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Open-source solution for bus-independent safety

Open-source solution for bus-independent safety
The real-time safety communication protocol openSAFETY lays the foundations for the first completely open, bus-independent safety standard for all Industrial Ethernet solutions and fieldbuses. We outline how the solution launched by the Ethernet POWERLINK Standardisation Group can serve the implementation of safe networks on any transport protocol.

At the 2010 Hannover Messe exhibition, the EPSG presented openSAFETY solutions for four of the most common Industrial Ethernet protocols, Modbus TCP, EtherNet/IP, SERCOS III, and POWERLINK, thereby demonstrating the safety software's interoperability with different protocols. In a press conference held by the EPSG on April 19th, 2010, Stefan Schönegger, General Manager of the EPSG, invited all interested parties to view the solutions at the EPSG's trade show booth. 

Moreover, Schönegger announced that the EPSG would also support users of additional communication systems who wished to implement openSAFETY. The safe transport protocol has the potential of becoming the standard protocol for safety-oriented data transfer in automation networks, not only because it is bus-independent, but also because its openness is a legal advantage: with an open-source license, openSAFETY affords manufac-turers and plant operators absolute investment security.

In view of the fact that heavy competition between various safety protocols would be highly disadvantageous for the developers of safety-oriented technology, the automation industry has been demanding a standard for safety systems for years and years. The development of safety solutions is very costly and certification requirements are extremely high. Considering that the target market is still very confined at the moment, a second fieldbus war would weigh heavily on all market players. For example, developing sensors in compliance with safety norms and compatible to a number of different safety protocols would mean much effort and risk for manufacturers.

Black Channel principle
Fully implementing the Black Channel principle, openSAFETY is interoperable with all fieldbuses, Industrial Ethernet solutions, and industry-specific communication solutions. The safety protocol's functionality does not depend on the particular protocol which transports 

the safety frames. All safety oriented mechanisms are fully integrated in the application layer, independent from the underlying trans-port protocol. The standardised Open Systems Interconnection (OSI) data communication model hierarchically structures the various data transport tasks, which information processing systems have to perform, in seven layers. The basic physical and data link layers make up the physical structure. 

The third and fourth layers are the so-called transport layers which, apart from managing the data transport chronologically and logically, match the data with the applications, ie with the session and presentation layers. Together, these four underlying layers comprise all transport-oriented tasks, thus forming a mode of transport for the application data. The topmost application layer has no defined task. It can provide various services to the particular applications which are not encompassed by the model. openSAFETY only specifies the application-oriented layers of the protocol stack. The safety mechanisms ensure the safe encoding and decoding of payload data.

The choice of transport protocol does not influence the functioning of openSAFETY, which is a suitable and uncomplicated safety solution not only for all the most common fieldbuses and Industrial Ethernet systems, but also for proprietary, non-certified bus systems which many companies only employ in-house. openSAFETY continuously checks all transmitted data for completeness, correct chronological order, and observation of the maximum transmission time. It registers any transmission error in hard real time. Therefore, even specific communication solutions and single-channel, unsafe transport networks can serve as communication medium without compromising safety.

openSAFETY is freely available on the internet. The protocol is available for downloading as an open-source software under a BSD license. Already TÜV-certified, openSAFETY is the 'plug-and-play' basis for implementing safe data communication. System designers wishing to implement a safety solution based on openSAFETY on their existing data communication system, can simply integrate the safety protocol in their bus system's application layer. The EPSG supports the implementation of openSAFETY on any transport protocol, for exmaple by offering support in certification and conformance testing.
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