The basics
A person enters an underground passage where radio communication and navigation are impossible. They drop a miniature radio repeater on the ground every 10 meters. Each repeater is connected to the next repeater by short-range radio. Datapackets jump from repeater to repeater, enabeling real-time communication, navigation and other digital data transfers modes. See illustration below.
The video shows how a datapacket from a user (red elipse) moves along the repeaters (green dots) and ultimately arrives at the other side of the network in an other user's UNCI Navigator.