Regular Ethernet is not capable of handling data transfer in real time. Additional measures like fully switched Ethernet and frame prioritization are not suitable either. First, it does not fit the flexibility needs of automation network topologies. Second, deterministic data transfer and timing precision still cannot be guaranteed. And third, it is quite complex to configure network utilization by selecting appropriate node and frame priorities.
Multiple industry groups have therefore introduced various new mechanisms to achieve real-time capabilities using Ethernet. These include non-standard access mechanisms on the physical medium using Ethernet frames that have to be decoded cyclically using special components as well as non-standard shortening of the Ethernet frames to lower transfer times even further.
POWERLINK was developed from the very beginning with the intent of providing standard conformity. As an open industrial standard, Ethernet requires non-proprietary real-time enhancements. POWERLINK enhances Ethernet according to the IEEE 802.3 standard with a mixed polling and time slicing mechanism. This results in:
- Guaranteed transfer of time-critical data within very short and precise isochronous cycles with configurable timing.
- Synchronization of all network nodes with high precision in the sub-microsecond range.
- Transmission of less time-critical data in a reserved asynchronous channel.
Current POWERLINK implementations have reached 200 µs cycle time with a timing deviation (jitter) below 1 µs.
Due to its standard compliancy it is possible to leverage and continue using any standard Ethernet silicon, infrastructure component or test and measurement equipment with POWERLINK. All IP-based protocols on higher layers, like TCP, UDP and above, can continue to be used without modifications. In particular, POWERLINK conforms to the following international standards:
- IEEE 802.3 Fast Ethernet
- IEC 61748-2
- IEC 61158
- IP-based protocols (UDP, TCP, etc.)
- Standard device profiles: according to CANopen EN 50325-4
- Standard Ethernet chips, no ASICs necessary
- IEEE 1588 for real-time domain synchronization (future versions)
