Correcting and updating this, partly based on Paul's message: wor...@ariadne.com (Dale R. Worley) writes: > I would suggest adjusting the VoLTE UE's to not send SDP (establish a > session) until they are prepared to send media, either ring-back tone or > user media. Otherwise the CPE has to test the provided media to see if > it is silent.
I forgot to note that a UAC (caller) or a switch acting on its behalf should only start to generate ringback to the user when it receives a 180 response. Other 1xx's don't indicate that ringing has started. Although if it receives a 181 or 182, it might be useful to provide the user with a short tone to indicate forwarding or queueing. Certainly, if SDP is received in a 180, but the device doesn't receive any media packets described by the SDP, then the device should generate its own ringback tone. If the device does receive media packets, the ideal action is to check whether the media contains silence. If the media is silent, the device should generate ringback, and if it is not silent, it should render the media. But checking for silence may be too much work in practice. Dale _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
