=) 2 (rounded to an integer number) scheduled UE/TTI are enough. Chapter 3 Hardware system dimensioning 111 System Waiting time as F(active/scheduled UE, system loading) assuming 2000 slot/second Ratio = 1 Ratio = 2 Ratio = 4 Ratio = 8 Ratio = 16 System Loading (%) FIGURE 3-7 System waiting time evaluation to evaluate scheduled UE/TTI. Option 2: Common Sense Above approach is complex even when we take many simplifications in the process. A dif- ferent model would be to look at the usage profile and see if this can help us provide a scheduling guideline. Consider a mmWave (3GPP: Frequency Range FR2) system with beam- forming employed. If we have 64 Connected Users evenly spread over (90-degree radius, 10-degree beam width) approximately 10 beam directions, each beam would be able to direct traffic at 8 users maximum. Given that users tend not to be perfectly evenly spread, we add some safety margin, let's double this to 16 users/beam. Assuming (per "Option 1") a ratio of 5 for Connected to Active UE count, we come to 3 Scheduled UE/TTI. Option 3: The Marketing Way "Do what the customer asks" or "do same or better than the competition" may not be the perfect engineering answer but often defines reality. Some rule-of-thumb numbers that can be used are a Scheduled: Connected UE ratio of 1:10 and Scheduled: Active UE ratio of 1:5 in the small cell application space. This would put our example requirements to 6 UE/TTI. 112 Open Radio Access Network (O-RAN) Systems Architecture and Design eCPRI, fronthaul bandwidth and latency The eCPRI standard and the control user and synchronization (CUS) plane interface that O- RAN defined to run on top of the eCPRI layer defines the fronthaul interface between the DU and the RU. This is the equivalent of a traditional Common Public Radio Interface (CPRI) (with the exemption of O-RAN defining frequency domain samples being transported as opposed to time domain), which is the challenge because CPRI is defined as a point-to-point interface with predictable latency and throughput. Even