Midbox traversal–offer in INV Alice atlanta.com biloxi.com Bob Alice can try to get STUN/TURN addresses If address in offer are not valid, atlanta sends 4xx proposing new addresses; if they are valid, open pinholes/create bindings Bob can try STUN to fetch addresses biloxi adds proposed answer for Bob, and forwards Bob responds with an answer for Alice, and (in NAT case) can include Bob’s actual addresses |