aspect. Since now the delay-critical radio layers and functions (scheduling, L1 retransmissions, etc.) operate over the low layer fronthaul, the delay tolerance is limited to around 50-100 us or up to a few hundreds of microseconds RTT, depending on the frequency band (sub- carrier spacing), TTI (transmission time interval), and the number of Hybrid-ARQ pro- cesses assumed at the terminal. 9.2.7 QoS Marking In the 5G Core, QoS is flow based, based on packet filters and individual flows within a PDU session. The related identifiers are the QoS flow identifier QFI, for the QoS profile, and the 5G QoS identifier 5QI, for the QoS characteristics of a flow. The N2 (NG-C) interface signals these identifiers to the 5G RAN. 9.3 Technologies In transport, QoS is mapped to the traffic class field of the IPv6 packet, or the type of service field of the IPv4 packet, and further when needed into the MPLS traffic class and into Ethernet 802.1Q priority bits, to ensure that the flow is correctly handled in the transport network. For stronger guarantees, traffic engineering techniques are required, for example, with Multiprotocol Label Switching Traffic Engineering (MPLS TE). Since the traffic volume is typically very downlink dominated, the downlink direction is especially important for addressing capacity bottlenecks, primarily with a combina- tion of link bandwidth upgrades while also ensuring proper QoS configuration. Technologies 9.3.1 Client Ports At the 5G nodes (gNB, gNB-DU, gNB-CU, etc.), physical interfaces that connect the mobile node to the network are in practice Ethernet ports. Figure 9.7 illustrates the Eth- ernet port speeds against the capacities calculated in the previous section. Requirements are collected from Figure 9.4 of the previous section: Cases A1-A3 dimension the F1 and NG interfaces based on one sector peak, which was assumed to be higher than the sum of the average rates of all sectors. Cases B1-B3 use the single user peak rate as the basis, leading to a lower capacity requirement. Cases A1 and B1 a