hat was primarily due to concerns with the complexity of the intra-PHY low-level split, its sensitivity to network interface latency, and stringent requirements on timing synchronization, compared with, for example, the high-level CU/DU split (described in Section 4.1). These factors are closely tied to RAN implementation and pose additional challenges in the interoperability testing, which can be somewhat challenging to be agreed in a large SDO such as 3GPP. Nevertheless, this idea has been considered in several smaller industry consortiums, where reaching consensus and defining a standardized split RAN interface are relatively easy to achieve. CPRI industry cooperation has specified the split option 8 (described in Section 4.1), which has been used by multiple vendors during LTE. That work continued for NR, leading to the eCPRI specification. eCPRI is a complete redesign of CPRI, which uses Ethernet-based transport. It supports NR and is capable of supporting several split options besides option 8 supported by CPRI. The eCPRI has specified message types for control plane, user plane, and synchronization plane. Furthermore, it is able to support both eCPRI and CPRI nodes in the same network. However, CPRI specifications are rather abstract and do not provide sufficient details for true multi-vendor interoperability. Later we discuss how the xRAN/O-RAN addresses these issues. At the same time, another standards organization - IEEE - formed a working group 1914 to explore the fronthaul protocol solutions. IEEE1914.3 specification, also referred to as NGFI, defines the encapsulation and mapping of radio protocols for transport over Eth- ernet frames. The IEEE1914.3 Ethernet-based transport can be used for example with the 3GPP split option 8 and option 7.1. It offers both structure-agnostic and structure-aware (CPRI frame structure) frames for I/Q data transmission. However, NGFI only defined the transport network aspects, not a fully functional fronthaul interface. For details about Radio over Ethernet (RoE) proto