UE-requested PDN Connection Call Flow
This section describes the UE-requested PDN connection call flow.

Step |
Description |
---|---|
1 |
The MME sends the Create Session Request for a new PDN connection to the S11-GTP-EP with a nonzero TEID. |
2 |
The E-T1 transaction is started. The S11-GTP-EP decodes the received UDP message and converts the message into the gGRPC message. Based on the IMSI value, the message is forwarded to the respective SGW-service pod which handles the UE session. The SGW-service pod receives the Create Session Request from the S11-GTP-EP. |
3 |
The S-T2 transaction is started. The SGW-service pod finds the subscriber context based on the local ingress TEID, and validates the Create Session Request content and updates the PDN and subscriber information. The SGW-service pod reads the UPF cache to provide the selected UPF. |
4 |
The SGW-service pod sends the Sx Establishment Request to the PFCP-EP. |
5 |
The P-T3 transaction is started. The PFCP-EP sends the Sx Establishment Response to the SGW-service pod. |
6 |
The P-T3 transaction is completed. The SGW-service pod sends the Create Session Request to the S5-SGW-EGRESS-GTP-EP with S11-U and S5-U TEID details. |
7 |
The E-T4 transaction is started. The Create Session Response is validated and the S5-U remote TEID is updated in the PDN. The S5-SGW-EGRESS-GTP-EP sends the Create Session response to the SGW-service pod. |
8 |
The E-T4 transaction is completed. The SGW-service pod sends the Sx Modify Request to the PFCP-EP. |
9 |
The P-T5 transaction is started. The PFCP-EP sends the Sx Modify Response to the SGW-service pod on expiry of the timer T5. |
10 |
The P-T5 and S-T2 transaction is completed. The GTP-EP receives the Create Session Response from the SGW-service pod. |
11 |
The E-T1 transaction is completed. The MME receives the Create Session Response from the S11-GTP-EP. |
12 |
The SGW-service pod updates the created session in CDL endpoint (database) with new PDN information. |
13 |
The MME sends the Modify Bearer Request with TEID to the S11-GTP-EP. |
14 |
The E-T1 transaction is started. The S11-GTP-EP routes the Modify Bearer Request to the SGW-service pod. The S11-GTP-EP sends the Modify Bearer Request to the SGW-service pod. |
15 |
The S-T2 transaction is started. The SGW-service pod sends the Sx Modify Request to the PFCP-EP pod on expiry of the timer S-T2. |
16 |
The P-T3 transaction is started. The PFCP-EP sends the Sx Modify Response to the SGW-service pod on expiry of the timer T3. |
17 |
R-T3 transaction is completed. The SGW-service pod sends the Modify Bearer Response to the MME. |
18 |
S-T2 transaction is completed The SGW-service pod sends the update session to the CDL endpoint. |