Feature Description
The dual connectivity enabled UEs support 4G-LTE and 5G-NR. Such UEs send a signal to the 4G Core Network, indicating that it’s a dual connectivity enabled device.
When the Dual Connectivity New Radio (DCNR) capable UE attempts to register in MME, the MME sets “UP Function Selection Indication Flags” IE with DCNR flag set to 1 in the “Create Session Request” message. After the S-GW receives this IE over S11, it sends this IE over S5 to P-GW. This IE transmission helps the SGW-C and PGW-C to select SGW-U and UPF, which supports dual connectivity with NR.
The SMF/P-GW-C supports Packet Data Unit (PDU) sessions from only 5G capable UE in 4G radio. Now, the SMF/PGW-C extends support for the PDU sessions from the 4G-only capable device and Option 3x Capable device (NR & LTE radio connected to the EPC).
SMF handles periodic Secondary RAT Usage Data Report from MME over S5/S8 interface in Modify-Bearer-Request, Delete-Session-Request, Delete-Bearer-Response, and Delete-Bearer-Command based on IRPGW (Intended Receiver P-GW) flag. SMF retains the Usage-Report if IRPGW = 1. SMF supports Multiple instances of Secondary RAT Usage Data Report IEs, reports are stored until they are sent out to CHF based on the triggers.
If CBR/UBR success/failure response comes without PRA ID, then in next GTP request P-GW sends the PRA again.
With release 2021-01-0 SMF supports the following features:
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DCNR based UPF selection.
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Handling SecondaryRatDataUsageReport from SGW/MME and relaying it to CHF.
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UE Presence-Reporting Feature Support.
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Handling Gtpv1 Messages for 4g-3g HO.
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SUPI+IP session and affinity key for 4G <-> WIFI HO.
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Avoiding sending of 5G QoS for 4G-Only UE ( Qos rules and Qos flow description).
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Handling 5GCNRS and 5GCNRI indication flags from SGW/MME.