Is there a way to create a point to point video calling using any open source SIP server or something like that and configure the accounts in an app to communicate with each other.  I understand there is Viber, Skype etc but sometime either due to network congestion or slow network or  some other reason these don't work and Viber says Poor network and stops video etc. when talking to someone in another country.

Ideally I would like to create two accounts and they should be able to communicate with each other using an app.  It's just a thought and maybe if this is possible quality might be better?