Notify receiver

I am completely new to Video and Audio calling. Based on the tuturial, I was able to successfully run Ionic open vidu app with video and audio calling. When i tested the app between two phones, I had to join the call to see the videos / audio. How do I make something similar to Whatsapp call instead of joining a room? How can i send notification or make ringtone at the receiver end?

@viswa.tk
Maybe this might help you workout how to do this.
https://webrtc.ventures/2015/09/sending-generated-audio-through-webrtc-as-a-live-feed/

Let me know how you go.