Industrial EtherNet
In the 1990s, the need for fast transmission, larger data volumes and many participants via a standardized medium increased. The IAONA(IndustrialAutomationOpenNetworkAlliance), with over 100 companies involved in its development, laid the foundations for Industrial Ethernet based on the IEE802.3 standard.
The 10 Mbit/s standard at the time and the collision-prone transmission were hurdles that had to be overcome. Only on the basis of Fast EtherNet technology with switch technology, full-duplex transmission and collision detection was the goal of a continuous infrastructure also vertically tangible. Both industrial protocols and IT protocols can be transmitted via the same medium.
The first standardized protocols on the market were ModbusTCP and EtherNet/IP. These were well suited to most applications and are therefore very widespread today.
There are many Industrial Ethernet protocols in which entire fieldbus protocols or data structures have been converted from the previous fieldbus medium to Ethernet. These were simply embedded in an EtherNet protocol framework.
| Fieldbus | IE variant |
|---|---|
| ModbusRTU | ModbusTCP |
| PROFIBUS | PROFINET |
| DeviceNet/ControlNet | EtherNet/IP |
| CANopen | EtherCAT |
| Sercos II | Sercos III |
| CC-Link | CC-Link IE Field |
However, the first Industrial EtherNet protocols only had limited real-time capability, as transmission times can vary depending on the infrastructure and data traffic load. At this time, the classic fieldbuses still had their advantages due to the deterministic (predictable) behavior of the transmission times. As each participant in an EtherNet network accesses the shared medium (Ethernet) as required, the time behavior is difficult to estimate compared to a master/slave-based network with fixed bus cycles.
The shared medium also breaks with the model of the classic automation pyramid of fieldbuses, in which there were specific systems for the different levels. Now a sensor at field level can supply process data to the PLC and at the same time quality and status data to a higher-level system.
Another advantage is the ability to create more complex structures and, for example, to segment networks and create defined transitions.
Due to the new possibilities of simultaneous bus access as required by each participant, the classic way of thinking in terms of master/slave participants was outdated and the concept of client/server architecture was coined. A participant provides data or services, for example, called a server. The client, in this case the active participant, accesses the data or services. Accordingly, in many Industrial EtherNet systems, several clients can access one server. However, there are also other terms for some Industrial EtherNet technologies, also due to modified functionality. However, these can be roughly categorized as follows:
| Classic fieldbus | Master | slave |
|---|---|---|
| ModbusTCP | Client | server |
| PROFINET | Controller | Scanner |
| EtherNet/IP | Scanner | Adapter |
| EtherCAT | Master | slave |
| Sercos III | Master | slave |
| Powerlink | Master | slave |
| OPC-UA | Client | server |
| MQTT | Broker | agent |
The problem of deterministic time behavior was tackled starting in 2010 with so-called "real-time-capable Industrial EtherNet protocols". These place a clear prioritization of communication on process data, such as PROFINET IO, CC-Link IE Field, ...
For applications in drive control, for example, there are also Industrial EtherNet variants that meet the requirements for minimum latency times, but which can only be used to transmit IT protocols to a limited extent. In order to achieve the required transmission times, special switches/hubs are required, as with PROFINET IRT or EtherCAT. Only in this category of Industrial EtherNet technologies are topologies for redundant wiring also provided. Here, the controller usually sets the pace and the term master/slave for participants was appropriate.
| Industrial EtherNet protocol | Real-time capable | Motion Control |
|---|---|---|
| ModbusTCP | EtherNet/IP | EtherCAT |
| PROFINET IO | PROFINET IRT | |
| Powerlink | Sercos III |
EtherNet development in factory automation
| 1970s | 1980s | 1990s | 2000s | today |
|---|---|---|---|---|
EtherNet | EtherNet | EtherNet | PROFINET | PROFINET |
Variety of transmission media
The transmission media already available in IT, such as copper and fiber optic connections, can be used for many protocols. The same applies to wireless connections such as WLAN or Bluetooth. The variety of possible transmission paths expands the range of applications enormously.
IT functions and IT protocols
Due to the ability of EtherNet devices to establish several simultaneous connections, industrial devices have the option of implementing IT functionality and IT protocols in addition to an Industrial Ethernet protocol.
Industrial devices with web servers that work with the HTTP protocol (Hypertext Transfer Protocol) can be configured and diagnosed or data visualized via a web interface.
Firmware updates, for example, can be imported via the FTP protocol (File Transfer Protocol).
The SNMP protocol (Simple Network Management Protocol) enables the monitoring of industrial components. In the IT world, this is already practised with servers, switches and routers in order to monitor their status, capacity utilization, etc.
Devices can also send e-mails using the SMTP protocol (Simple Mail Transfer Protocol).
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