Content for  TS 33.127  Word version:  18.6.0

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A.2  Interworking with EPC/E-UTRANp. 151

A.2.1  Generalp. 151

In EPC/E-UTRAN, the NFs that provide the POI functions are:
  • MME.
  • SGW.
  • PGW (optional).
  • HSS.
  • SCEF.
In a 5GS, the NFs that provide the POI functions are:
  • AMF.
  • SMF/UPF.
  • UDM.
  • SMSF.
  • NEF.
In an interworking scenario between the EPC and the 5GS, the AMF in 5GS and MME in EPC provide the IRI-POI functions for the related attach/registration related aspects. When the network topology includes SMF + PGW-C and UPF + PGW-U as the interworking NFs, it is recommended that these provide the POI functions for the PDU sessions as the target communication traffic coming from either of the two interworking networks pass through these NFs. In that case, the interception at the SGW and UPF (if present between the NG-RAN and the UPF + PGW-U) is not required unless the condition specified in the NOTE in clause A.2.2 applies.
In a non-roaming scenario, the IRI-POI present in the HSS + UDM also provide the LI functions. The IRI-POI present in the SMSF provides the LI functions for the SMS-related IRI events.

A.2.2  Topology view for a non-roaming scenariop. 152

The overall network configuration for interworking between EPC-EUTRAN and 5GS in non-roaming scenario with the LI aspects is shown in Figure A.2-1.
The 5G core system is shown using the service-based representation (as shown in TS 23.501) with the use of point-to-point LI system.
Copy of original 3GPP image for 3GPP TS 33.127, Fig. A.2-1: Network topology showing LI for interworking with EPC/E-UTRAN
Figure A.2-1 shows the network topology of 5G system in a service-based representation, however, all the LI-related interfaces remain to be point-to-point.
The IRI-POIs present in the AMF, MME, UDM, SMSF and SMF + PGW-C deliver the xIRI to the MDF2 and CC-POI present in the UPF + PGW-U delivers the xCC to the MDF3. The MDF3 address to CC-POI present in UPF + PGW-U is provided by the CC-TF present in the SMF over LI_T3 reference point.
The LIPF present in the ADMF provisions the IRI-POIs and the CC-TF present in the NFs with the intercept related data. The LI_X1 interfaces between the LIPF and the UPF + PGW-U is to monitor the user plane data.

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