Also, in the Ring-Open status, the network logical topology is a stub. For instance, in case of failure of a link connecting two MRCs, the MRM sets both of its ring ports to the forwarding state the MRCs adjacent to the failure each have a blocked and a forwarding ring port the other MRCs have both ring ports forwarding. In case of failure, the network works in the Ring-Open status (Figure 2). Loops are avoided because the physical ring topology is reduced to a logical stub topology. Conversely, both ring ports of all MRCs are forwarding. In this status, one of the MRM ring ports is blocked, while the other is forwarding. Forwarding ring ports forward all the received frames.ĭuring normal operation, the network works in the Ring-Closed status (Figure 1). Blocked ring ports drop all the received frames except the MRP control frames. Disabled ring ports drop all the received frames. MRM and MRC ring ports support three status: disabled, blocked, and forwarding. In an MRP ring, the ring manager is named Media Redundancy Manager (MRM), while ring clients are named Media Redundancy Clients (MRCs). MRP is supported by several commercial industrial Ethernet switches. MRP operates at the MAC layer of Ethernet switches and is a direct evolution of the HiPER-Ring protocol developed by Hirschmann in 1998.
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