Ethernet powerlink (EPL)
The real-time behavior of classic Ethernet is limited by the stochastic access methodCSMA/ CD. With EtherCAT and Ethernet Powerlink these restrictions are circumvented while maintaining the Ethernet concept. Since real-time Ethernet is particularly important for automation and production, the application areas of Ethernet-Powerlink( EPL) can also be seen here.
Real-time Ethernet with deterministic data exchange
Ethernet Powerlink is a Layer 2 protocol according to IEEE 802.3u, which enables deterministic real-time data exchange via Fast Ethernet. It is based on a hub structure and uses the Ethernet frame and also the components of Fast Ethernet. Like other fieldbuses, Ethernet-Powerlink can be used from the sensor- actuator level, the field level, up to the control level. The individual components can be addressed company-wide and via the Internet using IP addresses across all levels.
Ethernet-Powerlink operates in master- slave mode with an isochronous time slot procedure and supports data transport via Internet Protocol (IP), User Datagram Protocol( UDP) and the Transmission Control Protocol( TCP). This simple access method, Slot Communication Network Management( SCNM), forms the basis for determinism. In this process, the Managing Node( MN), which performs the function of the manager, distributes the access rights of the subscribers to the medium. It prevents collisions and sets the timing for synchronization of all participants. The devices, called Controlled Node( CN) in the EPL concept, transmit only when requested to do so by the manager.
Functions of the EPL protocol
The EPL protocol is a deterministic access method that runs in a delimited network segment, the real-time domain. The time-critical data traffic takes place in protected mode. In this mode, cycle times of 1 ms can be realized with more than 30 stations and 46 bytes ofuser data. The less time-critical data traffic is not handled in this network domain and therefore does not burden the realtime segment. Up to 240 stations can be connected to the real-time domain.
The frame length of EPL telegrams can be up to 1,500 bytes, and the cycle times for telegrams of standard length are around 100 microseconds. In terms of topology, all variants are conceivable for EPL; in addition, such a network can be extended with hubs and routers and connected to other IP networks.
In the application layer, Ethernet-Powerlink relies on CANopen.
The activities of Ethernet-Powerlink are driven by the Ethernet Powerlink Standardization Group( EPSG).