Compare star and mesh delivery during node failure

Steps

Screens captured against Contiki-NG Cooja Contiki-NG release/v4.9 c20b12cd, Cooja 4.8 (2022071901), Temurin 17.0.20.1, image sha256:b14d5afb0a2a852d9e72bbed607ead03f6ccc5f4d4dee44f0799110be2f4b609 on 2026-10-08; the tool may have moved on — the text steps are the contract.

1. 1 Step 1

   Do

   In the Cooja Network window, open mesh.csc in Cooja and pause near 89 s. Trace target mote 5’s arrow through its relay to root 1.

   You will see

   Seed 1 uses 50 m UDGM range and interference. At 85.065 s target 5 reports preferred parent 3 and Rank 422. The GUI arrow shows 5→3→1. Root 1 receives application traffic before the fault.

   Why it matters

   The before-state route identifies which dependency node 3 removal will break.

2. 2 Step 2

   Do

   In the Cooja Network window, click Start/Pause once. At the pause near 150 s, inspect node 3’s absence and target 5’s new route.

   You will see

   The ScriptRunner moves node 3 to (300,300) at 90.065 s. At the second pause target 5’s arrow points to node 2, then root 1. The headless log records the first new-parent event at 100.760728 s.

   Why it matters

   A changed path explains why a delivered packet can resume after a relay moves out of radio range.

3. 3 Step 3

   Do

   Filter Mote output for Preferred parent|Rank. Compare the two snapshots, then check mesh-headless.log for the target fault-window counters.

   You will see

   At 85.065 s target 5 reports parent 3, Rank 422. At 140.065 s it reports parent 2, Rank 425. The log counts 12 target requests sent and 10 received by root during the 90.065–210.065 s fault window.

   Why it matters

   Parent change and application delivery are separate measurements: 10.695728 s to new parent, 20.579856 s to first observed root receipt.

4. 4 Step 4

   Do

   In the Cooja Network window, open star.csc, let it pause near 89 s, and trace target 5’s direct arrow to root 1.

   You will see

   The same six mote positions and seed use 120 m UDGM range and interference. At 85.065 s target 5 reports parent 1 and Rank 296. It sends to root 1 directly, with no node-3 dependency.

   Why it matters

   The star route establishes a before-state for the same node-3 failure.

5. 5 Step 5

   Do

   In the Cooja Network window, click Start/Pause once. At the next pause, inspect target 5’s path and the post-fault application rows.

   You will see

   Node 3 moves out of range at 90.065 s, while target 5 keeps its direct root path. The first scheduled target request after the fault reaches root at 92.147568 s. Star-headless.log counts 12 of 12 target requests delivered during the fault window.

   Why it matters

   Target 5 needed no route recovery in this star because the removed node was a leaf, not its root.

6. 6 Step 6

   Do

   Filter the star Mote output for Preferred parent|Rank. Compare it with the mesh snapshots and both headless summaries.

   You will see

   Star target 5 reports parent 1 at both 85.065 and 140.065 s, with Rank 296 then 278. It delivered 12/12 fault-window requests; mesh delivered 10/12. Mesh first recovered root receipt was 110.644856 s; star had no route break to recover.

   Why it matters

   The comparison is about this chosen leaf or relay failure; radio ranges differ and whole-network traffic totals are not a controlled reliability estimate.