13 Communications Performance and Communications Load
13-8
NJ-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
z Checking the Usage of Capacity and Network Bandwidth for Tag Data Links
The percentage of the allowable communications bandwidth for tag data links for each built-in Ether-
Net/IP port is displayed as the Usage of Capacity and the bandwidth used for tag data link commu-
nications in the entire network is displayed as the Mbit/s. The usage of capacity and used network
bandwidth that are displayed in parentheses are for a Ethernet switch that does not use multicast fil-
tering. In this case, multicast packets will be sent to even the nodes without connection settings, so
the displayed values will include these packets as well. These values can be adjusted according to
instructions in
13-2-4 Changing the RPI.
z Checking the Total Number of Multicast IP Addresses in the Network
When using a Ethernet switch that provides multicast filtering, there must be enough multicast filters
for the network being used. The number of multicast IP address used in the entire network that is
displayed by the Network Configurator is based on connection settings. Make sure that the number
of multicast IP addresses used in the entire network does not exceed the number of multicast filters
supported by the Ethernet switch. If necessary, change to a Ethernet switch with enough multicast
filters, or adjust the usage of capacity and network bandwidth for tag data links (
Mbit/s) values given
for a Ethernet switch without multicast filtering (i.e., the values in parentheses). These values can be
adjusted according to instructions in 13-2-4 Changing the RPI.
z Checking the Total Maximum Network Bandwidth
The Network Configurator displays the total maximum bandwidth that can be used for the entire net-
work. This value indicates the maximum bandwidth that can be used on the transmission paths
when Ethernet switches are cascaded. If the value exceeds the bandwidth of a cascade connection
in the actual network (e.g., 100 Mbps), the maximum bandwidth for part of the communications path
may be exceeded, depending on how the network is wired. This may prevent the tag data links from
operating correctly. If this occurs, either calculate the bandwidth usage for each communications
path and be sure that the maximum bandwidth is not exceeded for any cascade connection, or
adjust the bandwidth for all cascade connections so that the total maximum network bandwidth is
not exceeded. Adjust the bandwidth according to instructions in
13-2-4 Changing the RPI.
The usage of capacity without multicast filtering can be adjusted against the tag data link’s allowable
bandwidth by using the packet interval (RPI) setting. If the RPI is made shorter, the usage of capacity
will increase. If the RPI is made longer, the usage of capacity will decrease.
The RPI can be set in any one of the following ways.
• Setting the same interval for all connections
• Setting a particular device’s connection
• Setting a particular connection
When the same RPI is set for all connections, the usage of capacity will basically increase proportion-
ally as the RPI is made shorter.
Example: If the RPI is set to 50 ms for all connections and the usage of capacity is 40%, the usage of
capacity may increase to 80% when the RPI is reduced to 25 ms for all connections.
Precautions for Correct UsePrecautions for Correct Use
Performing message communications or other network operations from the Network Configura-
tor (such as monitoring or other operations that place a load on the network) or from the user
application when the tag data link bandwidth usage of capacity is between 80% and 100% can
temporarily create an excessive load on the network and result in timeouts. If timeouts occur,
increase one or all of the RPI settings and reduce the usage of capacity.
13-2-2 Tag Data Link Bandwidth Usage and RPI
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