SIP REFER-to-BYE

The Oracle® Enterprise Session Border Controller’s SIP REFER-to-BYE capability addresses situations when other network elements do not support the REFER method but do offer blind transfer in a SIP BYE request. The target number is encoded in a Reason header of the BYE request. In such cases, the Oracle® Enterprise Session Border Controller terminates the REFER and passes the Refer-To number in a Reason header of the BYE.

You configure both SIP interfaces and SIP session agents with the refer-to-bye option to use this function:

• SIP interface—You add this ability to SIP interfaces facing the SIP elements that need to receive a BYE instead of a REFER. This setting only applies when the next hop is not a session agent.
• SIP session agent—The SIP session agent takes precedence over the SIP interface. You add this ability to SIP session agents that need to receive a BYE instead of a REFER. If the next hop SIP element—the remote target in the dialog—is a session agent, in other words, you need to configure the option for it. Note that when you use this option for SIP session agents, the SIP interface or realm on which the REFER is received takes precedence over the REFER-to-BYE capability.

When a REFER request arrives and the REFER-to-BYE capability applies, the Oracle® Enterprise Session Border Controller responds to it with a 202 Accepted and sends a NOTIFY to terminate the implicit refer subscription. This NOTIFY contains a message/sipfrag body with SIP/2.0 200 OK. Upon receiving the response to this NOTIFY, the Oracle® Enterprise Session Border Controller sends a BYE with an added Reason header (encoded with the Refer-To number) to the other end.

The network element that does not accept REFERs takes the BYE with the Reason header and issues a new initial INVITE that initiates transfer, which the Oracle® Enterprise Session Border Controller sees as starting a new and independent session.