Step 1 Capture and analyze upstream network packets of the SoftCo. The timeout period carried in the SoftCo registration request is 1800s, as shown in the following figure.
Step 2 Check the 200 OK message returned by the IMS network. According to the following figure, the user has changed the timeout period to 30s on the IMS network.
When the timeout period changes to 30s, the SoftCo sends a registration message to the IMS network every 15s (because the registration interval is half of the timeout period). This sharply increases the registration traffic. In response, the IMS network sends a 423 error code to the SoftCo, informing the SoftCo that it cannot respond to every registration message within such a short interval.
Step 3 Change the timeout period from 30s to 1800s. However, the IMS network changes the timeout period to 30s using its 200 OK response message. Constant and abnormal changes of the timeout period lead to the registration failure of some SoftCo users.
Step 4 Conclude the failure reason. The IMS network is running properly, and it is the SBC on the IMS network that is faulty.
Step 5 Change the SBC configurations on the peer office.