[topspin]

> How would routing be done without source/destination?

There is still a source/destination address. Routing still works. But those addresses are allowed to change without disrupting the connection because the connection isn't based on the values of these addresses.

> When the device changes networks, how does the origin and all routers along the way know

The routers don't need to "know" these things.

MPQUIC does this. To the network it's just UDP packets moving around. Connection state is dealt with at higher levels and doesn't rely on IP addresses.