This is similar to how Webex room systems communicate using Proximity: ultrasounds emitted by a room device are picked up by the laptops / mobile devices of participants and exchange info on how to join. So as you walk into a room, the Telepresence unit recognizes you and allows you a set of actions, but someone in the room next door won't be able to access.

This project is cool in that it's exchanging an actual SDP, which could be used for any media negotiation.