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Selecting the Network Devices Section 2-3
2-3-4 Switching Hub Functions
This section describes the switching hub functions that are important when
using an EtherNet/IP network. When using an EtherNet/IP Unit, set the follow-
ing two functions.
• Multicast filtering
• QoS (Quality of Service) for TCP/UDP port numbers (L4)
Multicast Filtering Multicast filtering transfers multicast packets to the specific nodes only. This
function is implemented in the switching hub as IGMP Snooping or GMRP.
“Specific nodes” are nodes equipped with an IGMP client that have made
transfer requests to the switching hub. (OMRON EtherNet/IP Units are
equipped with an IGMP client.)
When the hub does not use multicast filtering, multicast packets are sent to all
nodes, just like broadcast packets, which increases the traffic in the network.
Settings must be made in the switching hub to enable this function.
There must be enough multicast filters for the network being used.
QoS (Quality of Service)
Function for TCP/UDP
Port Numbers (L4)
This function controls the priority of packet transmissions so that packets can
be sent with higher priority to a particular IP address or TCP (UDP) port. The
TCP and UDP protocols are called transport layer protocols, leading to the
name L4 (layer 4) QoS function.
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 message communications traffic and packet
losses due to buffer overflow. Settings must be made in the switching hub to
enable this function and give higher priority to tag data link packets.
Support for the above two functions is as follows for the different types of
switching hubs.
Note If the Network Configurator is used to set the connection type in the connec-
tion settings to a multicast connection, multicast packets will be used. If the
connection type is set to a point-to-point connection, multicast packets will not
be used.
2-3-5 Precautions When Selecting a Switching Hub
The functions supported by the switching hub may affect tag data link trans-
mission delays and the configuration. In addition, if the switching hub supports
advanced functions, special settings are required for those functions.
Hub Multicast
filtering
L4 QoS Remarks
Unmanaged L2 switching hub None None ---
Managed L2 switching hub Provided. Provided. Both functions must
be set with a special
software tool.
OMRON W4S1-series Switching
Hubs
None Provided. L4 QoS is set using
a switch. No soft-
ware tool is neces-
sary.