ControlNet is an open industrial network protocol for industrial automation applications, also known as a
fieldbus
Fieldbus is the name of a family of industrial computer networks used for real-time distributed control. Fieldbus profiles are standardized by the
International Electrotechnical Commission (IEC) as IEC 61784/61158.
A complex automated industrial ...
. ControlNet was earlier supported by
ControlNet International, but in 2008 support and management of ControlNet was transferred to
ODVA, which now manages all protocols in the
Common Industrial Protocol
The Common Industrial Protocol (CIP) is an industrial protocol for industrial automation applications. It is supported by ODVA.
Previously known as Control and Information Protocol, CIP encompasses a comprehensive suite of messages and services f ...
family.
Features which set ControlNet apart from other fieldbuses include the built-in support for fully redundant cables and the fact that communication on ControlNet can be strictly scheduled and highly deterministic. Due to the unique physical layer, common
network sniffers such as
Wireshark
Wireshark is a free and open-source packet analyzer. It is used for network troubleshooting, analysis, software and communications protocol development, and education. Originally named Ethereal, the project was renamed Wireshark in May 2006 d ...
cannot be used to sniff ControlNet packets. Rockwell Automation provides ControlNet Traffic Analyzer software to sniff and analyze ControlNet packets.
Version 1, 1.25 and 1.5
Versions 1 and 1.25 were released in quick succession when ControlNet first launched in 1997. Version 1.5 was released in 1998 and hardware produced for each version variant was typically not compatible. Most installations of ControlNet are version 1.5.
Architecture
Physical layer
ControlNet cables consist of
RG-6
RG-6/U is a common type of coaxial cable used in a wide variety of residential and commercial applications. An RG-6/U coaxial cable has a characteristic impedance of 75 ohms. The term, ''RG-6'', is generic and is applied to a wide variety of ...
coaxial cable
Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...
with
BNC connector
The BNC connector (initialism of "Bayonet Neill–Concelman") is a miniature quick connect/disconnect radio frequency connector used for coaxial cable. It is designed to maintain the same characteristic impedance of the cable, with 50 ohm and ...
s, though optical fiber is sometimes used for long distances.
The network topology is a bus structure with short taps. ControlNet also supports a star topology if used with the appropriate hardware.
ControlNet can operate with a single
RG-6
RG-6/U is a common type of coaxial cable used in a wide variety of residential and commercial applications. An RG-6/U coaxial cable has a characteristic impedance of 75 ohms. The term, ''RG-6'', is generic and is applied to a wide variety of ...
coaxial cable
Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...
bus, or a dual
RG-6
RG-6/U is a common type of coaxial cable used in a wide variety of residential and commercial applications. An RG-6/U coaxial cable has a characteristic impedance of 75 ohms. The term, ''RG-6'', is generic and is applied to a wide variety of ...
coaxial cable
Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...
bus for cable redundancy. In all cases, the RG-6 should be of quad-shield variety.
Maximum cable length without repeaters is 1000m and maximum number of nodes on the bus is 99. However, there is a tradeoff between number of devices on the bus and total cable length. Repeaters can be used to further extend the cable length. The network can support up to 5 repeaters (10 when used for redundant networks). The repeaters do not utilize network node numbers and are available in copper or fiber optic choices.
The physical layer signaling uses
Manchester code
In telecommunication and data storage, Manchester code (also known as phase encoding, or PE) is a line code in which the encoding of each data bit is either low then high, or high then low, for equal time. It is a self-clocking signal with no DC ...
at 5 Mbit/s.
Link layer
ControlNet is a scheduled communication network designed for cyclic data exchange. The protocol operates in cycles, known as NUIs, where NUI stands for Network Update Interval.
Each NUI has three phases, the first phase is dedicated to scheduled traffic, where all nodes with scheduled data are guaranteed a transmission opportunity.
The second phase is dedicated to unscheduled traffic. There is no guarantee that every node will get an opportunity to transmit in every unscheduled phase.
The third phase is network maintenance or "guardband". It includes synchronization and a means of determining starting node on the next unscheduled data transfer.
Both the scheduled and unscheduled phase use an implicit token ring media access method.
The amount of time each NUI consists of is known as the NUT, where NUT stands for Network Update Time. It is configurable from 2 to 100 ms. The default NUT on an unscheduled network is 5 ms.
The maximum size of a scheduled or unscheduled ControlNet data frame is 510 Bytes.
Application layer
The ControlNet application layer protocol is based on the
Common Industrial Protocol
The Common Industrial Protocol (CIP) is an industrial protocol for industrial automation applications. It is supported by ODVA.
Previously known as Control and Information Protocol, CIP encompasses a comprehensive suite of messages and services f ...
(CIP) layer which is also used in
DeviceNet DeviceNet is a network protocol used in the automation industry to interconnect control devices for data exchange. It utilizes the Common Industrial Protocol over a Controller Area Network media layer and defines an application layer to cover a rang ...
and
EtherNet/IP
EtherNet/IP (IP = Industrial Protocol) is an industrial network protocol that adapts the Common Industrial Protocol (CIP) to standard Ethernet. EtherNet/IP is one of the leading industrial protocols in the United States and is widely used in a r ...
.
References
External links
ODVA websiteControlNet Networks and Communications from Allen-Bradley
{{List of Automation Protocols
Serial buses
Network protocols
Industrial automation