Ethernet rings


The question was asked: "Is is possible to connect different Ethernet switches (Manufacturer / Configuration / Specification) in a ring network ? If yes, then how could be the performance of data transfer?". My response was:

There are a number of international standards that deal with ring topologies. RSTP and MSTP are IEEE standards (802.1D and 802.1Q respectively) that work across vendors. These make a 'virtual break' in the ring that can close when a normally close link opens.

A more reliable (but more complex) alternative is HSR – high-availability seamless redundancy – IEC 62439-3, is vendor independent.

There are vendor specific modifications of standards, such as RuggedCom’s eRSTP that has faster ring repair, or Hirschmann’s HiPER Ring that gives faster ring recovery than RSTP. The Media Redundancy Protocol (MRP), IEC 62439-2, is a derivative of HiPER Ring.

One downside with RSTP is that recovery time increases with the number of devices and especially with the number of meshes. Another is that default parameters may vary between vendors so some tuning is required. RSTP does allow more flexibility in network design than with MRP (which is exclusively for rings).

Performance with HSR and MRP will be deterministic (0 ms for HSR and a defined setting for MRP). RSTP performance will depend on the configured parameters and number of devices, so I would recommend testing of the final design. Software simulation is also a good idea, and something that I don’t see much of in industrial network design

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