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NJ501 EtherNet/IP Performance And Network Load


EtherNet/IP Performance and Network Load.

To easily exchange data to other controllers the NJ501 supports EtherNet/IP on its standard Ethernet port. However to ensure the performance of the EtherCAT interface the traffic on the Ethernet interface is limited to 1000 packets per second. In comparison a standard CJ1W-EIP21 can handle 6000pps, a CJ2M PLC with build-in EtherNet/IP interface has a max of 3000pps. When calculating there is also a minimal 100ms heartbeat per connection. Or if RPI is >100 ms then heartbeat is the RPI.
 

An example:

There is communication between three nodes.

Node 1 has three connections where it produces on two connection to Node 2 and consumes over one connection from Node 3. Node 2 consumes from Node 3 over one connection.

Total number of package per second for Node 1 is: 500pps with the 2ms RPI, 10pps over the heartbeat, 5pps over the 200ms RPI for Node 2 and 2 pps over the 500ms RPI for Node 3. Total 500 + 10 + 5 + 2 = 517 pps.

For Node 2 it is 500pps with the 2ms RPI, 10pps over the heartbeat, 5pps over the 200ms RPI for Node 1 and 200pps over the 5ms RPI and 10 pps for the heartbeat to Node 3. Total 500 + 10 + 5 + 200 + 10 = 725 pps.

For Node 3 it is then 200pps over the 5ms RPI and 10 pps for the heartbeat to Node 2 and 2 pps over the 500ms RPI for Node 3. Total 200 + 10 + 2 = 212 pps.

You can see that Node two is getting close to the max of 1000pps. Advice is to go to about 80% of the maximum number of packages per second. The NJ501 supports a maximum of 32 connections. When the NJ501 is a Multicast producer every Multicast connection also counts as a connection.

For example there are 5 devices that each create a Mulicast connection with the same Requested Packet Rate (RPI) from the NJ501. Then, although there are no connections defined within the NJ501, and there is only one Ethernet Multicast message sent out from the NJ501, this is still 5 connections for the NJ501.

Network configurator can calculate the load.
In the Network Configurator you can adjust accordingly for all or for some connections. Network configurator can not take into account the Socket Communication.

With these bandwidth and connection limitations correctly choose multi-or single-cast. When selecting Multicast make sure you use Ethernet switches that can handle multicast traffic. In general this are Managed switches. If you use unmanaged switches then these Multicasts are handled as Broadcast messages and will be forwarded to all devices on the network. Be aware of broadcasters on the network, they will influence the number of packets. To be on the safe side stay below 80% packet load.



 




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Created 2011-12-28
Modified 2014-07-01
Views 4839

 

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