Content for TR 23.700-12 Word version: 17.1.0

7.1 Evaluation of solutions addressing key issue #1 7.2 Evaluation of Solutions addressing key issue #2 8.1 Conclusion of Solutions for Key Issue#1 8.2 Conclusions Related to key issue #2

7 Overall Evaluation p. 20

7.1 Evaluation of solutions addressing key issue #1 p. 20

Table 7.1-1: Pros and Cons of solutions for KI#1

Solution Id	Pros	Cons
Solution#1	If no NPLI is enabled at P-CSCF, there is no latency increased at call establishment, but only at registration procedure. It does not impact the PCF It meets the requirements by simple protocol extensions to Nudm, Nudr, and Nhss-ims (or Cx/Sh)	It impacts multimedia control plane IMS functions (e.g. HSS, S-CSCF) which are not managing user plane traffic. It impacts legacy diameter interfaces (e.g. Cx). It requires a complex configuration since each UPF instance added needs to be configured at each and every IMS node, even if they serve the same area and they require the same MGW involved in the multimedia session. It does not solve the scenario of UPF reallocation after the IMS registration.
Solution#4	It does not impact multimedia control plane IMS functions (e.g. HSS, S-CSCF), but only IMS nodes managing media plane. It does not impact legacy diameter interfaces. It is independent of how many UPF instances are added in the network since it uses the UPF service area (serving scope), regardless of how many UPF instances serve the same area. This result in a much simpler configuration and maintenance in IMS nodes. The media plane selection is based on the current UPF when the multimedia session is established, not in the UPF selected at PDU session establishment. It reuses existing SBI service for IMS AF/P-CSCF produced by PCF in a natural way to retrieve, in addition to Network Provided Location information, the UPF service area. The whole procedure is performed when the requesting IMS node is going to make use of the information, instead of doing in a proactive manner and impacting interfaces and internal S-CSCF registration binding storage with information which might not be used and might also be obsolete in the case of UPF reallocation.	It requires impacts in SBI interfaces (N5/N7) It requires N5 interaction if the current UPF is requested at Multimedia Session establishment. This interaction is not additional if NPLI is requested. NOTE 1: The benefits of the N5 interaction, even if the latency might be increased at establishment (if no NPLI is required) is that during the lifetime of the multimedia session (e.g. voice call) the packets sent/received are being forwarded using optimal user plane routing.
Solution#7	It does not impact multimedia control plane IMS functions (e.g. HSS, S-CSCF), but only IMS nodes managing media plane. It does not impact legacy diameter interfaces. It does not impact the PCF. It does not coupled with the IMS session establishment procedure. It is independent of how many UPF instances are added in the network since it uses the UPF service area (serving scope), regardless of how many UPF instances serve the same area. This result in a much simpler configuration and maintenance in IMS nodes.	It requires relevant IMS nodes e.g. P-CSCF, BGCF and IMS-AS to support SBI. It does not solve the scenario of UPF reallocation after the IMS registration.

7.2 Evaluation of Solutions addressing key issue #2 p. 21

Solution #3 differs from solution #2 mainly on how P-CSCF gets the serving AMF of the UE. P-CSCF doesn't directly communicate with HSS/UDM in solution #2. It depends on S-CSCF communicating with HSS/UDM. In solution #3, P-CSCF directly communicates with UDM by querying NRF. However, since IMS network can still uses N5 interface in 5G, it seems that there is no much benefit for the IMS network to use the SBI provided AMF to subscribe to notification of some events related to access network.

Table 7.2-1: Pros and Cons of Solution #5 for Key Issue #2

Solution Id	Pros	Cons
Solution#5	It avoids the O&M and replications of large configurations in IMS nodes for user plane nodes. It leverages the capabilities of some IMS nodes (e.g., P-CSCF) for NRF discovery based on UPF/UPF service area. It allows easy introduction of new user planes nodes by means of NRF notifications towards the control planes subscribing to the user plane nodes.	It requires IMS control plane nodes to support NF discovery via NRF. It adds the O&M and replications of large configurations to NRFs. It adds signalling load on Nnrf.

8 Conclusions p. 21

8.1 Conclusion of Solutions for Key Issue#1 p. 21

It is recommended to adopt solution#1 (Conveying UPF FQDN to IMS nodes) as basis for normative work.

It is also proposed to take Solution#4 to normative phase, since it avoids impacting NFs (HSS, S-CSCF) which are not related to user plane functions (see Table 7.1-1). The exchange of user plane information fits in a much more natural manner in PCF/P-CSCF, given that these NFs are already notified about other user plane events.

8.2 Conclusions Related to key issue #2 p. 21

Solution #2 and solution #3 will not be pursued.

Solution#5 (IMS User-Plane nodes discovery via NRF) is considered useful, so it is recommended to consider its adoption for normative work so that other solutions for Key Issue #1 (e.g., Solution #1, Solution #4) can also benefit from it.