1) Customer's gateways are overloaded, they could not generate RBT after receiving 180 Ringing.
2) Callers are not satisfied when Carrier Announcements (media received in 183 Session Progress) are not relayed.
The purpose is to:
generate Ring-Back Tones for gateways that do not support Ring-Back Tones generation;
pass Carrier Announcements when possible.
Other features that can be implemented in future with help of this core functionality
Ring-back music: enables subscribers to set music or even personalized recorded sounds as ring-back tones;
Ring-back advertising.
Overview
Not all the UAs are capable of Ring-Back tone generation when 180 Ringing is received. The customer has quite a lot of PSTN gateways that do not generate RBT after receiving 180 Ringing or 183 Session Progress. Also not all the vendors generate Ring-Back tone on their side when sending 183 Session Progress with SDP. Thus situations when the end-user hears silence till the call is picked up by the callee appear. To overcome this issue an intelligent generation of the Ring-Back tone on the PortaSwitch side is required.