Dear SIP-ISUP experts, we have a nasty situation in case of interworking SIP to ISUP. The INVITE request is mapped to ISUP/IAM, that's as expected. But then on the ISUP side we have a colored ringback tone service. This causes in an ISUP ACM message with both flags set: - Backward Call Indicator: subscriber free - Optional Backward Call Indicator: In-band info or pattern available The interworking implementation maps both flags to separate messages - Backward Call Indicator: subscriber free --> 180 Ringing - Optional Backward Call Indicator: In-band info or pattern available --> 183 Session progress.
The UA client receives both provisional responses and it depends on the sequence if the colored ringback tone is rendered. If 183 Session progress is the last on then the colored ringback tone is rendered. If 180 Ringing is the last one, then the colored ringback tone is followed by the local generated ringing tone, which leads to the colored ringback tone not being rendered. I think the interworking implementation should not provide both provisional responses (180 Ringing and 183 Session Progress) which are somehow contradicting. In case of colored ringback tone a single 183 Session Progress should be used. The interworking specification (3GPP TS 29.163) does not clarify the behavior when both flags in an ACM are set. What do you think? BR Franz Edler _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
