Ethernet Powerlink

Ethernet Powerlink is a deterministic real-time for standard Ethernet. It is an open protocol managed by the Ethernet POWERLINK Standardization Group (EPSG). It was introduced by Austrian automation company B&R in 2001.

This protocol has nothing to do with power distribution via Ethernet cabling or power over Ethernet (PoE), power line communication, or Bang & Olufsen's PowerLink cable.

Ethernet Powerlink expands Ethernet with a mixed polling and timeslicing mechanism. This provides:

Modern implementations reach cycle-times of under 200 µs and a time-precision (jitter) of less than 1 µs.

Powerlink was standardized by the Ethernet Powerlink Standardization Group (EPSG) and founded in June 2003 as an independent association. Working groups focus on tasks like safety, technology, marketing, certification and end users. The EPSG cooperates with the standardization bodies and associations, like the CAN in Automation (CiA) Group and the IEC.

The original physical layer specified was 100BASE-TX Fast Ethernet. Since the end of 2006, Ethernet Powerlink with Gigabit Ethernet supported a transmission rate ten times higher (1,000 Mbit/s).

Repeating hubs instead of switches within the Real-time domain is recommended to minimise delay and jitter. Ethernet Powerlink uses IAONA's Industrial Ethernet Planning and Installation Guide for clean cabling of industrial networks and both industrial Ethernet connectors 8P8C (commonly known as RJ45) and M12 are accepted.

The standard Ethernet Data Link Layer is extended by an additional bus scheduling mechanism which secures that at a time only one node is accessing the network. The schedule is divided into an isochronous phase and an asynchronous phase. During the isochronous phase, time-critical data is transferred, while the asynchronous phase provides bandwidth for the transmission of non time-critical data. The Managing Node (MN) grants access to the physical medium via dedicated poll request messages. As a result, only one single node (CN) has access to the network at a time, which avoids collisions, present on older Ethernet hubs before switches. The CSMA/CD mechanism of non-switched Ethernet, which caused non-deterministic Ethernet behaviour, is avoided by the Ethernet Powerlink scheduling mechanism.

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