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2 Installing Ethernet Networks

2-4

NJ/NX-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)

The functions supported by the Ethernet switch may affect tag data link transmission delays and the

settings in the Controller configurations and setup. In addition, if the Ethernet switch supports advanced

functions, special settings are required for those functions. When you select an Ethernet switch, it is

necessary to consider whether to select the Ethernet switch based on the kind and amount of commu-

nications you want to execute in the network. Refer to the following precautions when you select an

Ethernet switch. Refer to 14-2 Adjusting the Communications Load to estimate the communications

load for tag data links.

 Executing Tag Data Links Only

We recommend that you use an L2 Ethernet switch without multicast filtering or an L2 Ethernet

switch with multicast filtering. An L2 Ethernet switch with multicast filtering prevents increased traffic

due to unnecessary multicast packets, so the tag data links can operate at higher speed. If either of

the following conditions exists, the amount traffic will be the same for both kinds of L2 Ethernet

switches (with or without multicast filtering).

• The tag data links are set to share the same data with all nodes in the network. (The multicast

packets are transferred to all nodes in the network, just like a broadcast.)

• The tag data link settings are all one-to-one (unicast) and multicast packets cannot be used.

If multicast filters are being used, settings must be made in the Ethernet switch. There must be

enough multicast filters for the network being used.

 Executing Tag Data Links and Message Communications

We recommend an L2 Ethernet switch with multicast filtering and L4 QoS. If you set tag data links

for higher-priority transmission, it is possible to prevent problems such as transmission delays due

to message communications traffic and packet losses due to buffer overflow. You must make special

settings in the Ethernet switch when using the multicast filtering function and L4 QoS function.

2-1-4 Precautions for Ethernet Switch Selection

Selecting the Ethernet Switch Based on the Types of Network

Communications

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