5.34.6.2 N4 information sent from SMF to I-SMF for local traffic offload

The SMF generates N4 information for local traffic offload based on the available DNAI(s) indicated by the I-SMF, PCC rules associated with these DNAI(s) and charging requirement. This N4 information is sent from the SMF to the I-SMF after UL CL/Branching Point insertion/update/removal and the I-SMF uses this N4 information to derive rules installed in the UPFs controlled by the I-SMF.

The N4 information for local traffic offload corresponds to rules and parameters defined in clause 5.8.5, i.e. PDR, FAR, URR and QER. It contains identifiers allowing the SMF to later modify or delete these rules.

N4 information for local traffic offload is generated by the SMF without knowledge of how many local UPF(s) are actually used by the I-SMF. The SMF indicates whether a rule within N4 information is enforced in UL CL/ Branching Point or local PSA. If the rule is applied to the local PSA, the N4 information includes the associated DNAI. The I-SMF generates suitable rules for the UPF(s) based on the N4 information received from SMF.

NOTE: The SMF is not aware of whether there is a single PSA or multiple PSA controlled by I-SMF.

The following parameters are managed by the I-SMF:

• The 5G AN Tunnel Info.
• CN tunnel info between local UPFs.
• Network instance (if needed).

The N4 information exchanged between I-SMF and SMF are not associated with a N4 Session ID but are associated with an N16a association allowing the SMF to modify or delete the N4 information at a later stage.

The I-SMF generates an N4 Session ID and for each rule a Rule ID (unless the ones received from the SMF can be used) and maintains a mapping between the locally generated identifiers and the ones received from the SMF. The I-SMF replaces those IDs in the PDR(s), QER(s), URR(s) and FAR(s) received from the SMF. When the I-SMF receives the N4 information, the Network instance (if needed) included in the rules sent to the UPF is generated by I-SMF.