Blind transfer is when a call is routed to a third party, the original call is ended, and no check is made to determine whether the transferred call is answered or if the number is busy.
To do this, the Blueworx Voice Response application places the call on hold and sends a REFER message containing the TO header address of the third party to the original caller. This call then disconnects from Blueworx Voice Response and connects to the third party. If the transfer is unsuccessful, the original call is lost. Blind transfer does not require Blueworx Voice Response to make a call to the third party.
Blind call transfer is implemented using the SIP REFER method based on RFC 3515. A Blind transfer can be used if the phones connected in the network support the REFER method. Most phones publicize their capabilities in the ALLOW header which is commonly present in a SIP INVITE message. Some phones use the OPTIONS message to indicate these capabilities.