DFE) and the Baseband processor is Ethernet/IP based. Connectivity options include custom frame format, eCPRI or RoE as shown in Fig. 6-8 below. Ethernet based I/Q transport depends on Time Sensitive Networking capabilities in the Ethernet stan- dard (not discussed in this document) to guarantee frame timing. As shown in the figure above, different options in the RoE/eCPRI standards allow for map- ping of split option 7 to standardized formats. Standardization efforts (e.g., xRAN Fronthaul Working Group) are ongoing to define Ethernet/packet format across eCPRI and RoE. For illustrative purposes, below Fig. 6-9 shows the protocol mapping for eCPRI or IEEE1914.3, including optional UDP/IP layers. Transmission Control Protocol/Secure Transmission Control Protocol (TCP/SCTP) are not considered realistic protocol options given the strict requirements for latency that do not leave physical time for ack/nack and retransmission protocol support. The eCPRI standard protocol layering relies on UDP/IP/Ethernet addressing for source/desti- nation routing. Time synchronization is provided through standard IP mechanisms such as Chapter 6 User-plane application components 8 bits ecpriVersion ecpriReserved ecpriConcat ecpriMessage ecpriPayload eCPRI e