What defines upstream trace movement in a source-based network?

In a source-based utility network, upstream trace movement is characterized by the direction of flow being toward the subnetwork controller. This is crucial because the subnetwork controller typically represents a point from which sources of supply (like water or electricity) originate and are distributed. When tracing upstream, the objective is to identify the sources that feed into a specific point in the network, particularly focusing on where the resources are coming from rather than where they are going.

Choosing the scenario where the flow moves toward the subnetwork controller accurately reflects the nature of tracing upstream, as it aligns with the operational logic of understanding how resources flow into a network. In the context of utility management, being able to visualize and track this flow helps in maintenance, troubleshooting, and efficient resource management.

The other options do not define upstream movement accurately. Moving away from the subnetwork controller or describing the trace as moving downstream misrepresents the concept, as upstream by definition involves looking back towards the source rather than outwards or forward. Lastly, saying there is no defined flow contradicts the foundational principles of how upstream tracing operates in utility networks, where the flow direction is indeed significant.