Consultation Transfer For Qsig Path Replacement; Blind Call Transfer - AudioCodes E-SBC User Manual

CHAPTER 28 Configuring Supplementary Services

Consultation Transfer for QSIG Path Replacement

The device can interwork consultation call transfer requests for ISDN QSIG-to-IP calls. When the
device receives a request for a consultation call transfer from the PBX, the device sends a SIP
REFER message with a Replaces header to the SIP UA to transfer it to another SIP UA. Once the
two SIP UA parties are successfully connected, the device requests the PBX to disconnect the
ISDN call, thereby freeing resources on the PBX.
For example, assume legacy PBX user "A" has two established calls connected through the device
– one with remote SIP UA "B" and the other with SIP UA "C". In this scenario, user "A" initiates a
consultation call transfer to connect "B" with "C". The device receives the consultation call transfer
request from the PBX and then connects "B" with "C", by sending "B" a REFER message with a
Replaces header (i.e., replace caller "A" with "C"). Upon receipt of a SIP NOTIFY 200 message in
response to the REFER, the device sends a Q.931 Disconnect messages to the PBX, notifying the
PBX that it can disconnect the ISDN calls (of user "A").
This feature is enabled by the QSIGPathReplacementMode parameter.
The feature is applicable only to digital interfaces.

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).
For digital interfaces:
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, and CAS). 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:
● Tel-to-IP call: source number of the original call.
● IP-to-Tel call: destination number of the original call.
● 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.
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