SIP Refer Support

Let’s start with the simple scenario involving three parties: Alice, Bob and Carol. Alice calls Bob and Bob wants to connect Alice to Carol. Bob presses the Blind Transfer button on his desk phone and types Carol’s number. His phone hungs up and Alice should be connected to Carol. There is also a possibility that Carol will not answer timely or will be busy talking with somebody else. In that case, it’s needed to connect Alice to Bob again, and this is easy to implement with existing Restcomm features as we’ll see later.

For the described scenario, we will need two incoming phone numbers:

The number A has additional property called Refer URL which could be either Visual Designer application name or any other URL and is used to point to the refer application that will be executed during the call transfer. So configuration for number A should look like this:

During call transfer, Restcomm will check the SIP Refer request in order to extract the call transfer details and will create the following new parameters:

The above new parameters will be part of the HTTP request that Restcomm will do download the RCML and so at Visual Designer you can use the following new core variables:

For example, the Visual Designer application for number B that will be executed after call transfer can use <Dial><Number>$core_ReferTarget</Number></Dial> so what ever Bob dialed during the call transfered it will be in the Dial verb of the Refer application.

Call flow exceptions such as no answer, failed etc, should be handled the usual way, by using Dial Action or verbs after Dial.