Rockwell-automation Ethernet Design Considerations Reference Manual Manual de usuario descargar pdf (Pagina 34)

34 Rockwell Automation Publication ENET-RM002C-EN-P - May 2013

Chapter 3 Ethernet Infrastructure Features

Frames

Use multicast frames in these situations:

• Redundancy applications

• Communication with more than one destination

Multicast is more efficient than sending multiple, unicast streams to

multiple nodes.

• Video streaming

You must use unicast communication if the transmission routes through a Layer 3

device.

I/O devices generally produce at very fast rates, such as 10 ms, so it is easy to

flood the network with multicast traffic and force each end device to spend time

deciding whether to discard numerous multicast frames. If there are a lot of I/O

devices, they can easily use up a significant part of a router’s CPU time.

You must consider control network traffic propagating onto the plant

information network, as well as, plant information network traffic propagating

onto the control network. Some best practices include the following:

• Minimize device load due to unwanted IP multicast traffic

• Minimize switch load due to unwanted IP multicast traffic

• Minimize network load due to unwanted incoming IP multicast or

broadcast traffic

• Block IP multicast traffic generated within the EtherNet/IP subnet from

propagating onto the plant network

• Implement standard network troubleshooting tools

For more information, see Virtual LANs and Segmentation

on page 42 and

Internet Group Management Protocol (IGMP)

on page 55.

Layer 2

Switch

Layer 2

Switch

I/O

(producer)

Controller

(consumer)

Switch or

Router

To Plant Network

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Rockwell-automation Ethernet Design Considerations Reference Manual Manual de usuario Pagina 34