There are several features of the PROFINET protocol that system engineers can rely on to build highly available and fail-safe deterministic Real-Time Industrial Ethernet networks. To take advantage of fast recovery times of less than 200 ms in harsh environments, ring topologies are state of the art for the realization. To use them in PROFINET RT networks, one particular function of the protocol is critical: the PROFINET Media Redundancy Protocol, which is conveniently included and can be enabled in Hilscher's PROFINET IO controller products like PC-Cards, Embedded Modules and ASICs.
What is the Media Redundancy Protocol (MRP) and why is it used? A brief overview.
In PROFINET RT, devices are commonly organized in linear or star topologies with status, control, and diagnostic information communicating between device and machine controllers. However, if a central device fails, in the worst case it has an impact on the entire network. An alternative to ensure network availability is using a ring topology, which is not very common in Ethernet environments. MRP enables the use of ring topologies in PROFINET IO RT networks and allows the compensation of single failures in them.
For a proper operation, MRP is designed to use a Media Redundancy Manager, which monitors the ring topology at all times and, if a network failure is registered, provides information to the Media Redundancy Clients about the re-arrangement of the network to a line topology. All of Hilscher’s PROFINET IO controller products can act as a MRP Manager in PROFINET-IO networks. All PROFINET IO device products include the MRP Client functionality.
How does it work?
The Media Redundancy Manager (MRM) issues test frames in a certain interval to assess the integrity of the ring network. The Media Redundancy Clients (MRC) forward the test frames along the ring back to the MRM.
If the MRM does not receive the test frames back, it will be interpreted as network failure, informs all MRC about the network failure and sends control data to switch to a linear network configuration. In addition, an MRC that detects a LinkState change on one of its ports informs the MRM of this condition, which may reduce the time until the MRM itself detects the failure or repair.
What are the benefits of using MRP in your PROFINET IO network?
- Increasing the robustness of the networks
- Protection against loss of runtimes due to fast recovery times
- Easy to configure – simply select a ring manager and the ports in each device
- Media Redundancy Client is always implemented in Hilscher slave devices