Technologies - Realtime Ethernet

In Industrial automation the need for distributed intelligent systems has been growing steadily. Physically distributed systems are working together more and more to integrate common functions. Databases are now linked, service and diagnostics are undertaken by remote connections, usually by using TCP/IP.

Today different fieldbus systems are used by the industrial automation industry, sometimes leading to multiple fieldbus’s on the same machine. However, in the future Ethernet will be the universal bus system in industrial automation.

Originally Ethernet was established to interconnect office equipment, and is now 30 years old, and is based on the standard IEEE 802.3. Ethernets propagation in more recent times has lead to greater user knowledge, and a broader spectre of accessories to go with it. This high market penetration, and its international standard is guarantying its continued status.

Various protocols have been developed over time for Ethernet, examples being TCP/IP, XML, http, SNMP and many more. Obviously, there was a need to develop an industrial protocol, which fulfils the requirements for control in automation. The main problem was the realisation of realtime capabilities, which have to be guaranteed for time critical applications, but also to achieve transparency in accessing applications and protocols too . Real interoperability and worldwide access on automation systems had to be realized.

Today, a compliant standard based on IEEE 802.3 Ethernet has been developed or is in predevelopment, which guarantees such kind of Realtime capability. For this reason within a Realtime Network you have the guarantee of collision free communication. There are several standards available on the market.

Ethernet Powerlink

Today SND is supplying Ethernet Powerlink (EPL) as an implemented protocol.

EPL is a deterministic protocol because it avoids problems that are caused by the Ethernet bus access mechanism. Only one node on an EPL network is allowed to send, this is the Managed Node (MN). The MN invites all other nodes to share their data with all other nodes on the network. Other nodes are called Controlled Nodes (CN). A version 1 and 2 EPL network can include up to 239 CN that are cyclically accessed by the MN. The MN also produces a synchronization pulse that guarantees a very small jitter. This pulse is called Start of Cycle (SoC). In the cycle CNs are polled by the MN by use of a Poll Request (PReq). Every polled CN responds with a Poll Response (PRes). EPL also allows generic communication like TCP/IP. At End of Cycle (EoC) a cyclic period takes place that allows the inclusion of all these types of frames. Therefore it is possible to have a webserver on every application device for example, allowing easy user configuration.

EPL higher layer is a merger of CANopen and standard TCP/IP. This architecture allows the configuration of all EPL nodes over the well-known Can-Open device profiles with the flexibility of IP communication. Now it is possible to configure all types of devices from everywhere. Special routers that are able to communicate with EPL protocols, and normal Ethernet protect the EPL network from malicious intruders.

SND has many satisfied customers in this market. Further information can be gained from reading details in the Reference Customer section .

Key features of EPL stack from SND:

• dynamic switching between MN and CN and version 1 and 2
• optimised for fast response times and small memory usage
• fully integrated in HyNetOS^®/4NetOS^®, and benefiting from all the other advantages of the Operating System
• knowledge of hardware designs allowing powerful and cheap solutions

Advantage of open standards and a user organisation

For nearly all the different Realtime Ethernet Standards you will find standardisation groups, who are making a major step towards open solutions. These groups are supported by constructive cooperation of all the members with the aim of defining and creating real market standards. Addressing the variety of applications and specifications appears to be only possible in such strong organizations. Through these organisations, return on investment is more likely as it is possible to influence the technology, further development will be based on market demands and independent from a dominating market leader. This insures an evolving technology meeting the market needs. This enables increased market penetration.

These groups are working with the same principles as the former Fieldbus-Organizations. Usually it is the same historic groups that are promoting their unique Realtime Ethernet standard, details below: