Feature Description
Feature Name |
Release Information |
Description |
---|---|---|
Dual Stack Support on S1-U and N3 Interfaces |
2024.01 |
UPF supports both IPv4 and IPv6 transport on the S1-U and N3 interfaces. Default Setting: Enabled – Always-on |
3GPP specifies provisions for UEs capable of supporting both 5G and 4G NAS to connect to the E-UTRAN and 5G core network.
To forward data (G-PDUs and End Marker packets) during an EPS to 5GS handover, the SMF performs the following tasks:
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Provisions one PDR per E-RAB (that supports data forwarding for at least one QoS flow).
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Creates and associates one QER with each PDR to request the UPF to insert a GTP-U PDU Session Container extension header including the QFI. The PDR includes the QFI IE set to the QFI value of one of the QoS flows mapped to the E-RAB.
Data forwarding during handovers between 5GS and EPS is supported as follows. For reference, see 3GPP TS 38.300.
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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 toward SGW.
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For 4G to 5G handover, the source eNB forwards the received end markers in the EPS bearer tunnel to the SGW. Then SGW forwards them to the UPF. The UPF adds one QFI among the QoS flows mapped to that E-RAB to the end-markers. Then, the UPF sends those end-markers to the target NG-RAN node in the per PDU session tunnel.
Note | UPF supports dual-stack, which is IPv4 and IPv6 transport, over the S1-U and N3 GTP-U interfaces. |
Error Indication and GTP-U Path Failure
The UPF notifies an Error Indication message for a GTP-U peer to the sender when a GTP-PDU is received with a TEID that doesn’t exist. This notification ensures that there are no stale sessions or bearers, and maintains consistency in the network.
Error Indication and GTP-U Path Failure between SMF and UPF nodes are supported over the N4 interface. For the neighbor nodes, it’s supported over the S1u/S5u interfaces.
Behavior variations of local-purge or signal-peer for Error Indication and GTP-U Path Failure are considered in this implementation.
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When Error Indication is received, the UPF communicates the TEID and GTPU-peer information with the SMF to ensure deletion or modification of the GTPU-peer.
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On receiving a GTP-U packet with nonexisting TEID, the UPF generates and sends Error Indication with TEID and GTP-U peer entries.
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The deletion of a session or a bearer is decided based on the Path Failure detection at SMF or UPF.
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GTP-U Path Failure is detected using GTP-U echo messages between the UPF nodes, and between the UPF and SMF nodes.