1. Does the Ring require Managed Switches?
There’s nothing wrong with Managed Switches for the right application. Overall, they certainly have more functionality than Ring Switches. Consider however that they: (1) are more complex to configure and use; (2) they are ill suited for fast real-time systems (refer to the answer to the next question); and (3) they cost more than Real-time switches.

2. Is the Ring algorithm based upon Spanning Tree or Rapid Spanning Tree?
Spanning trees support more complex topologies than simple rings. That sophistication comes at a price. Spanning tree networks take time to configure themselves and they are NOT real-time. (The nature of spanning tree just isn’t suited for real-time.) Beware of great performance claims about Rapid Spanning Tree based Ring solutions. They may have a great “typical” detect and recovery time, but periodically (or under some circumstances), they will take a long time to switch over.

3. Does the Ring require a designated master switch?
Most Ring switch product offerings require a designated master. This means that there is a unique critical element on the network (not in the spirit of redundancy logistics). It also means that a configuration means is needed and that increases the skill level needed to repair a fault, and it will increase the mean time to repair the network.

4. Does the Ring employ prioritized messaging to test the ring integrity?
Some ring switch product offerings rely on a loss of the link signal to detect breaks. These ring schemes will not recover if there is a loss of cable integrity or internal failure within a switch. Some Ring algorithms send a test message as a backup scheme every few seconds. Clearly they are not reliable real-time solutions. If the test messages are not sent frequently and on a priority basis, they may arrive late or not at all. Beware!

5. What is the worse case recovery time of the ring?
If you are designing a real-time system, this is a fundamental question. Be sure that the response to the question does not contain the word “typically”.

6. Can you add or remove switches from the Ring while it is live?
Any network that relies on a designated master will have issues with a hot swap. (What if it is the Master Switch that needs replacement?) If the Ring is not a true real-time topology, watch out for recovery time if you swap out a switch. You may lose messages for an unacceptable period of time.

7. Do switches in the Ring require configuration?
The need for configuration increases the required skill level and increases the time to perform service. It probably adds the requirement for a computer to run the configuration process upon. (SIXNET Ring switches can be placed in a Ring straight out of the box.)

8. Is there a means to poll ring status?
To detect and find a network break?
Managed Switches provide SNMP agents to provide status information. You need special software and special skills to use this feature. SIXNET holds a patent on using common industrial protocols to report ring status. (Specifically Modbus registers are utilized.) Finding a network break is as easy as reading an open valve status – it just is a Modbus register. Any PLC or HMI product with Modbus capability can read and report network status with SIXNET real-time rings.