ControlNet is another member of the family of networks that implement common industrial protocol (CIP) at the upper layers. ControlNet combines CIP with the Concurrent Time Domain, Multiple Access (CTDMA) technology, thus producing a serial communication system, which allows deterministic, high-speed I/O and peer-to-peer connection in time-critical applications.
ControlNet connection has the following characteristics:
- It provides complete producer-consumer services for configuring, controlling and assessing intelligent devices over a single network.
- It provides deterministic and repeatable performance for both discrete and process applications.
- It supports various topology options like, trunk/drop line, ring, star, tree, and combination of any of these, using repeaters.
- It allows seamless removing and replacing nodes in the network.
- It can be used in potentially explosive atmosphere.
- It can detect duplicate node ID.
- It supports multiple media types like, coaxial cable, fibre optic, RG-6 quad shield cable etc.
- It can support up to 99 nodes and a bus speed of 5 mbits/s.
- It supports I/O or implicit messages involving time-critical data, as well as explicit messages like protocol information or service requests.
At the physical layer, ControlNet offers multiple choices of topologies and media options. The following table describes the options briefly:
|| 2 nodes
|| 32 nodes
|| 48 nodes
|| 49 – 99 nodes|
|| 1000 m (3280 ft)
|| 500 m (1520 ft)
|| 250 m ( 820ft)
|| Requires repeaters|
||Depends on fiber and termination quality, repeater capability|
| Coax or fiber with repeaters
||Depends upon no. of repeaters, repeater capability, fiber and termination quality|
| Maximum drop length
|| 1 m (3.3 ft)
|| 1 m (3.3 ft)
|| 1 m (3.3 ft)
|| 1 m (3.3 ft)|
With a fibre optic media, ControlNet incorporate a full-duplex, point-to-point link using a transmitter and receiver at both ends. Repeaters are used for extending the network and increasing the number of nodes per network segment.
In the data link layer, ControlNet uses Concurrent Time Domain, Multiple Access (CTDMA) algorithm, which ensures limited delivery.
ControlNet uses two types of messaging at the transfer and network layer.:
- Unconnected Messaging – it is used for establishing a connection and for transmitting infrequent, low-priority messages.
- Connected messaging – it is used for real-time I/O data transmission. For this kind of messaging, the ControlNet reserves the connection resource.
ControlNet supports three device classes:
- Messaging class
- Adapter class
- Scanner class
The following table states the uses and examples of the devices under each class.
| Device class
| Messaging class
|| Unscheduled explicit messaging received from all other classes
|| Computer Interface cards, network configuration and diagnostic tools etc. , software application that do not require real-time I/O response|
| Adapter class
|| Receiving scheduled I/O data connection requests from the scanner class and unscheduled explicit message requests from other classes
|| I/O rack adapters, different robots, weigh scales, welders, and drivers that send and receive real time scheduled data at the request of the PLCs and other controllers. |
| Scanner class
|| Sending scheduled I/O data connection requests to the adapter class
|| PLCs, controllers and robots etc. |