Media Redundancy Protocol
The Media Redundancy Protocol is a protocol for high-availability networks as required in critical automation applications. The availability is increased by adding redundancy .
Working principle
MRP allows individual failures to be compensated in a simple ring topology . Since no meshed topologies are supported, MRP is deterministic and much simpler than RSTP .
The Medium Redundancy Protocol (MRP) is based on a ring topology and guarantees recovery times between 200 ms and 500 ms (depending on the configuration). MRP uses a redundancy manager (RM or MRM) that closes the ring. In normal operation, the redundancy manager uses special test packages to check the continuity of the ring. However, it does not forward any packets and thus prevents them from circulating endlessly in the ring.
If a switch (SW) or a line, which are on a Port transmitted test packets at the other port no longer received. From now on, the redundancy manager forwards the packets in both directions and informs the switches about the topology change, so that they do not put their packets on the interrupted route, but send them via the redundancy manager.
The redundancy manager is usually a logical function in a switch and is shown here as a separate component.
background
The data network standard Ethernet allows only a single, i.e. unique data path between any two participants. If you connect several switches with cables, line, star and tree structures can be set up. If, for example, the switch in the middle of a star structure fails, all other switches are isolated from one another.
If a line structure is set up with switches and the two switches are connected to one another at the ends of the line, a ring structure is created. Now there are two paths between any two participants who are connected to different switches. This is not permitted in this way. A connection in the ring must therefore be switched off at the logical level. This means that the wiring is a ring, but the structure is actually a line.
There are various so-called protocols for this shutdown. In addition to the Rapid Spanning Tree Protocol RSTP, there is now the second standardized solution with the Media Redundancy Protocol. If one of the other lines in the - physical - ring fails, the line that was previously switched off is automatically activated. This means that all participants can continue to exchange data with one another despite the failure of a connection.
International standardization
MRP is based on the HIPER-Ring, a protocol for ring redundancy developed by Hirschmann and Siemens and presented in 1999. Corresponding products have been on the market since around the year 2000.
MRP has been defined in the IEC 62439 standard since April 2008. With the standardization, the patents of the two companies were also made licensable within the standard under RAND conditions.
The aim of this standard is redundancy procedures with defined convergence times. The methods should be independent of higher protocols and be suitable for the real-time Ethernet mechanisms that are described in the IEC 61784 standard.
bibliography
- IEC 62439 "Industrial communication networks: high availability automation networks" (in the IEC webstore )
Individual evidence
- ^ A. Giorgetti et al .: Performance Analysis of Media Redundancy Protocol (MRP) . In: IEEE Computer Society (Ed.): IEEE Transactions on Industrial Informatics . February 3, 2013, pp. 218-227. doi : 10.1109 / TII.2012.2186584 .
- ↑ HIOS - Hirschmann ™ Operating System . In: website . Hirschmann a Belden Brand. Archived from the original on May 12, 2013. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved August 17, 2013.
