How it works Audio calls (not video) Skype, who knows about WEBRTC, SIP telephony?

Question

Skype

Good afternoon
I'm interested in how Skype audio calls work - how one account is called to another. I assume that during registration you need to indicate and confirm your mobile number, after which calls via SIP telephony will be available? (virtual PBX)
Or how it can work?
I recently heard the news that you can not register on Skype at all, and make audio-video calls
. I would be grateful for an answer.
It would be even better if you answer, is it possible to make Audio calls from site to site?
WEBRTC

Answer 1

well, what is the question? WEbRTC can be done, even without skype