Topologies – Rockwell Automation Ethernet Design Considerations Reference Manual User Manual

Page 22

Rockwell Automation Publication ENET-RM002C-EN-P - May 2013

Chapter 2

Ethernet Infrastructure Components

Topologies

Ethernet networks are laid out in point-to-point configurations with one cable
for each device. Ethernet networks have active infrastructures that rely on
switches. You can design a network with individual switch devices and devices
with embedded switch technology.

Table 4 - Topologies with an Individual Switch

Topology

Description

Star

The most common EtherNet/IP network topology is a star, where end devices are connected and
communicate with each other via a switch. In a star topology, nodes are typically grouped closely
together.

Advantages
• Easy to design, configure, and implement
• Direct path between the infrastructure device

and the end device

• Remove and add devices without affecting the

rest of the network

• Increase port capacity on the switch to add

more devices

• Centralization can ease troubleshooting,

because the switch sees the activities of all of
the connected devices

Disadvantages
• Loss of network service in case of connection

failure (no resiliency)

• Primarily the single point of failure of the

centralized switch

Ring—switch based

A ring network is a single-fault tolerant ring network intended for the interconnection of automation
devices.

Advantages
• Ability to survive a single point of failure or a

device being powered down on the ring.

• Simplified cabling
• Ability to cover long distances with 100 m

between each copper segment

Disadvantages
• Additional configuration complexity
• Longer convergence times
• Variable number of hops can make

performance difficult to predict

Linear—switch based

A linear network is a collection of devices that are daisy-chained together.
A linear topology works best for a limited number of nodes.

Advantages
• Easy to design, configure, and implement
• Least amount of cabling
• Minimal amount of cable needed
• Ability to cover long distances with 100 m

between each link

Disadvantages
• Loss of network service in case of connection

failure (no resiliency)

• Creates the potential for bottlenecks
• Variable number of hops can make

performance difficult to predict

• Powering down a device or the failure of a

device in the center of the network affects
connectivity between any of the devices on
either side

• Each link in the chain represents network

delay

Redundant star

In a redundant star topology, every Layer 2 access switch has dual connections to a Layer 3 distribution
switch. Devices are connected to the Layer 2 switches.

Advantages
• Resiliency from multiple connection failures
• Faster convergence to connection loss
• Consistent number of hops provide

predictable and consistent performance

• Fewer bottlenecks

Disadvantages
• Additional wiring and ports required
• Additional configuration complexity

Switch

Layer 3

Layer 2