E-UTRAN PDN Modification without S-GW Change
The following figure shows the call flow derived from the 3GPP reference for PDN modification without S-GW change.

Step | Description | ||
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1 |
MME sends Modify Bearer Request (for ULI change) to S-GW. |
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2 |
S-GW forwards Modify Bearer Request to SMF.
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3 |
SMF sends Modify Bearer Response to S-GW. |
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4 |
S-GW forwards Modify Bearer Response to MME. |
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5 |
SMF sends the N4 Session Modification Request for query Usage Reporting Rule (URR) to UPF based on event triggers.
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6 |
UPF responds with the N4 Session Modification Response with Gy and RADIUS URR, SMF based on Gy, and RADIUS configuration, which can be enabled or disabled. |
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7 |
Based on URRs received in N4 Session Modification Response, Gy, and RADIUS signaling happens. |
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8 |
SMF sends CCR-U to OCS and RADIUSs Accounting Request to AAA. |
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9 |
OCS responds with CCA-U and AAA with RADIUS Accounting Response. |
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10 |
SMF sends N4 Session Modification Request for update URR to UPF. |
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11 |
UPF sends N4 Session Modification Response to SMF. |
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12 |
If an event trigger is armed, SMF sends CCR-U to PCRF.
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13 |
PCRF then sends CCA-U to SMF. |
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14 |
Bearer creation, update, or deletion happens based on Gx CCA-U contents. |