a a S1-U interface. IE E-UTRAN. In the Evolved Packet System (EPS), the elementary connectivity between a UE and an S-GW is an E-RAB, which uniquely identifies traffic flows that receives a common data for- warding treatment. An E-RAB is the concatenation of a radio bearer represented by the DRB ID and a S1 bearer represented by the S1-Tunnel Endpoint Identifier (TEID), the one-to-one mapping of which is managed by the eNodeB or en-gNB. Therefore, under the IE E-UTRAN, both DRB ID and S1-U UL/DL Transport Layer Information consisting of GTP-TEID are present, indicating the binding of the two identifiers. For the internal interface F1-U, the gNB-CU-UP provides uplink UP Parameters in the message Bearer Context Setup Response and the gNB-CU-CP provides downlink UP Parameters in the message Bearer Context Modification Request, both of which contain UP Transport Layer Information. A bearer can be an MCG bearer (with an RLC bearer only in the MCG), an SCG bearer (with an RLC bearer only in the SCG) or a split bearer (with RLC bearers both in the MCG and the SCG) and that's why under UP Parameters there is a Cell Group ID associated with each UP Transport Layer Information, specifying which cell group (MCG or SCG) the bearer belongs to. A split bearer has two UP Parameters items, one for MCG and the other for SCG. ¹2 IE NG-RAN. Compared with EPS, 5GS employs a different means to enforce QoS. First, the UPF clas- sifies the user-plane traffic and performs user-plane marking using a QoS Flow Indicator (QFI), which takes over the role of S1-TEID in EPS, leaving GTP-TEID less important in 5GS. Second, Unlike in EPS where the eNB performs one-to-one mapping of S1 bearers to DRBs, the gNB decides how to bind QoS flows to DRBs and what's more important there is no strict 1:1 relation between them. It is up to the gNB to establish the necessary DRB that QoS flows can be mapped to, and to release them when not needed (3GPP TS 23.501). That's why under each PDU Session Resource To Setup Item ¹³ (uniquely represented by PDU Sessi