# Measurement Routing

Measurement routing is defined in the tag configuration, that is read and cached upon module startup and every time the tag configuration changes (see **ConfigModule** documentation). The tag configuration is generated from the Asset Hierarchy automatically, by the Nexus platform, to ensure the desired functionality.

The possible routings are:

* **Hot Path:** Streams measurements directly to cloud storage, with minimal delay but also a higher cost. Applications are real-time services like dashboards, alerts, and low-latency analytics. Measurements are also stored for long-term retention with this option.
* **Cold Path:** Routes measurements to cloud in cost-efficient file batches, for long-term retention. The batching introduces a configurable delay, but also minimizes costs.
* **Local Historian:** Stores measurements in a historian database running on the edge device as a module, or alternatively within the on-premises network, for onsite trending and offline access.
* **Internal:** Routes the measurements to another edge module—for example, for enrichment, local calculations, or write-back.

Depending on the use case, you can send the same measurement to multiple targets—hot path for low-latency dashboards and alarms, cold path for low-cost storage, local historian for on-site trending, or other specific edge modules.

Routing can be:

* **Scheduled** (e.g., latest measurement routes at fixed intervals) or
* **On change**, where the module forwards only when a value updates.

In the figure below we have two data collector modules that read from PLCs and produce measurements. The measurements are sent to cloud and to a local historian running on the edge device, as a separate module. One of the data collectors also writing (calculated) measurements back to the PLC.

To support these scenarios, the **DataDistributionModule** uses different kinds of routing types.

<figure><img src="/files/emBSbzCoSFSKt0OppIvb" alt=""><figcaption><p>Example of measurement routing for edge application that uses hot-, cold-, internal- and local historian routing.</p></figcaption></figure>


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