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.

Call Flow for PDN Modification without S-GW Change
Call Flow Description for PDN Modification without S-GW Change
Step Description
1

MME sends Modify Bearer Request (for ULI change) to S-GW.

2

S-GW forwards Modify Bearer Request to SMF.

Note
If a session is present and not in disconnecting state, SMF sends success and does further processing.

3

SMF sends Modify Bearer Response to S-GW.

4

S-GW forwards Modify Bearer Response to MME.

5

SMF sends the N4 Session Modification Request for query Usage Reporting Rule (URR) to UPF based on event triggers.

Note

user-loc-change event triggers for ULI change

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.

7

Based on URRs received in N4 Session Modification Response, Gy, and RADIUS signaling happens.

8

SMF sends CCR-U to OCS and RADIUSs Accounting Request to AAA.

9

OCS responds with CCA-U and AAA with RADIUS Accounting Response.

10

SMF sends N4 Session Modification Request for update URR to UPF.

11

UPF sends N4 Session Modification Response to SMF.

12

If an event trigger is armed, SMF sends CCR-U to PCRF.

Note
USER_LOCATION_CHANGE event trigger for ULI change.

13

PCRF then sends CCA-U to SMF.

14

Bearer creation, update, or deletion happens based on Gx CCA-U contents.