5.17 5G UPF (for 5GC)

29.2443GPPInterface between the Control Plane and the User Plane nodesRelease 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

5.17.1 Introduction

The following clauses describe the 5GS specific functionalities of a UP function.

5.17.2 Uplink Classifier and Branching Point

The Uplink Classifier and Branching Point functionalities refer to the capability of the UPF to route uplink traffic flows of the same PFCP session (PDU session) to two or more PDU Sessions Anchors, and to route the downlink traffic flows from these PDU Session Anchors on the tunnel towards the UE. They are defined in 3GPP TS 23.501 [28] and 3GPP TS 23.502 [29].

Uplink Classifier is supported for PDU sessions of type IPv4, IPv6, IPv4v6 or Ethernet. The routing of the uplink traffic flows to different PDU Session Anchors is based e.g. on the destination IP address/Prefix of the uplink packets for an IP PDU session.

Branching Point is supported for multi-homed PDU sessions of type IPv6, i.e. PDU sessions with multiple IPv6 prefixes. The routing of the uplink traffic flows to different PDU Session Anchors is based on the source IP prefix of the uplink packets.

The SMF may insert an Uplink Classifier or Branching Point, during a PDU session establishment or modification, by provisioning:

– two or more UL PDRs, with the appropriate Packet Detection Information, and with corresponding FARs to route the uplink traffic flows towards the appropriate PDU Session Anchors;

– two or more DL PDRs, with the appropriate Packet Detection Information, and with one (or more FARs) to route the downlink traffic flows on the tunnel towards the UE.

NOTE 1: This uses the generic functionalities of the PFCP protocol described in this specification, with two or more DL PDRs (for the traffic coming from the different PDU session anchors).

NOTE 2: A UPF acting as an Uplink Classifier or Branching Point can also behave as a PDU Session Anchor for the PDU session.

The SMF may remove an Uplink Classifier or Branching Point, during a PDU session modification, by removing the UL (or modifying the FAR associated to the UL PDR) and DL PDRs that were setup for the traffic to/from the PDU Session Anchor(s) to be removed.

5.17.3 Data forwarding during handovers between 5GS and EPS

Downlink data may be forwarded during an inter-system handover between 5GS and EPS using direct or indirect data forwarding.

NOTE: Uplink data is not forwarded during an inter-system handover between 5GS and EPS in this release of the specification.

Direct data forwarding is performed directly between the source and target RAN, without the involvement of any UPF to forward the data.

Indirect data forwarding during handovers between 5GS and EPS is supported as follows (see 3GPP TS 38.300 [42]):

– For 5G to 4G handover, the source NG-RAN node sends one or several end markers including one QFI of those QoS flows mapped to the same E-RAB and sends the end marker packets to the UPF over the PDU session tunnel. UPF removes the QFI and maps to an appropriate E-RAB tunnel towards SGW.

– For 4G to 5G handover, the source eNB forwards the received end markers in the EPS bearer tunnel to the SGW which forwards them to the UPF. The UPF adds one QFI among the QoS flows mapped to that E-RAB to the end markers and sends those end markers to the target NG-RAN node in the per PDU session tunnel.

To forward data (G-PDUs and End Marker packets) during a 5GS to EPS handover, the SMF shall:

– provision one PDR per E-RAB (that supports data forwarding for at least one QoS flow), with the list of QFIs that are mapped to the E-RAB;

– request the UPF to remove the GTP-U PDU Session Container extension header (including the QFI) from the data by including the GTP-U Extension Header Deletion field set to ‘PDU Session Container’ in the Outer Header Removal IE of the PDR(s);

– associate to each PDR a FAR to forward the data to the GTP-U tunnel of the corresponding E-RAB, i.e. with an Outer Header Creation IE containing the F-TEID of the (forwarding) SGW for the corresponding forwarding GTP-U tunnel.

To forward data (G-PDUs and End Marker packets) during an EPS to 5GS handover, the SMF shall:

– provision one PDR per E-RAB (that supports data forwarding for at least one QoS flow);

– create and associate one QER with each PDR, including the QFI IE set to the QFI value of one of the QoS flows mapped to the E-RAB, to request the UPF to insert a GTP-U PDU Session Container extension header including the QFI;

– create one FAR for each data forwarding tunnel in 5GS (i.e. per PDU session), with an Outer Header Creation IE containing the F-TEID of the target NG-RAN for the corresponding forwarding GTP-U tunnel;

– associate each PDR to the corresponding FAR (i.e. to forward the data of each E-RAB to the data forwarding tunnel of the corresponding PDU session).