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# Software-in-the-Loop (SIL)

Software-in-the-loop testing exercises the whole safety chain on a single host,
with no cameras and no robot. It swaps the physical parts of the system — the
warehouse, the forklift, the cameras — for virtual equivalents driven by NVIDIA
Isaac Sim, while the production software runs unchanged: the VSS Warehouse
Blueprint for perception, the Safety Core for trust, fusion, and decisions, and
the communication layer that feeds the decision back to the simulated forklift.

That makes it the fastest way to see the system react end to end. You can start
before target hardware is available, iterate in minutes rather than
re-staging a physical scene, and rehearse scenarios that are unsafe or
impractical to stage with real workers and vehicles.

## Choosing a perception profile

| Quick start                                | When to choose it                                                                                                                              |
| ------------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------- |
| [SIL — 2D Perception](/halos/outside-in-safety/testing/sil/sil-2d) | The recommended starting point. Uses the VSS 2D profile, one pipeline per camera: the simplest setup and the highest frame rate.               |
| [SIL — 3D Perception](/halos/outside-in-safety/testing/sil/sil-3d) | Uses the VSS 3D (BEV) profile, where several cameras are grouped into a single bird's-eye sensor. Choose it when your target deployment is 3D. |

Both run on one host and need an Isaac Sim capable GPU; see
[Prerequisites](/halos/outside-in-safety/getting-started/prerequisites) for the hardware and software requirements.
If no such host is available, [Deploy on NVIDIA Brev](/halos/outside-in-safety/getting-started/brev-launchable) provisions
one in the cloud and brings the same 2D loop up from a notebook.

## Going deeper

The [Software-in-Loop Testing](/halos/outside-in-safety/testing/sil) section is the home for closed-loop testing. Once
the environment is up, it covers the
[architecture and data flow ](/halos/outside-in-safety/testing/sil/architecture), the
[Isaac Sim integration ](/halos/outside-in-safety/testing/sil/components/isaac-sim), and the
[action graph ](/halos/outside-in-safety/testing/sil/components/action-graph) that drives the
simulated scene.

To run the same closed loop with perception and the Safety Core on NVIDIA IGX
Thor hardware, see [Hardware-in-the-Loop Testing](/halos/outside-in-safety/testing/hil).