5G Core Part 2 — PDU Session Establishment and Call Flow
Introduction
Part 1 of this series of 5G articles provides a quick overview of the 5G System (5GS) particular its 5G mobile core (5GC). It briefly describes what are SMF, AMF, PCF, QoS Flow, SDF, DRB, and AN_Tunnel and CN_Tunnels etc…. It also shows how a UE (User Equipment such as a 5G Smartphone) can establish a PDU session via the new 5G new radio (gNB) to a Data Network (DN) for traffic exchange. For brevity, we left a lot of details out from the article but did highlight some missing details or questions in the Summary Section at the end of the article.
This is Part 2 of this series of 5G articles where we will examine the UE-Requested PDU Session Establishment in details with Wireshark traces to illustrate the messages and the parameters exchanged among the UE, gNB, AMF, SMF and UPF etc… for establishing a PDU Session between a UE and a DN.
When a UE establishes a PDU session to a DN for traffic exchange, a non-GBR (non Guaranteed Bit Rate) Default QoS Flow without any Uplink (UL) or Downlink (DL) Packet Filters is also setup to carry the UE’s traffic to the DN and vice versa. Additional GBR and non-GBR Dedicated QoS Flows can be setup for the UE to the DN to support more QoS demanded network applications such as voice and video via the UE-Initiated or the Network-Initiated PDU…
