Installation guide

Network Infrastructure for EtherNet/IP™
Planning the Infrastructure
3-14
network’s response time, infrastructure components and addressing techniques provide connectivity while
segregating plant-floor traffic.
3.2 Ethernet System Components
Industrial Ethernet systems require various infrastructure components to connect all the segments
together. These include hubs, switches (especially managed switches), media converters, cables, and
routers.
Classification of Ethernet Infrastructure Components
Ethernet infrastructure components are also known as Data Communications Equipment (DCE).
Control devices that send and receive messages, such as variable frequency drives, PLCs, PCs,
HMIs, machine vision devices, etc. are typically classified as Data Terminal Equipment (DTE).
3.2.1 Ethernet Hubs
Ethernet hubs, also referred to as repeaters or repeater hubs, are inexpensive electronic “repeaters” of
Ethernet data packets; they have no built-in intelligence. They amplify the signal and can extend the
distance and quantity of devices on a segment. All connected network devices hear all Ethernet data
packets on all of the Ethernet hub ports. Also, all network devices connected to a hub must communicate
at the same data rate.
Unlike switches, hubs only operate in a
half-duplex communications mode, so they retransmit
collisions to other devices. (See 4.3.1 Full-Duplex vs. Half-Duplex Implications.) The cost of hubs
initially was significantly lower than that of switches, so hubs were used as a lower-cost method of
adding devices to the segments connected by switches. Switch products—thanks to home and office
needs—have become ubiquitous, with prices dropping accordingly. Because switches do more and are
relatively inexpensive, hubs have lost favor and are disappearing from vendor catalogs and store shelves.
Industrial switches, borrowing on the technology of their commercial counterparts, provide an attractive
connect cost per device. It is possible to use switches (with all their performance benefits) in places where
cost constraints formerly resulted in the use of hubs. It is recommended that switches be used throughout,
and where economically feasible,
managed switches (configurable) or routers should be used.
3.2.2 Ethernet Switches
Ethernet switches are intelligent connection devices that generally use high-speed hardware to buffer
messages, analyze data frames, and connect the sending and receiving nodes in a virtual one-to-one
connection. Switches are a fundamental part of most networks. They make it possible for several users to
send information over a network at the same time without slowing each other down.
Ethernet Switch Terminology
Ethernet switches were historically referred to as bridges, multi-port bridges, or switching hubs.
The simple term switch is now the industry’s generally accepted term.
Switches are typically OSI Layer 2-type devices that allow all protocols to pass through. The Ethernet
switch is the most effective means of setting up Ethernet systems, especially on machine-control systems