Ethernet and TCP / IP are achieving wide acceptance in industrial automation. Fast Ethernet Switch (Switching) and Full Duplex Ethernet has become a powerful communication system with a special attraction to industrial users and manufacturers. However, at least one step is needed: to achieve a standard protocol for transmitting real-time.
Many organizations are working hard on an application protocol for Industrial Ethernet. Different approaches such as Ethernet / IP, PROFINET, IDA, Foundation Fieldbus HSE and Interbus are incompatible and not interoperable.
IAONA (Alliance for Industrial Automation Open Network for short) recently met with ODVA (ehternet / IP) and IDA mutually agreed for the common advancement of communication technology based on Ethernet TCP / IP.
The parties agreed to be developing different communication protocols in real time, but agreed to study and specify future extensions to unite these two standards. Common specifications will enable interoperability of technology solutions for switching, common components for the transmission medium and guidelines for installation and wiring.
COMMON FEATURES
Despite the different approaches of the layer 7, all concepts are stable and have a common heart: transmission technology (Layer 1), bus access method (CSMA / CD, Layer 2), Internet Protocol (IP, Layer 3), TCP and UDP (Layer 4), Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP) protocol Simple Network Management Protocol (SMTP) at Layer 7. All these are established in the industry of Information Technology (IT), as now, will mplementados unchanged.
However, one should note some differences that can be found in the protocols of real-time communication layer 7 and the objects and engineering models for system configuration. The different concepts can be subdivided into "packaging technology" (ehternet / IP, Foundation Fieldbus HSE and Modbus TCP / IP, "concepts and Proxy gateway" (PROFINET and Interbus) and a completely new system called IDA.
CONCEPTS OF ENCAPSULATION
The term encapsulation is used to describe the packaging of a web of wire in a container TCP or UDP. With all this, the fieldbus telegram almost invariably is "stuck" in the user information in a plot TCP / UDP before being sent over Ethernet. The advantage is that the completion of the specifications do not require much development. The first commercial devices are available and in use. It will also be easy to provide downward compatibility with field buses in which they are based, we could say that ehternet can be seen as a new transmission technology that can be used as an "alternative" or "combined with" buses established field.
In the figure below, Ethernet / IP uses CIP protocol is already recognized by DeviceNet and ControlNet, CIP telegrams are packaged in containers TCP / UDP before being transferred to Ehernet.
The disadvantage of encapsulation is that you have a protocol with lower efficiency. Ethernet headers are longer than the user information in accordance with this, the encapsulation is preferable to send large amounts of information (eg, software) rather than single words (for example, information input / output).
FASHION CONCEPTS (GATEWAY) AND PROXY
Here the main objective is to integrate segments, fieldbus segments in Industrial Ethernet. This is implemented through a protocol translator gateway or proxy server or the main advantage is that the existing field buses can be used in the future, but the disadvantage is heterogeneous networks with different system configurations and limited behavioral real time.
One of the proponents of this philosophy is Profinet (ver'figura below), here a PROFIBUS network is connected to an Ethernet-based network through a protocol translator (gateway).
REAL-TIME SYSTEMS
Distributed Automation Interface (IDA for short) is a completely new approach. IDA uses NDDS communication system, which is based on a model publisher / subscriber and provides a wide range of powerful application services. Applications publish information using broadcast or multicast communication and supports the information they need via the network. The entire communication is completely anonymous and neither the publisher nor the subscriber need to know who needs the information.
CONCLUSION
The current trends indicate that buses will continue to be used field-indeed, a single standard for real-time communication over Industrial Ethernet is unlikely and apparently doomed to failure. Standardization initiatives, such as IAONA are very important as they aim to minimize the differences between Ethernet networks to come.
