What the ISDN call transfer application does

The Blueworx Voice Response signaling model assumes that any type of call-transfer operation uses the same channel as the incoming call when it makes the call to the third party to prepare for a transfer. However, ISDN call transfer requires that the call to the third party is made on a different channel from that used for the original call. To match these two requirements, the ISDN call transfer application of Blueworx Voice Response for AIX modifies the ISDN Signaling Process and provides a custom server that performs the call to the third party when a TransferCall request is received.

Blueworx Voice Response implements ISDN call transfer in the following way:

  1. A call arrives at Blueworx Voice Response, and the application decides that the user needs to be transferred to a third party. The application uses the TransferCall state table action to initiate the transfer.
  2. The ISDN Signaling Process makes an outgoing call using the custom server and an outbound state table on another channel. When you create your voice application, you may have to modify the supplied outbound state tables, depending on the needs of your application (for example, the Ring Time parameter of MakeCall can be changed).
  3. When the third party has answered, the outbound state table informs the ISDN Signaling Process using the custom server.
  4. For a blind transfer, the ISDN Signalling Process then asks the switch to complete the transfer using a request and then ends the TransferCall action in the incoming state table. For screened transfer, the ISDN Signalling Process ends the TransferCall action in the incoming state table straightaway. Screened transfer is sometimes known as supervised transfer.
  5. When the TransferCall state table action returns in the original state table, a TerminateCall state table action is called.
  6. On receipt of the TerminateCall action, the ISDN Signaling Process asks the switch to complete the transfer using a request.
  7. The caller and third party should now be connected within the switch. The two call stubs connected to Blueworx Voice Response (the inbound call from the original caller and the outbound call to the third party) are terminated by the switch after a short time. If they do not get terminated, Blueworx Voice Response terminates them after a suitable guard time.
Parent topic: Using ISDN call transfer