Installation guide

Network Infrastructure for EtherNet/IP™
6-68
Infrastructure Application Scenarios
6.2.1 Systems with Low Device Counts
In the example shown in Figure 6-1, IP multicast traffic is produced by I/O devices and consumed by the
programmable controller. Here, IP multicast traffic produced by I/O
1
will be sent to all devices connected
to the switch, including I/O
2
through I/O
5
and the workstation.
Figure 6-1 Isolated Network with One Controller.
EXAMPLE 1
Assume that each device establishes one CIP connection to the controller with a 10-ms RPI. Each device
will generate 100 multicast packets per second and receive 100 unicast (“heartbeats” or output status)
packets per second from the controller. Each device will also receive 400 unwanted multicast packets per
second, and the workstation will receive 500 unwanted multicast packets per second.
EXAMPLE 2
Assume that each control device establishes four CIP connections with the controller. One connection
has a 10-ms RPI, and each of the other three connections has a 50-ms RPI. Each control device will
generate 160 multicast packets per second and will also receive 640 unwanted multicast packets per
second. The workstation will receive 800 unwanted multicast packets per second.
6.2.1.1 Use of Unmanaged Switches
In isolated systems with low device counts (10 or fewer), a low number of CIP connections, and modest
RPIs (higher than 10 ms), the level of unwanted multicast traffic may not cause a device overload
condition. In isolated systems with large device counts and, more importantly, a large number of CIP
connections, the use of unmanaged switches as expansions to managed switches may allow a balance of
cost versus performance. In applications with a low number of CIP connections that have modest RPI
requirements, the use of unmanaged switches can provide product cost savings over the use of all
managed switches. As a general rule, applications requiring fast RPIs and/or more than a few connections
should use managed switches with IGMP snooping capability.
8-port
Ethernet Switch
I/O
1
I/O
5
Programmable
Controller
Workstation