DTMF Transfer for Spiral Calls

A spiral call occurs when a call’s signaling messages loop back through the Oracle® Enterprise Session Border Controller. Most commonly the signaling path is from one UA, through the Oracle® Enterprise Session Border Controller, to a call server, back through the Oracle® Enterprise Session Border Controller, to another UA. The media path is from one UA, through the Oracle® Enterprise Session Border Controller, to the other UA. For DTMF indication processing, only the call legs between the endpoints and Oracle® Enterprise Session Border Controller are considered.

The Oracle® Enterprise Session Border Controller evaluates that the signaling path to and from the call server terminates on the same IP address and port on the Oracle® Enterprise Session Border Controller. This means that it’s a spiral call. In addition, the media IP addresses and ports in the SDP indicate that the Oracle® Enterprise Session Border Controller does not need to send the media into the call server’s realm.

An issue occurs when DTMF indication is relayed either by RFC 2833 or DTMF audio tones for a spiral call. Since the DTMF indication is in the media path, the call server remains unaware of the signaling; no media-based DTMF indication digits will ever reach the call server. In order to include the call server in the DTMF-indication signaling, you should set the dtmf-in-audio and/or rfc-2833 mode used for the realm or signaling interface where the call server is to dual.