l as <100 microseconds. Queueing delay incurred through the slot-based timing architecture of the air interface as well as the latency incurred by scheduler prioritization of other users. This topic is discussed in more detail below when we discuss the Transmission Time Interval. Assuming prioritization of low-latency users and light system loading with regards to these low-latency users, queueing delay should be limited to below 10 milliseconds. Air interface latency associated with the MAC/PHY processing and HARQ retransmission. This latency is discussed in detail in 3GPP 36.912 for LTE where similar math can be applied for 5G/NR. For Frequency Division Duplexed (FDD) operation in LTE, the one-way latency through the RAN is calculated as DUP [milliseconds] = 1.5 + 1 + 1.5 + 4 + n X where n is the number of HARQ retransmissions. Considering a typical case where there would be 0 or 1 retransmission, the approximate average U-plane latency is given by DUP, typical [milliseconds] = 4 + p X 8, where p is the error probability of the first HARQ retransmission. The minimum latency is achieved for a 0% HARQ Block Error Rate (BLER), but a more reasonable setting is 10% HARQ BLER. DUP,O%HARQ_BLER [milliseconds] = 4 (0% HARQ BLER) DUP,10%HARQ_BLER [milliseconds] = 4.8 (10% HARQ BLER). Time Division Duplexed (TDD) numbers are slightly worse. Assuming a 30KHz subcarrier spacing and 500 milliseconds slot time in 5G/NR (as opposed to 1 millisecond slot time in LTE), these numbers can be divided by two to achieve an estimated <3 millisecond RAN latency. 110 Open Radio Access Network (O-RAN) Systems Architecture and Design Aggregate latency through the RAN is estimated as 5-10 milliseconds in a realistic one- way latency through the RAN before optimizations such as discussed in Ultra Reliable Low Latency Communication (URLLC) protocols come into play. Users/transmission time interval The "UE/TTI" metric relates to the definition of how many users (User Equipment (UE)) should be scheduled each 3GPP slot (Transmission Time Interv