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Ethernet Services in a M580 or Quantum Hot Standby system

Published date: 30 September 2019

The Ethernet Services that work in a M580 or Quantum Hot Standby system
Ethernet Services for M580 or Quantum Hot Standby system
Product Line
M580 Quantum
Unity Pro
In the hot standby solution, two identically configured PLC systems are set up to control the same application. One PLC, the primary, runs the application and updates the other secondary (standby) PLC. The standby maintains awareness of the application status but does not perform any control functions. In the event of a failure in the primary PLC, the standby PLC takes over the primary PLC responsibilities. When the PLC that has failed becomes operational again, it comes back up in the hot standby system as the new secondary PLC.
The NOEs coordinate the swapping of IP addresses. After closing both the client and the server connections, each NOE sends a swap UDP message to its peer NOE. The sending NOE then waits a specified timeout (500 ms) for the peer swap of UDP messages. Either after receiving the messages or after a timeout, the NOE changes its IP address.

NOTE: The Ethernet module (NOC, NOE) in a Hot Standy system will only use the configured IP address if the CPU in its rack is in a Run Primary state. If the CPU in the rack with the Ethernet card is not in Run Primary state (such as OFFLINE or STANDBY state) then that Ethernet card uses the configured +1 IP address.

NOTE: NOEs must communicate with each other in order to swap IP addresses. Schneider Electric recommends that you connect the primary and secondary NOEs to the same switch because: Communication failures between the NOEs increases the time to swap.

Connecting 2 NOEs to the same switch minimizes the probability of a communication failure. NOTE: Schneider Electric recommends that you use a switch (not a hub) to connect the NOEs to each other or to the network. Schneider Electric offers switches; please contact a local sales office for more information.

The NOE waits for either a change in the controller’s Hot Standby state or the swap of UDP messages. Then the NOE performs 1 of 2 Hot Standby actions.
If the NOE . . .  Then  
1. Detects that the new Hot Standby state is either primary or standby  The NOE changes the IP address.  
2. Receives a swap UDP message  The NOE transmits a Swap UDP message and swaps the IP address.  

All client/server services (I/O scanner, global data, messaging, FTP, SNMP, and HTTP) continue to run after the switch from the old to the new primary NOE.
NOTE: Failure of an NOE module is not a condition for the primary system to leave the primary state.

Hot Standby and NOE Module Functionality :The following table identifies the Ethernet services that are available and unavailable in a hot standby solution with 140NOE771x1 Family  

I/O Scanning          - Available  
Global Data            - Available  
Modbus Messaging - Available  
FTP/TFTP              - Available  
SNMP                    - Available  
HTTP Server          - Available  
DHCP                    - Unavailable  

NOTE: Only the 140NOE77101 or 140NOE77111 (TCP/IP Ethernet modules) support a Modicon Quantum Hot Standby with Unity V2.0 system or higher.

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