Test a gateway actuator fail-safe boundary

Observe a connected ventilation rule, remove its gateway dependency, and decide what independent mechanism must establish the safe state.

Packet Pete, your practice guide

Packet Pete
Predict the reading, then compare it with the measurement.

Cisco Packet Tracer

Desktop lab

Tier 3 · Install required · Cisco account required

Version tested: Cisco Packet Tracer 9.0.1 on Ubuntu 22.04 (Apptainer/Xvfb); project saved and reopened 2026-09-10. Date: 2026-09-10.

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Steps

Screens captured against Cisco Packet Tracer Cisco Packet Tracer 9.0.1 on Ubuntu 22.04 (Apptainer/Xvfb); project saved and reopened 2026-09-10 on 2026-09-10; the tool may have moved on — the text steps are the contract.

  1. Step 1

    Do
    Open lab.pkt in Packet Tracer and inspect the named Things in the Logical workspace.
    You will see
    Home Gateway0, CO2-Sensor, Fan, Window, Smoke-Watch, Fail-Safe-Siren, and Local-Fire-Sprinkler are visible.
    Why it matters
    Naming each sensor, dependency, action, and evidence source makes the test boundary reproducible.

  2. Step 2

    Do
    On the Logical canvas, read the chapter-specific names beneath the devices and compare their roles.
    You will see
    The Logical canvas shows fail-safe alarm and local sprinkler devices in this lab's named workspace.
    Why it matters
    Different physical jobs can share a network while still requiring different thresholds, safe states, and operating evidence.

  3. Step 3

    Do
    On the Logical canvas, trace the solid PC0 cable and any visible dotted wireless associations back to Home Gateway0.
    You will see
    The solid black line connects PC0 to Home Gateway0; where dotted lines are visible, they mark wireless associations.
    Why it matters
    A visible association is evidence of topology, not by itself proof of authentication, registration, or delivery.

  4. Step 4

    Do
    On the Logical canvas, identify each object that has no visible gateway line; do not count it as registered evidence.
    You will see
    Objects without a line to Home Gateway0 remain visibly outside the registered control path.
    Why it matters
    Packet Tracer physical objects are not automatically network endpoints, so an absent line must remain explicit.

  5. Step 5

    Do
    On the Logical canvas, use the model captions and names to separate sensing, actuation, service, and physical-context roles.
    You will see
    The device names and model captions distinguish sensors, actuators, service endpoints, and physical context.
    Why it matters
    Role labels keep a plausible diagram from being mistaken for measured control-loop behavior.

  6. Step 6

    Do
    Close and reopen lab.pkt, then compare the restored Logical workspace with this evidence image.
    You will see
    After reopening the saved project, the same lab-specific names, positions, and connection lines remain visible.
    Why it matters
    A reopen check proves persistence of the saved topology without inventing runtime readings or protocol semantics.

Chapter checks

These questions refer to the chapter’s examples. Use the return links to review their answers.

  1. Your control loop feeds the watchdog only after each iteration, with no other task feeding it. It normally takes 80ms, and the watchdog timeout is 100ms. What happens if SD card logging makes one iteration take 150ms?

    Return to the chapter’s knowledge check

  2. Why can relay OFF be a safe default for an overheating hazard but an unsafe default for a freeze-protection load?

    Return to the chapter’s knowledge check

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