In the beginning, there was cabling - lots of cabling. Every sensor, actuator, and display was connected by a separate cable that grew like a hydra from a controller, the brains of a traditional control system. If a solenoid needed to be triggered in response to the activation of a limit switch then the signal traveled from the limit switch, through cabling to the controller, which processed the information and sent a command to the solenoid over yet another cable. These direct wired systems were subsequently replaced with time or frequency division multiplex systems that allowed one common cable to be shared among multiple devices. Installation was simpler and less expensive, the controller was more complex and, as before, a central point of failure should its program fail to execute properly.
Next up were intelligent, distributed networks in which devices communicated directly with one another on a peer-to-peer basis, without the need for a central controller. Locally intelligent and able to communicate on shared communication medium with any other device on the network, these networks allowed reconfiguration of system functionality via software download over the network. Peer-to-peer communications allowed the direct exchange of information between any or all of the devices without intervention by any central device, eliminating the single point of failure issue.
Regardless of the specific architecture used, in all cases the objective of the control network was to deliver status information as quickly as possible to all devices that needed updates. The protocols we’re highly optimized for short control packets, and nary a bit was “wasted” on ancillary data or status.
The same optimization guidelines applied to the microcontrollers running the devices. To keep costs down and thereby allow the networks to be pervasively deployed down to the lowest cost sensor/actuator, processors were optimized for high throughput and processing short packets.
The popularity of IP connectivity spawned the development of IP-based control networks in which Ethernet or Wi-Fi forms a backbone for linking different sections of a control network. While controllers were the first devices to sit on an IP network, increasing numbers of native IP sensors and actuators are reaching the market.
Many IT departments prohibit the connection of any IP-based, control-related sensor/actuator, controller, gateway to their corporate networks out of concerns about network integrity and security. IT managers are legitimately concerned that the high offered traffic of control networks, some of which run at 100% channel utilization, will overwhelm their Ethernet networks and cause unintentional denial of services. Others are concerned that control networks, the security standards of which are rarely a high priority, could become unprotected back-doors into the corporate network.
What is rarely if ever discussed is how exposed the enterprise is to unauthorized manipulation of the control devices themselves. These systems control the power at the heart of every business and institution, and it is paramount that they be protected against unauthorized manipulation. It is to this point that we’ll return in the next installment of this series.
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