PDU Session Establishment
The following figure illustrates the call flow of PDU session establishment.

Step | Description |
---|---|
1. | Call Setup |
2. |
SMF performs a Policy Create exchange with PCF. In this exchange, the SMF might receive Charging Data that is associated to a PCC Rule. This indicates that charging is enabled for the session in progress. It is possible that PCF has enabled Static/Predefined rules. These rules can be also enabled with charging, based on the configuration. |
3. |
Once charging is detected at SMF, it initiates a Charging Data Request Initial exchange with CHF. In this exchange SMF may receive the following from CHF:
|
4. | N1N2 Exchange and SM Context Update Exchange |
5. | SMF initiates N4 session establishment request exchange with UPF, and in the same request it relays information that is related to charging in the Create URRs. |