[OpenSBC] Getting OpenSBC to Generate a "Ring" on 180 Ringing Messages

[OpenSBC F. <ope...@op...>]

I've just put OpenSBC 1.1.5 RC3 between sipXecs 3.10.2 and our SIP Trunk because the Trunk won't handle REFERs -- causing the auto-attendent to not function properly for calls originating from the PSTN (transfers fail). With OpenSBC in place, set to handle REFERs locally, attended transfers now work. But once OpenSBC gets the REFER and attempts to connect to the new number, it doesn't generate a "ringing" sound, even though its receiving 180 Ringing messages from sipXecs. Is this an expected behavior for OpenSBC, or is there something I haven't configured? I've looked around for a media file that would be played by OpenSBC to produce the ring, but I couldn't find anything. Any thoughts would be appreciated!