Feature Description

The SMF leverages the 3GPP provision for the access and mobility procedures. With this provision, the SMF integrates the Charging Function (CHF) and Policy Control Function (PCF). SMF supports the following integration functions:

  • CHF and PCF Integration for Intra-AMF and Inter-AMF N2-Based Handovers—SMF supports this function when a UE moves from one NG-RAN to another NG-RAN for Data Forwarding Tunnel (DFT) and Indirect Data Forwarding Tunnel (IDFT) cases.

  • CHF and PCF Integration for N26 4G to 5G Handover—SMF supports the EPS to 5GS procedures with the N26 interface. SMF establishes Uplink (UL) Packet Detection Rule (PDR) or Downlink (DL) PDR toward with the qualified EPS Bearer Identity (EBI) list in 5GS and replicate EBIs to the respective flows. SMF also creates IDFT to support the Downlink forwarding traffic between SGW-U to NR over UPF.

  • CHF and PCF Integration for N26 5G to 4G Handover—SMF supports 5GS to EPS procedures with the N26 interface. PGW-C establishes UL PDRs or DL PDRs toward SGW-U with qualified flows in 5GS and replicate EBIs to respective flows. PGW-C also creates an IDFT tunnel to support Downlink forwarding traffic between NR to SGW-U over UPF. Session-Level or Rating-Group level Charging Triggers are received during PDU Session establishment or in response to SMF-initiated Charging Update Request or CHF-initiated Charging Update Notify response in EPS procedures.

  • CHF and PCF Integration for Xn Handover—SMF supports the Xn-based inter NG-RAN handover with and without UPF reallocation. The SMF supports Xn handovers for intra-AMF mobility only. SMF processes the received SM context update request that includes the path switch request N2-based message and the access-ide parameters. These parameters identify the CHF and PCF triggers that are received during PDU session establishment.

  • CHF and PCF Integration for Service Request Procedures—SMF supports the service requests from both the UE and network-initiated procedures. Either a UE in CM-Idle state or the 5GC uses the Service Request procedure to request the establishment of a secure connection to an AMF. The UE in both the CM-Idle and in CM-Connected state use the Service Request procedure to activate a User Plane connection for an established PDU Session. The UE does not initiate a Service Request procedure if an ongoing Service Request procedure exists.

SMF saves the CHF and PCF triggers that SMF receives from CHF and PCF as part of session creation or PCF or UE-initiated modifications. When a UE triggers access and mobility procedures for the preceding functions, SMF identifies the triggers from CHF and PCF against the received access parameters. Then, SMF sends an update toward CHF and PCF.