Page 87 - ITU-T Focus Group IMT-2020 Deliverables

ITU-T Focus Group IMT-2020 Deliverables 3

Similarly, it is assumed that the user plane core network functions are required to interface only with their
respective control plane core network functions. And hence the interconnection model between them can
be point-to-point interface based. However, if it is decided to allow any control plane function to interface
with any user plane function then the principles of this solution can be extended to interconnect control
plane and user plane core network functions as well.
The solution assumes that multiple control plane core network functions are required to interact with
multiple other control plane core network functions in the next generation core network architecture.
NOTE – Unless explicitly specified, the term "network function" refers to "control plane core network
function" in this solution. Just for the sake of understanding the "control plane core network functions" in
the EPC context are MME, control plane of PGW, PCRF, HSS, control plane of TDF, TSSF, RCAF, SCEF etc.

Figure 6.1.1-5 – Non-roaming reference model for the interconnection of network functions

Below is a sample call flow of the management of the binding between the UE's session and its corresponding
serving NF, at the IRF.

Figure 6.1.1-6 – Sample call flow of UE-NF binding management at IRF

1) When a UE's session is created at an NF, e.g. during the procedures such as attach, new PDU session
establishment, relocation etc., the NF updates the IRF by sending "Add UE binding" message. The
IRF creates new binding in its binding repository.
For updating the existing binding, the NF sends "Update UE binding" message to the IRF. Correspondingly,
the IRF updates the binding repository. This could take place if the NF changes its instance for an existing
UE's session, e.g. due to scale-in, scale-out or restoration feature.

When the existing UE's session is released by the NF, e.g. during relocation or PDU session release
procedures, the NF sends "Remove UE binding" message to the IRF. The IRF clears its binding repository for
the UE's session.

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