Rockwell-automation Ethernet Design Considerations Reference Manual Uživatelský manuál stáhnout pdf (Strana 22)

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

D D D

D D

Switch

SwitchSwitch

D D

Switch

D D

Switch

D D

Switch

D D

Layer 3 Layer 3

Layer 2

D D

Layer 2

D D

1 2 ... 17 18 19 20 21 22 23 24 25 26 27 ... 105 106

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