2.2. Blind Call Transfer

A blind transfer is initiated the same way as a supervised transfer. However, after dialing the destination number, the extension performing the transfer hangs up and does not wait to determine the outcome of the call. The call is released to the PBX. Blind transfers are used in most voice mail applications. A blind call transfer is equivalent to the following manual operations:

1. answer a call
2. put the call on hold
3. press the transfer key
4. dial the destination number
5. hang up.

The call is immediately sent to the new extension. It is up to the PBX to determine what to do if the transferred call is not answered (because of busy or no answer). Usually, if a transferred call is not answered it is routed back to the voice mail system, and eventually to the operator (or an automated attendant).

The advantage of a blind transfer is that the immediate release to the PBX frees the voice processing resources to handle new calls rather than being used to perform call progress. The only potential drawback of a blind transfer is when phone traffic is heavy, in which case the application may need to handle a call overflow condition.

An application can perform blind transfers without special integration tools. However, by using a PBX Integration board and the Unified API to access the called number ID from the PBX, the application can differentiate between:

• a new call coming in that needs to be processed: "Hello and thank you for calling Dialogic Corporation."
• a call that was transferred at least once already and is being routed by the PBX into voice mail: "You've reached the desk of Marcia Jones in Engineering, please leave a message."

If the call was transferred, the application can use the called number ID to send the call directly into the appropriate voice mail box, allowing the caller to leave a message without having to navigate through a series of menus for a second or third time.

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