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Content for  TS 33.127  Word version:  18.6.0

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A.3 Multiple DN connections in a PDU session  A.3.1 General  A.3.2 Topology view for a non-roaming scenario 
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A.3  Multiple DN connections in a PDU session  p. 154

A.3.1  General  p. 154

According to TS 23.501, a PDU session can involve multiple UPFs, but regardless of how many UPFs are involved in the session, the session only connects to a single DN through one or more DN connections (i.e. connections to the same DN).
When a PDU session involves multiple UPFs, the interception of user plane packets can be done in two ways:
  • At one UPF (branching UPF) through which all the user plane packets pass through.
  • At anchor UPFs.
When the second approach is chosen with branching UPF being one of the anchor UPFs, redundant delivery of CC should be avoided.
In a non-roaming scenario, the IRI-POI present in UDM also provide the LI functions.
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A.3.2  Topology view for a non-roaming scenario  p. 154

The overall network configurations to illustrate the LI with multiple DN connections (to the same DN) in a PDU session is illustrated in Figure A.3-1 and Figure A.3-2.
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.3-1: Network topology showing CC-POI at one UPF
Figure A.3-1: Network topology showing CC-POI at one UPF
(⇒ copy of original 3GPP image)
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The IRI-POIs present in the AMF, MME, UDM, SMSF and SMF deliver the xIRI to the MDF2 and CC-POI present in the branching UPF (shown as UPF-1) on the common path to both DN connections delivers the xCC to the MDF3. The MDF3 address to CC-POI present in UPF-1 is provided by the CC-TF present in the SMF over LI_T3 reference point. In this view, all user plane packets pass through UPF-1.
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 is to monitor the user plane data.
Copy of original 3GPP image for 3GPP TS 33.127, Fig. A.3-2: Network topology showing CC-POI at two UPFs
Figure A.3-2: Network topology showing CC-POI at two UPFs
(⇒ copy of original 3GPP image)
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The IRI-POIs present in the AMF, MME, UDM, SMSF and SMF deliver the xIRI to the MDF2. In this example, there is a branching UPF (UPF-B), an anchor UPF for the DN (UPF-A1) and another anchor UPF for the same DN (UPF-A2). The second approach (i.e. CC interception at the anchor UPFs) mentioned in clause A.3.1 is used to provide the CC interception. The UPF-A1 delivers the xCC generated from the user plane packets that flow from UE to the DN via UPF-A1 to the MDF3. The CC-POI present in the UPF-A2 delivers the xCC generated from the user plane packets that flow UE to the DN via UPF-A2 to the MDF3. The MDF3 address in the CC-POIs present in UPF-1 and UPF-2 are 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 UPFs are to monitor the user plane data.
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