SIP REFER Method Call Transfer

In prior releases, the Oracle® Enterprise Session Border Controller supports the SIP REFER method by proxying it to the other UA in the dialog. A handling mode has been developed for the REFER method so that the Oracle® Enterprise Session Border Controller automatically converts a received REFER method into an INVITE method, thus allowing the Oracle® Enterprise Session Border Controller to transfer a call without having to proxy the REFER back to the other UA.

This function can be configured for a specified realm or session agent. When both elements have the SIP REFER method call transfer functionality configured, the session-agent configuration takes precedence over realm-config.

The Oracle® Enterprise Session Border Controller has a configuration parameter giving it the ability to provision the handling of REFER methods as call transfers. The parameter is called refer-call-transfer. When this feature is enabled, the Oracle® Enterprise Session Border Controller creates an INVITE message whenever it receives a REFER. The Oracle® Enterprise Session Border Controller sends this INVITE message to the address in the Refer-To header. Included in the INVITE message is all the unmodified information contained in the REFER message. The previously negotiated codec is also still used in the new INVITE message. NOTIFY and BYE messages are sent to the UA upon call transfer completion.

If a REFER method is received containing no Referred-By header, the Oracle® Enterprise Session Border Controller adds one, allowing the Oracle® Enterprise Session Border Controller to support all call agent screen applications.

In addition, the SIP REFER method call transfer feature supports the following:

Both unattended and attended call transfers
Both successful and unsuccessful call transfers
Early media from the Referred-To party to the transforee
REFER method transfer from different sources within the destination realm
The REFER event package as defined in RFC 3515. This applies for situations where multiple REFER methods are used within a single dialog.
Third party initiated REFER method signalling the transfer of a call by associating the REFER method to the dialogue via the REFER TargetDialog.
The Referred-To party can be both in a different realm (and thus a different steering pool) from the referrer, and in the same realm
The associated latching should not prohibit the Referred-To party from being latched to while the referee is still sending media.