1. According to the message trace result, the IMS_A sends 180 to PSTN_C after it received the invite message. When the ATS receives the 180, it does not process it and pass it through to the PSTN_C side. We can see that the Call Waiting service is not triggered compare to the CW service flow.
2. Owing to the CW service not triggered, and analyzing the inter traces of ATS, it can be seen that the parameter of ucMAXMutiCallNum is 2. That means a single subscriber can support 2 concurrent calls. This will cause the CW service not triggered. The ucMAXMutiCallNum parameter can be seen by the following capture:
3. According to the incorrect parameter, MAXPARACALL can be re-configured on ATS by MOD SBR and set it to 1: Then the CW service will be triggered successfully。