Which of the following utilities primarily utilizes the DNP3 protocol?

The DNP3 (Distributed Network Protocol) is specifically designed for the communication between various devices in the field of electrical utility automation and is prominently used by water utilities. It is favored in these applications because it enables reliable and efficient data exchange over long distances in environments that may be challenging for communication.

Water utilities use DNP3 to remotely monitor and control water distribution systems, ensuring efficient operation, data collection for billing, monitoring sensor data, and managing flow controls. The protocol's robust specifications are tailored for the demands of utility control systems, like real-time data analysis and alarms for unexpected conditions, making it essential for the management and operational efficiency of water utilities.

Other sectors like telecommunications, automotive, and healthcare have their own specialized protocols suited for their unique operational requirements, which is why the DNP3 protocol is not suitable for those industries.