http://ipop-project.org/learn/architecture/
IPOP’s architecture and design have evolved since the project’s inception from one based on a structured P2P library (Brunet) connecting all peers into a global overlay, to the current design based on TinCan links that connect peers to trusted peers where trust relationships are extracted from online social network providers. At its core, IPOP leverages existing technologies (Jingle/WebRTC) and standards (STUN, TURN, XMPP) to tunnel IP packets over P2P links between two computers – even when they are both behind firewalls and/or Network Address Translators (NATs). Users can choose to deploy their VPNs on existing public XMPP infrastructure such as Google Hangouts or their own personal XMPP server.