Hello Experts,
What could be the possible reasons for false Ring Back Tone (RBT) in VoLTE?
Short CST (Call Setup Time).
VoLTE devices play the ringtone locally. This can be due to a device profile issue caused by the device vendor or may occur in roaming scenarios, where the device activates the visited network’s profile.
This might be due to Device validation issue in EIR.So Usually in a IMS network there are two IDs which a suer can subscribe in to.Those are IMPI and IMPU.IMPI is IP multimedia public which is the SIP URI or TEL URI.and other one is IMPI is the private ID which varies per netork.If your mobile network do dievice validation via EIR then IMPI will be IMEI most of the time. if Not can be IMSI.So what will happen is during initial registration impi get bind to PCSCF core IP which is called SGC most of the time so after that whole network can refer UE to that point.for Announcement Ring Back Tone,Call hold tone etc.For that kind of network if you bring and unregistered device or Unauthorised device or latest device which havent received the device certification might have a chance of facing this issue.