iOS transfer RTP VoIP call to background

Question

I need some help with a design decision. I am currently building an iOS app that requires VoIP capabilities and I have some questions.

1. I understand that iOS can only maintain a TCP connection in the background. If I have a RTP connection open during a call will that call be lost when the user enters the background? If so how does Skype and others do this?

2. If I have to simply stream audio over TCP to keep a conversation going in the background, does anyone have a suggestion on how to keep the audio in sync in the event of the jitter buffer running empty during a call?

Answer 1

Answer to (1):

iOS VoIP apps may keep a single TCP socket at background, usually your SIP socket, to allow incoming calls (INVITEs).

While your app has an active call, and goes to background, It has no restrictions , you can keep as many sockets as you want.

Here is a more detailed answer from another thread

Regarding the SIP stack implementation, you may want to check open-source PJSip stack