NAT

As Reid previously introduced in his An Intro to WebRTC’s NAT/Firewall Problem post, NAT traversal is often one the more mysterious areas of WebRTC for those without a VoIP background. When two endpoints/applications behind NAT wish to exchange media or data with each other, they use “hole punching” techniques in order to discover a direct communication path that goes from one peer to another through intervening NATs and routers but not traversing any relays. “Hole punching” techniques will fail if both hosts are behind certain types of NATs (e.g. symmetric NATs) or firewalls. In those cases, a direct communication path cannot be found and it’s necessary to use the services of an intermediate host that acts as a relay for the media or data packets, which typically sits on the public Internet. The TURN (Traversal Using Relays around Nat) protocol allows an endpoint (the TURN client) to request that a host (the TURN server) act as a relay. So far TURN, along with ICE and STUN, has seen little deployment. Now that it is a fundamental piece of WebRTC, it is gaining some momentum. In fact, at the IETF we’re now starting a new effort that will focus on enhancements to TURN/STUN that will be applicable to WebRTC deployments. This new effort is called TRAM (Turn Revised And Modernized), and we’re currently discussing its charter. ...  Continue reading