The water distribution network comprises of three components
- Remote Terminal Units (RTU) which are field operational units performing local process control
- Central Human Machine Interface (HMI) which provides visualization and control of RTU activity individually and collectively from a central location
- An interconnecting network comprising of radios, switches, routers and transport media
Each RTU has a router which acts as a layer-3 device and includes a gateway and a firewall. Each RTU will also be a separate IP subnet to facilitate encoding of location and other information in the IP addressing. The HMI is a redundant pair of SCADA nodes running as virtual machines on two physical servers at a single location which are also fire-walled from the other network components.
This real-world system was first tested in a virtual laboratory environment comprising of hardware, software and interconnections as close to the actual system as possible.
The HMI VM was cloned into the simulation environment. The RTU PLCs are modeled using Rockwell Automation's SoftLogix. A VM was used for each instance of SoftLogix. Each SoftLogix simulated six controllers in a single 17 slot virtual rack. NetSim emulator was used to interconnect these two components and to emulate the 3rd component i.e. the radio network.
In this virtual lab, numerous test scenarios were constructed and executed repetitively for normal operation as well as perturbed operation. Impairment scenarios were studied which included escalating latency, bandwidth constriction at various points, jitter tolerance, packet loss, packet reordering, route loss, fail-overs and single point of failure identification. An optimal design was then arrived at based on the simulation results.