5.34.7.2 SMF event exposure service

Consumers of SMF events do not need to be aware of the insertion / removal / change of an I-SMF as they always subscribe to the SMF of the PDU Session.

Except for the events documented in the present clause, the I-SMF does not need to support the events defined in clause 5.2.8.3.1 of TS 23.502 [3].

For Events "First downlink packet per source of the downlink IP traffic (buffered / discarded / transmitted)" and UPF event exposure for User DataUsage Measures and User DataUsage Trends, when an I-SMF is involved in the PDU Session, the SMF subscribes / unsubscribes onto I-SMF for the PDU Session ID on behalf of the event consumer (e.g. at I-SMF insertion or when a consumer subscribes or un subscribes while an I-SMF serves the PDU Session) and the I-SMF or I-UPF directly notifies the event consumer. At I-SMF change, the related SMF event subscriptions are not transferred from source I-SMF to the target I-SMF. The SMF may trigger new subscription event to the target I-SMF if the SMF wants to receive the corresponding SMF or UPF event or to continue the UPF event subscription for the final consumer. At I-SMF change or removal the corresponding subscription is removed in the source I-SMF when it removes the context associated with the PDU Session Id.