Blind Call Transfer

Blind call transfer is done (using SIP REFER messages) after a call is established between call parties A and B, and party A decides to immediately transfer the call to C without first speaking to C. The result of the transfer is a call between B and C (similar to consultation transfer, but skipping the consultation stage).

You can also use the ManipulateIP2PSTNReferTo parameter to manipulate the destination number according to the number received in the SIP Refer-To header. This is applicable to all types of blind transfers to the PSTN (e.g., TBCT, ECT, RLT, QSIG, FXO). During blind transfer, the device initiates a new call to the PSTN and the destination number of this call can be manipulated if the parameter is enabled. The following is an example of such a blind transfer:

1.

IP phone A calls PSTN phone B, and the call is established.

2.

A performs a blind transfer to PSTN phone C. It does this as follows:

a.

A sends a SIP REFER message (with the phone number of C in the Refer-To header) to the device.

b.

The device sends a Q.931 Setup message to C. This feature enables manipulating the called party number in this outgoing Setup message.

The manipulation is done as follows:

1.

If you configure a value for the xferPrefix parameter, the value (string) is added as a prefix to the number in the Refer-To header.

2.

This called party number is then manipulated using the Destination Phone Number Manipulation for IP-to-Tel Calls table.

3.

The source number of the transferred call is taken from the original call, according to its initial direction:

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Tel-to-IP call: source number of the original call.

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IP-to-Tel call: destination number of the original call.

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If the UseReferredByForCallingNumber parameter is set to 1, the source number is taken from the SIP Referred-By header if included in the received SIP REFER message.

This source number can also be used as the value for the 'Source Phone Pattern' field in the Destination Phone Number Manipulation for IP-to-Tel Calls table. The local IP address is used as the value for the 'Source IP Address' field.