Attended call transfer - Enforcing the use of MS Teams infrastructure (vs REFER/Replaces)
In https://learn.microsoft.com/en-us/microsoftteams/troubleshoot/phone-system/direct-routing/issues-with-call-transfers, the following is stated: A call transfer can be made by using any of the following methods, in order of preference: - Using a Session Initiation Protocol (SIP) Refer message. - Using an SIP Invite message that has a Replaces header. This method is mostly used for call queue responses. - Using an internal Microsoft Teams infrastructure. This method isn't visible to SBC. The method is used only if the first two methods are not supported. Assuming I am disabling the first two methods: using REFER request & using "Replaces" header - Disabling REFER by not including it in the "Allow" header - Disabling "Replaces" by rejecting the incoming INVITE from MS SIP Proxy with a 420 response along "Unsupported: replaces" header according to RFC3261 section 8.1.3.5 How can the 3rd method be enforced and let MS Teams infrastructure handles the attended call transfer transparently by bridging the two calls and tearing down the session with MS Teams user who triggered the consultative call? In my setup, I am not including REFER in "Allow" (requests and responses) & I am rejecting the 3rd INVITE received once doing consultative transfer with a 420. However, I end up with a failed call transfer because the 3rd method mentioned in the documentation is not taking place.