Initial Attach Call Flow
This section describes the Initial Attach call flow.

Step |
Description |
---|---|
1 |
The MME sends the Create Session Request with TEID value zero to the S11-GTP-EP. |
2 |
Transaction E-T1 is started. The S11-GTP-EP forwards the Create Session Request to the Service-POD (SGW). |
3 |
Transaction S-T2 is started to validate the Create Session Request. The Service-POD (SGW) sends the Allocate Id Request to the Node-Mgr. |
4 |
The Node-Mgr sends the Allocate Id Response to the Service-POD (SGW). |
5 |
The Service-POD (SGW) reads the cache to perform the UPF selection. |
6 |
The Service-POD (SGW) sends the Sx Establishment Request to the PFCP-EP. |
7 |
Transaction P-T3 is started. The PFCP-EP sends the Sx Establishment Response to the Service-POD (SGW). |
8 |
Transaction P-T3 is completed. The Service-POD (SGW) sends the Create Session Request to the S5-SGW-EGRESS-GTP-EP. |
9 |
Transaction E-T4 is started. The S5-SGW-EGRESS-GTP-EP sends the Create Session Response to the Service-POD (SGW). |
10 |
Transaction E-T4 is completed. The Service-POD (SGW) sends the Sx Modification Request to the PFCP-EP. |
11 |
Transaction P-T5 is started. The PFCP-EP sends the Sx Modification Response to the Service-POD (SGW). |
12 |
Transactions P-T5 and S-T2 are completed. The Service-POD (SGW) sends the Create Session Response to the S11-GPT-EP. |
13 |
Transaction E-T1 is completed. The S11-GPT-EP forwards the Create Session Response to the MME. |
14 |
The Service-POD (SGW) sends the Create Session to DB message to the CDL-Endpoint. |
15 |
The MME sends the Modify Bearer Request with TEID to the S11-GTP-EP. |
16 |
Transaction E-T1 is started. The S11-GTP-EP sends the Modify Bearer Request to the Service-POD (SGW). |
17 |
Transaction S-T2 is started. The Service-POD (SGW) sends the Sx Modification Request to the PFCP-EP. |
18 |
Transaction P-T3 is started. The PFCP-EP sends the Sx Modification Response to the Service-POD (SGW). |
19 |
Transaction P-T3 is completed. The Service-POD (SGW) sends the Modify Bearer Response to the S11-GTP-EP. |
20 |
Transaction S-T2 is completed. The S11-GPT-EP forwards the Modify Bearer Response to the MME. |
21 |
Transaction E-T1 is completed. The Service-POD (SGW) sends the Update Session to CDL message to the CDL-Endpoint. The session is updated in CDL. |