5G Core Part 3 — User Plane and GTP-U Tunnels
Introduction
We show in the 5GC Part 2 — PDU Session Establishment and Call Flow of this series of 5G articles that after a UE (e.g., 5G smartphone) successfully completes its Registration and PDU Session Establishment procedures to a DN in a 5G System (5GS), a PDU Session with a Default QoS Flow is created between the UE and the DN. A bidirectional user plane paths are created for UE and DN traffic exchange as follows:
- Uplink (UL) traffic user plane path — UE → gNB → UPF → DN
- Downlink (DL) traffic user plane path — DN ← UPF ← gNB ← UE
The QoS characteristics of the bidirectional Default QoS Flow of the PDU Session are determined by the profile of the UE defined in the Unified Data Management (UDM) as well as the policies defined for the UE on the Policy Charging Function (PCF) of the 5GS’ SBA control plane.
The Default QoS Flow is a non-Guaranteed Bit Rate (non-GBR) QoS Flow without any UL and DL Packet Filters on the UE and the UPF for traffic binding. In other words, the Default QoS Flow is the default data path or QoS Flow between the UE and the DN if the UL and DL traffic do not match any Packet Filters for binding the traffic to any Dedicated QoS Flows. Please see the 5G Core Part 4 — Dedicated QoS Flow and PDU Session Modification for more details…
