 transmitting Unacknowl- edged Mode (UM) RLC entity, or a transmitting side of Acknowledged Mode (AM) and the routing function of a receiving side of AM. Consequently, high-RLC implements receiv- ing TM RLC entity, receiving UM RLC entity, or a receiving side of AM except the routing function and reception of RLC status report. The main advantage of this option (compared with option 3-1) is that it does not introduce additional latency requirements on the fronthaul. Option 4 In this option, also referred to as RLC-MAC split, MAC, PHY, and RF reside in the DU. PDCP and RLC are in the CU. This option was considered in the study primarily for completeness, as no advantages have been identified. Option 5 In this option, also referred to as intra-MAC split, RF, PHY, and some part of the MAC layer (e.g. Hybrid ARQ [HARQ], which has more stringent timing requirements) are in the DU. The rest, that is, upper-MAC, RLC, PDCP, and RRC, are in the CU. The main benefits of this option are: 1. Even further resource pooling gains, as more functionality (compared with lower- numbered options) is centralized in the CU. 2. Efficient interference management across multiple cells and enhanced scheduling technologies such as Coordinated Multi-point (CoMP) and Carrier Aggregation (CA), with multi-cell view, as the scheduler (which is normally part of the MAC protocol layer) is centralized in the CU. The main disadvantage is the extra complexity of the interface between the CU and the DU. Option 6 In this option, also referred to as MAC-PHY split, physical layer and RF are in the DU. All the protocol stack layers are in the CU. This option has all the benefits of option 5 (resource pooling, efficient scheduling, etc.). Additionally, resource polling gains are somewhat bigger (as even more functionality is centralized in the CU) and more advanced scheduling optimizations become possible, for example joint transmission. This comes at the cost of subframe-level timing requirements on the fronthaul interface. Furthermore, round trip fronth