uld result in an even bigger difference com- pared to RF only at the site solution. Moving MAC/RLC to the CU naturally results in somewhat higher data rates, as now retransmission handling has moved to the CU, and thus some packets end up being sent multiple times through the F1 interface in addition to the extra control signaling that becomes necessary. A lower layer split with enhanced CPRI (eCPRI) shown in Figure 5.7 is being consid- ered in the O-RAN Alliance [2] organization outside 3GPP, and the interface has also 5.4 5G RAN Architecture 5G Core CU-CP CU-UP PDCP-C PDCP-U Control Physical Layer Figure 5.6 5G radio access network architecture with control and user plane separation for CU with the higher layer split. L1 upper 4 Gbps eCPRI 10-30 Gbps 160 Gbps (dark fiber) L1 lower Higher Layer Functional split Lower Layer Functional split RF only at the DU Figure 5.7 Impact on backhaul connectivity with different functional split options. been defined in the Common Public Radio Interface (CPRI) under the name eCPRI, cor- responding to the lower layer split options as studied in 3GPP [3]. The key difference with the eCPRI interface is that in unlike the earlier CPRI interface versions, eCPRI is packet based and thus facilitates options other than dark fiber, such as Ethernet. 3GPP will not address in Release 15 or 16 further such lower layer functional splits in later releases, but at least in Release 16 this is not planned to be included. Thus, from that perspective, the F1 specification in Release 15 covers only the higher layer functional split. The term F2-interface referring to the eCPRI interface has been used outside 3GPP to refer to the 5 5G Architecture Decoding Rate Matching Descrambling Coding Demodulation Rate Matching Scrambling Equalizer L1 upper Split 7.3 Modulation Diversity eCPRI 10-30 Gbps Combiner Layer Mapping Channel Estimation Split 7.2 Resource Element Resource Element L1 lower Mapping Demapping Beamforming Port Reduction Lower Layer Functional split Split 7.1 CP insertion CP removal Downl