How to write a SIP blind transfer application

The Blueworx Voice Response signaling model assumes that a blind transfer operation uses the same channel as the incoming call when it makes the transfer to a third party.

Blueworx Voice Response implements VoIP SIP blind call transfer in the following way:

1. A call arrives at Blueworx Voice Response and the application recognizes that the caller needs to be transferred to a third party.
2. The application uses the TransferCall state table action to initiate the transfer.
3. In preparation for the transfer SV541 must have a TO_HDR tag assigned to the URL address of the third party; for example:

   AssignData(SV541, "PUT_TAG",  "TO_HDR","sip:chris@99.22.30.96:5060")

   XFER_TIMER can also be added to SV541 if required to set a timeout value for the transfer attempt. Set this to 0 if true blind transfer is required.
4. The TransferCall state table action must be placed after AssignData in the state table (this must be at the point that the transfer is required to be invoked). For a blind transfer the ring time and ring time parameters must be 0, for example, TransferCall("", "", 0, 0, 0).

   The TransferCall state table action can be used in its traditional form (by using numbers without setting SV541), however this would require the system to be configured to use a SIP proxy server.

5. The call is ended.