Installation guide

Network Infrastructure for EtherNet/IP™
Planning the Infrastructure
3-15
on the manufacturing floor. In fact, the use of Ethernet switches is the preferred means of Ethernet
interconnect of EtherNet/IP systems. Typical industrial switches can connect four or more network
segments or Ethernet devices. Each of these connections (ports) typically supports both 10-Mbps and
100-Mbps data rates. Many of the newer switches will support 1-Gbps data rates as well.
3.2.3 Switches: Key System Elements
Switches are the key components that provide the determinism and throughput required for control
applications. They do this through several key features:
• Switches learn which device addresses are connected to each of their several ports. They
then send data received at one port only to the port that is connected to the target station.
This reduces unnecessary traffic.
• If a switch is connected to a segment containing half-duplex devices (which may be
connected via hubs), collisions from that segment are isolated to that segment and are not
passed on to other devices or segments connected to other ports.
• The Ethernet connections (ports) on switches typically support and automatically
configure themselves for either half-duplex or full-duplex communications. Using full-
duplex communications from a switched port directly to a device turns off the traditional
Carrier Sense Multiple Access with Collision Detection (CSMA/CD) mechanism so
that collisions are impossible.
The switch’s ability to eliminate collisions is the most important mechanism to provide real-time
capability for Ethernet-based control systems. If the data load increases on any one segment such that
performance is affected, a switch may be added to split the data load between two or more segments,
resulting in higher throughput. In addition, managed switches can prioritize traffic with up to eight traffic
classes, allowing the preferential handling of real-time traffic over supervisory traffic (e.g., file transfer,
web sessions, etc.).
3.2.4 How Switches Add Flexibility
The capabilities of switches increase the flexibility of the overall system in a number of ways:
• Switches can simultaneously communicate with and pass network messages between
devices or segments operating at different data rates (10 Mbps, 100 Mbps, or 1 Gbps).
• Provided with both types of ports, they can connect to both fiber-optic and twisted-pair
cables, allowing developers to use a mix of media in the same system.
• Managed switches come with added functions. Each has its own IP address, through
which users can enable/disable or configure the added functions. The features included
with a managed switch vary from vendor to vendor. Some vendors offer managed
switches that provide added diagnostics, addressing functions, and redundancy. Others
can be configured to help manage traffic through configuration optimization of Ethernet
features (e.g., virtual LANs, Quality of Service), bandwidth allocation, user
authentication, and other sets of features.