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摘要：概述了幾種工業以太網協議及其特征，并介紹了IAONA組織。

關鍵詞：以太網；IAONA

Abstract: The paper gives a short overview of some Industry Ethernet Protocols and their features, and introduces the organization of IAONA.
Key words: Ethernet; IAONA

Introduction
While single organizations at the beginning of the Ethernet area were keen on (and partially still are...) providing the all-embracing all-round solution by their own industrial Ethernet implementation, meanwhile the notion that special applications need special protocols is starting to pervade.

IAONA's partner-organizations ETG (EtherCAT Technology Group), EPSG (Ethernet Powerlink Standardization Group), IGS (Interessengemeinschaft SERCOS interface), Modbus-IDA and ODVA (Open DeviceNet Vendor Association) commonly have the goal to fosteoverview of some features of the considered industrial protocolsr the development of Ethernet and the related protocol family TCP/IP. Thereby it has to be noted that each of these organizations possesses its own solution - e.g. in the real-time area - which is tailored to the needs of the specific customer groups; these solutions therefore vary in form and extent of their respective technology. However, for all organizations certain topics are of the same relevance and therefore can be solved by comprehensive architectures and concepts. Examples for this are both IAONA's Installation Guide and IAONA's Handbook for Network Security as well as the in common written general handbooks (German and English edition available) on industrial Ethernet.

The Overview of Industrial Ethernet  Protocols
Since the foundation of IAONA in 1999 several Ethernet based industrial protocols, caused by strong differing and partly contradicting user requirements, have been developed. In the following a short overview of some of these protocols will be given:

EtherCAT (Ethernet for Control Automation Technology)

EtherCAT (Ethernet for Control Automation Technology) is the Ethernet-based real-time automation concept developed by the German company Beckhoff. In contrast to other Ethernet-based automation solutions, the Ethernet packet is no longer received, then interpreted and copied as process data at each device within the network. Instead, the Ethernet frame is processed on the fly: For each module within the network, data addressed to that device are read, while the telegram is forwarded on to the next device. Similarly, input data are inserted while the telegram passes through. The telegrams are only delayed by a device in a few nanoseconds which should provide increasing performance of the system compared with other Ethernet-based solutions. The last device within the network segment sends the frame back to create a logical and physical ring structure. All transferred data comprises fully compatible Ethernet frames; each device converts these Ethernet frames to an internal fieldbus.

The real-time Ethernet frames have priority over other data (such as those required for configuration or diagnosis, etc.) via an internal prioritisation system. Configuration data are transmitted in the time gaps if sufficient time is available or by using a specific service channel. Fully maintained Ethernet functionality of the operating system achieves compatibility with conventional IP protocols.

Figure1: EtherCAT Stack

The basic development phase and the technical evaluation have been finalished, currently the implementation from FPGA to ASIC is in progress. Slave controllers and ASICs will be available from the second quarter of 2005.

EtherNet/IP

EtherNet/IP, based on Ethernet TCP or UDP IP, is a stack extension for automation industry communication. The 'IP', in EtherNet/IP, stands for Industrial Protocol. EtherNet/IP was introduced by the ODVA (Open DeviceNet Vendor Association) towards the end of 2000, development and specification work is achieved by the SIGs (Special Interest Groups). ODVA has more than 300 members world-wide, a Conformance Test Lab for Europe is headed by the University of Magdeburg.

Basically, in EtherNet/IP the upper-level Control and Information Protocol (CIP) which is already used in ControlNet and DeviceNet is adapted to Ethernet TCP/IP and UDP/IP respectively. The specification of EtherNet/IP is public and free of charge at ODVA's website. In addition to typical office applications like HTTP, FTP, SMTP and SNMP, EtherNet/IP provides a Producer/Consumer service allowing the transmission of time-critical messages between controller and I/O modules.

Secure data transmission of non cyclic messages (program up/download, configuration) is realised using TCP and time-critical transmission of cyclic control data is handled by UDP stack. To reduce implementation efforts of EtherNet/IP, standard device profiles for different types of devices, e.g, pneumatic valves or motion controllers, have been predefined.

The CIP protocol will currently be extended to follow real-time and safety requirements. CIPsync is an extension realising time synchronisation mechanisms in distributed systems using a method based on IEEE 1588 standard while CIPsafety is an extension integrating safety mechanisms and enabling safety control systems based on Ethernet/IP. Both extensions are currently under development. First products for CIPsafety are announced for 2005 and for CIPsync for 2006.

Figure 2: EtherNet/IP Stack

ETHERNET Powerlink
Originally, ETHERNET Powerlink has been developed by the Austrian company Bernecker + Rainer (B&R). After publishing the ETHERNET Powerlink standard in April 2002, now B&R is working together with companies and organisations like Hirschmann, Lenze, Kuka, and the Zurich University of Applied Sciences Winterthur (as co-ordinator of the ETHERNET Powerlink Standardization Group, EPSG). This consortium will enhance the ETHERNET Powerlink standard to meet the requirements of synchronous drives (motion control) and other specific devices. For example, synchronisation mechanisms based on IEEE 1588 standard will be implemented.

Figure 3: Powerlink Stack

In ETHERNET Powerlink the TCP (and UDP) IP stacks in Layer 3 and 4 are extended by the ETHERNET Powerlink protocol. An additional middleware is based on TCP (and UDP) IP as well as the ETHERNET Powerlink stack (asynchronous data transfer). Moreover, there is a stack for the fast, cyclic data transfer (isochronous data transfer).

The ETHERNET Powerlink stack completely controls the data traffic on the network. The method is called Slot Communication Network Management (SCNM) and will provide real-time capability over Ethernet. Each station has timed and strongly limited communication rights and can send data to each other station within the network. At a particular time only one station can access the bus so collisions are impossible and so achieve strict deterministic performance. In addition to these individual time-slots for isochronous data transfer, the SCNM provides common time-slots for asynchronous data transfer. An extended version (Version 2) contains communication and device profiles based on CANopen (in cooperation with the CAN in Automation (CiA) group). Version 3 of ETHERNET Powerlink includes time synchronisation mechanisms based on the IEEE 1588.
For ETHERNET Powerlink the first products are available on the market.

JetSync
The German company Jetter offers a method of synchronisation via Ethernet TCP/IP which it is called JetSync. It uses technology similar to IEEE 1588 but also supports asynchronous communication. The company claims that its system leads to a more open and flexible structure than achieved by using strict synchronisation time-slot methods. JetSync supports motion control applications as well as transmission of ordinary asynchronous data through TCP/IP. This, says the company, achieves compatibility using standard components for communication between PLCs, drives, remote I/O modules and SCADA components. Jetter claims that synchronisation of motion axes to better than 10μs axis jitter can be achieved just using TCP/IP alone running on a standard Ethernet infrastructure.

Modbus/TCP
The recently merged Modbus-IDA Group (domicile is in the USA) is working towards further development of the IDA architecture for distributed control systems using Modbus/TCP for the message structure.

Modbus/TCP is a derivate of the Modbus protocol and was developed by Modicon (Schneider Electric), the specification has been published in 1999 and is available in the Internet at no charge. Since 2004, Modbus/TCP protocol is available as PAS (Publicly Available Specification).

Modbus/TCP is based on Ethernet and standard TCP/IP and mounts directly on Layer 4 (TCP/UDP). It defines a simple structured, open and widely used transmission protocol for a master-slave communication. An comprehensive architecture concept does not exist, basically a Modbus telegram is embedded in the frames of the under-lying layer (TCP, IP, …) and transferred via the physical medium.

Figure 4: Modbus/TCP Stack

The Modbus telegram consists of the address of the slave, the Modbus function code, the data to be transferred and a checksum which will not be used here since the error detection mechanisms of the under-lying layers (Layers 1-4) will be used instead. The function code represents the action the slave has to perform. In a simple manner a Modbus/TCP compliant slave (e.g. I/O module) can be controlled with a small number of Modbus functions.

The Modbus/TCP protocol has been submitted to the IETF (Internet Engineering Task Force) to introduce it as an Internet standard. This could mean e.g. that Modbus/TCP like ftp, would be implemented in all common operating systems.

Since ModbusTCP is the "oldest" Ethernet based industrial protocol the number of available devices using this protocol is very high.

SERCOS (SErial Real-Time COmmunication System)
SERCOS (SErial Real-Time COmmunication System) has been developed by an industrial consortium in co-operation with ZVEI and VDM in the 1980s.
Marketing, further technical development work and standardisation activities are under responsibility of the IGS (Interest Group SERCOS interface) which was founded in 1990.

After SERCOS interface has been approved as international standard in 1995 (IEC 61491), further development steps took place within the second SERCOS generation, e.g. increasing of transfer rate.

Figure 5: SERCOS Stack

Real-time behaviour and determinisms will be achieved by using time-slot mechanisms (Time Division Multiplex Access or TDMA) and hardware synchronisation. The time-slots allow for transmission of time-critical and non-critical data in alternation. SERCOS was originally developed as drive interface but includes conventional I/O modules as supported devices.

SERCOS III has been designed for Industrial Ethernet. Plans include replacement of the hardware based communication interface with more flexible solutions, for instance in supporting several software based automation protocols and the use of standard hardware components (Ethernet coupler instead of fibre optic coupler). SERCOS III is currently in the implementation phase. First soft drivers and a starter kit are available to improve product development.

Safeethernet
As a product of the German company HIMA, the safeethernet protocol uses a network based on standard Ethernet and hence allows the application of standard IT protocols. As the name suggests, application areas include safety-related automation systems, products are available since the late 1990's.

In addition to the protocols described above, more protocols have defined. With IEC, there are currently 10 Publicly Available Specifications. 

Conclusion
Considering the available Ethernet based protocols for automation industry it becomes obvious, that Ethernet is even suited for motion control applications. Based on its requirements, the user has to decide which protocol he should apply within his system. Here he has to consider several aspects: Mainly, the question regarding real-time capabilities, but also the investigation of further development strategies and the application of the protocols have to be considered. The table 1 gives an overview of some features of the considered industrial protocols.

Table 1 overview of some features of industrial protocols

*) Values given by manufacturers.

The Organization  of IAONA
IAONA currently has a board of directors with five members, which is supported by the business office located in Magdeburg at the Otto-v.-Guericke-University. Currently members of the board are:

■　B. Dumortier, Responsable Certification de produits, Secretary TC 65 of IEC (Industrial Process Measurement and Control), Schneider Electric Industries SA, Grenoble, France;
■　Prof. R. Keller, Hirschmann Electronics GmbH, Neckartenzlingen;
■　K. Voss, Managing Director, ODVA, Ann Arbor, USA;
■　Dr. G. Beckmann, Lenze Drive Systems, Aerzen;
■　Jürgen Gorka, WAGO Kontakttechnik, Minden.

The business office is headed by Dr. K. Lorentz and Dr. A. Klostermeyer who also head the Center Distributed Systems at the IAF of the University of Magdeburg.

IAONA's technical work is done within the Joint Technical Working Groups (JTWGs), which are open to all members of IAONA. Furthermore, the JTWGs are open for all members of the IAONA partner organizations and invited (external) experts.

The coordination of the common technical work of the above mentioned organizations on the platform IAONA is done by the Technical Steering Committee (TSC). The formation of the structure and the rules was carefully done to allow for balance, equality, and transparency in order to insure that no single group dominates IAONA.

Figure 6: Structure of IAONA's TSC

As explained above, most remarkable for the JTWGs is especially the co-operation on technical topics which embraces all partner organizations. Additional to this, IAONA invites interested external experts to co-operate and work within these groups. The participation within these working groups is free of charge for all members of IAONA. The practical work of the JTWGs is done by usage of the latest Internet technologies, thus a physical presence of the experts is not obligatory. The convocation and closing of JTWGs lies within the responsibility of the TSC. It establishes the JTWGs according to the users', members' and partner organisations' demand.

作者簡介：Kai Lorentz（1969-），男，博士，現任IAONA工業以太網學術團體主席。