n what is required for the user plane. See an analysis of the bit rate of these flows in LTE in [3]. With dual connectivity (5G-5G or 5G-4G), the gNB may divert part of the traffic to the other base station, via the Xn/X2 interface. With X2, the 4G air interface may be used for additional throughput, in case 5G air interface conditions are poor. For this traffic, the X2 transport link needs to have the amount of bandwidth that 4G is estimated to be able to support. If the base stations are co-sited, that transport link is site internal. With 5G-5G, dual connectivity is supported by the Xn interface. The behavior of this interface is similar. 9.2.5 Low Layer Fronthaul Capacity At the low layer split interface, the transport capacity depends on the exact split, how many bits are utilized for the sample data, whether compression is used, and on which protocol stack is deployed on that interface. This causes a range of results when calculating the required bit rates. Figure 9.5 shows a comparison between legacy CPRI and the O-RAN standard [4] with split option 7-2 (see Chapter 5, Figure 5.8 and the related discussion in Chapter 5 for split options). The transport overhead is included. In the given value range, the low value approximates the floor that can be reached, the value being very close to the backhaul requirement. The bit rates become even higher than the high value in the range if a large sample width (e.g. 16 bits) is deployed and compression is omitted. The bold text in Figure 9.5 represents the user plane bit rate with compression of sam- ple data. The CPRI rate is shown for comparison, and a significant reduction in the bit rate is evident. 9.2 Capacity and Latency 2 streams 4 streams 8 streams 16 streams 0,2-0,5 Gbit/s 0,4-1 Gbit/s 0.8-2 Gbit/s 1.6-4 Gbit/s 20 MHz 16 Gbit/s (CPRI) 32 Gbit/s (CPRI) 64 Gbit/s (CPRI) 128 Gbit/s (CPRI) 1-2,5 Gbit/s 2-5 Gbit/s 4-10 Gbit/s 8-20 Gbit/s 100 MHz 80 Gbit/s (CPRI) 160 Gbit/s (CPRI) 320 Gbit/s (CPRI) 640 Gbit/s (CPRI) 2-5 Gbit/s 4-10 Gbit/s 8-20 Gbit/s 16-40 Gbit/s