IEC 62439 PRP: Bumpless recovery for highly available, hard real-time industrial networks

Availability of automation networks can be increased by providing redundant links and nodes. Although many specifications of industrial Ethernet have been submitted to the International Electrotechnical Committee (IEC), they do not disclose methods to implement network redundancy. The IEC SC65C worked out a standard for implementing redundancy in switched Ethernet networks applicable to a variety of industrial networks, with different solutions depending on the grace time of the plant and on the level of redundancy desired. This paper describes IEC 62439´s parallel redundancy protocol (PRP), a redundancy method applicable to hard real time systems, based on full duplication and parallel operation of two redundant networks. PRP nodes send on both networks at the same time, and receive from both, providing bumpless recovery. Duplicate discarding and management functions complement the standard.