Redundancy in communication networks is critical in substation automation, processing, and manufacturing application. Although there are several media redundancy communication protocols, instant switchover to backup or secondary pathways with zero reconfiguration time is required for protection of electrical substation, synchronized drivers, high-power inverters, and printing machines. Parallel Redundancy Protocol (PRP) meets these criteria and is commonly used in substation automation especially for process bus implementation.
- IEC Standard (IEC 62439-3, Clause 4) providing redundancy for standard Ethernet based networks
- Two physical network ports are used for communication, which are connected to independent networks respectively.
- Each Ethernet frame is duplicated and transmitted on both the networks.
- The receiver discards the duplicate frame and forwards a single copy to the higher layers of network stack.
- The entire process of duplicating on the transmit side and discarding the duplicates on the receiver is done
seamlessly and unknown to the application. - The two networks have to be independent but need not be identical. However they should have similar timing delays.
- Failure of a network component on a network still ensures that the duplicate is received by the receiver.
- Can be easily scaled to large complex networks, but the cost of duplicate network resources also scales correspondingly.
We have advanced level expertise with the design and implementation of the PRP on the Texas Instruments Sitara platform with Linux/RTOS running on the ARM core and the firmware running on the Programmable Real-time Unit (PRU) core within the Industrial Communication Sub-System (ICSS). Frame duplication on the transmit side and duplicate discard on the receive side has been offloaded to the firmware to improve the OS performance on the ARM host. The implementation has been tested rigorously under heavy traffic conditions in conjunction with the PTP protocol. Further enhancements in the performance of the driver and the firmware is currently work in progress.