Design loop tracing for Stingray

[michielbdejong]

As I'm designing Stingray, having implemented the flood probes and pin probes from #4, there comes a point in the algorithm where a node becomes aware of a proof of loop and starts a loop trace.
This loop trace is linked to the probeId and goes out in both directions.

In all cases a loop trace is started when a pin probe comes back.

       North
        |
West - Alice  - East
        |        |
       South ___/

What if you received a probe from multiple directions?
One easy approach is to send the Loop trace back to the sender of the Probe message that triggered it.
And when forwarding a Loop trace, there will generally only be one from of the Probe...

I'll draw some diagrams with Flood-Pin-Trace in different colours to see if this works.

[michielbdejong]

Don't skip the PIN!

FLOOD may find a loop in a P shape, where the origin is not on the loop.
Sending a PIN back, it will spread along both directions of the FLOOD, and ensure that when that loops back, it's a single-direction loop.
Then the TRACE can go into the opposite direction to single out the right branch of the PIN tree.

[michielbdejong]

Reusing this design for Butterfly