Processing of Usage Reporting Rules
After enabling the RADIUS accounting, the SMF creates the Usage Reporting Rule (URR) and relays the rule to the UPF through the Create URR Information Element (IE). The Create URR IE is present in the N4 Session Establishment Request and it contains the volume and time limits as per the configuration.
The SMF associates the RADIUS URR only to the dynamic Packet Detection Rules (PDRs) and not for the static and predefined rules. With AAA group name in N4 session establishment request, the UPF associates the static and predefined PDRs with the RADIUS URR. The UPF sends the usage report for the RADIUS URR when the Volume limit or the Time limit is hit. Then, the SMF sends the usage in the Interim-Update Accounting-Request message to the RADIUS server.
The SMF receives the usage report for RADIUS URR in N4 Modification Response or N4 Deletion Response when any one of the following conditions are met:
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CC event condition is hit and the SMF performs Query URR
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Session Delete Response is sent
The SMF stores the values of Volume and Time thresholds reported for a previous session and reports the cumulative usage by adding the currently reported value to the stored value. The SMF sends the cumulative usage report in Accounting-Request Interim-Update and Accounting-Stop messages.
On receiving the usage report from UPF, the SMF identifies the URR IDs that are to be sent to the CHF server and to the RADIUS server. For example, if the URR ID is associated to “0x80 00 00 09”, then the SMF sends this URR ID to the RADIUS server, and the other URR IDs to the CHF server.