When tag data links and message communications are executed on the same network, tag data
links can be sent at higher priority to prevent problems such as transmission delays due to mes-
sage communications traf
fic and packet losses due to buffer overflow.
Settings must be made in the Ethernet switch to enable this function and give higher priority to tag
data link packets.
These functions are supported by Ethernet switches as described in the table below.
Ethernet switch type Multicast filtering L4 QoS Remarks
Unmanaged L2 Ethernet switch Not supported Not sup-
ported
---
Managed L2 Ethernet switch Supported Supported Both functions must be set
with a special software tool.
OMRON Ethernet switch
(W4S1-series Ethernet switches)
Not supported Supported L4 QoS is set with a switch.
No software tool is necessa-
ry
.
Additional Information
If the Network Configurator is used to set the connection type in the connection settings to a
Multicast Connection, multicast packets are used. If the connection type is set to a Point to
Point Connection, multicast packets are not used.
2-1-4
Precautions for Ethernet Switch Selection
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 the
functions.
When you select an Ethernet switch, it is necessary to consider what kind of data transmission and
how much traf
fic you use over the the network.
Refer to the following precautions when you select an Ethernet switch.
Refer to 15-2 Adjusting the Communications Load on page 15-7 to estimate the communications
load for tag data links.
Selecting the Ethernet Switch Based on the Type of Network Com-
munications
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 traf
fic due to unnecessary multi-
cast packets, so the tag data links can operate at higher speed.
If either of the following conditions exists, there is no difference in the traffic condition whether mul-
ticast filtering is supported or not.
• The tag data links are set to share the same data with all nodes in the network. (Multicast pack-
ets are transferred to all nodes in the network, just like broadcast transmission.)
• The tag data link settings are all one-to-one (unicast) and multicast packets cannot be used.
2 Installing Ethernet Networks
2-4
NJ/NX-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
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