How to open an ionic 3 app even when the app gets closed/killed?

I am creating a video call application in ionic 3. I can able to recieve call and communicate while my app is in open and background mode(maning when it is in minimized state). But when i close the app the connection to the server is getting closed and i am unable to call the peer. Note: I am using Kurento Media Server for video call. Please provide a solution how can i make my app to get in touch with server forever even if the app is closed/killed.

I do not believe it is possible for anybody to communicate with your app if it is not running.

Thanks for your reply. If that is not possible how apps like whatsapp able to recieve call even it is in the closed state. Please explain on this so that i can follow in my app also.